Endometriosis
Synonyms/Description
Endometriosis signifies the presence of endometrial tissue outside the endometrial cavity. These ectopic glands respond to the cyclical hormones, thus causing microscopic internal bleeding and pain during the course of the menstrual cycle. This ectopic tissue bleeds episodically, causing inflammation, adhesions, and scarring. These ectopic glands can also react to hormones of pregnancy.
Etiology
The exact cause of endometriosis is unknown and there are multiple theories. In addition, the true prevalence of this condition is also unclear because endometriosis is not always symptomatic. There does, however, appear to be a higher incidence in women who are diagnosed with infertility and pelvic pain.
Endometriosis can occur in many forms, including the formation of cysts known as endometriomas (chocolate cysts), which typically develop in ovarian tissue. Endometriosis can also occur in the uterus with the propagation of endometrial glands through the junctional zone into the myometrium, a condition known as adenomyosis (see Adenomyosis). Endometriosis can also take the form of small deep implants of endometrial tissue in many different places in the body, including the wall of the bladder, the anterior abdominal wall, the bowel wall, and the uterosacral ligaments, as well as other pelvic sites. Rarely, endometriosis can occur in distal sites such as the lung, potentially causing hemoptysis.
Ultrasound Findings
Endometrioma
The typical appearance of an endometrioma is that of a unilocular cyst with homogeneous low-level echoes and through transmission of sound. The ground-glass texture of the cyst content is very characteristic and makes 90% of endometriomas easily recognizable. Some benign endometriomas also have solid components (often echogenic) in the inner aspect of the cysts, but these are typically without discernible blood flow and represent clot. When interrogating endometriomas with color Doppler, there is no discernible flow in the cyst (only in the wall) and there is usually no visible streaming of the low-level echoes within the cyst, thus distinguishing it from cystadenomas and other cysts. Patients with endometriomas often have adhesions so that tubal disease in the form of a hydrosalpinx or other signs of adhesive disease may be a common finding.
When the cyst wall is thickened and irregular, the possibility of malignancy, specifically endometrioid carcinoma, must be considered. Typically endometrioid carcinoma looks like an endometrioma but with internal solid nodularity that contains abundant color Doppler flow. In a study of 309 endometrioid cysts surgically removed, 1.2% were classified as borderline, and 3.4% as invasive endometrioid tumors. Patients with malignancies were typically older (median 52 years) compared with those with benign cysts (median 34 years). All of the malignant and borderline tumors were characterized as having solid components with evidence of color flow, compared with only 7.8% of the benign lesions.
Decidualized Endometrioma
If the patient is pregnant, the endometrioma may become decidualized and have ultrasound characteristics suggestive of a malignancy. The stromal transformation of endometrial cells within the endometrioma can occur because of high levels of progesterone in pregnancy. In gravid patients, these cysts can contain internal solid nodularity with blood flow, and are indistinguishable from borderline or even frank ovarian cancers sonographically.
Therefore such cysts may potentially be watched with frequent serial ultrasounds before making a final decision to remove the cyst during the pregnancy. If the cyst remains unchanged, it is unlikely to be malignant, and removal can be planned after delivery.
Deep Penetrating Bowel Wall and Pelvic Implants
Sonographically, deep implants of endometriosis are small solid masses with little if any detectable blood flow using color Doppler. The bowel wall implants are nodular and fusiform swellings of one side of the bowel wall. This swelling is often adherent to the back of the cervix, thus hindering any sliding of the uterus past the bowel on exam. Bazot reports a sensitivity and specificity of 78.5% and 95.2%, respectively, for detecting disease in that location, suggesting that ultrasound (in experienced hands) is accurate in diagnosing rectosigmoid endometriosis. Hudelist and colleagues report a sensitivity and specificity of 91% and 98%, respectively, and positive likelihood ratio and negative likelihood ratios of 30.4 and 0.1, respectively, for detecting bowel wall endometriosis using ultrasound. Although MRI can also detect implants of endometriosis, evidence shows that pain-guided transvaginal ultrasound is likely more sensitive for detecting bowel involvement.
Implants in the rectovaginal septum are also nodular, small, rounded, solid structures best seen along the most distal portion of the cervix and along the posterior fornix and upper vagina. Implants may also be found on the pelvic ligaments such as the uterosacral ligaments and para pelvic regions.
Bladder Wall, Ureter, and Anterior Abdominal Wall Lesions (Also See Bladder Masses)
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