prevalence and ultrasonographic characteristics of …
TRANSCRIPT
i
PREVALENCE AND ULTRASONOGRAPHIC CHARACTERISTICS OF
THYROID INCIDENTALOMAS IN NIGERIAN ADULTS
BY
Mojisola Adejoke OLUSOLA-BELLO (MB, BS. Ib)
DEPARTMENT OF RADIOLOGY
UNIVERSITY COLLEGE HOSPITAL
IBADAN
A DISSERTATION SUBMITTED IN PARTIAL FULFILMENT OF THE
REQUIREMENTS FOR THE AWARD OF THE FELLOWSHIP OF THE
NATIONAL POSTGRADUATE MEDICAL COLLEGE OF NIGERIA IN
THE FACULTY OF RADIOLOGY (FMCR)
NOVEMBER, 2011
ii
CERTIFICATION BY SUPERVISORS
We hereby declare that the study titled ‘Prevalence and ultrasonographic
characteristics of thyroid incidentalomas in Nigerian adults’ was developed
and conducted by the candidate Dr. Mojisola A. Olusola-Bello. This study was
developed after identification and discussion on the need to research into the topic.
We supervised the conduct of the study, analysis and write up of the final
report. We therefore certify that the candidate has conducted the study.
…………………………………………
DR A. M. AGUNLOYE MB.BS, FMCR (NIG), FWACS
CONSULTANT RADIOLOGIST
DEPARTMENT OF RADIOLOGY
UNIVERSITY COLLEGE HOSPITAL, IBADAN
……………………………………….
DR A.O ADEYINKA MB.BS, FMCR (NIG), FWACS
CONSULTANT RADIOLOGIST
DEPARTMENT OF RADIOLOGY
UNIVERSITY COLLEGE HOSPITAL, IBADAN
iii
ATTESTATION BY HEAD OF DEPARTMENT
I testify that this dissertation titled ‘Prevalence and ultrasonographic
characteristics of thyroid incidentalomas in Nigerian adults’ was developed
and conducted by the candidate Dr. Mojisola A. Olusola-Bello. This study was
developed after identification and discussion on the need to research into the topic.
The study was supervised by Dr. A. M. Agunloye and Dr. A. O. Adeyinka.
....................................................................
PROF. M.O. OBAJIMI (FWACS, FMCR)
HEAD OF DEPARTMENT
DEPARTMENT OF RADIOLOGY
UCH, IBADAN.
iv
DECLARATION
I declare that this study titled ‘Prevalence and ultrasonographic characteristics
of thyroid incidentalomas in Nigerian adults’ is my original work and the write-
up of results, analysis and discussion were all done by me under the supervision of
my supervisors as attested to above.
---------------------------------------------------
DR Mojisola A OLUSOLA-BELLO
RADIOLOGY DEPARTMENT
UCH, IBADAN
v
DEDICATION
This work is dedicated to the Almighty God who brought me into this programme
and saw me through.
vi
ACKNOWLEGEMENT
My profound gratitude goes to Professor M. O. Obajimi who accepted me for
residency training in Radiology.
I am indebted to my supervisors Drs. Abiodun Adeyinka and Atinuke Agunloye
who took the pains to read through and guide me throughout the course of this
work.
I am also grateful to Professor Ayotunde Ogunseyinde, my mentor, for the
training, support, encouragement and motherly advice she gave me during my
residency training.
This research work would not have been completed without the assistance and
encouragement given to me by all my consultants Dr O.M Atalabi,
Dr.J.Ehimiyein, Dr.G.I Ogbole, Dr. A.T.S. Adeniji Sofoluwe, Dr.A.J Adekanmi
and Baba Okubanjo-as he is fondly called.
The Doyen of Radiology, Professor SB Lagundoye, thank you sir for taking
interest in me and encouraging me.
I am especially grateful to Dr A.O Adebayo who tutored me and made sure I did
all the statistical analysis properly.
To my sister and friend Tinuke Akinmoladun, Residency would not have been
fun without your presence.
All my colleagues Drs. Ukperi, Soyemi, Umeh, Bassey, Yusuf and Iseko, I say a
big thank you to you all.
My Junior Colleagues especially Drs. Olatunji, Olusunmade, Nuhu, Hafiz and
Olabinri, Thank you for your assistance. To all the Radiographers especially Mrs
vii
Ayodele and Mrs Ajayi, I really appreciate you. Also, to all the nursing staff
especially my friends CNO Obajimi and PNO Ogungbade, thanks for your
support. The secretaries, typists, clerical staff and porters, I appreciate you all.
To my parents, brothers and sisters; thank you for your encouragement and
support. You are the best family one can ever ask for.
Lastly but definitely not the least, I appreciate my Darling husband for his
prayers, support, encouragement and patience throughout the entire duration of
the work. Oluwasemilore Adeola, my adorable daughter, thank you for
understanding and paying the price. The stress is over now.
I remain eternally grateful to the Almighty God, for seeing me through the
shadows of Radiology. GLORY BE TO GOD!
viii
TABLE OF CONTENTS
Title page ……………………………………………………………………… i
Certification by supervisors…………………………………………………….. ii
Attestation by HOD……………………………………………………………. iii
Declaration by candidate……………………………………………………… iv
Dedication ……………………………………………………………………... v
Acknowledgement ……………………………………………………………. vi
Summary ………………………………………………………………………. 1
Introduction…………………………………………………………………….. 2
Ultrasonographic anatomy of the thyroid gland 4
Aims and objectives 10
Justification……………………………………………………………………... 11
Literature Review………………………………………………………………. 13
Materials and methods…………………………………………………………. 26
Results………………………………………………………………………….. 31
Discussion ……………………………………………………………………… 45
Conclusion……………………………………………………………………... 51
References……………………………………………………………………… 54
1
SUMMARY
INTRODUCTION: Thyroid lesions are common and range from the incidental,
asymptomatic, small solitary nodule to the large and partly intrathoracic masses. Thyroid
lesions that are not palpable but identified by radiological imaging such as ultrasonography,
computed tomography and magnetic resonance imaging are defined as Incidentalomas of
the thyroid gland.
AIM OF STUDY: The aim of this study was to document the normal volume of the thyroid
gland and determine the prevalence of thyroid incidentaloma, as well as describe the
ultrasound characteristics of incidentalomas in the Nigerian adults in the study area.
MATERIALS AND METHODS: This was a prospective study that examined 340
subjects over a period of 6 months. They were selected randomly from patients presenting
for ultrasound examination of other parts of the body. The subject had their neck examined
by palpation and ultrasound in the ultrasound suite of the department of Radiology, UCH
Ibadan, using a General Electric LogicP5 ultrasound machine with a 6-10MHz linear
transducer.
RESULTS: Three hundred and forty (340) subjects which comprised of 153 males and 187
females were examined. The mean volume of the thyroid gland was 6.58±2.47cm3. The
volume of the male thyroid glands (6.96±2.41cm3) was significantly higher than that of the
females (6.27±2.47cm3, p value 0.01). The prevalence of thyroid incidentaloma in this study
was 22.4%. Thyroid incidentalomas were more common in females than males but this was
not statistically significant. The prevalence of thyroid incidentaloma significantly increased
with age up to the seventh decade. Majority of the lesions were solitary, homogenous and
cystic.
CONCLUSION: The volume of the thyroid gland in this environment is smaller than
previously documented by ultrasound before the middle of the last century. This finding is
probably due to increase in dietary iodine intake. However, the prevalence of thyroid
incidentalomas documented in the study area is high (22.4%) and they were commoner in
women and older subjects.
2
INTRODUCTION
Thyroid lesions are common and range from the incidental, asymptomatic, small
solitary nodule to the large and partly intrathoracic masses.
These thyroid lesions may be detected by direct (visual) observation or palpation
of the nodule. About 4-7% of the adult population has a palpable thyroid nodule1, 2.
Knowledge of the prevalence of thyroid disease in the general population is based
on clinical epidemiologic studies and autopsy series. However, clinical
examination by means of inspection and palpation is a relatively insensitive and
observer-dependent screening method for detecting enlargement or nodularity of
the thyroid gland. The sensitivity is even lower for diffuse lesions of the thyroid
gland3.
At autopsy, as many as 50% of clinically normal glands have nodules 3, 4. On the
other hand, autopsy series as a rule are not representative of the general population
because of age distribution.
Thyroid lesions that are not palpable but identified by radiological imaging such as
ultrasonography, computed tomography and magnetic resonance imaging are
defined as incidentalomas of the thyroid gland 5-7. Although a vast majority of
incidental thyroid lesions are benign, a small percentage show features of
malignancy.8-10
3
The identification and characterization of non-palpable thyroid nodules
(incidentalomas) on ultrasound (US) has significantly increased owing to the
widespread use of ultrasonography in evaluation of the neck.5-8
Ultrasound examination is sensitive, non-invasive, cheap and readily available.
