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Presented by Dr. Jonathan Epstein and prepared by Austin McCuiston.
A 45 year old female was incidentally found to have a 3 cm renal mass on imaging.
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1. Question
A 45 year old female was incidentally found to have a 3 cm renal mass on imaging.
Correct
Answer: Oncocytoma
Histology: The tumor is composed of cells with abundant eosinophilic cytoplasm. Focally, cells are arranged in nests in a fibromyxoid stroma. In this area the well-preserved nuclei that with fine chromatin are uniformly round with variably sized nucleoli. However, the majority of cells have prominent atypia, yet the atypia appears degenerative nuclear atypia with multinucleation, pseudoinclusions, and indistinct smudgy chromatin. Mitotic figures and necrosis are absent.
Discussion: One of the most characteristic features of oncocytoma is that cells are arranged in nests, acini, tubules or microcysts in a fibromyxoid stroma. When the tumor has this pattern at low power, 95% of the time the diagnosis is oncocytoma. In order for me to diagnose oncocytoma, well-preserved nuclei should be uniformly round with variably sized nucleoli. Pyknotic dark nuclei with crenated irregular edges should be discounted. Scattered cells with degenerative nuclear atypia with multinucleation and pseudoinclusions can be seen in a typical oncocytoma, where the atypical cells are often clustered. This case is unusual in that the atypical cells are more diffusely spread throughout the tumor. However, if this tumor was a high grade renal cell carcinoma with this degree of atypia, one would expect to see numerous mitotic figures and necrosis which are absent. Similarly, a ki67 in this case was very low, in contrast to what would be seen in a high grade renal cell carcinoma. In addition to degenerative nuclear atypia, oncocytomas can extend into the perirenal fat and can show vascular invasion, including the main renal vein, and still be benign. Chromophobe renal cell carcinomas can uncommonly be high grade with increased cellularity, necrosis, and increased mitotic figures, but retains typical cytological features of plant-like cell borders, crinkly nuclei surrounded by koilocytosis. Immunohistochemically, CK7 tends to be diffuse in chromophobe renal cell carcinoma and is negative to patchy in oncocytoma. However, some chromophobe carcinomas are patchy or negative for CK7, such that the only definitive result is that diffuse CK7 positivity rules out oncocytoma. Hales colloidal iron is often not specific and I do not rely on it, but in the classic case shows diffuse cytoplasmic staining.
Incorrect
Answer: Oncocytoma
Histology: The tumor is composed of cells with abundant eosinophilic cytoplasm. Focally, cells are arranged in nests in a fibromyxoid stroma. In this area the well-preserved nuclei that with fine chromatin are uniformly round with variably sized nucleoli. However, the majority of cells have prominent atypia, yet the atypia appears degenerative nuclear atypia with multinucleation, pseudoinclusions, and indistinct smudgy chromatin. Mitotic figures and necrosis are absent.
Discussion: One of the most characteristic features of oncocytoma is that cells are arranged in nests, acini, tubules or microcysts in a fibromyxoid stroma. When the tumor has this pattern at low power, 95% of the time the diagnosis is oncocytoma. In order for me to diagnose oncocytoma, well-preserved nuclei should be uniformly round with variably sized nucleoli. Pyknotic dark nuclei with crenated irregular edges should be discounted. Scattered cells with degenerative nuclear atypia with multinucleation and pseudoinclusions can be seen in a typical oncocytoma, where the atypical cells are often clustered. This case is unusual in that the atypical cells are more diffusely spread throughout the tumor. However, if this tumor was a high grade renal cell carcinoma with this degree of atypia, one would expect to see numerous mitotic figures and necrosis which are absent. Similarly, a ki67 in this case was very low, in contrast to what would be seen in a high grade renal cell carcinoma. In addition to degenerative nuclear atypia, oncocytomas can extend into the perirenal fat and can show vascular invasion, including the main renal vein, and still be benign. Chromophobe renal cell carcinomas can uncommonly be high grade with increased cellularity, necrosis, and increased mitotic figures, but retains typical cytological features of plant-like cell borders, crinkly nuclei surrounded by koilocytosis. Immunohistochemically, CK7 tends to be diffuse in chromophobe renal cell carcinoma and is negative to patchy in oncocytoma. However, some chromophobe carcinomas are patchy or negative for CK7, such that the only definitive result is that diffuse CK7 positivity rules out oncocytoma. Hales colloidal iron is often not specific and I do not rely on it, but in the classic case shows diffuse cytoplasmic staining.
