ischioanal

Ischioanal, or ischiorectal, refers to the ischioanal (ischiorectal) fossa, a fat-filled space on each side of the anal canal within the perineum. The fossae form part of the potential spaces of the perineum and serve as a conduit for neurovascular structures supplying the anal and perineal regions.

Anatomy and boundaries: Each ischioanal fossa is bounded medially by the external anal sphincter and the levator ani muscle, laterally by the obturator internus muscle and its fascia, superiorly by the pelvic diaphragm, and inferiorly by the skin of the perineum. Anteriorly the space communicates with adjacent perineal compartments. The pudendal canal (Alcock’s canal) runs along the lateral wall of the fossa and contains the internal pudendal vessels and pudendal nerve, which give off the inferior rectal branches that supply the anal canal and surrounding tissues.

Contents: The fossa contains fat and neurovascular structures, notably the internal pudendal vessels, pudendal nerve and its branches, inferior rectal vessels and nerves, and perineal branches. Lymphatics are present as well.

Clinical significance: The ischioanal fossa is a common site for infections such as ischioanal abscess, presenting with perineal or buttock swelling, severe pain, and sometimes fever. Management typically involves incision and drainage, with attention to preserving the anal sphincter and surrounding structures. Imaging (CT or MRI) may delineate extent. The fossa is also the region where pudendal nerve blocks or Alcock’s canal injections are performed for anesthesia during perineal or anorectal procedures.