A perineal fistula is a type of anorectal malformation (ARM) that involves a misplaced anal passage that is often narrowed. With a perineal fistula, the abnormal anal opening is located outside of the sphincter muscle complex, such that the fistula usually has very few voluntary sphincter muscle fibers surrounding it.
Perineal fistula and other anorectal malformations are generally present from birth. More than half of all patients with anorectal malformations have other conditions such as spinal abnormalities, kidney and urinary tract abnormalities, congenital heart defects, or limb defects.