**4.1 Ultrasound**

Ultrasound as discussed is usually the first investigation done in subject suspected of any pelvic disease. USG has the advantage of having good resolution, easy accessibility, less expensive, and is free of ionizing radiation. Three modes are available- transabdominal, transvaginal and endorectal scanning.

For transabdominal scanning 3-5 MHz convex probe is used. Full bladder is must for this technique in order to properly visualize the uterus and the ovaries. It is very useful in cases of suspected bladder involvement and abdominal wall endometriosis. Kidneys should be examined for hydronephrosis

Transvaginal scanning (TVS) is done with probe of high frequency 6-7.5MHz positioned in vagina. Full bladder is not a pre requisite for this mode of USG and procedure is well

and its exact incidence is not known. This is diagnosed only if there is no evidence of metastasis from any primary sites and the surrounding tissue has presence of benign as well

The disease most commonly affects the ovaries and the pelvic peritoneum. DIE classically affects the rectovaginal septum and the uterine ligaments (69.2%), the vagina (14.5%), the rectosigmoid bowel (9.9%), and the bladder and ureter (6.4%) in the order of frequency.

The diagnosis of endometriosis is conventionally made by laparoscopy but over the time the imaging techniques have evolved to greatly facilitate the pre operative diagnosis. Further laparoscopy has limited role in visualizing atypical non pigmented extraperitoneal sites of

By and large ultrasound is the first preliminary investigation done to assess the pelvic disease in reproductive age group. Although it has limited role in detection of superficial implants, it is useful in the diagnosis and treatment of endometriomas. MRI provides a good alternative with high specificity and sensitivity for detecting deep infiltrating (DIE) endometriosis as well as endometriomas. The main drawback of MRI is again inability to detect small peritoneal infiltrates (< 3mm). Introduction of fat saturated T1 weighted image on MRI has consistently improved its accuracy in distinguishing between ovarian mass with

Computed tomography usually gives ill defined results, thus is not very helpful. Conventional investigations like barium enema or intravenous urography may prove useful in detection of visceral endometriosis. Their use however is limited in current practice due

Further sections of this chapter will first discuss the various imaging modalities in detail followed by the characteristic appearance of diverse typical and atypical forms of

Ultrasound as discussed is usually the first investigation done in subject suspected of any pelvic disease. USG has the advantage of having good resolution, easy accessibility, less expensive, and is free of ionizing radiation. Three modes are available- transabdominal,

For transabdominal scanning 3-5 MHz convex probe is used. Full bladder is must for this technique in order to properly visualize the uterus and the ovaries. It is very useful in cases of suspected bladder involvement and abdominal wall endometriosis. Kidneys should be

Transvaginal scanning (TVS) is done with probe of high frequency 6-7.5MHz positioned in vagina. Full bladder is not a pre requisite for this mode of USG and procedure is well

as the malignant endometrial tissue.

Rarely lungs and CNS may be involved.

lipids from endometriomas.

to excessive radiation dose.

transvaginal and endorectal scanning.

examined for hydronephrosis

endometriosis.

**4.1 Ultrasound** 

**4. Diagnostic modalities for evaluation of endometriosis** 

involvement and the areas especially concealed by pelvic adhesions.

**3. Locations** 

accepted by most of the patients. TVS has superior image quality and resolution as compared to TAS. Thus it has high sensitivity (92%) and specificity (99%) in detecting endometriomas. The typical ultrasound findings include a cystic mass with diffuse, lowlevel echoes (figure 1).

Fig. 1. Grey-scale Transvaginal ultrasound of an endometrioma(M). Note the characteristic diffuse, low-level echoes of the endometrioma giving a solid appearance

Depending on the age of the haemorrhage, the contents of the cyst, may vary in appearance. At times, an endometrioma may resemble a cystic-solid or entirely solid mass. Punctate echogenicities in the wall of endometriomas are less commonly seen but add specificity to the diagnosis. Endometriomas can be multilocular with internal thin or thick septations and thick irregular walls. Mild vascularity may be identified on color Doppler (figure 2). Color Doppler US shows no blood flow in the fine septations, whereas blood flow can often be detected in thick septations because of revascularization of chronic haematoma. Internal moving echos within endometrioma may reveal color signal.

