Who Needs MRI in Suspected Endometriosis? A Retrospective Observational Diagnostic Study of Added Value Beyond TVUS

Background: Magnetic resonance imaging (MRI) is commonly used as a complementary examination after transvaginal ultrasonography (TVUS) in suspected or clinically known endometriosis, yet its incremental value in real-world imaging-based assessment remains insufficiently quantified.

Methods: This retrospective single-center study included 124 women evaluated at a tertiary endometriosis center who underwent both specialist TVUS and pelvic MRI. Imaging findings were compared at the patient and compartment levels. MRI added value was assessed by identifying MRI-detected endometriosis in patients with negative TVUS and additional compartment involvement or lesion characterization in patients with positive TVUS. Agreement metrics and McNemar tests were used for compartment-level comparison.

Results: TVUS was negative in 35/124 patients (28.2%). Among these, MRI detected findings suggestive of endometriosis in 21/35 (60.0%), most commonly in the posterior compartment. TVUS was positive in 89/124 patients (71.8%); MRI confirmed endometriosis in 85/89 (95.5%) and identified additional compartment involvement in 33/85 (38.8%), involving 39 additional compartments, most frequently posteriorly. At the compartment level, MRI showed significantly higher detection than TVUS in the posterior compartment (p<0.001), particularly for uterosacral ligament and rectal/rectosigmoid involvement, and in the middle compartment (p=0.01), where MRI mainly clarified indeterminate adnexal findings, confirmed endometriomas or hematosalpinges, detected contralateral disease, and downgraded suspicious TVUS findings. In the anterior compartment, MRI did not significantly increase detection (p=0.79), although it improved delineation of ureteral involvement, bladder wall infiltration, and lesion continuity. High overall but low positive agreement anteriorly reflected the small number of concordantly positive cases.

Conclusions: In a real-world tertiary-center cohort, MRI provided substantial added value beyond TVUS, particularly in symptomatic TVUS-negative patients and in posterior and middle compartment mapping. MRI may support imaging-based diagnosis, patient counseling, follow-up planning, and multidisciplinary treatment decisions.