Dr.Omneya Nagy ElmakhzangySpecial Fetal Care UnitAin Shams University

ULTRASOUND DIAGNOSIS OF PLACENTAL INVASION

DEFINITION AND TYPES • Placenta accreta refers to an abnormality of placental

implantation in which the anchoring placental villi attach to myometrium rather than decidua, resulting in a morbidly adherent placenta.

• Placenta increta (chorionic villi penetrate into the myometrium) and placenta percreta (chorionic villi penetrate through the myometrium to the uterine serosa or adjacent organs..

• The pathogenesis is primarily attributed to defective decidualization of the implantation site

LOCALIZE YOUR PLACENTA

IS IT IMPORTANT TO DIAGNOSE?• In 1950, placenta accreta was rare, occurring in 1 in 30,000

deliveries in the United States . During the 1980s and 1990s, the incidence markedly increased, ranging from 1 in 533 to 1 in 2510 deliveries . The marked increase has been attributed to the increasing prevalence of cesarean delivery in recent yeas (uptodate sep.2014).

• Placenta accreta is undoubtedly a challenge, but with proper diagnosis and preparation, the goal is to decrease the morbidity of this rapidly increasing obstetric complication.

• In other words Proper Diagnosis gives a chance for a well prepared and well planned management

DIAGNOSTIC PERFORMANCE OF DIFFERENT ULTRASOUND MODALITIES

Sensitivity (%) Specificity (%) Positive predictive value (%)

Risk

Grey scale 95 76 82 93

Colour Doppler 92 68 76 89

Three-dimensional power Doppler

100 85 88 100

RCOG Green–top Guideline No. 27 , January 2011

1ST TRIMESTER PLACENTA ACCRETA

• Placenta accreta (and percreta) does occur in the first trimester. It is usually discovered during dilatation and curettage when massive bleeding occurs due to placental invasion of the myometrium by placenta (H¨ opker M, 2002)

• Individuals who are at risk for placenta accreta at term are also at risk for placenta accreta in the first trimester.

• This type of pregnancy, in which a sac is abnormally attached in the lower uterus, needs to be differentiated from ‘Cesarean scar pregnancy’ because in the latter, the pregnancy is entirely contained within the myometrial confines of the scar, with no part within the cavity itself.

Placenta Percreta in a patient with five previous Cesarean sections. The sac is low in the uterus and appears to be attached to the bladder wall.

Reproduced with permission of AIUM, J Ultrasound Med 2003

Placenta accreta at 8 weeks. This pregnancy progressed to term. Note that there is little myometrium between the sac and the bladder (arrow).

Reproduced with permission of AIUM, J Ultrasound Med 2003

Placenta increta at 6 weeks. Note almost no myometrium between the sac and bladder wall (arrow).

Reproduced with permission of AIUM, J Ultrasound Med 2003

SIGNS SUGGESTIVE OF PLACENTAL INVASION ON GRAYSCALE ULTRASOUND:

• Loss of the retroplacental sonolucent zone

• Irregular retroplacental sonolucent zone

• Thinning or disruption of the hyperechoic serosa–bladder interface

• Presence of focal exophytic masses invading the urinary bladder

• Abnormal intraplacental lacunae.

ABNORMAL PLACENTAL LACUNAE

• Visualization of lacunae had the highest sensitivity (79%) in the 15–20-week range and a sensitivity of 93% in the 15–40-week gestational age time frame (ISUOG 2005).

• They usually, but not always, have turbulent flow within them, and they appear irregular, often more linear rather than rounded and smooth bordered. They do not have the highly echogenic border that standard venous sinuses have.(Tornado-shaped flow)

• To predict placenta accreta the lacunae have to be highly vascular intraplacental rather than well defined extraplacental low flow blood vessels

Vascular sinuses in patients without placenta accreta. -Vascular areas lie between the placenta and myometrium ratherthan within the placenta; they have low flow. - Large well-defined vessels with low flow at the edge of the placenta

MYOMETRIAL THICKNESS

• Measurement of the thickness of the lower uterine segment in women who had had a previous Cesarean section and had a low-lying anterior placenta or placenta previa by measuring between the bladder wall and the retroplacental vessels, as seen by color Doppler.

• All patients later proven to have placenta accreta had myometrium of less than 1 mm, which was as predictive of accreta as lacunae.

Normal ‘clear’ or echolucent space between theplacenta and myometrial wall .

Lack of the clear zone in a normal anterior placenta

The area near the arrow appears to be abnormal, possibly due in part to drop-out. Thetransducer should be perpendicular to the bladder wall during evaluation of its integrity

Translucency zone

DOPPLER IN DIAGNOSIS OF PLACENTAL INVASION

• Christian Andreas Doppler ( 29 November 1803 – 17 March 1853) was an Austrian mathematician and physicist. He is celebrated for his principle — known as the Doppler effect — that the observed frequency of a wave depends on the relative speed of the source and the observer.

