Ossifying renal tumor of infancy  (ORTI)  is an extremely rare benign pediatric renal tumor.

Less than 25 cases have been reported, mostly within the first year of life (age range 6d-30mths, mean 6.7m). There is a predilection for males (male to female ratio 6:1).

Presentation symptoms include painless gross hematuria and rarely with an abdominal mass. Unilateral mass located in the renal pelvis and calyces with occasional extension into the collecting ducts, leading to hydronephrosis or pelvicalyceal dilatation ¹.  Rarely coexistence with other malignant tumors has been reported.

Nodular, often calcified mass with firm, grey-white, cut surface.

The tumor consists of core surrounded by osteoblasts blends at the periphery with a blastemal-like spindle cell component with infiltrative growth.  The osteoid matures with the age of the patient.

EMA, Vimentin and STAB2 were positive in osteoblasts and WT-1 in spindle cells; CK, PAX8 and PAX2 negative.

The tumor is benign, and so far, reported patients remain well without recurrence or metastasis after operation.²

Trisomy 4 has been reported in a small group of tumors.^2-4