[Giant epidermal cyst in the perineum extending into the pelvic space in the patient with polycystic kidney disease: a case report].

A 75-year-old man with autosomal dominant polycystic kidney disease was admitted to our hospital with the chief complaint of a giant mass in the left side of the perineum that had gradually developed in size during the previous 20 years. Palpation revealed a neonatal head-sized cystic mass with no tenderness. Magnetic resonance imaging (MRI) demonstrated a well-circumscribed homogeneous mass extended to the dorsal side of the bladder. It was excised surgically without any injury of rectum or urinary tract. The resected specimen was 23 x 18 x 12 cm in size and 1.2 kg in weight. The pathological diagnosis was epidermal cyst. Cases with an epidermal cyst extending into the pelvic space are extremely rare with few cases having been reported in the world.