Constant existence of the sensory branch of the nerve to the pyramidalis distributing to the upper margin of the pubic ramus.

Twenty-one sides of 11 adult Japanese cadavers were investigated, and 2 of 21 sides exhibited absence of the pyramidalis. We observed that all of the nerves to the pyramidalis included the sensory nerve branch, which distributed to the aponeurotic tissue in the upper area of the pubic ramus. To investigate the clinical relevance and developmental process of the pyramidalis, detailed innervation patterns of the pyramidalis and the lumber plexus were examined and compared with the case of absent pyramidalis. The nerves to the pyramidalis could be classified into five types by the derivative nerves and two subtypes by their courses associated with the funiculus spermaticus. In the cases of absent pyramidalis, similar sensory branches distributed close to the upper area of the pubic ramus. We deduced that the sensory branch extended along with the muscular branch to the pyramidalis after development of the pyramidalis and that only the sensory branch remained in cases in which the pyramidalis disappeared. The two subtypes might associate with descensus testis. Surgeons performing inguinal hernia repair using a mesh and tension-free surgical technique should preserve the nerves around the funiculus spermaticus to avoid diminished proprioception in the lower abdominal wall.