[A case of multilocular renal cyst showing neoplastic features]

A 45-year-old woman was hospitalized with complaint of upper right abdominal pain. By serial examination, it was difficult to distinguish renal cyst from renal cancer. But, because of the frequency of the attacks of upper abdominal pain, nephrectomy was undertaken. The tumor measured 5 X 5 X 3 cm, was distinct from normal renal tissue, and consisted of a small cyst. Histologically, we diagnosed a multilocular renal cyst, and its lining cells showed small atypia and adenomatous proliferation. We concluded that this multilocular renal cyst showed neoplastic features.