Prediction of incidental obturator hernia using preoperative computed tomography: the distance between the obturator internus muscle and the pubic bone

Non-incarcerated obturator hernias (OH) are often difficult to diagnose preoperatively and occasionally are identified incidentally during laparoscopic groin hernia repair. Three anatomic pathways for OH protrusion have been described. Although increased distance between the obturator externus and pectineus muscles (OE–P gap) according to axial computed tomography (CT) has been considered suggestive, this measurement cannot adequately assess all herniation pathways. The present study considered whether measuring distance between the obturator internus muscle and the pubic bone (OI–P gap) using preoperative coronal CT could identify incidental OH (IOH) during transabdominal preperitoneal repair (TAPP). We retrospectively reviewed female patients who underwent elective TAPP between 2017 and 2025. OE–P and OI–P gaps both were measured in preoperative CT images. Patients were divided into IOH and non-IOH groups, between which clinical variables and imaging findings were compared using the Wilcoxon test. Among 79 patients, IOH was identified in 9 (11%). No significant differences between groups were observed in age or body mass index. While the OE–P gap was comparable between IOH and non-IOH groups (2.5 mm vs. 2.7 mm, P = 1.000), the OI–P gap was significantly larger in the IOH than in the non-IOH group (13.6 mm vs. 9.7 mm, P = 0.005). An OI–P gap cutoff value of 12.9 mm showed sensitivity of 67% and specificity of 93% in diagnosing IOH. Large OI–P gap in coronal CT images was associated with IOH and could be a useful in its detection.