Fate of bilateral renal lesions missed on preoperative imaging: A report from the National Wilms Tumor Study Group

Purpose: In children undergoing nephrectomy for Wilms tumor exploration of the contralateral kidney has been recommended to detect occult tumors missed on preoperative evaluation. In this review of the National Wilms Tumor Study (NWTS) 4 cases of bilateral Wilms tumors (BWT) we evaluate incidence and outcome of missed bilateral lesions. Materials and Methods: NWTS-4 enrolled 3,335 patients from August 1986 through September 1994. There were 188 patients with BWT or 5.6% of the total registered. The operative records, pathology and imaging reports were reviewed. Results: In 11 cases synchronous BWT was diagnosed at surgical exploration, which represents 5.9% of the bilateral cases but only 0.3% of all NWTS-4 cases. Two patients did not undergo preoperative imaging and were excluded from analysis. The size of the missed lesions was less than 1 cm in 6 patients and 1 to 2 cm in 3. Computerized tomography was performed in all patients except one who entered early in the study. Management of missed lesions included enucleation in 2 cases, biopsy in 6 and no surgery in 1. No patient underwent irradiation. The postoperative chemotherapy regimen consisted of doxorubicin, dactinomycin and vincristine in 6 children, and dactinomycin and vincristine in 3. Median followup was 9 years. There were no recurrences in any kidney with a missed lesion. All 9 patients were alive and disease-free at last followup. Conclusions: Routine contralateral renal exploration will identify few occult tumors not detected on preoperative imaging. Omission of routine exploration will not likely affect the outcome or management of newly diagnosed Wilms tumor provided preoperative computerized tomography or magnetic resonance imaging is performed. The outcome in these patients was excellent.