Accuracy of current imaging modalities in the diagnosis of synchronous bilateral Wilms' tumor. A report from the National Wilms Tumor Study Group.

BACKGROUND: Five percent of patients with Wilms' tumor will present with bilateral disease. Recent reports suggest that preoperative imaging studies can exclude contralateral disease reliably, obviating the need for formal surgical exploration of the contralateral kidney. This study was undertaken to determine the accuracy of preoperative imaging in diagnosing bilateral Wilms' tumor.

METHODS: The charts of 122 patients with synchronous bilateral Wilms' tumor enrolled in National Wilms Tumor Study-4 were reviewed. With the exception of one child, all had an abdominal computed tomography (CT), ultrasound, or magnetic resonance imaging performed.

RESULTS: There were nine patients (7%) in whom the diagnosis of bilaterality was missed by the preoperative imaging studies. All but one of the missed lesions were small, five less than 1 cm and three 1-3 cm. The accuracy of each imaging modality was correlated with tumor size. Computed tomography was more sensitive in detecting bilaterality than ultrasound. However, there was not a single study that was able to detect more than 50% of lesions less than 1 cm in greatest dimension.

CONCLUSIONS: This review indicates that even with current advances in imaging technology, synchronous bilateral Wilms' tumor will go unrecognized in 7% of patients if formal exploration of the contralateral kidney is omitted. Although this represents a small percentage of all patients presenting with Wilms' tumor, preoperative diagnosis of bilaterality is essential if parenchymal-sparing procedures are to be performed. Until a more reliable indicator of bilateral disease is found, exploration of the contralateral kidney continues to be recommended.