The occurrence of Wilms tumor in horseshoe kidneys: A report from the National Wilms Tumor Study Group (NWTSG)☆

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Abstract

Background/Purpose: An increased incidence of Wilms tumor has been noted in patients with a horseshoe kidney. These represent a difficult diagnostic and therapeutic challenge. The charts of all National Wilms Tumor Study Group (NWTSG) patients with Wilms tumor occurring in a horseshoe kidney were reviewed. Methods: From 1969 to 1998, 8,617 patients were enrolled in the NWTSG. Forty-one patients were found to have a Wilms tumor arising in a horseshoe kidney for an incidence of 0.48%. Their records were reviewed retrospectively. Results: Horseshoe kidney was not recognized preoperatively in 13 patients, 10 of whom were evaluated with computed tomography (CT). Four of the 10 also had renal ultrasonography and one an intravenous pyelogram (IVP). Two of the 13 were evaluated with an IVP only, and the last had no preoperative imaging studies performed. Stage at presentation was stage I, 10 pts; stage II, 10; stage III, 12; stage IV, 6; stage V, 3. Primary surgical resection was performed in 26 patients, including 23 nephrectomies and 3 partial nephrectomies. Fifteen children were treated with preoperative chemotherapy after initial biopsy of the tumor. The mean total remaining renal parenchyma after all operations (excluding treatment of relapses) was approximately 75%. Surgical complications occurred in 14.6% of patients, including 2 urine leaks, 2 ureteral obstructions, and 1 ureteral injury. Two patients had transient renal failure. Conclusions: The diagnosis of horseshoe kidney often was missed on preoperative imaging. Accurate preoperative diagnosis is important in planning the operative approach and may help to decrease complications related to transection of the urinary collecting system. Although 37% of patients with Wilms tumor arising in a horseshoe kidney were judged inoperable at initial exploration, all were amenable to resection after chemotherapy. J Pediatr Surg 37:1134-1137. Copyright 2002, Elsevier Science (USA). All rights reserved.

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Materials and methods

From 1969 to 1998, 8,617 patients were registered with the NWTSG. Of this group, 41 were identified as having a Wilms tumor in a horseshoe kidney defined as a midline renal fusion. For the purpose of the study, the horseshoe kidney was divided into left and right halves. Tumors arising in the right or left halves of the horseshoe kidney were defined as right- and left-sided tumors, respectively; one arising in the isthmus was defined as such, and if there were multiple tumors in 2 or more of

Results

Forty-one patients with Wilms tumor arising in a horseshoe kidney were identified among the 8,617 in the NWTSG database. This represents 0.48% of the patients registered with the NWTSG. There were 13 boys and 28 girls. The median age at diagnosis was 40 months. The tumor was confined to the right kidney in 18 patients, the left kidney in 15, the isthmus in 5, and was bilateral in 3 children.

Other congenital anomalies were found in 18 patients (Table 1).

. Associated congenital anomalies identified

Discussion

The frequency of horseshoe kidneys in patients with Wilms tumor has been shown previously to be higher than in the general population.4, 9, 10 Most reports cite an incidence of 1 in 400. Horseshoe kidney was present in 0.49% of the patients with Wilms tumor registered to the NWTSG. This suggests that Wilms tumor is 1.96 times more common in patients with horseshoe kidney than in the general population. Genitourinary anomalies (hypospadias, cryptorchidism, renal fusion anomalies) are present in

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Copyright © 2002 Published by Elsevier Inc.