Imaging Tools for Endometriosis: Role of Ultrasound, MRI

the endometrioma.

and Other Imaging Modalities in Diagnosis and Planning Intervention 441

The signal intensity of MRI depends on the contents of the endometrial implants. The contents of these implants mainly include the proteins and degraded blood products, the ratio of which varies according to the stage of the haemorrhage and thus the variation in the signal intensity can be noted on MR images. The acute haemorrhage may give hypointense (dark) signal on the T1 and T2 weighted images. In contrast the lesions containing degraded blood products like methemoglobin, proteins and iron may be seen as hyperintense (bright) on T1 (figure 3) and hypointense (dark) on T2 weighted images(figure 4). Multiple high signal lesions, usually in the ovaries, on T1-weighted images, also are highly suggestive of endometriosis. The diagnostic MR imaging features of endometrioma include cystic mass with high signal intensity on T1-weighted images and loss of signal intensity on T2-weighted images. This phenomenon is referred to as "shading" as a result of high protein and iron concentration from recurrent hemorrhage in

The advent of fat saturated T1 weighted technique has greatly enhanced the value of MRI in differentiating among endometriomas and lipid containing ovarian tumors like dermoid cysts. Use of contrast medium (Gadolinium) has not shown any advantage over plain MRI

M

Fig. 3. Axial fat saturated T1Weighted image reveals T1 hyperintense lesions in the left

ovary (M) suggestive a chocolate cyst/endrometrioma of the ovary.

for the purpose but it may be useful when malignant lesion is suspected.

Fig. 2. Transvaginal ultrasound of an endometrioma color Doppler image showing mild peripheral vascularity. Internal color signals are likely related to moving internal echos.

Spectral Doppler reveal low-resistance waveforms which may not be helpful in differentiating endometriomas from other masses including malignancy.

Transrectal sonography uses biplane convex flexible rectal probe of 6.5MHz. The probe is flexible and can be advanced into the sigmoid colon to look for any signs of invasion by endometriosis. Patient preparation with rectal enema is required before endorectal sonography. The rectum and the surrounding area in the perimetry show five alternating hyper and hypoechoic layers respectively. The endometriotic deposits are visualized as triangular or round hypoechoic lesions on transrectal USG. It is superior to MRI with reported high sensitivity and specificity of 97% and 80%.

#### **4.2 Magnetic resonance imaging**

MRI is a non invasive intervention by which whole pelvis can be visualized in different planes. It can be very useful in patients in whom ultrasound findings are equivalent and in carefully selected high risk population. It is especially beneficial in identifying endometriomas, adhesions, superficial peritoneal implants and extraperitoneal lesions, particularly those in the rectovaginal space and uterosacral ligaments as well as in solid endometriotic nodules. In view of longer imaging times required for MRI, antiperistaltic medication to decrease the bowel movement can minimize motion related artifact and also enhances the visualization of the bowel involvement.

M

Fig. 2. Transvaginal ultrasound of an endometrioma color Doppler image showing mild peripheral vascularity. Internal color signals are likely related to moving internal echos.

differentiating endometriomas from other masses including malignancy.

reported high sensitivity and specificity of 97% and 80%.

enhances the visualization of the bowel involvement.

**4.2 Magnetic resonance imaging** 

Spectral Doppler reveal low-resistance waveforms which may not be helpful in

Transrectal sonography uses biplane convex flexible rectal probe of 6.5MHz. The probe is flexible and can be advanced into the sigmoid colon to look for any signs of invasion by endometriosis. Patient preparation with rectal enema is required before endorectal sonography. The rectum and the surrounding area in the perimetry show five alternating hyper and hypoechoic layers respectively. The endometriotic deposits are visualized as triangular or round hypoechoic lesions on transrectal USG. It is superior to MRI with

MRI is a non invasive intervention by which whole pelvis can be visualized in different planes. It can be very useful in patients in whom ultrasound findings are equivalent and in carefully selected high risk population. It is especially beneficial in identifying endometriomas, adhesions, superficial peritoneal implants and extraperitoneal lesions, particularly those in the rectovaginal space and uterosacral ligaments as well as in solid endometriotic nodules. In view of longer imaging times required for MRI, antiperistaltic medication to decrease the bowel movement can minimize motion related artifact and also The signal intensity of MRI depends on the contents of the endometrial implants. The contents of these implants mainly include the proteins and degraded blood products, the ratio of which varies according to the stage of the haemorrhage and thus the variation in the signal intensity can be noted on MR images. The acute haemorrhage may give hypointense (dark) signal on the T1 and T2 weighted images. In contrast the lesions containing degraded blood products like methemoglobin, proteins and iron may be seen as hyperintense (bright) on T1 (figure 3) and hypointense (dark) on T2 weighted images(figure 4). Multiple high signal lesions, usually in the ovaries, on T1-weighted images, also are highly suggestive of endometriosis. The diagnostic MR imaging features of endometrioma include cystic mass with high signal intensity on T1-weighted images and loss of signal intensity on T2-weighted images. This phenomenon is referred to as "shading" as a result of high protein and iron concentration from recurrent hemorrhage in the endometrioma.