High frequency, real-time US examination is therefore an ideal screening method
for nodular as well as diffuse thyroid disease.
Ultrasonography can also provide guidance for diagnostic procedures (Fine Needle
Aspiration Cytology or Biopsy –FNAC/FNAB) and therapeutic procedures. It also
facilitates the monitoring of effects of treatment of thyroid disease as it is relatively
cheap, available and does not use ionizing radiation.
Several sonographic features have been identified and described as being
suggestive of malignancy. There have also been attempts to describe sonographic
features that are both sensitive and specific for malignant thyroid lesions.
This study aims to determine the prevalence of thyroid incidentalomas in Nigerian
adults and describe the ultrasonographic features of the lesions discovered.
Findings will also be compared with those from other studies.
4
ULTRASONOGRAPHIC ANATOMY OF THE THYROID GLAND
The thyroid gland is an endocrine organ that plays an important role in regulating
the body’s metabolism and calcium balance. It is situated in the anterior cervical
region. It has a butterfly shape with two lateral lobes connected by an isthmus in
the midline. It is attached to the laryngo-tracheal duct and follows its movement
during swallowing. The lobes extend from the level of the thyroid cartilage of the
larynx superiorly to the level of the sixth tracheal ring inferiorly.
B-mode ultrasound imaging with a high frequency probe provides excellent detail
of the thyroid gland. The normal thyroid gland has a homogenous echotexture of
medium echogenicity.
A normal thyroid lobe on transverse section (Figs 1 and 2) has a triangular shape,
with three edges. The echogenicity is similar to that of the parotid glands, and
higher compared to that of the adjacent strap muscles of the neck.
The antero-lateral surface is bordered by the strap muscles (sternohyoid and
sternothyroid) that have a fibrillar structure and are hypoechoic compared to the
thyroid. The sternocleidomastoid muscle is situated lateral to the most lateral
point of the thyroid lobe. The muscles are covered by the fascia cervicalis, the
platysma muscle and the skin.
The postero-lateral surface is in contact with: the internal jugular vein, the
parathyroid glands (usually not seen, unless they are enlarged), the vagus nerve
(not seen on sonography), the common carotid artery, and the longus coli muscle.
The left lobe is also in contact with the esophagus which can be mistaken for a
thyroid nodule, but real-time ultrasound shows peristalsis in the esophagus when
the patient is asked to swallow.
5
Fig1. B mode ultrasound of the neck: Transverse view showing the right lobe of the thyroid
gland, (double arrows) which shows a homogenous high reflective echogenicity. The isthmus of
the thyroid gland is seen at it arches over the trachea (black arrow). Only the anterior wall of the
trachea is seen (arrowhead). Strong reverberation artifacts due to air are seen posteriorly. The
anterolateral relation of the lobe is the strap muscles (white arrows) which are hypoechoic. The
internal jugular vein (white curved arrow) and common carotid artery (double curved arrows) are
seen posterolaterally.
6
Fig2. Schematic diagram of an axial section of the neck showing the lobes of the
thyroid gland joined at the center by the isthmus.
7
The medial surface of the gland is in contact with: the trachea, the recurrent nerve
(not seen on sonography) and the inferior thyroid artery. On the ultrasound image,
only the anterior wall of the trachea is visible and behind it, we see the acoustic
shadowing created by the extreme reflection from the tissue-air interface.
Sometimes a reverberation artifact can be seen as numerous parallel lines behind
the anterior wall of the trachea.
On longitudinal section, the thyroid lobe has an ovoid shape (Fig 3 and 4). The
anterior surface is covered by the strap muscles and the posterior surface is in
contact with the structures described previously. In some cases, vessels can be
detected within the parenchyma, in longitudinal or transverse section. Their
differentiation from small cysts is possible with color or power Doppler
examination which shows blood flow in the vessels.
The thyroid vascular network can be evaluated by Color Doppler and Power
Doppler ultrasound. The normal appearance of the vascular network on ultrasound
is restricted to the main thyroid vessels and their branches. The parenchymal
arteries are not visible in normal thyroid glands.
The internal jugular vein and the internal carotid arteries seen as anechoic
structures on the posterolateral sides of the lobes of the thyroid gland may also be
seen as color-filled structure on color Doppler ultrasound.
8
Fig3: B mode ultrasound of the thyroid gland: longitudinal view shows
homogenous echogenicity of the gland parenchyma.
9
Fig 4. Schematic diagram showing the longitudinal view of the thyroid gland
10
AIMS AND OBJECTIVES
General objective
The main purpose of the study is to determine the prevalence of incidentalomas of
the thyroid gland on ultrasound in adult Nigerians.
Specific objectives
1. To document the volume of normal thyroid gland in adult males and females in
the study area.
2. To correlate findings of thyroid incidentalomas with the age distribution and
gender of subjects.
3. To describe the ultrasonographic patterns of thyroid incidentalomas
11
JUSTIFICATION
With widespread use of sensitive imaging modalities like high frequency
ultrasound, computer tomographic imaging and magnetic resonance imaging in
clinical practice, there has been a raised number of incidentally discovered lesions
in the various organs of the human body, the thyroid gland inclusive. Incidental
thyroid nodules are being discovered with increasing frequency and controversial
issues relating to management and importance of thyroid incidentalomas are
becoming increasingly common in radiologic practice.5,7
However, there is paucity of data on thyroid incidentalomas in this environment. It
is therefore important to evaluate the potential importance of thyroid
incidentalomas in this environment by first determining the prevalence and
describing the characteristics of such lesions. This would assist in clinical
decisions regarding the need for further investigations of thyroid incidentalomas, in
the subjects and in other patients in whom incidental lesions are discovered while
being investigated for other conditions.
Ultrasound is readily available, cheap, does not utilize ionizing radiation and
repeatable. Therefore, the use of ultrasound as a screening tool for thyroid
incidentalomas is justified.
12
Also, subjects who are discovered to have incidental nodules with high risk of
malignancy would be referred for further investigations and those with features of
benign lesions, for follow up.
13
LITERATURE REVIEW
The thyroid gland is the first of the body’s endocrine gland to develop, on
approximately the 24th day of gestation. The gland originates as a proliferation of
endodermal epithelium on the median surface of the developing pharyngeal floor
and descends to its definitive position in the neck, where it becomes a superficial
organ, made up of two lateral lobes and a central isthmus on either side of the
trachea.11
The size of the normal thyroid gland is said to vary from 10-15mls for women and
12-18ml for adult men12 with an average weight of 11.6g in women and 14g in
men.12,13 The size is affected by dietary iodine intake. Before the middle of last
century, a typical normal thyroid gland was considered to be about 20-25g with an
accepted upper normal size of 30g.14 The recent remarkably lower sizes have been
adduced to increased intake of dietary iodine by the general population
worldwide.13
The size of the normal thyroid gland also varies with age and sex. In a study by
Yokoyama et al15, the thyroid size was noted to be larger in adult men than in adult
women as estimated by ultrasonography. This finding was corroborated by
Hegedus16 as well as Berghout et al.17 In contrast, some studies carried out in
iodine deficient subjects in Switzerland by Gerber et al18 and in former Czecho-
slovakia by Silink and Reisenauner19 showed that women had larger thyroids than
14
men. Data from iodine replete Slovakia showed no difference in mean values of
thyroid volume between males and females.19 It has been suggested that the female
thyroid tends to be smaller than the male thyroid under relatively sufficient iodine
intake.
The volume of the thyroid gland has also been noted to increase with age. In a
study by Reiners and colleagues20, they found that the mean thyroid volume of
their subjects peaked at 45years of age and showed no further increase in higher
age groups.
The thyroid gland is easily palpated clinically because it is located superficially.
However, a normal thyroid gland is usually not palpable. The size of the thyroid
gland was evaluated exclusively by clinical palpation until the early eighties.13
The incidence of thyroid nodules detected by palpation alone is estimated to be
about 0.1% with a prevalence rate of 4-7% in general population.1, 2
The sensitivity of palpation of the thyroid gland in terms of size and nodularity is
38%21, therefore clinical palpation of the thyroid gland is not a precise tool for
assessing abnormality of the thyroid gland. Its reliability is influenced by the size
and location of the thyroid nodule, the size and shape of the neck and the
experience of the examiner.
