Perirenal tailgut cyst (cystic hamartoma).

Tailgut cysts are rare congenital multicystic lesions preferentially occurring in the retrorectal space. They are assumed to arise from the remnant of embryonic tailgut and occasionally exhibit malignant transformation. The authors herein describe the clinical, radiologic, and pathologic features of an unusual perirenal tailgut cyst with an emphasis on its histogenesis and distinction from other intraabdominal cystic lesions.