Endometriosis is a common gynecological condition where tissue similar to the uterine lining grows outside the uterus. This misplaced tissue can lead to inflammation, scarring, and various symptoms, including pelvic pain. Ultrasound plays an important role as a primary imaging tool in the initial assessment and management of endometriosis. It offers a non-invasive and relatively quick method to visualize the reproductive organs and detect associated abnormalities.
Visual Signatures on Ultrasound
Ultrasound can identify specific visual characteristics of endometriosis, particularly certain types of lesions. One of the most common manifestations seen on ultrasound is an endometrioma, often referred to as a “chocolate cyst.” These are benign ovarian cysts filled with old blood, which gives them a characteristic dark, thick, glue-like appearance. Endometriomas appear as avascular, unilocular cysts with low-level, homogeneous internal echoes, often described as a “ground-glass” appearance due to hemorrhagic debris. This appearance is observed in about half of cases.
Endometriomas can also present with less typical features, such as being multilocular, meaning they have multiple compartments separated by septations. While they do not show internal vascularity, some may have hyperechoic wall foci, which are bright spots. These cysts can vary in size, from 2 to 5 centimeters, though they may reach up to 20 centimeters. In some instances of severe endometriosis, both ovaries may be adhered together, appearing close behind the uterus, a finding known as “kissing ovaries.”
Deep infiltrating endometriosis (DIE) involves lesions that grow 5 millimeters or deeper into organs, such as the bowel, bladder, or rectovaginal septum. On ultrasound, DIE often appears as hypoechoic nodules, which are darker than surrounding tissue, or as irregular thickening of the affected organ’s wall. For example, bowel endometriosis may show as hypoechoic thickening of the bowel wall, or as solid nodules. These lesions are poorly vascularized.
Bladder endometriosis presents as hypoechoic linear or nodular lesions within the bladder wall. These nodules may have irregular contours and can cause a loss of bladder wall mobility. In the rectovaginal septum, endometriosis can appear as hypoechoic, heterogeneous, or spiculated masses. The “sliding sign,” which assesses organ mobility, can help identify adhesions, such as the rectum to the retrocervical region or the bladder to the uterus.
Ultrasound Modalities for Endometriosis Imaging
Ultrasound examination for endometriosis involves two main types: transvaginal ultrasound (TVS) and transabdominal ultrasound (TAS). TVS is the preferred method for assessing pelvic endometriosis due to its ability to provide higher resolution images. With TVS, a slender transducer is inserted into the vagina, allowing close proximity to the pelvic organs. This enables detailed visualization of the uterus, ovaries, fallopian tubes, and surrounding tissues.
Transabdominal ultrasound involves placing a transducer on the external abdomen. While it can be used as a preliminary scan or for assessing larger pelvic masses, its utility for detailed endometriosis assessment is limited. TAS is less effective at visualizing deep-seated lesions compared to TVS. A full bladder may be requested for TAS to optimize views, whereas for TVS, an empty bladder is preferred for clearer imaging.
TVS is effective for evaluating the ovaries for endometriomas and for assessing deep infiltrating endometriosis in areas like the rectovaginal septum, bowel, and bladder. The proximity of the transducer allows for dynamic assessment of organ mobility, which can indicate the presence of adhesions. The detail provided by TVS helps clinicians understand the extent and location of endometriotic lesions, which is important for treatment planning.
Understanding Ultrasound’s Diagnostic Scope and Limitations
While ultrasound is a tool in assessing endometriosis, it has specific capabilities and limitations. It excels at identifying endometriomas, with most cases demonstrating characteristic features like the “ground-glass” appearance. Ultrasound can also effectively detect deep infiltrating endometriosis in locations such as the bowel and bladder. These findings help guide treatment decisions and surgical planning.
Ultrasound has limitations, especially in detecting superficial peritoneal endometriosis. This type of endometriosis, involving lesions less than 5 millimeters deep on organ surfaces, is the most common form but often cannot be reliably visualized with ultrasound. Therefore, a “normal” ultrasound result does not definitively rule out the presence of endometriosis, particularly the superficial form. Laparoscopic surgery remains the definitive method for diagnosing all forms of endometriosis.
Factors such as the small size and specific location of lesions, or the presence of extensive adhesions, can make ultrasound diagnosis challenging. Despite these limitations, ultrasound remains a non-invasive first-line imaging modality for suspected endometriosis, helping to identify visible disease and guiding further diagnostic steps.