RHABDOID TUMOR OF THE KIDNEY IN CHILDREN - A COMPARATIVE-STUDY OF 21 CASES

OBJECTIVE. Rhabdoid tumor of the kidney (RTK) is unique among children renal neoplasms in its frequent association with primary or metastati c CNS lesions. Previous reports suggest that RTK has characteristic CT features. It has been proposed that if CT could accurately predict th e correct diagnosis of RTK preoperatively, then imaging protocols migh t be modified during the examination to include imaging of the brain. We wished to determine if RTK could be reliably distinguished from oth er renal neoplasms of early childhood. MATERIALS AND METHODS. We retro spectively reviewed clinical, radiologic, and pathologic records of 21 patients with RTK. The study group included 13 males and eight female s who were newborn to 36 months old (mean, 11 months). The study group was compared with 153 patients who were 3 years old or younger and wh o had solid renal masses. From this comparison group a subset of 54 pa tients 1 year old and younger was also selected for comparison with 13 (62%) of the 21 patients in the study group who were 1 year old or yo unger. Both comparison groups consisted of patients whose case materia l was consecutively added to the radiologic pathology archives at our institution. Diagnoses of the group of 153 patients were Wilms' tumor (n = 93), mesoblastic nephroma (n = 44), clear cell sarcoma of the kid ney (n = 12), renal cell carcinoma (n = 3), and undifferentiated sarco ma (n = 1). RESULTS. A prominent eccentric crescent with the attenuati on of fluid, representing subcapsular renal hemorrhage or peripheral t umor necrosis adjacent to tumor lobules, was revealed on CT scans in 1 5 (71%) of the 21 patients with RTK and in seven (54%) of the 13 patie nts with RTK who were 1 year old or younger. Nineteen (12%) of 153 pat ients in the larger comparison group, representing patients with all t umor types, had CT features identical to those of the RTK group, inclu ding six (4%) patients with pathologic confirmation of subcapsular ren al hematomas. Six (11%) of the 54 comparison patients 1 year old and y ounger had CT features identical to those of the RTK group, and all pr oved to have mesoblastic nephroma. Associated CNS lesions were seen on CT or MR imaging in 11 (52%) of the 21 patients with RTK, but none wa s seen in the comparison group of patients. CONCLUSION. On CT, a perip heral crescent with the attenuation of fluid is characteristic of RTK. However, 12% of renal neoplasms that occur more commonly than RTK in children had CT findings indistinguishable from those of RTK. Because the prevalence of RTK is relatively low, and because the CT findings a re not pathognomonic, a renal mass seen on CT in a child is unlikely t o represent RTK regardless of its CT features. We therefore conclude t hat the routine addition of CT of the brain for pediatric patients wit h renal masses that show a peripheral crescent of fluid attenuation is not justified. Supplemental imaging of the brain should be based on c linical findings or tissue diagnosis.