SIGNS SUGGESTIVE OF PLACENTAL INVASION ON COLOR DOPPLER

• Diffuse or focal lacunar flow

• Vascular lakes with turbulent flow (peak systolic velocity over 15 cm/s)

• Hypervascularity of serosa–bladder interface

• Markedly dilated vessels over peripheral subplacental zone.

Gray-scale image of a tornado-shaped sinus (moth Eaten) Color Doppler image showing placenta accreta with many sinuses.

Color Doppler images showing diffuse dilated intraplacental vasculature and marked periplacental vascularity between bladder anduterine serosa , compared with a normal placenta at the same gestational age

Color Doppler image of a tornado-shaped sinus

Am J Obstet Gynecol 2004

Color Doppler of placenta percreta with invasion of bladder wall

3D POWER DOPPLER

WHY DO WE USE 3D ACQUISITION RATHER THAN 2D?

The use of color and power Doppler in the early 1990's has improved perinatal diagnosis of complex C.V.S malformations over the grey scale ultrasound.

The draw back in using 2D color or power Doppler is that they generally allow the visualization of vessels running in a straight course or lying on the same 2D plane.

In most cases the examiner has to mentally reconstruct a spatial image of the vessels examined.

In recent years 3D Doppler has helped in the reconstruction of the vessels of interest and thus improves the understanding of the spatial appearance of the Vascular tree.

The images acquired were close to X-ray or MR angiography.

TECHNICAL BACKGROUND

Two main aspects have to be taken in consideration when acquiring a volume image :

1- Volume Data Acquisition.

2-Image rendering .

VOLUME DATA ACQUISITION

There are two ways to achieve :

1- Static 3D mode which is a series of still images.

2- A 4D mode which can be either by a real time 3D scanning or an offline 4D which is one of the recent advents in the software that allows spatial and temporal image correlation known as "STIC".

IMAGE RENDERING

It is the process of creating a 3D visual presentation of parameters of interest.

The main principle behind this is "planar geometric projection" i.e a 2D image to represent the 3D data the third dimension impression is acquired through online rotation of the image along X , Y and Z axis

The exam can show the vessel of interest alone "Inversion mode" or along with the gray scale image in what's called the "Glass body rendering mode".

ARE WE LOOKING AT A VESSEL OR AT A SPECIFIC ORGAN

VASCULARITY?

If a specific vessel is targeted we simply apply 3D power or Color Doppler on the vessel of interest but if an organ or a structure as a whole is targeted we use a software technology known as VOCAL (virtual organ computer aided analysis).

QUANTIFYING THE BLOOD FLOW BY 3D POWER DOPPLER

1- VI (Vascularization index): Vascularization index is the ratio of the number of color voxels (volumetric pixel) to the total number of voxels in the sampled tissue, thus it represents the percentage of vascularized tissue

2- FI (flow index) : Flow index is the average colour value of all colour voxels and it describes the mean velocity of flow in the sampled tissue.

3- VFI (vascularization flow index) : is the average colour value of all colour and grey voxels and describes both: the vascularization and the blood flow.

SIGNS SUGGESTIVE OF PLACENTAL INVASION BY 3D POWER DOPPLER

• Numerous coherent vessels involving the whole uterine serosa–bladder junction (basal view)

• Hypervascularity (lateral view)

• Inseparable cotyledonal and intervillous circulations, chaotic branching, detour vessels (lateral view).

RARE FORMS OF INVASIVE PLACENTA

FUNDAL INVASIVE PLACENTA

PLACENTA ACCRETA WITHOUTPLACENTA PREVIA OR UTERINE SCAR

• These patients may present at birth, but often present earlier with an acute abdomen and copious free blood within it (heamoperitonium)

• There are no ultrasound series published as yet that have evaluated the ultrasound appearance of these atypical situations.

• The present ultrasound literature exclusively addresses the appearance in patients at risk, either with placenta previa or previous uterine surgery or both.

ROLE OF MRI

• Compared to US. US examination is fundamental in the diagnosis due to its low cost and wide availability

• . US has a sensitivity of 83% and a specificity of 72%. When it is associated with Color Doppler, a sensitivity close to 97% and a specificity of 92% has been reported.

• The positive predictive value (PPV) of MR is of 100% (65% US), while the negative predictive value (NPV) is greater for ultrasound (98% versus 82%).

• MRI should be reserved for cases with equivocal ultrasound findings or to evaluate uterine zones difficult to assess with US, like the posterior aspect of the placenta.

SPECIFIC FINDINGS OF PLACENTAL INVASION ON MRI

•- Bulging of the uterus.- Placenta of heterogeneous signal intensity on T2WI.- Dark and thick intraplacentarian bands on T2-weighted images

FOR FURTHER INFORMATION ON DIAGNOSIS AND MANAGEMENT OF PLACENTAL INVASION

• http://www.uptodate.com.search.sti.sci.eg:2048/contents/clinical-features-and-diagnosis-of-placenta-accreta-increta-and-percreta?source=search_result&search=placenta+accreta&selectedTitle=1~38

• RCOG Green-top Guideline No. 27