15
The accuracy of thyroid palpation depends greatly on the experience of the
examiner. Interobserver variation in examination of the thyroid gland by palpation
has been assessed by some authors. Brander et al22 discovered a good correlation
among examiners, who were internists, in the assessment of thyroid size. In
contrast, Veith et al23 found that in one third of their cases, examiners disagreed
about the size of the thyroid gland and presence of nodules. In a study by Jarlov et
al24 interobserver variation was shown to be less among examiners who had more
experience than among those who had different levels of training.
Current ultrasonographic technology permits high resolution imaging that is more
accurate than clinical palpation or other imaging techniques.25-27 Tan et al25
reported that in 151 patients with a clinical diagnosis of a solitary nodule,
ultrasonography showed that 73(48%) had other nodules. Eighty nine per cent
(89%) of the clinically palpable nodules were 1cm in diameter or larger. In 72% of
patients with more than one nodule, nodules that had not been identified by
palpation were smaller than 1cm in diameter.
Brender et al22, in a retrospective analysis also compared results of clinical
examination with those of ultrasonography and found that only 12 of 32 (38%)
clinically solitary nodules were truly solitary on ultrasonographic examination as
16
15 patients (47%) actually had several nodules while 5 patients had normal glands.
They also found that most non-palpable nodules were smaller than 1cm in
diameter.
Katz et al28 reviewed the accuracy of thyroid ultrasonography in assessing the
volume of the thyroid gland in 28 patients whose thyroid glands were also examined
at autopsy. The correlation between the ultrasonographic finding and pathologic
finding of adenomatous goiter was good with ultrasonography having a sensitivity of
89% and a specificity of 84% in that study.
At autopsy, as many as 50% of clinically normal glands have nodules. 1, 2 In 1955,
Mortensen and colleagues4 examined thyroid glands removed during autopsy from
821 patients at the Mayo Clinic. These glands had all been found to be normal on
clinical examination. The authors reported that 406 glands (49.5%) contained one or
more nodules; 306 of these (37.3% of 821) were multinodular, and 100 (12.2% of
821) contained single nodules. Of the 406 nodular glands, 144 (35.5%) had nodules
that were larger than 2.0 cm in diameter.
In an autopsy series of 215 patients who did not have thyroid disease, Furmanchuk
and coworkers28 also documented nodules in the thyroid glands of 70 patients
(32.5%), a slightly lower percentage prevalence than that recorded by Mortensen and
colleagues4.
17
High frequency, real time ultrasound is an ideal screening method for nodular as
well as diffuse thyroid disease.
Thyroid lesions that are not palpable but identified by radiological imaging such as
ultrasonography, computed tomography and magnetic resonance imaging are
defined as incidentalomas of the thyroid gland.5-7
Incidental abnormalities of the thyroid gland are commonly encountered by the
sonographer / sonologist at a rate of 19% to 67%.30-34
Brander et al3 recorded a prevalence rate of 27.8% for incidentalomas on ultrasound,
in a prospective screening study and this was corroborated by Woestyn et al35who
recorded a prevalence rate of thyroid incidentalomas of 27%. However, Horlocker et
al36 and Stark et al37 reported higher rates of 46.2% and 40% respectively probably
because their studies were not randomized and were carried out on hyperparathyroid
patients. Kang et al38however recorded the lowest prevalence rate of 13.4% in a
retrospective study involving 1475 patients who had routine check of the neck for
other reasons other than thyroid gland disease.
18
Prevalence of incidentalomas has been noted to increase with age. Brander et al 3 in
their study reported the highest prevalence of incidentalomas in the fourth decade.
This was corroborated by Hegedus L10 as well as Oertel and Klinck39who noticed an
increase in prevalence of incindentalomas in healthy men in the second decade of
life from 8% to 24% in the third decade. Woestyn et al35 also found a prevalence of
27% generally but this increased to about 40% in the seventh decade. It was
concluded that the highest frequency is found in the seventh and eighth decade in
men and in the seventh decade in women.
Incidentalomas are also more common in women and this is in concordance with
both clinical and autopsy findings.3, 10, 35
Incidental findings of thyroid lesion may be solitary, multiple or diffuse. The lesions
detected by Brander et al3 were solitary in 57%, multiple in 22% and diffuse in 22%
of cases. The lesions may also be unilateral or bilateral but are usually unilateral.
Scott et al8 noted unilateral lesions in 50.6% and bilateral lesions in 49.4% of those
with incidentalomas.
An incidentaloma can be characterized on ultrasound by determining its size,
echogenicity, border characteristics, presence or absence of calcifications. Its
internal vascularity can also be assessed on Doppler ultrasound. The most significant
19
difference between benign and malignant incidentalomas is shown by the margin,
echotexture and presence of calcification.43-49
Microcalcification is a common finding in patients with palpable thyroid papillary
carcinoma but is not often seen in a non-palpable nodule. However,
microcalcification was found to be the most sensitive and accurate criterion in
determining that an incidentaloma may be malignant.47,48 Solbiati et al 49 also
suggested that detection of microcalcification in thyroid nodules on high frequency
sonography, although uncommon, can be considered nearly specific for malignancy.
An irregular or microlobulated margin is a general finding of malignancy.
Microlobulation is a more common finding than an ill-defined margin in non-
palpable thyroid malignancy and it may be associated with smaller mass and less
invasive tumor characteristics.28,50-52
Malignancy is also suggested by a hypoechoic thyroid lesion.28,38,50-52 However, since
most non-palpable thyroid nodules are hypoechoic, previous authors have attempted
to differentiate markedly hypoechoic lesions from other hypoechoic lesions. Only
markedly hypoechoic lesions that are much less echogenic than the medium-level
echogenicity of the strap muscles are considered to be suggestive of malignancy.47, 51
20
The vascularity of an incidentaloma has also been used to determine the nature of
the lesion. A study by Frates et al53 analyzed the relationship between intrinsic
vascular flow patterns on Doppler imaging and risk for malignancy in thyroid
nodules. They concluded that solid hypervascular (greater than 75% flow on colour
Doppler cross sectional imaging) nodules have a higher likelihood of malignancy.
Forty two percent, (42%) of the malignant lesions in their series were hypervascular
while only 14.7% of the nodules that were malignant were just vascular (less than
75% flow). However, in a retrospective study by Lannuccilli et al48 there was no
significant difference in the vascularity of benign and malignant lesions using
doppler ultrasound. None of the malignant nodules was hypervascular while 8.3% of
the benign lesions were hypervascular.
Exposure of the upper body to radiation increases the risk for nodular growth in
thyroid glands.40 Numerous studies have confirmed the increased risk for
malignancy in these nodules. In a prospective study of 2118 patients who had been
exposed to radiation and had had surgery, Deaconson et al41 found a frequency of
malignancy in nodules as high as 50%. Most of the malignant lesions were papillary
carcinomas. Other studies have shown the overall incidence of malignancy in
irradiated glands to be as high as 32% to 57%.40, 42 The malignancy rate among
thyroid incidentalomas in the general population is 12% to 28%.38, 43.
21
Specific combinations of sonographic features to determine the risk for malignancy
in thyroid nodules have been documented. A study by Kang et al38 found that a
combination of US characteristics namely-the margin, echostructure and presence of
calcification showed meaningful statistical differences between benign and
malignant nodules. They used the criteria established in a previous study by Koike
et al. 44 They had assigned sonographic index points to each nodule based on its
sonographic appearance (Table 1) and concluded that a sonographic index score of
2 or less was 88.9% sensitive and 74.4% specific for benignity.
22
Table1. Index points 0f thyroid nodules based on sonographic appearance to
determine the risk of malignancy.38
Nodule
Ultrasound
Characteristics
Index Points
Border
Well defined 0
Poorly defined 1
Shape
Regular (round) 0
Irregular (tall or wide) 1
Echo structure
Cystic 0
Solid 1
Mixed 2
Echogenicity
Isoechoic or hyperechoic 0
Hypoechoic 1
Hypoisoehoic 2
Calcification
Absent 0
Fine (few/countable) 1
Other(too numerous to
count)
2
Index score is aggregate of index points.
≤2 = likely benign
≥ 3 = likely malignant
23
In another study by Papini et al54, it was concluded that the combination of
hypoechogenicity with irregular margins, an intrinsic vascular flow pattern, or the
presence of microcalcifications was 87% sensitive in identifying malignant nodules
within their study population. However, in the study by Lannuccilli et al48 the same
criteria yielded lower sensitivity and specificity of 35.3% and 75% respectively.
Kim et al47 proposed that the presence of punctuate microcalcifications, an irregular
or microlobulated margin, marked hypoechogenicity (relative to the strap muscles in
the neck), and a shape that is more tall than wide are sufficient criteria to suggest
malignancy of a thyroid nodule. The presence of at least 1 of these characteristics
was reported to have a sensitivity and specificity of 93.8% and 66% respectively for
malignancy in their study population.
