Comparative anatomy of the ischiorectal fossa and pudendal canal in humans and domestic animals

Abstract

Increasing development of veterinary medicine and use of non‐rodent research models have led to the frequent use of the comparative approach to focus on the anatomy of human and other species. However, as the anatomy of any species has not been studied as much as human, comparisons often fail to produce meaningful conclusions. This is particularly the case when the species compared to human are domestic mammals, which already offer significant structural differences due to their wide variation as species. For example, the ischiorectal fossa (ischioanal fossa in humans) and the pudendal canal, both important elements of the pelvic and perineal regions, are barely described in domestic mammals. This is especially true for the pudendal canal and the neurovascular elements contained in it. As part of our efforts to study the anatomy of pelvis and perineum in several species we have focused on the ischiorectal fossa and pudendal canal using human and domestic animals. Using silicone casts and dissections of the ischiorectal fossa, pelvic wall, and perineum of dogs (n=16), goats (n=9), pigs (n=9), horse (n=3), cats (n=3), and humans (n=22), we have initially defined the particular shapes of the fossa, the pudendal canal and the structural elements that contribute to make their walls in these species (e.g. pelvic diaphragm, sacrotuberal ligament, etc.). Moreover, we have also defined the specific neurovascular elements contained in them (caudal rectal and pudendal nerves, internal pudendal vessels, etc.). Among some interesting findings we found that, unlike in humans, the pudendal canal in domestic animals is not within the ischiorectal fossa. In these species, there is a ‘conceptual’ fossa and a ‘real’ one. The pudendal nerve and vessels (and other associated elements) are compressed against the pelvic wall by the pelvic diaphragm to form the pudendal canal. Then, unlike in humans, the pelvic diaphragm separates caudally from the pelvic wall to generate a ‘real’ ischiorectal fossa.Support or Funding InformationMidwestern University Intramural Funds