Original Articles

Journal of Diagnostic Medical Sonography26(5) 215 223 The Author(s) 2010Reprints and permission: http://www. sagepub.com/journalsPermissions.navDOI: 10.1177/8756479310378892http://jdm.sagepub.com

Scanning the Post-Thyroidectomy Neck: Appearance and Technique

Teresa Bieker, MBA, RT(R), RDMS, RDCS, RVT1

Abstract

Thyroid cancer is the most common type of endocrine cancer. In 2009, there were approximately 37,200 cases newly diagnosed. Sonography is becoming the modality of choice to evaluate the neck preoperatively and postoperatively. Accurate scanning and evaluation is essential for proper diagnosis, surgical approach, and staging.

Keywords

sonography, thyroidectomy, thyroid cancer, lymph node

Thyroid cancer is the most common endocrine cancer but represents only 1% of all cancers. In 2009, there were approximately 37,200 new cases, with 27,200 of those occurring in women and 10,000 occurring in men. Two thirds of the patients diagnosed are between the ages of 20 and 55 years, with a median age of 45 years. Between 1975 and 2001, there has been a 52% increase in reported cases of thyroid cancer.1,2 This is in part due to incidental findings on imaging studies, including sonography.

There are several types of thyroid cancer, including papillary, follicular, medullary, and anaplastic. Papillary and follicular types are classified as well-differentiated thyroid cancers, which arise from thyroid follicular cells. They are the most common types, accounting for approximately 80% to 90% of all thyroid cancers. Medullary and anaplas-tic are considered poorly differentiated thyroid cancers and account for 5% to 10% and 1% to 2%, respectively.2,3 Radiation exposure is a known risk factor for thyroid can-cer. Other causes include occupational risks, diet, lifestyle, parity, and family history.3

Treatment PlansThyroid cancer is treatable with 10-year survival rates of 98% (papillary), 92% (follicular), 80% (medullary), and 13% for the fast-growing anaplastic thyroid cancer.3,4 Most patients with differentiated thyroid cancer are con-sidered low risk. Factors that may affect outcome include age, distant metastasis, local invasiveness, cervical lymph node metastasis, tumor size, multifocality, and tumor sub-type.46 For example, older patients with distal metastasis have an increased risk for mortality. Also, local lymph node metastasis places the patient at an increased risk for

distal metastasis.6 Early detection of differentiated thyroid cancer and metastases leads to more successful treatments and outcome.7

There have been many advances in the diagnosis and treatment of differentiated thyroid cancer.8 However, even with an excellent survival rate, the recurrence rate of dif-ferentiated thyroid cancer is 9% to 30%, with the majority of recurrences presenting within the first decade following diagnosis. Most recurrences present locoregionally, within the thyroid bed or in the cervical lymph nodes.3,6,911 Also, the majority of differentiated thyroid cancer metastases affect the ipsilateral neck and can be multiple. Twenty percent to 50% of patients will have regional lymph node metastasis at the time of diagnosis.4 Approximately 60% to 75% of recurrences will be in the cervical lymph nodes (zones III and IV), whereas 20% will occur within the thyroid bed (zone VI). Zone II and V nodes are less com-monly affected. Only 5% of recurrences will affect the trachea or muscle. Metastasis to the lymph nodes gener-ally does not affect survival rates; however, metastasis to the trachea or muscle decreases survival rates.4,10,12,13

For patients diagnosed with thyroid cancer, total or near-total thyroidectomy is the standard treatment.6,8,14 If abnormal lateral cervical lymph nodes are present, a neck dissection is also performed.4 Following thyroidectomy, patients are closely monitored for recurrence within the thyroid bed and cervical nodes as well as distal metastasis.