Ultrasonographic features most often associated with benign thyroid lesions include
purely cystic nodules, hyperechoic nodules, sharp margination, coarse calcification
and peripheral vascularity.48
Horvath et al55 developed a standardized ultrasound characterization and reporting
data system of thyroid lesions for clinical management, using the BIRADS model
(Breast Imaging Reporting and Data System). During the first stage of their study,
they reviewed ultrasound findings of thyroid nodules to define their characteristics.
They established 10 ultrasound patterns using all the characteristics which include:
24
(i) echostructure (homogenous or heterogenous), (ii) echogenicity (hyperechoic,
hypoechoic or cystic), (iii) shape, (iv) orientation, (v) acoustic transmission, (vi)
borders, (vii) surface, (viii) presence or absence of a capsule,(ix) calcifications and
(x) vascularization. In the last stage of the study, the TIRADS model (Thyroid
Imaging Reporting and Data Systems) was validated (table 2) to improve patient
management and cost effectiveness avoiding unnecessary fine needle aspiration
biopsy (FNAB). The sensitivity, specificity, positive predictive value, negative
predictive value and accuracy were 88, 49, 49, 88 and 94% respectively.
No statistically significant differences in age, nodule size and number of lesions
were found between benign and malignant incidentalomas.38
Current ultrasonographic technology permits high resolution imaging that is more
accurate than other imaging modalities like computed tomography and
radionuclide studies. Shetty et al56 in a retrospective study, reviewed ultrasound
examination of patients whose incidental thyroid nodules were discovered on
computed tomography (CT) and correlated the findings with US. They concluded
that the CT appearance of the incidental thyroid lesions correlated with the
sonographic appearance but ultrasound examination was more sensitive than CT in
detecting incidental lesions. This concurred with an earlier study carried out by
Stark et al37. Ultrasound was also found to provide better accuracy than CT in
measuring lesions in the thyroid gland.56
25
Table 2: Thyroid Imaging Reporting and Data System (TIRADS) model
developed by Horvath et al55
Description of US pattern US pattern Malignancy TIRADS
Anechoic with hyperechoic spots,
non- vascularized lesion.
Non encapsulated, mixed expansile,
with hyperechoic spots, vascularized
lesion, “grid” aspect (spongiform
nodule).
Colloid Type 1
Colloid Type 2
0%
TIRADS 2
Benign findings
Non encapsulated, mixed with solid
portion, isoechogenic, expansile,
vascularized nodule with
hyperechoic spots
Hyper, iso or hypoechoic, partially
encapsulated nodule with peripheral
vascularization, in Hashimoto’s
thyroiditis
Colloid Type 3
Hashimoto
pseudo- nodule
<5%
TIRADS 3
Probably benign
Solid or mixed hyper, iso or
hypoehoic nodule with a thin
capsule
Hypoechoic lesion with ill-defined
borders, without calcification
Simple
Neoplastic
pattern
De Quervain
pattern
5-10%
TIRADS 4A
Undetermined
Hyper, iso or hypoechoic,
hypervascularized, encapsulated
nodule with a thick capsule,
containing calcifications (coarse or
microcalcifications)
Hypoechoic, non encapsulated
nodule, with irregular shape and
margins, penetrating vessels, with or
without calcifications
Suspicious
Neoplastic
pattern
Malignant
pattern A
10-80%
TIRADS 4B
Suspicious
Iso or hypoehoic, non encapsulated
nodule with multiple peripheral
microcalcifications and
hypervascularization.
Non encapsulated, isoehoic mixed
hypervascularized nodule with or
without calcifications, without
hyperechoic spots
Malignant
pattern B
Malignant
pattern C
>80%
TIRADS 5
Consistent with
malignancy
Cancer,
confirmed by
previous biopsy
100% TIRADS 6
Malignant
26
Bae et al7 reviewed the images of patients who had Fluoro Deoxy Glucose-
Positron Emission Tomography/Computed Tomography, FDG-PET/CT for
reasons other than thyroid lesion and recorded a prevalence rate of 8.4% of thyroid
incidentalomas. No specific findings to suspect malignancy in the incidental
thyroid nodules were recorded. The prevalence of malignancy in patients with
incidentally found thyroid lesions on FDG-PET/CT was 23.2% after FNAC. Focal
FDG uptake and a high SUV max (Standardized Uptake Value) were the factors
related to an increased risk of malignancy.
Kuma and associates42 examined the long-term outcome of untreated benign
thyroid nodules. Among 134 patients with cytologically benign thyroid nodules
who were followed for 9 to 11 years, most nodules remained benign. Only 1
patient (0.7%) had a nodule that had been considered benign but that increased in
size during follow-up; after surgical excision, this nodule was shown to be a
papillary carcinoma. Hence,most benign thyroid nodules remain benign for a long
time.
27
MATERIALS AND METHODS
STUDY DESIGN
The study was a cross sectional study. Subjects were selected by random sampling
from volunteers and patients referred for ultrasound examination of other parts of
the body who had no physical or clinical evidence of thyroid disease.
STUDY AREA
The study was conducted in the Ultrasound suite of the Radiology department of
University College Hospital, Ibadan. The subjects were recruited over a period of
six months (July 2010 to December 2010).
SAMPLE SIZE
The sample size was calculated using Leslie Kish formula57 for estimating cross
sectional studies.
n = Z2pq
e2
Where
n = the desired sample size when population is more than 10,000
Z2 = the abscissa of the normal curve that cuts off an area at the tails (1- equals the
desired confidence level)
p = the prevalence of incidentalomas estimated to be 27.8% by Brander et al3
q =1-p
e = the desired level of precision (maximum error of estimate)
28
At 95% confidence level, with e=0.05 and p=0.278
Z = 1.96 and q = 1-p = 0.722
Then n = 1.962 x 0.5 x 0.5 =308
0.052
The sample size was increased to 340.
SAMPLING TECHNIQUE
Subjects that were examined were selected by simple random sampling on daily
basis. Those that did not have palpable thyroid mass after examination were
included.
INCLUSION CRITERIA
1. Subjects over the age of 18years.
2. Volunteers or patients who were referred to the ultrasound unit in the Radiology
department of the University College Hospital for reasons other than thyroid
disease.
EXCLUSION CRITERIA
1. Subjects less than 18 years.
2. Subjects who had evidence of thyroid disease
3. Subjects who had family history of thyroid disease
4. Subjects with visible or palpable thyroid masses.
5. Subjects who have had any form of irradiation to the neck.
6. Subjects who were pregnant.
7. Patients who did not consent to the examination.
29
TECHNIQUE
Patients who presented for ultrasound examination of other parts of the body and
who have fulfilled the inclusion criteria had their necks examined by the researcher
to ensure they had no palpable thyroid nodules.
The patients were asked to sit and their necks were observed for any visible mass.
The examiner then stood behind the patient and encircled her fingers around the
patient’s neck. The patient was asked to flex his/her neck partially to relax the
overlying muscles. The patient’s neck was palpated for any mass in the region of
the thyroid gland, just below the cricoid cartilage. The patient was then asked to
swallow to draw a small retrosternal thyroid goiter above the examining fingers.
Patients who did not have palpable thyroid nodule then had their necks scanned
for thyroid incidentalomas by the researcher.
A General Electric LogiqP5 ultrasound machine was used for the examination of
the thyroid gland. A 6- 10MHz linear transducer was used to visualize both lobes
of the thyroid gland.
30
All clothing and jewellery were removed from the neck and with the subject supine
on the scanning table, the neck was slightly extended. A high frequency linear
probe (6-10MHz) was used to scan both lobes of the thyroid gland in the axial and
longitudinal planes. The sizes of the lobes of the thyroid and the isthmus were
measured and the volumes of the lobes of the thyroid gland were calculated
according to the ellipsoid model (length [cm] x width [cm] x depth [cm] x 0.5).57
When incidentalomas were seen in either of the lobes or the isthmus; the number
of the incidentalomas was documented. The size, shape, margin, echotexture and
echogenicity of the masses were also documented. The masses were checked for
calcifications and colour flow Doppler was used to assess blood flow to masses
demonstrated within the thyroid gland. When the incidentalomas were multiple,
the largest was measured and assessed for the different features. The
incidentalomas were classified using the TIRADS classification developed by
Horvath et al55. When subjects had incidentalomas in both lobes of the thyroid
gland with different TIRADS classification, the higher classification was recorded
for the subject. Other neck masses seen during the examination were recorded.
