Special considerations for the evaluation of Endometriosis on MRI

The role of MRI on the evaluation and diagnosis of Endometriotic lesions

Key Points

Highlights:

• Currently, MRI has an irreplaceable role in the delineation and diagnosis of endometriosis including its various uncommon localizations.
• As the features on MRI may differ depending on the site, visualizing and characterizing of these lesions in the least invasive and accurate manner will aid in the appropriate management of this disease.

Importance:

• Effective management of endometriosis requires accurate and consistent imaging techniques for diagnosis.
• MRI has been shown to offer improved sensitivity and specificity in the detection of unusual localizations of endometriosis.

Key Results:

• Atypical endometriosis can localize to the cervix, vagina, round ligaments, ureter, and nerves. Rare localizations may include the upper abdomen and subcutaneous fat of the abdominal wall.
• Superficial lesions are bright on T1 soon after menstruation (8-12 days post menstruation) and heterogeneously hyperintense on T2-weighted images long after the menstrual episode (12+ days after menstruation). 
• Deeply infiltrating endometriotic lesions are solid and fibrous in nature and are hypointense on both T1 and T2-weighted images.
• Endometriosis of the round ligament is seen as a fibrous and thickened ligament on T2-weighted images.
• Both bladder and ureteral endometriosis can be categorized as either extrinsic or intrinsic depending on the depth of endometriotic invasion. 
• Endometriosis of the nerves of the sacral plexus is difficult to visualize and should be evaluated and diagnosed by an expert radiologist.
• Abdominal wall endometriosis is the most frequent location for extrapelvic involvement and includes many different sites such as subcutaneous soft tissue and rectus muscles.
• Rare forms of endometriosis involving the thoracic region may present as respiratory symptoms and should be evaluated via imaging.

What’s done here?

• The focus of this article is to describe and discuss the evaluation of atypical and rare extrapelvic endometriotic lesions on MRI.
• Doing so will allow radiologists to reassess how these lesions are evaluated so that appropriate diagnosis and management of these lesions can be performed.

Lay Summary

Pelvic endometriosis may involve either superficial peritoneal or ovarian tissues or may spread to the organs and ligaments of the pelvis in what is known as deeply infiltrating endometriosis (DIE). According to the size and location of these lesions, patients can experience mild discomfort to excruciating pain. Accurate evaluation of endometriotic lesions can only be achieved by knowing the anatomy of each organ and its intimate structural relations. Visualizing and characterizing these lesions in the least invasive and accurate manner will aid in the proper management of this disease.

The team of Institute of Radiology of Catholic University of the Sacred Heart, Agostino Gemelli Hospital, Rome, Italy, published their findings in Diagnostic and Interventional Radiology, their paper entitled "Shining light in a dark landscape: MRI evaluation of unusual localization of endometriosis." Atypical endometriosis can localize to the cervix, vagina round ligaments, ureter, and nerves. Rare localizations include the upper abdomen and subcutaneous fat of the abdominal wall. Since endometriotic lesions are conditional to hormones involved in the menstrual cycle, the timing of the imaging study will influence the characterization of endometriotic lesions on MR. When imaging is performed soon after menstruation, lesions are very bright on T1-weighted images due to the presence of large amounts of pooled blood around these lesions.

Superficial lesions change their appearance soon after menstruation compared to 12+ days after menstruation. Deeply infiltrating endometriotic lesions are solid and fibrous and are hypointense. T2-weighted imaging should be relied upon to evaluate these lesions due to its high-resolution. Lesions with adhesions are harder to evaluate because they may obscure the visualization of adjacent organ structures.

Vaginal endometriosis is usually located in the posterior fornix or upper part of the posterior vagina. Transvaginal ultrasound has poor sensitivity for detecting endometriosis and is hypointense on T2-weighted images. Endometriosis of the round ligament will be seen as a fibrous and thickened ligament on T2-weighted images. However, the presence of hemorrhage presents as high signal intensity on T1.

Bladder endometriosis can either involve the serosal surface of the bladder closest to the uterus (extrinsic involvement) or invade the muscular layer and attach inside the lumen of the bladder (intrinsic involvement). Urologic symptoms are the most common complication due to this form of endometriosis. MRI is especially accurate in detecting bladder endometriosis since it can detect irregular margins or protrusions in the bladder lumen caused by endometriotic lesions. Since these findings may also mimic cancer, a cystoscopy and biopsy should be performed to make a definitive diagnosis.

Endometriosis of the ureters can also be categorized as either extrinsic or intrinsic. Like endometriosis of the bladder, extrinsic endometriosis of the ureter encases the ureters whereas intrinsic endometriosis of the ureters is marked by the invasion of the musical or muscular layer of the ureter. Evaluation of the ureters on MRI is hard, but if nodules are seen adjacent to the ureter or obliteration of the fat interface between these two structures, then an endometriotic lesion should be suspected. The presence and grade of ureteral endometriosis on MRI affect surgical management.

Endometriosis of the sacral plexus nerves is difficult to visualize and should be evaluated by an expert radiologist. Abdominal wall endometriosis is the most frequent location for extrapelvic involvement, includes many different sites such as subcutaneous soft tissue and rectus muscles. Ultrasound and MRI should be used to diagnose abdominal wall lesions and rule out other possible diagnoses. Rare sites include subdiaphragmatic or pleura locations where patients may experience chest or shoulder pain, or breathing difficulty associated with menses. MRI for these types of endometriotic lesions may need a particular acquisition method with breath-holds to achieve the best images.

"Successful treatment requires lesion removal with radical surgery, and, when surgery is indicated, MRI can provide a road map that allows adequate pre-surgical guide the surgeon for complete eradication of all possible endometriotic implants" concluded researchers.

Research Source: https://www.ncbi.nlm.nih.gov/pubmed/?term=PMID%3A+28703103