Ischio-anal fossa hydatid cyst.

Extrahepatic hydatid disease has been reported in several locations, including the pelvis, and it often poses a diagnostic challenge. There are very few reported cases of primary perineal ischio-anal fossa hydatid cysts. We present a case of a 46-year-old female who had complained of painless left perianal mass for 8 months. The first clinical and radiological diagnosis was a cystic lesion of the perianal region. However, surgical and pathological examination revealed the diagnosis of hydatid disease of ischio-anal fossa. The patient underwent surgical excision. At 1-year follow-up, the patient was disease-free. Hydatid disease of the perianal area, although rare, must be kept in the differential diagnosis of pathologies of any perianal mass or lump.