31
STATISTICAL ANALYSIS
The data generated was analyzed and presented using frequency tables,
percentages and charts as appropriate. Chi square test and Spearman’s correlation
were used to test association between qualitative variables at 5% level of
significance. The statistical package used was SPSS 17.0Version.
32
RESULTS
A total of 340 subjects were examined. This comprised of 153(45%) males and
187 (55%) females. Their ages ranged from 18 years to 83 years with a mean age
of 42.78±15.48years. The highest proportion of the respondents, 100 (29.4%) were
within 30-39 years of age and within this group, 48 (14.1%) were males and 52
(15.3%) were females, while the least frequent were those above 70 years of age
( Table 3 and Fig. 5).
The mean total volume of both lobes of the thyroid gland was 6.58±2.47cm3 with a
range of 2.17 to 15.7cm3.The right lobe of the thyroid gland was significantly
bigger (mean volume of 3.43±1.44cm3) than the left lobe of the thyroid gland
which had a mean volume of 3.16±1.29cm3 (p value =0.000). Both lobes of the
thyroid gland were significantly bigger in males (6.96cm3± 2.4 cm3) than in
females (6.26±2.47cm3), with p value of 0.01. The volume of the thyroid glands
also increased with age and peaked at the 7th decade in males while in females, the
peak volume was recorded in the 6th decade. This association between thyroid
volume and age was significant with a p value of 0.02 (Table 4).
33
Table 3: Age and sex distribution of subjects.
Age group (years) Male (%) Female (%) Frequency (%)
<30 37 (10.9%) 32 (9.4%) 69 (20.3%)
30-39 48 (14.1%) 52 (15.3%) 100 (29.4%)
40-49 20 (5.9%) 40 (11.8%) 60 (17.6%)
50-59 15 (4.4%) 27(7.9%) 42 (12.4%)
60-69 21 (6.2%) 26 (7.6%) 47 (13.8%)
>70 12 (3.5%) 10(3%) 22(6.5%)
Total 153(45%) 187(55%) 340(100%)
34
Fig 5: Age and sex distribution of 340 subjects.
35
Table 4: mean volume of the thyroid glands by age.
AGE
GROUP(years)
MALE(mean
volume in
cm3±SD)
FEMALE(mean
volume in
cm3±SD)
TOTAL(mean
volume in
cm3±SD)
<30 6.39±1.55 5.81±2.09 6.11±1.84
30-39 6.93±2.00 5.94±1.97 6.41±2.04
40-49 7.05±2.71 6.34±2.30 6.57±2.45
50-59 7.31±2.99 6.94±3.53 7.07±3.31
60-69 7.80±3.22 6.27±2.50 6.95±2.91
≥70 6.83±3.16 7.39±3.01 7.09±3.03
TOTAL 6.96±2.41 6.27±2.47 6.58±2.47
p value= 0.02 (significant)
36
Seventy six (76) subjects had incidental lesions in either lobe of their thyroid
glands with a 22.4% prevalence of the thyroid incidentaloma. The diameter of the
incidentalomas ranged from 0.2cm to 2.7cm on the right (mean ±SD 0.69±0.46cm
and mode of 0.4cm) and 0.1cm to 2.1cm on the left (mean ±SD 0.73±0.47cm and a
mode of 0.3cm).
The incidence of thyroid incidentaloma was higher in females (Table 5). The sex
difference was however not statistically significant (P=0.09).
The prevalence of incidentaloma was the same, 49 (14.4%), in both right and left
lobes. However 23 subjects (6.8%) had incidentalomas in both lobes, of these, 9
(2.6%) were males and 14 (4.1%) were females. For both lobes of the thyroid
gland, the prevalence of thyroid incidentalomas was still higher in females than
males (Table 6).
The prevalence of thyroid incidentaloma significantly increased with age, from the
third to the seventh decade (P value = 0.001). The subjects in the 7th decade (60-69
years) had the highest incidence rate in both lobes of the thyroid gland (Table 7).
Overall, most incidentalomas were single lesions, 75.5% on the right and 69.4% on
the left. In subjects with multiple lesions, the highest number of lesions seen on
either side was 5 (Table 8).
37
Table 5: The prevalence of thyroid incidentaloma
Presence of Incidentaloma in
either lobe
Yes (%) No (%) Total (%)
Male 28(8.2%) 125 (36.8%) 153(45%)
Female 48 (14.1%) 139(40.9%) 187 (55%)
Total 76(22.4%) 264 (77.6%) 340(100%)
P value is 0.09 (not significant).
Table 6: Prevalence of incidentalomas in both lobes of the thyroid gland.
Incidentalomas (%) No incidentaloma (%) Total (%)
Male Female Total Male Female Total
Right
lobe
16(4.7%) 33 (9.7%) 49(14.4%) 171 120 291(85.6%) 340
(100%)
Left lobe 21(6.2%) 28(8.2%) 49(14.4%) 165 125 290(85.3%) 339*
(99.7%)
Total 39 61 98**
*One male subject had aplasia of the left thyroid lobe
**some subjects had incidentaloma in both lobes of the thyroid gland (9males and
14 females).
38
Table7: Age distribution of thyroid incidentalomas.
Right lobe Left lobe Total
Age group
(yrs.)
Frequency (%) Frequency (%) Frequency (%)
<30 4 (5.8%) 5(7.2%) 9(13%)
30-39 10(10%) 3 (3%) 13(13%)
40-49 7 (11.7%) 8(13.3%) 15(25%)
50-59 9 (21.4%) 13 (31%) 22(52.4%)
60-69 14 (29.8%) 16(34%) 30(63.8)
>70 5 (29.4%) 4(23.5%) 9(52.9%)
Total 49 49 98*
P value is 0.001 (significant).
*some subjects had incidentaloma in both lobes of the thyroid gland (9males and
14 females).
Table 8: The number of incidentalomas seen within the lobes of the thyroid
gland.
Number of lesions Right lobe (%) Left lobe (%)
1 37 (75.5%) 34 (69.4%)
2 6 (12.2% 9 (18.4%)
3 1 (2%) 1 (2%)
4 0 (0%) 2 (4.1%)
5 5 (10.2%) 3 (6.1%)
Total 49 (100%) 49 (100%)
39
Most of the incidentalomas had smooth margins (89.8% on the right and 85.7% on
the left).
In terms of the echogenicity, majority of the lesions (49%) in the right lobe were
cystic (Fig 6) while majority of lesions (61.2%) in the left lobe were hypoechoic to
the thyroid gland (Fig 7). Seven (14.3%) and 2 (4.1%) of the lesions were
hyperechoic on the right and left respectively (Fig 8).
Homogenous lesions were also seen more frequently bilaterally (right 65.3% and
left 59.2%) than heterogenous lesions (Fig 9 and 10).
Microcalcifications were the commoner type of calcifications seen within the
thyroid incidentalomas-15 cases, (30.6%) on the right and in 10 cases (20.4%) on
the left. Macrocalcifications on the other hand were seen in 7cases (14.3%) on the
left and in 5 subjects (10.2%) on the right.
On colour Doppler ultrasound, 11(22.5%) of the 49 lesions on the right and 14
(28.5%) of the 49 lesions on the left had some form of color flow while the
remaining lesions showed no color flow (Table 9).
40
Fig 6. Transverse ultrasound of the right lobe of the thyroid gland showing a well defined cystic lesion
within it (white arrow). A similar but smaller lesion is seen lateral to it.
Fig7. B mode ultrasound of the left lobe of the thyroid gland (transverse view) showing two
heterogeneously hypoechoic lesions (white arrows).
41
Fig 8. Transverse ultrasound of the right lobe of the thyroid gland showing a homogenously hyperechoic
mass within it (white arrows).
Fig9. B mode ultrasound of the left lobe of the thyroid gland (transverse section). There is a
heterogeneously hypodense mass within the lobe of the thyroid gland (white arrow). The mass is
hypoechoic when compared to the thyroid gland but is not hypoechoic to the strap muscles
anterior to the thyroid gland.
42
Fig10. Transverse ultrasound of the right lobe of the thyroid gland showing a heterogeneously
cystic mass in the thyroid gland (white arrow).
