OSSIFYING RENAL TUMOR OF INFANCY - A CLINICOPATHOLOGICAL STUDY OF 9 CASES

We studied nine ossifying renal tumors of infancy (ORTI), including al l five previously reported cases. There were eight boys and one girl r anging in age from 6 days to 14 months. Gross hematuria was the presen ting sign in all nine patients. Eight tumors arose in the left Kidney and six in the upper pole. All seven patients with follow-up informati on were free of recurrence. All lesions were attached to a renal papil la and presented mainly within the calyceal lumen. Two resembled stagh orn calculi clinically. All tumors contained varying proportions of os teoid, osteoblastic cells, and spindle cells. The spindle cell compone nt had features strongly suggesting that they represented hyperplastic intralobar nephrogenic rests (ILNR). The proportion of osteoid and de gree of osseous maturation increased with increasing age of the patien t. ORTI is a distinctive clinicopathologic entity, possibly representi ng a distinctive interaction between ILNR in the renal papilla with di stal collecting duct or urothelial cells in the developing kidney.