1Department of Radiology, University of Colorado, Aurora, CO, USA

Corresponding Author:Teresa Bieker, MBA, RT(R), RDMS, RDCS, RVT, Department of Radiology, University of Colorado, Box F720, Aurora, CO 80045, USAEmail: tbieker@msn.com

216 Journal of Diagnostic Medical Sonography 26(5)

A postoperative evaluation includes physical palpation of the neck by an endocrinologist or surgeon, neck sonogram, and laboratory evaluation of tumor markers, including serum thyroglobulin (Tg) and thyroglobulin antibodies.11 Depending on the extent of the disease, radioactive iodine ablation therapy, iodine 131 whole-body scanning, chest radiography, computed tomography (CT) or magnetic resonance imaging (MRI) of the neck and chest, and/or positron emission tomography (PET) imaging may be performed.4,5,9,11,12,14,15

In the past, iodine scanning was used to detect metasta-sis within the lateral neck. However, it has limited sensitiv-ity, especially within the lateral neck.12,15 Neck sonography and laboratory evaluation are recommended every 6 to 12 months to evaluate the thyroid bed as well as the lateral neck for 3 to 5 years following surgery.4,5,8,11

Lab WorkAfter a total or near-total thyroidectomy, Tg plays a criti-cal role in the evaluation of thyroid cancer.16 Tg is a spe-cific protein that is secreted from thyroid tissue.9,16 The sensitivity and specificity of Tg are high in detecting thy-roid cancer when followed by thyroidectomy and iodine ablation therapy.8 In patients free from disease, the serum Tg levels should be undetectable (

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normal lymph nodes during routine screening of the neck.18,19 The number of normal lymph nodes visualized increases with age.18 Benign cervical lymph nodes are sonographically characterized by their location, shape, size, echogenicity, vascular pattern, and presence of an echogenic hilum.

Benign cervical lymph nodes are typically located in the submandibular (zone I), parotid (zone II), upper cer-vical (zone II), and posterior triangle (zone V) regions.17,18

Normal cervical lymph nodes are typically oblong, oval, cigar, or kidney bean shaped (Figures 1 and 2).4,19 Reported size criteria are variable; however, it has been shown that normal nodes have a short- to long-axis ratio of less than 0.5.1719 Also, the size of lymph nodes varies

depending on the location. For example, nodes within the submandibular and superior zones are typically larger than those located more inferiorly in the neck.18,19 Inflam-mation from the oral cavity can be the reason for increased size or reactive nodes in the submandibular and upper neck zones (Figure 3).18,19 In general, lymph nodes vary in size from 3 to 25 mm.19

Sonographically, normal cervical lymph nodes typically have a central echogenic hilus surrounded by a hypoechoic cortex.4 The echogenic hilum, a strong acoustic reflector, is continuous with the surrounding tissues and can often be identified against the more hypoechoic fat and cortex (Figure 4).17,18 The presence of an echogenic hilus is a strong predictor of a benign node.7,1820 Approximately

Figure 1. Normal oval-shaped lymph node with an echogenic hilum located in zone III.

Figure 2. Jugular lymph nodes are commonly located in chains. Each lymph node should be evaluated for normal characteristics. These three normal lymph nodes with echogenic hilum are located within zone IV.

Figure 3. (A, B) Reactive lymph nodes within zone II in two different patients. It is not unusual to see larger lymph nodes near the submandibular gland.

Figure 4. Normal lymph node within zone VI. Note the hypoechoic cortex and echogenic hilum.

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84% to 92% of nodes with an echogenic hilum are con-sidered benign.20 In small nodes, an echogenic hilum may be difficult to visualize sonographically.4 Nevertheless, in the majority of normal lymph nodes greater than 5 mm in diameter, a echogenic hilum can be identified.18

A hilar vascular pattern or even avascularity can be seen within normal cervical lymph nodes (Figure 5).1720 Small nodes, less than 5 mm, often appear to be avascu-lar.17 Flow within the larger submandibular and upper cervical lymph nodes may be increased, but peripheral vascularity should not be seen in normal lymph nodes.19

Multiple characteristics should be visualized to con-firm benignity. A sole benign criterion is not sufficient for an accurate diagnosis.17

Sonographic Appearance of Abnormal NodesSimilar to normal nodes, abnormal nodes are character-ized by their location, shape, size, vascular pattern, and presence of an echogenic hilus. Abnormal nodes also have additional important characteristics, including echo-genicity, calcifications, and cystic changes.