43
Table 9: ultrasound features of incidentaloma
Frequency
Right Left
Margin
Well defined 44(89.8%) 42(85.7%)
Ill defined 5(10.2%) 7(14.3%)
Echogenicity
Hyperechoic 7 (14.3%) 2 (4.1%)
Hypoechoic to thyroid 16 (32.7%) 30 (61.2%)
Hypoechoic to muscle 2 (4.1%) 0 (0%)
Cystic 24 (49%) 17 (34.7%)
Texture
Homogenous 32(65.3%) 29(59.2%)
Heterogenous 17(34.7%) 20(40.8%)
Calcification
Microcalcification 15(30.6%) 10(20.4%)
Macrocalcification 5(10.2%) 7(14.3%)
No calcification 29(59.2%) 32(65.3%)
Color flow
Internal flow 7(14.3%) 8(16.3%)
Peripheral flow 4(8.2%) 6(12.2%)
No flow 38(77.5%) 35(71.4%)
44
Majority of the lesions, 41 (53.95%) were classified as TIRADS 2 (benign
findings) while only 2 lesions (2.6%) were classified as TIRADS 4 (undetermined/
suspicious findings). These two suspicious lesions were recorded in a male subject
and in a female subject in the 5th decade. The male subjects had most of their
lesions falling in the TIRADS 3 classification while most females had lesions in
the TIRADS 2 classification (Table 10).
One congenital abnormality, an absent left lobe, was documented in one male
subject. In this subject, the strap muscles of the neck were seen in the thyroid bed
(Fig 11)
45
Table10: Age group and TIRADS classification of incidentaloma.
MALE
FEMALE
AGE
GROUP
(YRS)
TIRADS2
TIRADS3
TIRADS4
TOTAL
TIRADS2
TIRADS3
TIRADS4
TOTAL
<30 1 2 0 3 3 1 0 4
30-39 1 4 0 5 4 3 0 7
40-49 1 3 0 4 5 3 1 9
50-59 2 2 1 5 7 4 0 11
60-69 5 3 0 8 9 4 0 13
>70 1 2 0 3 2 2 0 4
TOTAL 11 16 1 28 30 17 1 48
TIRADS: Thyroid Imaging Reporting And Data Systems
TIRADS 1- Normal thyroid gland
TIRADS 2- Benign findings
TIRADS 3- Probably benign findings
TIRADS 4- 4A-Undetermined and 4B- Suspicious
46
Fig 11. B mode ultrasound of the thyroid (transverse section). Aplasia of the left lobe of the thyroid gland
in a 39year old man. Fig 11A shows the right lobe of the thyroid gland ( white arrow heads) seen just
below the strap muscles of the neck (white arrows) and lateral to the shadow of the trachea (white double
arrow). A well defined hyperechoic incidentaloma is seen within the right lobe of the gland (black
arrows). In Fig 11B, the left lobe of the thyroid gland is not seen. The strap muscles (white arrows) are
seen lateral to the trachea (white double arrow) and the common carotid artery (curved arrow) is seen just
posterior to the strap muscles.
A B
47
DISCUSSION
Many studies have been done to determine the volume of the thyroid gland in
different geographic locations and at different times in the same location. This
cross-sectional study documented the mean volume of the thyroid gland to be
6.58±2.47cm3 with a range of 2.17cm3 to 15.7cm3. This value is less than that
previously documented and used as reference value (20-25g) in the middle of last
century.14
However, the value documented is close to that of Ahidjo et al59 who studied 173
subjects in Maiduguri and documented a mean volume of 8.55±1.82cm3. It is also
similar but less than that documented by Ghervan12 in Romania who documented
an average volume of 11.6ml in women and 14ml in men. This value is also
corroborated by Langer13who in his review noted that the volume of the thyroid
gland documented in recent papers are remarkably lower than previous values.
This has been attributed to the high iodine intake in such countries where the
studies have been carried out. Also in former Czechoslovakia, the volume of the
thyroid gland recorded when the country was declared an iodine deficient country
was higher than when it became iodine replete19. It may be assumed that the
subjects in the study have normal iodine values. Further research may be needed to
correlate the volume of the thyroid gland with thyroid function tests as well as
follow up the trend in the volume of thyroid gland in this environment. Although
48
ultrasound examination can be operator dependent, the ultrasound measurement of
the volume of the thyroid gland and its correlation to the true gland volume has
been found to be very close.15 Other three dimensional imaging modalities like
computed tomography (CT) and magnetic resonance imaging (MRI) may be more
accurate in determining the volume as they are less operator dependent. However,
these imaging modalities are not appropriate for screening of apparently normal
individuals. This is because Computed tomography (CT) though becoming more
available, uses ionizing radiation and its use may not be justified in normal
individuals. Magnetic resonance imaging (MRI) does not use ionizing radiation but
is expensive and is not readily available.
The volume of the right lobe of the thyroid gland is significantly higher than the
left with significant statistical difference between the right and left lobe volumes in
both sexes (p =0.000). This finding is in agreement with a previous study done
locally.59 It may appear that the right lobe of the thyroid gland is dominant but
further research will be needed to evaluate the structural anatomy and function of
these lobes.
49
The volume of the thyroid gland was significantly larger in males than females,
with a difference of 0.70cm3. This finding is in agreement with the findings of
other authors.15,16, 17,58 This finding is usually attributed to the fact that structural
anatomy is generally larger in males than in females due to the larger body surface
area and higher weight. However, Gerber et al 18 and Silink and Reisenauner19 had
documented that women had larger thyroid glands than men but they noted that
those studies were done in iodine deficient subjects.
The volume of the thyroid gland has also been noted to increase with age. In this
study, the volume of the thyroid gland increased significantly with age and peaked
in the 6th and 7th decade in females and males respectively. This is similar to the
findings of Reiners et al 20 who found the thyroid volume to peak at 45years of
age. However, their peak age is lower than that recorded in this study. The finding
has been attributed to higher Thyroid Stimulating Hormone (TSH) level in
advanced age or lower iodine intake in higher age groups.20
Thyroid incidentalomas are thyroid lesions detected during imaging investigations
unrelated to the thyroid gland. With the increasing use of cross-sectional imaging,
the prevalence of these lesions is on the increase. The prevalence of thyroid
incidentaloma is also known to be high in iodine deficient regions. The clinical
importance of these thyroid incidentalomas is that they raise the suspicion of
50
thyroid malignancy. However, their management is still controversial and it is not
economically feasible to perform a complete functional assessment or Fine Needle
Aspiration on all noted thyroid incidentalomas.
In the evaluation of the potential importance of thyroid incidentalomas in this
environment, it is imperative to first determine the prevalence of thyroid
incidentalomas.
In this study, the overall prevalence of incidentally detected thyroid incidentaloma
is 22.4%. This value is similar to that recorded from previous studies. Brander et
al3 recorded a prevalence rate of 27.8% for incidentalomas, in a prospective
screening study conducted in Finland where goiter is not endemic and Woestyn et
al16 also recorded a prevalence rate of thyroid incidentalomas of 27% in Belgium.
However, Horlocker et al 7 and Stark et al 8 recorded higher incidence rates
probably because their studies were not randomized and were carried out in
hyperthyroid patients. Kang et al19 recorded a lower prevalence rate of 13.4% in a
retrospective study involving 1475 patients who had routine check of the neck for
reasons other than thyroid gland disease. This low prevalence rate may be due to a
larger sample size and also to the fact that it was a retrospective study.
Mohammadi et al60 also recorded a low prevalence of thyroid incidentaloma of
13.6% in Bushehr, Southern Iran and attributed this low prevalence to the result of
51
the effort of the country in finding a solution to iodine deficiency by introducing
iodized salt 15 years before their study was carried out. Efforts have also been
made in Nigeria to increase the iodine intake of individuals by the production of
iodized salt which commenced since 1993. However, it is difficult to establish the
iodine status of all the patients in this study.
The prevalence of thyroid incidentalomas increased with age and peaked at the
seventh decade in both sexes. This finding was also similar to findings in previous
studies.13,16,59 Brander et al3 in their study reported the highest prevalence of
incidentalomas in the fourth decade but Woestyn et al16 found that the overall
prevalence of 27% in the study population increased to about 40% in the seventh
decade. They concluded that the highest frequency is found in the seventh and
eighth decade in men and in the seventh decade in women. In this study, the
highest incidence in men was also in the seventh decade. Age should therefore be
considered a risk factor for developing thyroid incidentaloma.
The prevalence of thyroid incidentalomas was also commoner in women and this is
in accordance with previous clinical and autopsy findings.3, 10, 16 This may be
because the thyroid gland in women is known to respond to hormonal changes
during pregnancy and the post- partum period by increasing and reducing in size
52
respectively. The menstrual cycle is also known to alter the thyroid size in healthy
women.59
Majority of the incidentalomas seen in this study were solitary and in 37 (75.5%)
and 34 (69.4%) of the incidentalomas on the right and left respectively. This
finding is also in agreement with the findings of Brander et al 3who recorded
solitary incidentaloma in 57% of their subjects. However, the percentage of
solitary lesions found in this study was slightly higher than that found by Brander
et al 3. This may be because the ages of the subjects they studied ranged from 19
to 50 years while in this study older subjects up to 83 years were included in the
study.
