MRI Pelvis is the Next Step After Unrevealing Transvaginal Ultrasound
When transvaginal ultrasound is negative or indeterminate in a patient with suspected endometriosis, MRI of the pelvis (with or without IV contrast) should be obtained as the next imaging study. 1, 2
Why MRI After Negative Ultrasound
MRI pelvis demonstrates excellent diagnostic performance for deep infiltrating endometriosis (DE), with 90.3% sensitivity and 91% specificity for deep pelvic disease. 1, 2 This makes it the appropriate next step when clinical suspicion remains high despite unrevealing ultrasound.
The large field of view afforded by MRI decreases the need for multiple additional imaging studies that are sometimes required to supplement ultrasound examinations, which do not include the entire urinary or gastrointestinal tracts. 1
MRI is particularly valuable because it provides global pelvic assessment and can identify disease in locations beyond the reach of transvaginal ultrasound, including the upper urinary tract, bowel beyond the rectosigmoid, and extrapelvic sites. 3
Contrast vs. Non-Contrast MRI
MRI with IV contrast is preferred over non-contrast MRI because contrast enhancement improves differentiation of benign ovarian endometriomas from ovarian malignancies—an important distinction given that patients with endometriosis are at risk for endometriosis-associated malignancies. 1, 2
IV contrast also helps establish the diagnosis of other pelvic conditions that may present with similar symptoms, such as uterine fibroids or infectious/inflammatory disorders. 1
However, MRI without IV contrast remains sufficient for detecting deep endometriosis itself if contrast is contraindicated, though assessment of ovarian lesions and other pelvic pathology is limited without it. 1
Technical Optimization for MRI
Moderate bladder distention and vaginal contrast are recommended to improve lesion conspicuity involving the bladder and vaginal structures. 1, 4
MRI protocols tailored for endometriosis detection should be used, including T1-weighted sequences (both fat-saturated and non-fat-saturated) and T2-weighted sequences in all three planes. 5, 6
What NOT to Order
- CT pelvis (with or without IV contrast) has no role in the diagnostic work-up of suspected endometriosis and should not be ordered as initial or follow-up imaging. There is no relevant literature supporting its use for this indication. 1, 2
Critical Pitfall to Avoid
A negative ultrasound does not exclude endometriosis, particularly superficial peritoneal disease, which is poorly detected by all imaging modalities including MRI. 2, 4 When symptoms persist despite negative imaging, maintain clinical suspicion and consider empiric treatment or surgical evaluation based on clinical diagnosis alone. 4
Standard "community" transvaginal ultrasound has significantly lower accuracy than expanded protocol ultrasound performed by specialized operators. 1, 2 If the initial ultrasound was not performed using an endometriosis-specific protocol by a trained examiner, consider whether repeat expanded protocol ultrasound might be appropriate before proceeding to MRI. 1, 7
MRI Performance by Anatomic Location
MRI shows 92.4% sensitivity and 94.6% specificity for intestinal endometriosis, 88% sensitivity and 83.3% specificity for deep infiltrating endometriosis in posterior locations, and 50% sensitivity and 97.3% specificity for bladder wall endometriosis. 4
This location-specific performance data helps guide surgical planning and reduces the risk of incomplete surgeries requiring reoperation. 4, 5