Abnormal cervical lymph nodes can be identified within any zone of the neck; however, abnormal-appearing lymph nodes within the upper/mid-jugular (zone III), low jugular (zone IV), paratracheal region (zone VI), and supraclavicular region are more likely to be thyroid metastases than those elsewhere in the neck.7,9,14

When recurrent disease is present, the lymph node will lose its ovoid, elliptical shape and become more rounded.4,6,10,1720 It has been reported that malignant nodes are larger in size; however, this criterion cannot be

used in isolation because metastases can be identified in small nodes.17,18 In addition, reactive lymph nodes tend to be larger in size. Lymph nodes that are increasing in size on serial sonograms should be concerning for metastases.18

When malignant cells invade a lymph node, the hilum becomes displaced and is no longer identified sonograph-ically.20 Absence of the fatty hilum, therefore, is a strong characteristic of recurrence (Figure 6).6,7,9,17,18 Approxi-mately 96% of malignant nodes lack a fatty hilum.19 However, it should be borne in mind that small, normal lymph nodes may not display a visible fatty hilum.17

In addition to a lack of a fatty hilum, malignant lymph nodes typically are hypoechoic when compared with the surrounding tissues. This is the case with medullary thy-roid cancer and lymphoma. With recurrent papillary thy-roid cancer, however, the lymph node is commonly hyperechoic (Figure 6).4,17,18,20 This hyperechoic appear-ance is likely due to the presence of thyroglobulin within the lymph node.17

With disruption of the hilum, vascular patterns also change within malignant lymph nodes. Peripheral, irreg-ular flow can be seen with color Doppler.4,6 Peripheral or mixed (peripheral and hilar) flow has been shown to be highly suggestive of malignancy.17,18,20 Tumor infiltra-tion into the lymph nodes results in the change from hilar to peripheral flow (Figure 7).17 The clinical benefit of pulsed Doppler for determining benign versus malignant lymph nodes is debatable and is not considered routine protocol.17,18,20

In general, calcifications within malignant lymph nodes are rare. However, with recurrent medullary and, in par-ticular, papillary thyroid cancer, calcifications within the

Figure 6. Chain of abnormal, rounded, hyperechoic lymph nodes within zone III. Note the lack of an echogenic hilum.

Figure 5. Normal hilar flow within a cervical lymph node.

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node may be seen sonographically (Figure 8).6,7,10,11,14,17,20 Calcifications are typically small (microcalcifications) and peripherally located.17,18,20 Shadowing from the calcifica-tion may or may not be visualized.18

When the cervical lymph node becomes cystic, it is highly suggestive of recurrent papillary thyroid cancer (Figures 9 and 10).6,7,9,14,17,18 The cystic change is caused by necrosis secondary to tumor invasion. Regardless of size or other characteristics, when the node is cystic, is must be considered abnormal.20 Together, microcalcifica-tions and cystic change within a lymph node have a spec-ificity of near 100% for recurrent disease.4,9

Again, a sole criterion should not be used to diag-nose an abnormal lymph node. These nodes are often characterized as suspicious and can be followed with serial sonograms or Tg levels or may be biopsied. Multi-ple characteristics are needed for a more accurate sono-graphic diagnosis (Figure 11).

Zone VI AbnormalitiesAfter a total or near-total thyroidectomy, the paratracheal region should be homogeneous and uniform in appear-ance. It is not unusual, however, to visualize small masses within the thyroid bed. Zone VI masses can include postoperative scarring, muscle, necrosing fat, suture gran-ulomas, parathyroid glands, lymph nodes, remnant tissue, and metastasis. Suture granulomas are typically hypoechoic with a central echogenic focus. Recurrence in zone VI can appear round or oval in shape and is hypoechoic or nearly

Figure 7. (A, B) Abnormal, peripheral flow within an abnormal lymph node in two different patients. Also note the rounded, echogenic appearance, microcalcifications, and lack of an echogenic hilum.