Apart from being solitary, most of the incidentalomas were also unilateral as
recorded by previous authors8. The diameter of the incidentalomas recorded ranged
from 0.2cm to2.7cm on the right (mean 0.69cm) and 0.1cm to 2.1cm on the left
(mean 0.73cm). This finding is similar to those of Brander et al22 and Tan et al25
who stated that most of the incidentalomas were less than 1cm. A nodule smaller
than 1 cm in diameter often escapes clinical palpation, unless it is located
superficially. The highest diameter of thyroid incidentaloma documented in this
study was 2.7cm and 2.1cm on the right and the left lobes respectively. These
53
lesions were not clinically palpable probably because they were located deep
within the lobe of the thyroid gland.
Most of the lesions on the right were cystic (49%) and those on the left were
hypoechoic to the thyroid gland (61.2%). Purely cystic nodules are said to be
benign while hypoechoic nodules that appear more hypoechoic than the strap
muscles of the neck are said to be suspicious of malignancy.47 It is not cost
effective to perform ultrasound guided fine needle aspiration for histology or
biopsy for all the detected thyroid incidentalomas. However, several authors have
correlated ultrasound characteristics with histopathologic findings to determine
incidentalomas that would need biopsy.37,38,44,48,53,54 Using the classification of
Horvath et al55 most of the lesions detected in this study were classified as
TIRADS 2. Only 2 of the 76 lesions were in TIRADS 4 classification which has a
5-80% probability of being malignant (5-10% for 4A and 10-80% for 4B). US-
guided Fine needle aspiration cytology or histology is recommended for patients
with TIRADS 4 classified nodules. However, most incidentally discovered nodules
are usually benign. The low risk for malignancy was also confirmed by Brander
and coworkers,3 who reported that none of 30 patients who were randomly selected
for fine-needle aspiration biopsy had thyroid cancer. Most of the occult carcinomas
in thyroid incidentaloma reported by other authors were cases of papillary
54
cancer.2,27,28,31,61 Papillary cancer has an indolent course and an excellent prognosis
and because they are not aggressive, conservative treatment is appropriate.
Overall, the prevalence of thyroid incidentaloma in this environment is high and is
commoner in females and also increases with age. Those incidentalomas that have
a high probability of being malignant will need to be further evaluated with
histology in a follow up study.
One male subject was found to have aplasia of the left lobe of the thyroid gland.
Aplasia of a lobe of the thyroid gland is said to be a rare congenital anomaly of the
thyroid gland. The true prevalence of this anomaly is not known since it is usually
diagnosed incidentally. However, it is found in about 1 in 2000 school children in
iodine sufficient area and is not associated with functional defects.62 Further
research with a larger sample size will be needed to document the incidence of
congenital abnormalities of the thyroid gland in this environment.
55
CONCLUSION
This study has documented the volume of the normal thyroid gland of adult
population in Ibadan to be 6.58±2.47cm3. The volume is smaller than has been
previously quoted and is similar to recent findings in other parts of the country and
the world. The volume of the thyroid gland is higher in men and is noted to
increase with age.
Real time ultrasound with high frequency transducers and Doppler facility has
been used to demonstrate small lesions in the thyroid gland of apparently normal
subjects. The prevalence of thyroid incidentaloma is high (22.4%) in the study
population in Ibadan. These lesions are often cystic and hypoechoic. In this study,
the prevalence of thyroid incidentaloma was higher in women and varied with age,
reaching the highest value in the 7th decade.
56
LIMITATIONS OF THE STUDY
This study was carried out in volunteers and patients who were referred to the
ultrasound suite of the Radiology department for examination of the other parts of
the body and therefore may not show the true prevalence of thyroid incidentaloma
in the study area.
57
RECOMMENDATIONS
1. The volume of the thyroid gland is on the downward trend in recent studies.
Further research is recommended to correlate iodine sufficiency and the
volume of the thyroid in this environment.
2. The incidence of incidentalomas appears to be high in the general
population. Because of the continued widespread use and high sensitivity of
ultrasonography, many small, non- palpable thyroid nodules will be
discovered incidentally during the course of carotid, parathyroid, or other
ultrasonographic examinations of the neck. Careful follow-up is necessary
for lesions that are discovered during these studies.
3. The thyroid function tests should be correlated with the findings of the
thyroid incidentalomas.
58
REFERENCES
1. Vander JB, Gaston EA and Dawber TR. The significance of non-toxic thyroid
nodules. Ann Intern Med 1968; 69: 537-540.
2. Singer PA, Cooper DS and Daniels GH. Treatment guidelines for patients
with thyroid nodules and well differentiated thyroid cancer. Arch Intern Med
1996; 156: 2165-2172.
3. Brander A, Vikinnksoki P, Nickels J and Kirisaari L. Thyroid gland: US
Screening in a Random Adult Population. Radiology 1991; 181: 683-687.
4. Mortensen JD, Woolner LB and Bennet WA. Gross and microscopic findings
in clinically normal thyroid gland. J Clin Endocrinol Metab 1955; 15:1270-
1280.
5. Choi JY, Lee KS, Kim HJ, Shim YM, Kwon OJ, Park K et al. Focal thyroid
lesions incidentally identified by integrated 18F-FDG PET/CT: Clinical
significance and improved characterization. J Nucl Med 2006; 47:609-615.
6. Mitchell J and Parangis. The Thyroid Incidentaloma: an increasingly frequent
consequence of radiologic imaging. Semin Ultrasound CT MR 2005; 26: 37-
46.
59
7. Bae JS, Chae BJ, Park WC, Kim JS, Kim SH, Jung SS et al. Incidental
thyroid lesions detected by FDG-PET/CT: Prevalence and risk of thyroid
cancer. World Journal of Surgical Oncology 2009; 7:63.
8. Scott RS, Mathew JM, Phillip SM, Kenneth SA and Charles AA. The
significance of incidental thyroid abnormalities identified during carotid
duplex ultrasonography. Arch Surg.2005; 140: 981-985.
9. Youserm DM, Huang T, Loevner T and Langlotz CT. Clinical and Economic
Impact of Incidental Thyroid Lesions found with CT and MR. Am J
Neuroradiol 1997; 18: 1423-1428.
10. Hegedus L. Clinical practice: The Thyroid Nodule. N Engl J Med 2004; 351:
1764-1771.
11. Organ GM and Organ CH. Thyroid gland and surgery of the thyroglossal
duct: Exercise in applied embryology. World J Surg 2000; 24: 886-890.
12. Ghervan C. Thyroid and Parathyroid Ultrasound. Medical Sonography
2011;13: 80-84
13. Langer P. Discussion about the limit between normal thyroid and goiter:
Minireview. Endocrine Regulations 1999; 33:39-45
14. Seker S and Tas I. Determination of thyroid volume and its relation with
isthmus thickness. Eur J Gen Med 2010; 7:125-129.
60
15. Yokoyama N, Nagayama Y, Kakezono F, Kiriyama T and Morisa S.
Determination of the volume of the thyroid gland by a high resolution
ultrasonic scanner. J Nucl Med 1986; 27:1475-1479
16. Hegedus L. Thyroid size determined by ultrasound. Danish Med Bull. 1990;
37: 249-263.
17. Berghout A, Wiersinga WM, Smits NJ and Touber JL. The value of thyroid
volume measured by ultrasonography in the diagnosis of goiter. Clin
Endocrinol 1988; 28: 409-414.
18. Gerber D. Schilddruesengewichte and Jodsalzprophylaxe. Schweiz med
Wochenschr 1980; 110: 2010-2016.
19. Silink K and Reisenauner R. Geographical spread of endemic goiter and
problems of its mapping. In: Endenmic Goiter and allied Diseases (Eds K
Silink and K Cerny) 1966VEDA, Bratislava 1966
20. Reiners C, Wegscheider K, Schicha H, Theissen P, Vaupel R, Wrbitzky R
and Schumm-Drager P. Prevalence of thyroid disorders in working
population of Germany: ultrasonography screening in 96,278 unselected
employees. Thyroid 2004; 14: 926-932.
21. Christensen SB and Tibblin S. The reliability of the clinical examination of
the thyroid gland. A prospective study of 100 consecutive patients surgically
treated for hyperparathyroidism. Ann Chir Gynaecol. 1985;74:151-154
61
22. Brander A, Viikinkoski P, Tuuhea J, Voutilainen L and Kivisaari L. Clinical
versus ultrasound examination of the thyroid gland in common clinical
practice. J Clin Ultrasound. 1992; 20:37-42.
