A rare anal mass: anal leiomyoma presented as perianal fistula.

Leiomyoma of the anal canal originating from the internal anal sphincter is an extremely rare clinical entity. Generally, it does not produce any clinical signs unless it is large enough to cause obstruction, discomfort, bleeding or pain. The diagnosis is often made incidentally during rectal examination due to other perianal disease or check-up. Herein we report a case of internal anal sphincter leiomyoma diagnosed unexpectedly during rectal examination in a patient with perianal fistula, and treated successfully with surgical excision. We present a review of the literature, the diagnostic strategies, differential diagnosis, prognosis and treatment modalities of this lesion.