Simple cyst arising in a transplanted kidney: a case report.

A 17-year-old girl was hospitalized for evaluation of gradually decreasing function of a kidney transplanted 8 years earlier. A plain film of the abdomen showed a possible renal calculus. Excretory urography proved that this calcification was slightly anterior to the kidney but in the upper pole a well rounded mass was discovered. An echogram confirmed the diagnosis of benign renal cyst. Malignant cystic lesions obviously must be differentiated from those that are benign. Patients on immunosuppressive therapy are known to have a higher incidence of malignancy than the general population. A malignant tumor may require withdrawal of immunosuppressive therapy and removal of the transplanted organ, whereas a benign cyst would require no therapy unless it becomes infected or produces obstruction.