[Two cases of heterotopic bone formation in the kidney and clinico-pathological study of 36 cases reported in Japan].

We report two cases of heterotopic bone formation in the kidney. One patient was a 54-year-old man who consulted his family physician with the complaint of fever-up and nocturia. X-ray examination revealed a calcification in the left kidney and location of the pelvis for outside. Therefore, abdominal CT scan and selective renal angiography were performed. As a malignant renal tumor with hypovascularity could not be neglected, left nephrectomy was performed on August 18, 1980. Grossly, the resected kidney was 230 g in weight and had a 8 X 3 cm mass with a white cut surface and bone-like tendency. Histopathologically, a well-developed bone with erythropoietic bone marrow was found outside of the renal capsule. The other patient was a 52-year-old man with the complaint of painful swelling of left scrotum and lumbago. X-ray examination revealed bilateral renal stones and left ureteral stone. Bilateral nephrolithotomy and left ureterolithotomy were performed, and some stones and a part of bilateral renal pelvis which was bony hard and white in color were resected. Histopathologically, there were well-developed bone formation and infiltration of inflammatory cells in renal pelvic membrane. Among 36 reported cases in Japan, 16 cases were in male and 20 cases in female patients. Our second case was the first cases of bilateral renal heterotopic bone formation complicated with bilateral renal stones in 5 reported cases with renal stones. Including our first case, 5 cases which had heterotopic bone formation in renal capsule have been reported.