Case of the Week

2020-44 / November 2

Contributors: Priti Lal, Christopher Preciado, Matthew B. Palmer, Sean R. Williamson

A man in his late 60s underwent a nephrectomy for a slowly growing renal mass. He had a prior diagnosis of oncocytoma on a core biopsy 7 years ago.

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Quiz

1. What is the correct diagnosis?

a. Chromophobe renal cell carcinoma, eosinophilic variant

b. Clear cell renal cell carcinoma with eosinophilic change

c. High grade oncocytic tumor

d. Oncocytoma

e. None of the above

This well circumscribed renal tumor measured 3.3 cm. The cut surface was smooth, mahogany brown with a well-formed central scar. The tumor was composed of oncocytic cells arranged in nests with a prominent central scar. The cells reveal prominent intracytoplasmic vacuoles with round nuclei. Rare entrapped tubules and a single focus of calcification was also noted. One focus of lymphovascular invasion was identified at the periphery near the tumor capsule. Given the prominent cytoplasmic vacuoles, differential diagnoses of succinate dehydrogenase-deficient RCC, chromophobe renal cell carcinoma, and oncocytoma were included. Accordingly, a panel of immunohistochemical stains were performed. The tumor revealed membranous staining for KIT without mast cells noted. SDHB staining was normal (retained). The vacuoles were negative for SDHB immunohistochemistry. The tumor was negative for CK7, CAIX, vimentin, CD10, and AMACR. Given the staining pattern and the morphologic appearance a diagnosis of oncocytoma with prominent intracytoplasmic vacuoles and lymphovascular invasion was made. Electron microscopic photomicrographs were developed from FFPE block and revealed numerous mitochondria. Although the reference from Koller et al describes vacuoles in mitochondria, we could only demonstrate intracytoplasmic vacuoles. Morphologically, intracytoplasmic vacuoles and lymphovascular invasion have been previously described is oncocytomas; however, they have not been described in the same case.

1. Williamson SR. Renal Oncocytoma with perinephric fat invasion. Int J Surg Pathol. 2016, 24(7) 625-626

2. Koller A, Kain R, Haitel A, Mazal PR, Asboth F, Susani M. Renal oncocytoma with prominent intracytoplasmic vacuoles of mitochondrial origin. Histopathology 2000, 37, 264-268

3. Wobker SE, Przybycin CG, Sircar K, Epstein JI. Renal oncocytoma with vascular invasion: a series of 22 cases. Hum Pathol. 2016 58:1-6.

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