Figure 8. Multiple examples of abnormal lymph nodes showing microcalcifications. (A) Complex lymph node that is recurrent papillary carcinoma by biopsy. (B) Hypoechoic lymph node with microcalcifications that was biopsy-proven recurrent medullary carcinoma. (C) Hyperechoic lymph node with microcalcifications. This lymph node was recurrent papillary carcinoma.

Figure 9. Multiple enlarged cystic lymph nodes extending from zone III to zone IV. Pathology confirmed recurrent papillary thyroid cancer.

Figure 10. Another example of an enlarged cystic lymph node within zone IV. Also note the multiple microcalcifications.

220 Journal of Diagnostic Medical Sonography 26(5)

anechoic; however, benign structures may appear simi-lar (Figures 1215).4,12,21 Masses within zone VI can be followed with serial sonography, correlated with serum Tg levels, and/or biopsied.

Equipment and Scanning ProtocolPostsurgical neck scanning is highly operator dependent. Careful scanning is necessary when evaluating the neck.

Becoming efficient at neck scanning requires experience, as well as a thorough knowledge of neck anatomy, poten-tial pathology, and zones (Table 1 and Figure 16).

The patient is positioned supine with the neck hyper-extended. A pillow may be placed under the patients shoulders to assist in extending the neck. Typically, a 12-MHz or higher linear array transducer is used. A lower frequency may be necessary for thicker necks. A small footprint 8- to 10-MHz curved-array transducer is also

Figure 11. It is important to correlate sonography findings with the patients surgical history. In this case, the focal areas within the sternocleidomastoid muscle are autotransplanted parathyroid glands.

Figure 12. Hypoechoic oval mass within zone VI. The differential diagnosis includes recurrent disease, parathyroid, or abnormal lymph node.

Figure 13. Zone VI abnormalities. (A) Hyperechoic oval mass within zone VI is a biopsy-proven recurrent papillary carcinoma. (B) A more hypoechoic mass deep within zone VI in another patient. This was also recurrent papillary carcinoma.

Figure 14. Small, hypoechoic area within zone VI. The differential diagnosis includes recurrent disease, parathyroid, abnormal lymph node, granuloma, or scarring.

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Figure 15. Focal echogenic foci within zone VI that likely represents a suture in the thyroid bed.

helpful for evaluating the supraclavicular and subman-dibular regions as well as the sternal notch. Gentle com-pression may also be useful to distinguish nodal borders, an echogenic hilum, and microcalcifications.

System settings should be optimized for each patient, including power output, time gain control, compound imaging, and dynamic range. Color Doppler settings should also be optimized. Ideal settings include medium persis-tence, low wall filter, and low pulsed repetition fre-quency (~700 Hz). Color gain should be increased to the point of noise, then decreased until the noise disappears.1719

In a transverse and longitudinal plane, evaluate the submental area, zone I. Sweep side to side, scanning to the lateral border of the right submandibular gland and to the lateral border of the left submandibular gland. Then scan superior from the mandible inferiorly to the hyoid bone.

Next, the anterior cervical and paratracheal lymph nodes of zone VI should be evaluated. In a transverse plane, scan from the hyoid bone inferiorly to the manu-brium. The thyroid bed is located in the mid to lower portion of zone VI. With an absent thyroid, it is not unusual to see the carotid arteries directly adjacent to the trachea. It is helpful to scan zone VI with the patients neck hyperex-tended, as well as turned to the contralateral side. By turning the patients head, artifact within zone VI can be reduced.

With the central neck completed, the lateral neck is then assessed to evaluate the superior, mid, and inferior jugular chain. In a transverse plane, scan from the posteriolat-eral border of the submandibular gland inferiorly to the level of the hyoid bone. Continue to sweep inferiorly in a

transverse plane to the medial edge of the internal jugular vein (IJV). This completes zone IIA. For zone IIB, poste-rior to the IJV, scan in a transverse plane from the man-dible inferiorly to the level of the hyoid bone.

