Atypical Epidermoid Cyst in Renal Pelvis and Histogenetic Implications
A 73-year-old female was admitted for surgical removal of a left renal pelvic mass. She has taken antihypertensive agents for 30 years and received percutaneous coronary intervention due to stable angina 3 years ago. During routine follow-up, a renal mass was incidentally detected 2 months ago. She denied any episodes of renal colic or urolithiasis. On physical examination, there was no tenderness on the area of costovertebral angle. Laboratory values revealed a marginal elevation of serum creatinine (1.21 mg/dL). Urinalysis and urine cytology showed no evidence of inflammation or malignant cells. The ultrasonography showed an echogenic mass within the renal pelvis and mild dilation of several calyces. The calcified lesion was not found on plain radiograph of the abdomen (kidneys, ureters, and bladder). An abdominopelvic computed tomography revealed a noncalcified soft tissue mass in the left renal pelvis on precontrast enhancement scan. It showed slight enhancement after contrast administration (). The preoperative radiologic diagnosis was favored as a urothelial carcinoma of the renal pelvis. A conventional left nephroureterectomy was performed.\nThe cut surface of the resected specimen revealed a 5×3×2 cm-sized, well-defined ovoid, cystic mass which was compactly filled with white and reddish tan-colored amorphous materials in the pelvis. Histologically, the cystic lumen contained multiple keratinous materials and much of the cystic lining epithelia were denuded. The remaining portion was lined with hyperplastic urothelium and keratinizing squamous epithelium (). These two epithelial areas were sharply demarcated from each other. Immunohistochemical staining using antibodies against uroplakin II (1:100; Santa Cruz Biotechnology Inc., Santa Cruz, CA, USA) and cytokeratin 7 (CK7) (1:100; Dako, Glostrup, Denmark) was performed to identify epithelium-specificdifferentiation. The cells lining urothelia were strikingly positive for uroplakin II () and CK7. In contrast, most of the cells in the lining of squamous epithelia were negative for these urothelial specific antibodies. However, some portion of the squamous epithelia interestingly contained a few uroplakin-positive cells () and some more CK7-positive cells.