Endometriosis is a chronic, inflammatory condition where tissue similar to the lining of the uterus grows outside the uterine cavity. This misplaced tissue, most commonly found in the pelvis on the ovaries, fallopian tubes, and the lining of the abdomen, responds to hormonal changes during the menstrual cycle. The resulting inflammation and bleeding can lead to severe pelvic pain, painful periods, and the formation of scar tissue and adhesions. Diagnosis is frequently delayed because its symptoms often overlap with other conditions.
The Role of Ultrasound in Detection
Ultrasound is typically the first-line imaging tool used when a healthcare provider suspects endometriosis based on a patient’s symptoms, such as chronic pelvic pain or infertility. It is preferred because ultrasound is non-invasive, widely available, and more cost-effective compared to other advanced imaging methods. The examination can be performed using either a transabdominal approach or a transvaginal approach.
The transvaginal ultrasound (TVUS) is generally considered superior for pelvic assessment because the probe is positioned closer to the pelvic organs, providing higher-resolution images. This allows the sonographer to obtain detailed, real-time views of the uterus, ovaries, and surrounding structures. While the ultrasound cannot definitively diagnose endometriosis, it is a valuable part of the diagnostic process that guides the next steps in management.
Specific Visual Markers in Imaging
Ultrasound is highly effective at identifying certain types of endometriosis, particularly those that form larger masses or cysts. The most recognizable sign is the presence of an endometrioma, commonly nicknamed a “chocolate cyst,” which is an endometriosis-filled cyst on the ovary. These cysts contain old, dark, thick blood and typically present on ultrasound with a homogeneous, “ground-glass” appearance due to the diffuse, low-level internal echoes. Endometriomas are generally unilocular or multilocular with smooth walls, and they often lack internal blood flow on Doppler imaging, which helps distinguish them from other types of ovarian masses.
Ultrasound can also detect Deep Infiltrating Endometriosis (DIE), which is when the lesions penetrate deeper than five millimeters beneath the peritoneal surface. An experienced sonographer can identify these nodular lesions in locations like the uterosacral ligaments, rectovaginal septum, and on the surfaces of the bladder or bowel. These lesions often appear as solid, fixed masses that can distort the normal anatomy of the pelvic organs. Dynamic ultrasound techniques can assess for “soft markers,” such as reduced organ mobility or tenderness localized to a specific area, which are indirect signs of inflammation and adhesions caused by the disease.
Limitations and Missed Disease
Despite its utility, ultrasound has significant limitations in fully capturing the extent of endometriosis, meaning a clear scan does not exclude the disease. The most common type of the disease, superficial peritoneal endometriosis, often involves tiny, flat lesions that are too small or shallow to generate a visible image on routine ultrasound. These millimeter-sized implants lie on the lining of the pelvic cavity, and the low contrast resolution of ultrasound in this area means they are frequently missed.
A negative or “normal” ultrasound result, particularly one performed without specific endometriosis protocols, can create a false sense of security for both the patient and the provider. The absence of visible endometriomas or deep infiltrating disease does not rule out the possibility of painful superficial lesions. Symptoms, such as severe pain during periods or intercourse, must remain the primary driver for further investigation, even after an inconclusive imaging report.
Next Steps Following Imaging
The path following an ultrasound depends heavily on its findings and the patient’s ongoing symptoms. If the ultrasound successfully identifies endometriomas or signs of deep infiltrating disease, the results are used to plan treatment. Management may involve starting hormonal therapies to reduce the growth of the lesions or, in more severe cases, planning for surgical excision. The detailed mapping of the lesions by the ultrasound helps surgeons better prepare for the complexity of the operation.
If the ultrasound is negative, but the patient continues to experience debilitating symptoms, further diagnostic steps are necessary. The definitive way to diagnose endometriosis, especially the superficial form, remains laparoscopy. This minimally invasive surgery involves inserting a camera into the abdomen to directly visualize the pelvic cavity and take tissue biopsies for confirmation. Laparoscopy is the gold standard because it allows for the precise identification and simultaneous removal of all types of endometriotic lesions.