Working inferiorly, continue to scan in a transverse plane along the internal jugular vein. Zone III is from the hyoid bone to the cricoid cartilage, whereas zone IV extends from the cricoid cartilage inferiorly to the clav-icle. Once the zone is evaluated in the transverse plane, scan through it in a longitudinal plane. At times, depend-ing on the patients anatomy and habitus, the zones are evaluated a second time with a small-faced high-frequency transducer.

Zone V is the posterior/lateral neck and should be scanned with the patients head turned to the contralateral side. Make a sweep in both transverse and longitudinal planes from posterior to the patients ear to the clavicle. Zones VA and VB are divided at the level of the cricoid cartilage. Zone V is posterior to the sternocleidomastoid muscle.

Finally, with a high-frequency small-faced transducer, scan along the clavicle and into the sternal notch. Angle inferiorly to visualize posteriorly and deep to the clavicle. In the sternal notch, angle laterally and inferiorly to evalu-ate the entire region.

The entire process should be repeated for the contra-lateral side. Both normal and abnormal lymph nodes should be documented. If the node appears normal, it should be imaged, but it is not necessary to measure it. Any abnormal lymph nodes, however, should be mea-sured in all three planes and evaluated with color Dop-pler. When evaluating lymph nodes with color Doppler, the color box should be adjusted to the size of the node. Nodal vascular patterns are categorized into four types:

(1) Hilar: flow branches radially from the hilum.(2) Peripheral: flow is present along the periphery

of the node but does not arise from the hilar vessels.

(3) Mixed: hilar and peripheral flow is present.(4) Absence of flow despite optimal Doppler

settings17,18

Accurate labeling of the zone is needed for all lymph nodes. This is essential for follow-up examinations as well as operative guidance. Abnormalities in zone VI are considered the central compartment and are included and evaluated during a thyroidectomy. Abnormal lymph nodes in zones II, III, IV, and V, however, are in the lateral neck and may require a neck dissection, which is a more exten-sive surgery.

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Table 1. Anatomical Landmarks for Each Zone of the Neck2224

Zones Landmarks Nodal Group

IA Midline; anterior to the digastric muscle and superior to the hyoid bone.

Submental

IB Lateral to zone IA but medial or anterior to the submandibular gland Submandibular nodesIIA Anterior or medial to the interior jugular vein but lateral/posterior to

the submandibular gland; superior to the hyoid boneUpper internal jugular chain; more

superiorly, the parotid nodesIIB Posterior to the interior jugular vein Upper internal jugular chain; more

superiorly, the parotid nodesIII From the level of the hyoid bone inferiorly to the cricoid arch; lateral

to the common carotid arteryMiddle internal jugular chain

IV From the level of the cricoid arch inferiorly to the level of the clavicle; lateral to the common carotid artery

Lower internal jugular chain

VA Posterior to the sternocleidomastoid muscle, from the base of the skull to the cricoid arch

Supraclavicular fossa/posterior triangle (spinal accessory chain and transverse cervical chain)

VB Posterior to the sternocleidomastoid muscle from the croicoid arch to the level of the clavicle

Supraclavicular fossa/posterior triangle (spinal accessory chain and transverse cervical chain)

VI Anterior/medial to the common carotid arteries from the level of the hyoid to the manubrium

Anterior cervical nodes, pre- and paratracheal

VII Anterior/medial to the common carotid arteries, inferior to the sternal notch

Anterior, upper mediastinal nodes

Supraclavicular Lateral to the common carotid artery; at or inferior to the clavicle Supraclavicular nodes

Figure 16. Schematic drawing showing zone landmarks. Adapted from Som PM, Curtin HD, Mancuso AA. An imaging-based classification for the cervical nodes designed as an adjunct to recent clinically based nodal classifications. Arch Otolaryngol Head Neck Surg 1999;125:388396.

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Conclusion

With thyroid cancer on the rise, endocrinologists, sur-geons, radiologists, and sonographers will be faced with an increased number of patients. Many of these patients will benefit from neck sonography. In the proper hands, sonography can continue to emerge as the first modality used for preoperative and postoperative diagnosis, screening, and staging of thyroid cancer.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the authorship and/or publication of this article.

Funding

The author(s) received no financial support for the research and/or authorship of this article.

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