[Diffuse xanthogranulomatous pyelonephritis in infant]

We report a case of a renal mass in a 4-month boy, which occured during the assessment of a pelvi-calyceal dilatation diagnosed at 23 weeks of gestational age. There was no history of urinary infection, fever or weight loss. Physical examination revealed a mass of the left flank with significant flank tenderness. Laboratory test showed a biological inflammatory syndrome and urine culture was negative. Investigations including ultrasound and computed tomography scan were suggestive of diffuse xanthogranulomatous pyelonephritis with a non-functioning left kidney. Left total nephrectomy was performed through a lumbar incision with an extraperitoneal approach. The kidney was enlarged with a dilated pelvis containing pus upstream of a proximal ureteral atretic segment. Pathological examination of the kidney confirmed the diagnosis of diffuse xanthogranulomatous pyelonephritis. The boy remains well at 1 year follow-up. Xanthogranulomatous pyelonephritis is very rare in infants. It is an uncommon severe progressive renal infection resulting in destruction of renal parenchyma, histologically replaced by xanthomatous cells and granulomatous reaction. Pathogenesis of xanthogranulomatous pyelonephritis remains unclear. But it is well known that urinary tract obstruction and renal lithiasis are determining factors. It can occur in variant clinical forms but its symptoms remain non-specific. Curative treatment consists in nephrectomy and definitive diagnosis is made on histological examination of the kidney. This diagnosis should be discussed when a renal mass occurs in a context of malformative uropathy and xanthogranulomatous pyelonephritis have to be included in the differential diagnosis of renal mass in infants and children.