Answer: Renal medullary carcinoma

Histology: This neoplasm appears to rise in the renal medulla. Characteristically, it exhibits a reticular, yolk sac-like or adenoid cystic appearance, often with poorly differentiated areas in a highly desmoplastic stroma. The tumor may be mixed with neutrophils, and is usually marginated by lymphocytes. The nuclei are clear and vesicular, and have prominent nucleoli. One of the most helpful clues to diagnosis is the presence of sickled red cell forms in the vasculature throughout the kidney.

Discussion: Renal Medullary Carcinoma was first clearly described by Davis, et al. (American J Surg Pathol 19:1-11, 1995). The vast majority of patients have had some form of sickle hemoglobinopathy. In Davis’ series, the dominant tumor mass was in the medulla, and ranged from 4cm-12cm in diameter. Satellite tumors in the renal cortex and pelvic soft tissues were usually present, as were venous and lymphatic invasion. Most of the tumors had metastasized when first discovered, and none was confined to the kidney at the time of nephrectomy. Davis and associates thought that these tumors probably arose in the tubular epithelium, in or near the renal papilla. They noted that the tumor arose in the same site that is associated with hematuria in patients with Sickle Cell Trait. Renal Medullary Carcinoma has thus become known as the “7th Sickle Cell Nephropathy” (along with unilateral hematuria, papillary necrosis, nephrotic syndrome, renal infarction, inability to concentrate urine and nephritis.)

The histologic features of this neoplasm are distinct, and are clearly different from those of conventional or papillary renal cell carcinoma. The epithelial nature of the neoplasm with itsgland formation, is quite different from the epithelial Wilms’ tumor, which tends to have much more bland nuclear features. Failure of the tumor to grow in an intraluminal fashion in the tubules in the renal pelvis are features that separate Renal Medullary Carcinoma from high-grade urothelial pelvic neoplasms.