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Abstract Cystic hamartoma of the renal pelvis is a rare benign tumor in the same category as mixed epithelial and stromal tumors. We present a 33-year-old woman with a solid and cystic intrarenal tumor extending into the renal pelvis. She underwent radical nephrectomy and ureterectomy under the diagnosis of renal tumor or renal pelvic tumor. Histopathologically, the tumor was composed of a biphasic proliferation of epithelial and mesenchymal elements. We believe the present case is best classified as a cystic hamartoma of the renal pelvis in the category of mixed epithelial and stromal tumors because of the coexistence of hamartomatous lesions, such as the proliferation of adipose cells and well to poorly differentiated fibromuscular lesions.
Cystic hamartoma of the renal pelvis is a rare benign tumor of the kidney.1 Histopathologically, it is characterized by a biphasic proliferation of epithelial and mesenchymal elements. Similar tumors have been reported by various names and there is considerable controversy regarding the nomenclature of these tumors.2 We present a new case that is best classified as a cystic hamartoma of the renal pelvis in the category of mixed epithelial and stromal tumors.
A 33-year-old woman presented with asymptomatic gross hematuria. Physical and biochemical examinations were normal and urine cytology was negative. Computed tomography revealed a 7-cm heterogeneously enhanced mass with cystic lesions at the upper pole of the right kidney extending into renal pelvis (Fig. 1). The tumor showed a low-intensity area in T1-weighted imaging and an iso- to low-intensity area in T2-weighted imaging of MRI. Regional lymph node swellings and tumor thrombus were not recognized. Angiography showed a mixture of hypervascular and hypovascular areas. Retrograde pyelography revealed a filling defect in the right renal pelvis. Under the diagnosis of renal tumor or renal pelvic tumor, the patient underwent embolization of the renal artery, radical nephrectomy and ureterectomy with bladder cuff in November 2002. The specimen revealed a vaguely circumscribed solid and cystic mass measuring 7.0 × 5.0 × 4.0 cm without renal capsular invasion and penis-like solid mass protruding into the renal pelvis measuring 9.0 × 2.0 × 1.8 cm (Fig. 2). Microscopically, the tumor had no pseudocapsule and was composed of a biphasic proliferation of epithelial and mesenchymal elements with cystic spaces.
The epithelial component consisted of tubules and cysts lined with columnar cells, some showing slit-like conformations (Fig. 3a) and papillary projections. The stromal component, which consisted of spindle cells, ranged from paucicellular fibromuscular areas to markedly cellular areas (Fig. 4a). There were numerous vessels and adipose cells scattered throughout the stroma. Blastemal cells and mitotic figures were not identified. The stroma was strongly positive for vimentin (a marker of mesenchymal cell; Fig. 3b) and the tubular and cyst epitheliums were strongly positive for AE1/AE3 (a marker of epidermal cytokeratin; Fig. 3c). The paucicellular fibromuscular stroma was negative for α-smooth muscle actin (SMA), but the markedly cellular area and the thick-walled blood vessels were strongly positive (Fig. 4b). Stains for CD34 (a marker of endothelial differentiation, solitary fibrous tumors and leukemia), S-100 (a marker of neuroectodermal tumors) and HMB45 (a marker of angiomyolipomas and related tumors) were negative in both the epithelium and the stroma. Estrogen and progesterone receptors were detected in the nuclei of spindle cells. As mentioned, we believe the present case is best classified as a cystic hamartoma of the renal pelvis in the category of mixed epithelial and stromal tumors. The patient was free of disease after a 12-month follow-up period.
Since 1973, 50 cases of mixed epithelial and stromal tumors have been reported by various names, such as cystic hamartoma of the renal pelvis, adult mesoblastic nephroma, multilocular cystic nephroma and cystic-partially differentiated nephroblastoma.2–4 There is controversy regarding the nomenclature of these tumors. They are distinctive benign tumors characterized by a biphasic proliferation of epithelium and stroma. The histological characteristics of the present case were quite similar to those previously reported.
Cystic hamartoma of the renal pelvis was originally reported by Pawade et al.1 in 1993 and formed as an intrarenal multicystic mass adjacent to the pelvicalyceal system. Histopathologically, it had a component of tubules and cysts lined with cuboidal to columnar cells and a component of fibroblastic stroma with scattered smooth muscle bundles. Multilocular cystic nephroma and cystic partially-differentiated nephroblastoma are composed entirely of cysts without any solid components. Also, cystic partially-differentiated nephroblastoma contains foci of immature elements or blastema cells. Mesoblastic nephroma is a congenital neoplasm that occurs in infancy, but a few cases of so-called adult mesoblastic nephroma have been reported.3 The appellation of adult mesoblastic nephroma should not be used because mixed epithelial and stromal tumors were reported to have none of the genetic alterations of mesoblastic nephroma.5
Adsay et al. suggested that cystic hamartoma of the renal pelvis and multilocular cystic nephroma should be presented under the name of mixed epithelial and stromal tumor of the kidney and that the spindle cells of all mixed epithelial and stromal tumor cells were diffusely and strongly positive for muscle markers such as SMA.2 Also, Cystic partially-differentiated nephroblastoma should be distinguished from these entities by the presence of blastema cells. The appellation of multilocular cystic nephroma was not appropriate to the present case due to the presence of solid nodular areas.6 In the present case, immunohistochemical stains for AE1/AE3 confirmed the epithelial nature of the cysts and tubules. The diffuse stains for vimentin confirmed the mesenchymal nature of the stroma and the strong SMA staining of cellular muscular stroma and thick walled blood vessels indicated well smooth muscle differentiation. The poor SMA staining of paucicellular fibromuscular stroma indicated poor muscular differentiation, in comparison with diffusely and strongly stained stromal tumor cells as Adsay et al. reported.2
The present case is best classified as cystic hamartoma of the renal pelvis in the category of mixed epithelial and stromal tumors because of the coexistence of hamartomatous lesions, such as well to poorly differentiated fibromuscular lesions, and the proliferation of adipose cells.