The advent of fat saturated T1 weighted technique has greatly enhanced the value of MRI in differentiating among endometriomas and lipid containing ovarian tumors like dermoid cysts. Use of contrast medium (Gadolinium) has not shown any advantage over plain MRI for the purpose but it may be useful when malignant lesion is suspected.

Fig. 3. Axial fat saturated T1Weighted image reveals T1 hyperintense lesions in the left ovary (M) suggestive a chocolate cyst/endrometrioma of the ovary.

Imaging Tools for Endometriosis: Role of Ultrasound, MRI

**5. Different types of endometriosis** 

**5.1 Superficial implants** 

by such lesions.

neoplasm.

endometrioma.

the pericystic space.

lesions usually resolve on follow up.

**5.2 Endometriomas** 

and Other Imaging Modalities in Diagnosis and Planning Intervention 443

Role of MRI has been analyzed by various authors in the past. Stratton et al in a study reported 69% sensitivity and 75% specificity for detecting endometriosis confirmed on biopsy. MRI proposed diagnosis in nearly all patients with the severe form of the disease but by and large could recognize only small number of endometriotic areas as compared to

With this background in mind, the next section of the chapter will discuss in detail the

Both USG and MRI has major limitation in diagnosing this type of endometriosis as already discussed. Endoscopy remains the standard practice to determine the extent of involvement

Transvaginal sonography (TVS) is universally most frequently used imaging tool for evaluation of endometriomas. USG features of chocolate cysts are diverse. The classical appearance is that of a cystic structure with diffuse low level internal echoes and echogenic wall foci. The cyst may be unilocular or multilocular. It may contain thin or thick septa. Sometimes there may be wall nodularity. Wall nodularity if present requires further investigation to rule out malignancy. Imaging alone cannot exclude malignant

It is interesting to note that out of 20% of the endometriomas exhibiting wall nodularity, 35% had hyperechogenic wall foci (Patel et al). Effort should be made to distinguish between wall nodularity and the hyperechogenic foci within the wall. The latter when present in lesion with low level echoes and no features of malignancy is indicative of

Differential diagnoses of chocolate cyst include haemorrhagic cyst, dermoid cyst and cystic neoplasms. Dermoid cyst usually exhibit either echogenic shadow due to its fat content or acoustic shadowing due to calcium which aids in the diagnosis. To differentiate between haemorrhagic cyst and chocolate cyst can be a difficult task. The haemorrhagic cyst usually displays high level internal echoes within a thin walled cyst which may advance with time and emerge as a more complex cyst. Formation of fibrin may imitate thin septa but these

The accuracy of USG can be further improved by color Doppler flow studies. Blood flow in the endometrioma is through the regularly spaced vessels running in the hilar region and

MRimaging is another tool for identifying endometriomas. Due to the cyclical bleeding endometriomas contain blood products at different age. They are seen as bright or hyperintense lesions on T1 weighted image. On T2 they appear more hypointense or dark with foci of hyperintensity, imparting it the classical appearance of 'shading'. Shading is

surgery. Thus it is relatively less sensitive in determining the extent of the disease.

features specific to different types of endometriosis on USG and MRI.

Fig. 4. Axial T2Weighted image showing the lesions are hypointense on T2W images.

The solid nodules of DIE appear as low intermediate signal on T1 weighted with punctuate areas of high signal and uniform low signals on T2 weighted images. The high signal zone is the consequence of foci of haemorrhage bounded by fibrous tissues. However it is difficult to identify superficial peritoneal implants on MRI.

Adhesions in the pelvis are one of the hallmarks of the disease. They appear as low signal areas of stranding. Adhesions are also suggested by the fixed retroverted uterus, angulated loops of bowel or displacement of the ovaries. Complications of endometriosis such as bowel implants and ureteral obstruction can often be detected on MRI.

It is now feasible to see the visceral deposits on MRI directly. Rather some studies claim MR imaging to be more specific than endorectal USG with sensitivity and specificity of 90-92% and 91 to 98% respectively (Gougoutas CA et al). MRI has valuable role in identification of nerve invasion (sciatic endometriosis) and abdominal wall lesions. The accuracy of MRI has been improved with the introduction of newer approach particularly endocavitary and phased array coils.

Role of MRI has been analyzed by various authors in the past. Stratton et al in a study reported 69% sensitivity and 75% specificity for detecting endometriosis confirmed on biopsy. MRI proposed diagnosis in nearly all patients with the severe form of the disease but by and large could recognize only small number of endometriotic areas as compared to surgery. Thus it is relatively less sensitive in determining the extent of the disease.

With this background in mind, the next section of the chapter will discuss in detail the features specific to different types of endometriosis on USG and MRI.
