L LSUHSC-S Renal Pathology Consultative Services Interesting Case
Case Study #: 19 9/20/07			By: Stephen M. Bonsib, M.D.			318-675-4557 phone 318-675-4541 fax sbonsi@lsuhsc.edu
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Clinical History:
A 3 year old male presented with flank pain and constitutional symptoms with fever. A 4 cm left renal mass was identified. An FNA was attempted but no pus or tumor cells were obtained. A radical nephrectomy was performed.
				Figure 1:
				4 cm tumor
				Figure 2:
				Perirenal (extracapsular) tissue
				Figure 3:
				Section of the tumor
					Figure 4:
					Section of the tumor
Question:	What is the most common renal tumor in a newborn? What is the most common renal tumor in a 3 year old? What is the usual clinical context and pattern of renal involvement in most lesions of this general type? What is your final diagnosis?
Answer:
1. What is the most common renal tumor in a newborn? The most common tumor in a newborn is a mesoblastic nephroma. Although often referred to as congenital mesoblastic nephroma, this tumor does occasionally occur in older children and even adults. Mesoblastic nephroma is very rare. There is a classic form and a cellular form. Although a MN is a benign tumor, cellular MN demonstrates the same translocation as infantile fibrosarcoma, t(12:15)(p13:q25) that results in a fusion of the ETV6 and NTRK genes. 2. What is the most common tumor in a 3-year old? Wilms tumor is the most common tumor in this age range. This was the clinical diagnosis in this case at the time of nephrectomy. The febrile symptoms lead to the FNA procedure in anticipation of obtaining pus and identifying an infectious etiology. It is important to know that had a Wilms tumor been diagnosed, the performance of a needle biopsy or open biopsy would upstage the patient to stage 2 even if the Wilms tumor had otherwise been renal limited. However, FNA does not upstage a Wilms tumor 3. What is the usual clinical context and pattern of renal involvement in most lesions of this type? The final diagnosis as noted below is xanthogranulomatous pyelonephritis (XGP). The most common clinical scenario with this lesion is urinary tract infection with obstruction due to a staghorn calculus. The usual pattern is diffuse involvement of the renal pyramids and the collecting system. Final diagnosis: Xanthogranulomatous pyelonephritis, focal type The focal type of XGP is very rare. It is encountered most often in children is usually regarded as a neoplasm because it forms a discrete mass lesion. A correct preoperative diagnosis is rare and most patients are treated by nephrectomy. Nephrectomy is often the correct treatment because effective treatment of the associated infection is rarely possible. In this case cultures of the lesion grew staphylococcus. Furthermore, the large size of the lesion relative to the kidney and its central location precluded a partial nephrectomy in this case. The fever promptly remitted post nephrectomy.
References:		Eur J. Pediatr Surg 12:42, 2002 Nephrol dial Transplant 12:1028, 1997. Pediatr Radiol 24:213, 1994.