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29 April 2011 Case of the Week #204
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Thanks to Jennifer Jeung, University of Florida (USA), for contributing this case. To contribute a Case of the Week, follow the guidelines on our Case of the Week page.
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Case of the Week #204
A 60 year old Caucasian man had an incidental 5 cm solid left lower pole renal mass on computed tomography (CT) scan. There was no evidence of metastatic disease or masses elsewhere on abdominal and chest CT scans. The patient underwent a left radical nephrectomy, and a tan, soft, well-encapsulated mass 4.0 x 4.0 x 3.0 cm was present in the lower pole. No renal vein involvement was identified. Microscopically, the tumor invaded through the capsule with extension into the perinephric and pericalyceal adipose tissue and was pathologic stage pT3 pNX.
H&E (left two images, CD56 and chromogranin)
What is your diagnosis?
Primary renal well differentiated neuroendocrine tumor (carcinoid)
The tumor was also immunoreactive for synaptophysin and negative for CD10, RCC-Marker, EMA and TTF-1 (images not shown). Prominent neurosecretory granules were present by electron microscopy:
Primary renal well differentiated neuroendocrine tumors (carcinoid) are rare, with less than 100 cases reported (PathologyOutlines.com). They are low grade (well differentiated) neuroendocrine tumors with low power patterns of tightly packed cords or trabeculae. The tumor cells have finely granular cytoplasm, uniform nuclei and stippled chromatin, similar to carcinoid tumors at other sites. A recent study of 9 cases, which included this case, demonstrated that perinephric extension is common (Hum Pathol 2011 Apr 13 [Epub ahead of print]). Most tumors express either chromogranin, synaptophysin or CD56, and in this study, 8 of 9 expressed CD99. Renal carcinoid tumors are thought to derive from nonnephrogenic elements, because they are negative for paired box genes 2 and 8, which are renal associated transcription factors.
The differential diagnosis of primary renal well differentiated neuroendocrine tumor (carcinoid)includes tumors with neuroendocrine appearing nuclear features or complex architectural patterns. This includes:
● Carcinoid metastatic to the kidney: BMC Urol 2010;10:22
● Primitive neuroectodermal tumor (PNET): vaguely lobular growth of highly cellular, round to oval, poorly differentiated cells with minimal to modest pale staining cytoplasm and hyperchromatic nuclei; negative for neuroendocrine markers; 90% have EWS/FLI1 fusion product by RT-PCR
● Small cell carcinoma: diffuse growth of small cells with minimal cytoplasm, indistinct nucleoli, high mitotic activity; often extensive tumor necrosis; also Azzopardi phenomenon (blood vessels deeply encrusted with basophilic material consistent with DNA)
● Metanephric adenoma: small, uniform, closely packed tubules or papillae in loose stroma, composed of small cells with minimal cytoplasm, bland nuclei that may overlap, uniform chromatin, glomeruloid bodies, rare mitoses
● Neuroblastoma: 80% age 4 years or less; small blue cell tumor with Homer-Wright rosettes
Treatment is excision with follow-up, because nodal and distant metastases are common.
Nat Pernick, M.D., President
and Liz Parker, B.A., Associate Medical Editor
30100 Telegraph Road, Suite 408
Bingham Farms, Michigan (USA) 48025
Alternate email: NatPernick@gmail.com