Two Distinct Types of Type M Hernia: Pulsion Hernia and Traction Hernia

Medial inguinal hernia (Type M hernia), also referred to as a direct hernia, has traditionally been considered a singular disease. However, differences in the origin of the fat tissue entrapped within the hernia defect suggest the existence of two distinct subtypes. Notably, intraoperative differences observed between supravesical hernia (SH) and conventional medial hernia (CMH) indicate distinct pathogenetic mechanisms underlying each subtype. This study aims to demonstrate that Type M hernia comprises two pathogenetically distinct subtypes, supported by a comprehensive literature review.

To investigate the distinct pathogenesis of SH and CMH, we retrospectively analyzed 138 cases of transabdominal preperitoneal (TAPP) repair performed between January 2023 and December 2024. Among these cases, 12 were intraoperatively diagnosed as SH and 49 as CMH. Laparoscopic findings were evaluated, with particular focus on the origin of the fat tissue incarcerated within the hernia defect.

In 10 of the 12 SH cases (83%), the entrapped fat tissue originated from the superficial layers of the preperitoneal fat (Layer S). In contrast, in 44 of the 49 CMH cases (90%), it primarily originated from the deep layers (Layer D). Additionally, in 4 of the 12 SH cases (33%), only a minimal peritoneal depression was observed, with little to no involvement of layer D.

Type M hernias can be classified into two subtypes: those primarily involving Layer S, as observed in SH, and those involving Layer D, as observed in CMH. Intraoperative findings suggest that SH develops due to traction forces acting on the abdominal wall, whereas CMH is primarily attributed to increased intra-abdominal pressure. These findings indicate that Type M hernia consists of two pathogenetically distinct subtypes: traction hernia and pulsion hernia.