Second‐line MRI after expert transvaginal ultrasound in selected patients with suspected complex deep endometriosis: A prospective cohort study

Introduction The objective of this study was to evaluate the added diagnostic yield of second‐line magnetic resonance imaging (MRI) after expert transvaginal ultrasound (TVS) for preoperative mapping of deep endometriosis (DE). Material and Methods In this prospective observational cohort study, women with suspected DE scheduled for surgery after expert ultrasound were included. TVS was performed according to the International Deep Endometriosis Analysis (IDEA) protocol. MRI was selectively performed as a second‐line investigation in patients with suspected advanced disease, inconclusive TVS, or advanced symptoms despite negative TVS findings. Surgical visualization served as the primary reference standard, with histopathology used as a secondary reference standard when available. Diagnostic performance (sensitivity, specificity, predictive values, likelihood ratios, and Cohen's κ ) was assessed for TVS, MRI, and their combination, and stratified by prior surgical status. For the combined approach, a positive result was defined as a positive finding on either modality (TVS or MRI), representing a rule‐out strategy. Results Among 221 women with suspected deep endometriosis, 189 underwent surgery, of whom 112 had both TVS and MRI; 55 had previous abdominal surgery. Combined imaging improved sensitivity for rectosigmoid DE (+10.3%; +6 true positives (TP), +3 false positives (FP)) and uterosacral ligament involvement (+29.2%; +14 TP, +12 FP) but reduced specificity for endometriomas (−19.0%; true negatives (TN) 18 to 14), obliteration of the pouch of Douglas (−13.3%; TN 14 to 8), and uterosacral ligaments (−20.3%; TN 35 to 23). Most lesions missed by TVS were in the mid or upper rectum. Accuracy for the urinary bladder and ureters decreased with the addition of MRI (82.2% to 75.7%). Sensitivity for rectosigmoid lesions was higher with the combined method (TVS + MRI) in women with prior surgery. Conclusions Among selected complex patients undergoing second‐line MRI after expert TVS, combined imaging increased detection of rectosigmoid and uterosacral ligament lesions, but at the cost of reduced specificity. The sensitivity for rectosigmoid disease was greatest among patients with prior abdominal surgery, although this subgroup finding should be considered exploratory. These findings are consistent with a selective rather than routine role for MRI after expert TVS.