A Case of Renal Schwannoma
A 40-year-old woman presented with left flank pain of 2 weeks duration. She had no other urologic symptoms and no history of gross hematuria. A physical examination indicated a palpable hard mass over the left upper quadrant, but no flank tenderness. The results of laboratory studies, which included a complete blood count, a blood chemistry analysis, urinalysis, and a urine culture, were within normal limits. The results of a urine cytologic examination were also negative. Computed tomography (CT) revealed a renal tumor approximately 7.1 cm in size in the left renal pelvis area. The mass was low-attenuated, lobulated, and minimally enhanced. The mass was primarily located in the renal hilum, and the renal pelvo-calyceal system was not identified. In addition, the renal tumor was well demarcated from the renal parenchyma, and the mass was abutting the posterior aspect of the pancreas body and the inferior aspect of the spleen via the renal parenchyma (). A retrograde pyelography (RGP) was performed to identify the renal pelvis tumor. On RGP, the left ureteropelvic junction was kinked, the upper calyces were obliterated, and the calyx was filled with an irregular collection of contrast ().\nWe decided to perform a nephroureterectomy because the renal pelvis tumor could not be excluded completely. The left kidney was removed by retroperitoneal laparoscopic surgery, and then the lower ureter and bladder cuff were excised by using an open maneuver. At the time of surgery, the mass was well dissected from the adjacent tissues and was not adherent to the spleen or pancreas.\nGrossly, the tumor was well-circumscribed, 6.8×6.5×3.5 cm in size, and located in the renal pelvis, compressed adjacent to the renal parenchyma. The tumor was oval shaped and lobulated, and the cut surface was light yellow to gray-white in appearance ().\nHistologic examination showed that the tumor consisted of a solid proliferation of spindle-shaped cells of relatively uniform appearance with small amounts of indistinct cytoplasm and oval dark-stained nuclei. The tumor cells were indistinguishable from those of an angiomyolipoma (which has scanty adipose tissue and blood vessels), gastrointestinal stromal tumor (GIST), or leiomyoma. The characteristic histologic findings of a schwannoma, i.e., a highly ordered cellular component (Antoni A) that palisades (Verocay bodies) with a plus myxoid component (Antoni B), were not identified. However, a peripheral cuff of lymphoid aggregates, suggestive of schwannoma rather than GIST, was observed (). Interlacing bundles of spindle cells showed neither nuclear atypia nor mitotic figures ().\nImmunohistochemical staining with HMB45, S-100, smooth muscle actin (SMA), calponin, desmin, C-kit, and Ki-67 was performed. The tumor cells showed diffuse strong positivity for S-100 protein (). The tumor cells were negative for HMB45, SMA, calponin, desmin, and C-kit. Our final pathologic diagnosis was primary renal pelvic schwannoma.