23. Veith FJ, Brooks JR, Grigsby WP and Selenkow HA. The nodular thyroid
gland and cancer. A practical approach to the problem. N Engl J Med. 1964;
270:431-436.
24. Jarlov AE, Hegedus L, Gjorup T and Hansen JM. Observer variation in the
clinical assessment of the thyroid gland. J Intern Med. 1991; 229:159-161.
25. Tan GH, Gharib H and Reading CC. Solitary thyroid nodule. Comparison
between palpation and ultrasonography. Arch Intern Med. 1995; 155:2418-
2423.
26. Solbiati L, Volterrani L, Rizzatto G, Bazzocchi M, Busilacchi P, Candiani F,
et al. The thyroid gland with low uptake lesions: evaluation by ultrasound.
Radiology. 1985; 155:187-191.
27. Stark DD, Clark OH and Moss AA. Magnetic resonance imaging of the
thyroid, thymus, and parathyroid glands. Surgery. 1984; 96:1083-1091.
28. Katz JF, Kane RA, Reyes J, Clarke MP and Hill TC. Thyroid nodules:
sonographic-pathologic correlation. Radiology. 1984; 151:741-745.
62
29. Furmanchuk AW, Roussak N and Ruchti C. Occult thyroid carcinomas in
the region of Minsk, Belarus. An autopsy study of 215 patients.
Histopathology. 1993; 23: 319-325.
30. Dean DS and Gharib H. Epidemiology of thyroid nodules. Best Pract Res
Clin Endocrinol Metab 2008; 22(6): 901-911.
31. Gerry HT and Hossein G. Thyroid incidentalomas: Management Approaches
to non-palpable nodules discovered incidentally on thyroid imaging. Annals
of Internal Medicine 1997; 126(3): 226-231.
32. Kakkos SK, Skopa CD, Chalmonkis AK, Karachalios D, Spliliotis JD,
Harkoftakis JG et al. Relative risk of cancer in sonographically detected
thyroid nodules with calcifications. J Clin Ultrasound 2000; 28: 347-352
33. Khurana KK, Richards VI, Chopra PS, Izquierdo R, Rubens D and
Mesonaro C. The role of ultrasonography guided fine-needle aspiration
biopsy in the management of non-palpable and palpable thyroid nodules.
Thyroid 1998; 8: 511-515.
34. Nack KS and Bury RF. Review: Imaging the thyroid. Clin Radiol 1998; 53:
630-639.
35. Woestyn J, Afschrift M, Schelstraetek K and Vermuele A. Demonstration
of nodules in the normal thyroid by echography. Br J Radiology 1985; 58:
1179-1182.
63
36. Prevalence of incidental nodular thyroid disease detected during high
resolution parathyroid ultrasonography. In: Mediros-Neto G, Gaitan E, Eds.
Frontiers in thyroidology. Ninth International Thyroid Congress, Sao Paulo,
Brazil, 1985. New York Plenum, 1985; 1309-1312.
37. Stark DD, Clark OH, Gooding GA and Moss AA. High resolution
ultrasonography and computed tomography of thyroid lesions in patients
with hyperparathyroidism. Surgery 1983; 94: 863-868.
38. Kang HW, No JH, Chung JH, Min YK, Lee MS, Lee MK et al. Prevalence,
clinical and ultrasonographic characteristics of thyroid incidentalomas.
Thyroid 2004; 14: 29-33.
39. Oertel JE and Klinck GH. Structural changes in the thyroid glands of healthy
young men. Med Ann DC 1965; 34:75-77.
40. Wagner DH, Recant WM and Evans RH. A review of one hundred and fifty
thyroidectomies following prior irradiation to the head, neck and upper part
of the chest. Surg Gynecol Obstet. 1978; 147: 903-908.
41. Deaconson TF, Wilson SD, Cerletty JM and Komorowski RA. Total or near
total thyroidectomy versus limited resection for radiation-associated thyroid
nodules: a twelve-year follow-up of patients in a thyroid screening program.
Surgery. 1986; 100: 1116-1120.
64
42. Kuma K, Matsuzuka F, Yokozawa T, Miyauchi A, Sugawara M. Fate of
untreated benign thyroid nodules: results of long-term follow-up. World J
Surg. 1994; 18:495-8.
43. Nam Goong IS, Kim HY, Gong G, Lee HK, Hong SJ, Kim WB and Shong
YK. Ultrasonography-guided fine-needle aspiration of thyroid
incidentaloma: correlation with pathological finding. Clin Endocrinol (Oxf)
2004; 60: 21-28.
44. Koike E, Noguchi S, Yamashita H, Murakami T, Ohshima A, Kawamoto H
et al. Ultrasonographic characteristics of thyroid nodules: prediction of
malignancy. Arch Surg 2001; 136:334-337.
45. Burguera B and Gharib H. Thyroid incidentalomas: prevalence, diagnosis,
significance and management. Endocrinol Metab Clin North Am 2000; 29:
187-203.
46. Gharib H. Changing concepts in the diagnosis and management of thyroid
nodules. Endocrinol Metab Clin North Am 1997; 26: 777-800.
47. Kim EK, Park CS, Chung WY, Oh KK, Kim DI, Lee JT et al. New
sonographic criteria for recommending fine-needle aspiration biopsy of non
palpable solid nodules of the thyroid. Am J Roentgenol 2002; 178:687-691.
65
48. Lannuccilli JD, Cronan JJ and Monchik JM. Risk for malignancy of thyroid
nodules as assessed by sonographic criteria. J ultrasound Med 2004; 23:
1455-1464.
49. Solbiati L, Arsizio B and Ballarati E. Microcalcifications: a clue in the
diagnosis of thyroid malignancies. Radiology 1990; 117(suppl): 140
50. Propper RA, Skolnick ML, Weinstein BJ and Dekker A. The non specificity
of the thyroid halo sign. J Clin Ultrasound 1980; 8:129-132.
51. Solbiati L. Thyroid gland. In: James EM, ed. Diagnostic Ultrasound St
Louis: Mosby, 1998: 703-729.
52. Brkljacic B, Cuk V, Tomic-Brzac H, Bence-Zigman Z, Delic-Brkjacic D and
Drinkovic I. Ultrasonic evaluation of benign and malignant nodules in
echographically multinodular thyroids. J Clin Ultrasound 1994; 22: 71-76.
53. Frates MC, Benson CB, Doubilet PM, Cibas ES and Marqusee E. Can color
Doppler sonography aid in the prediction of malignancy of thyroid nodules?
J Ultrasound Med 2003; 22:127–131.
54. Papini E, Guglielmi R, Bianchini A, Crescenzi A, Taccogna S, Nardi F,
Panunzi C et al. Risk of malignancy in nonpalpable thyroid nodules:
predictive value of ultrasound and color-Doppler features. J Clin Endocrinol
Metab 2002; 87:1941–1946.
66
55. Horvarth E, Majlis S, Rossi R, Franco C, Niedmann JP, Castro A and
Dominguez M. An Ultrasonogram reporting system for Thyroid nodules
stratifying cancer risk for clinical management.
56. Shetty Sk, Mahor MM, Hahn PF, Halpan EF and Aquino SL. Significance of
incidental thyroid lesions detected on CT: Correlation among CT,
Sonography and Pathology. Am J Roentgenol 2006; 187: 1349-1356.
57. Leslie Kish. Population values and statistics. In: Survey Sampling. John
Wiley and Sons Inc. New York. 1965; 3-26.
58. Knudsen N, Bols B, Bülow I, Jørgensen T, Perrild H, Ovesen L and
Laurberg P. Validation of ultrasonography of the thyroid gland for
epidemiological purposes. Thyroid 1999; 9:1069–1074.
59. Ahidjo A, Tahir A and Tukur MA. Ultrasound determination of thyroid
gland volume among adult Nigerians. The Internet Journal of Radiology
2006;4 :2
60. Mohammadi A, Amirazodi E, Masudi S and Pedram D. Ultrasonographic
Prevalence of Thyroid Incidentaloma in Bushehr, Southern Iran. Iran J
Radiol 2009; 6 (2): 65-68.
61. Moon WJ, Jung SL, Lee JH, Na DG, Baek JH, Lee YH, Kim HS, Byun JS
and Lee DH. Benign and malignant thyroid nodules: US differentiation-
multicenter retrospective study. Radiology 2008; 247(3): 762-770.
67
62. Korpal-Szczyrska M, Kosiak W and Sineton D. Prevalence of thyroid
hemiagenesis in an asymptomatic school children population. Thyroid
2008;18(6):637-639.