Presentation
Reduced renal function lead to urinary tract imaging, which in turn lead to this exam.
Patient Data
In the lower pole, there is a round enhancing lesion measuring 3.1 cm in diameter without internal calcification. No apparent extension into the IVC. Only tiny para-aortic nodes evident. A few simple cysts are noted elsewhere in the right kidney. There are cysts in the left kidney as well.
The left kidney is relatively small, measuring 8.6 cm as opposed to 11.3 cm on the right side. The cortex on the left side is also relatively thinned.
This patient went on to have a partial nephrectomy.
Histology
MACROSCOPIC DESCRIPTION: "Partial nephrectomy": The specimen consists of a segment of kidney weighing 23g and measuring 42x52x30mm. Resection margins are inked. Serial sectioning reveals a well circumscribed, nodular, partly tan, yellow tumor 30x23x25mm. Tumor abuts the inked resection margins. Within the tumor there are focal areas of hemorrhage. There is no invasion beyond the renal capsule.
MICROSCOPIC DESCRIPTION: The sections of kidney show a circumscribed moderately hypercellular tumor enclosed within a fibrous capsule of varying thickness. Tumor cells have round oval and angulated hyperchromatic nuclei and a variable amount of cytoplasm which contains dense eosinophilc, PTAH positive granules. No mitotic figures or areas of necrosis are identified and no capsular or vascular invasion is seen. The adjacent renal parenchyma is unremarkable. Immunohistochemistry shows patchy staining for CK7 in tumor cells. Occasional CD10 positive cells are also noted.
FINAL DIAGNOSIS: Oncocytoma
Case Discussion
This case illustrates how renal oncocytomas can be indistinguishable from renal cell carcinomas on imaging.
Gross pathology image courtesy of Dr Alpha Tsui, Royal Melbourne Hospital.
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