Ischioanal fossa

The ischioanal fossa (Ischiorectal fossa) is an anatomical space located in the perineum, in the anorectal region. It is the largest space in this area and is bounded by the pelvic diaphragm superiorly, the obturator internus muscle laterally, and the skin and superficial fascia of the perineum inferiorly. The fossa is filled with fat and connective tissue (fat body of ischioanal fossa), which allows for the expansion of the anal canal during defecation and provides a cushion for neurovascular structure.

The fossa is somewhat prismatic in shape, with its base directed to the surface of the perineum, and its apex at the line of meeting of the obturator and anal fasciæ. The anterior recess of ischioanal fossa extends anteriorly above the urogential diaphragm.

Boundaries

• medially: the Sphincter ani externus and the anal fascia;

• laterally: the tuberosity of the ischium and the obturator fascia;

• anteriorly: the fascia of Colles covering the Transversus perinæi superficialis, and the inferior fascia of the urogenital diaphragm;

• posteriorly: the Glutæus maximus and the sacrotuberous ligament.

Content:

Crossing the space transversely are the inferior hemorrhoidal vessels and nerves; at the back part are the perineal and perforating cutaneous branches of the pudendal plexus; while from the forepart the posterior scrotal (or labial) vessels and nerves emerge. The internal pudendal vessels and pudendal nerve lie in Alcock's canal on the lateral wall. The fossa is filled with fatty tissue across which numerous fibrous bands extend from side to side.