A New Concept for the Surgical Anatomy of Posterior Deep Complex Fistulas: The Posterior Deep Space and the Septum of the Ischiorectal Fossa

This study was designed to investigate the pathophysiology of posterior complex fistula with reference to pelvic anatomy.

Three hundred twenty posterior complex fistula patients, operated on between 1995 and 2004, were examined. Thirty patients underwent preoperative magnetic resonance imaging. We also conducted two cadaver dissections. Posterior complex fistulas were classified by the extension forms of secondary ducts.

The septum of the ischiorectal fossa, which comprises membranes between Alcock’s canal and the anal canal, was newly identified intraoperatively and confirmed by magnetic resonance imaging and dissection. The ischiorectal fossa was separated by the septum of the ischiorectal fossa; the upper portion was the inferior levator space, and the lower was the clinical ischiorectal space. Primary lesions were found mainly in the posterior deep space (the anterior border was the internal sphincter, the superior border was the inferior surface of the puborectalis, the inferior and lateral borders were the anterior surfaces of the external sphincter; 97 percent). The primary opening was located in a posterior anal crypt (96 percent). The prevalence of posterior complex fistula limited to the posterior deep space, extending to the inferior levator space, the clinical ischiorectal space, or both, were 21, 14, 53, and 12 percent, respectively. The primary duct from a crypt proceeds diagonally into the internal sphincter to the posterior deep space. The posterior deep space is adjacent to the clinical ischiorectal space and the inferior levator space bordering on the external sphincter. If an abscess penetrates the sphincter from the posterior deep space, it can reach the clinical ischiorectal space and/or the inferior levator space.

Recognition of the posterior deep space, the septum of the ischiorectal fossa, the inferior levator space, and the clinical ischiorectal space may be crucial for effective surgical management of posterior complex fistula.