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Presented by Dr. Jonathan Epstein and prepared by Austin McCuiston.
A 65 year old female underwent a partial excision for a renal mass.
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1. Question
A 65 year old female underwent a partial excision for a renal mass.
Correct
Answer: Oncocytoma
Histology: The architecture and cytology in this case is typical of oncocytoma. The tumor is arranged in discrete nests as opposed to the more sheet-like growth in chromophobe RCC. Cytologically, there are large, round-to-polygonal cells with abundant eosinophilic cytoplasm. Well-preserved nuclei that with fine chromatin are uniformly round with variably sized nucleoli. At the perimeter of the tumor, the lesion extends out into the peri-renal adipose tissue without inducing a stromal reaction. There is a central scar where the cells lose their oncocytic appearance and have more clear scant cytoplasm.
Discussion: Extra-renal extension into peri-renal adipose tissue may be seen in 20% of oncocytomas. Invasion of renal vessels including the main renal vein can also be rarely seen. Both of these features do not affect the 100% benign nature of oncocytomas. In contrast to chromophobe RCC, oncocytomas lack raisenoid nuclei with irregular, wrinkled, notched nuclear membranes and perinuclear halos, yet not every cell will have irregular nuclei. CK7 tends to be diffuse in chromophobe but can be negative or patchy. CK7 is patchy in oncocytomas and never diffuse. A pitfall is the tubules in the central scar of oncocytomas are typically diffuse CK7 positive. Hybrid tumor is used when there are discrete classic areas of chromophobe RCC and oncocytoma in the same tumor.
Incorrect
Answer: Oncocytoma
Histology: The architecture and cytology in this case is typical of oncocytoma. The tumor is arranged in discrete nests as opposed to the more sheet-like growth in chromophobe RCC. Cytologically, there are large, round-to-polygonal cells with abundant eosinophilic cytoplasm. Well-preserved nuclei that with fine chromatin are uniformly round with variably sized nucleoli. At the perimeter of the tumor, the lesion extends out into the peri-renal adipose tissue without inducing a stromal reaction. There is a central scar where the cells lose their oncocytic appearance and have more clear scant cytoplasm.
Discussion: Extra-renal extension into peri-renal adipose tissue may be seen in 20% of oncocytomas. Invasion of renal vessels including the main renal vein can also be rarely seen. Both of these features do not affect the 100% benign nature of oncocytomas. In contrast to chromophobe RCC, oncocytomas lack raisenoid nuclei with irregular, wrinkled, notched nuclear membranes and perinuclear halos, yet not every cell will have irregular nuclei. CK7 tends to be diffuse in chromophobe but can be negative or patchy. CK7 is patchy in oncocytomas and never diffuse. A pitfall is the tubules in the central scar of oncocytomas are typically diffuse CK7 positive. Hybrid tumor is used when there are discrete classic areas of chromophobe RCC and oncocytoma in the same tumor.