23 March 2005 Case of the Week #1


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This case was contributed by Dr. N. Volkan Adsay, Wayne State University, Department of Pathology, Detroit, Michigan (USA). Due to some technical problems, additional images from other sources are also included. We invite you to contribute a Case of the Week by sending an email to NPernick@PathologyOutlines.com with microscopic images (any size, we will shrink if necessary) in JPG or GIF format, a clinical history, your diagnosis and any other images (gross, immunostains, EM, etc.) that may be helpful or interesting. We will write the discussion (unless you want to), list you as the contributor, and send you a check for $35 (US) for your time after we send out the case. Please only send cases with a definitive diagnosis.



Case of the Week #1


The patient was a 46 year old man with a 4 cm mediastinal mass, but no lesions in the lung or at other sites. The lesion was excised.


Gross: not available in this case, but typically well circumscribed, light tan and solid. Hemorrhage and necrosis may be present.


Micro images:

(1) CD21/CD35 stain highlights ovoid spindle cells #1a; #1b; #1c


Note: images 2-4 are from a different tumor (published in Mod Path 2002;15:50)


(2) The tumor consists of vague whorls of spindle cells in a storiform growth pattern, with lymphocytes and plasma cells present


(3) Tumor cells have indistinct cell borders; occasional multinucleated giant cells are present (arrows)


(4) Strong immunostaining for CD21 (left) and CD35 (right)


Micro: The tumor consists of fascicles, sheets, storiform or whorled patterns of a syncytium of oval and spindled cells, with pale to eosinophilic cytoplasm, oval nuclei with finely dispersed chromatin and small nucleoli; variable lymphocytes and plasma cells, often with perivascular cuffing. Multinucleated tumor giant cells are often present.


Immunohistochemistry: The tumor cells are positive for CD21 and CD35, negative for CD1a, and variable for S100, CD68 and EBV


EM: not available in this case, but typically numerous interwoven long cytoplasmic processes joined focally by desmosomes


Diagnosis: Follicular dendritic reticulum cell tumor / follicular dendritic cell sarcoma




These tumors affect lymph nodes and extranodal sites, including the liver, oral cavity, bowel and spleen. They typically have low grade malignant behavior, with local recurrence common and occasional distant metastases to liver or lung. Poor prognostic factors are intraabdominal location, size > 6 cm, 6 or more mitotic figures/10 HPF, atypia and coagulative necrosis. An inflammatory pseudotumor-like variant, localizing in the liver and spleen, has also been reported (AJSP 2001;25:721).


These tumors are often misdiagnosed. The differential diagnosis for these tumors includes other reticulum cell tumors (see below), as well as melanoma, thymoma, other sarcoma, some carcinomas and possibly inflammatory myofibroblastic tumors. Immunostains are usually required for definitive diagnosis.


Lymph nodes have several types of reticulum cells (reticulum means netlike formation or structure), which are nonlymphoid, nonphagocytic cells that capture and present antigens and immune complexes. Follicular dendritic reticulum cells are found in B cell zones, particularly in germinal centers. Interdigitating reticulum cells are found in T cell zones, and are related to Langerhans cells. Fibroblastic reticulum cells are found in the parafollicular and deep cortex areas.


Immunohistochemical markers for these reticulum cells and related tumors are:


Follicular dendritic cells: positive for CD21, CD35; negative for cytokeratin, CD1a; variable for EBV, S100 and CD68


Interdigitating dendritic cells: positive for S100, vimentin, fascin, focal CD68; negative for CD1a, CD21, CD35, B and T cell markers, actin, desmin, keratin.


Langerhans cells: positive for S100, CD1a, CD68, vimentin.


Fibroblastic reticulum cells: positive for vimentin, smooth muscle actin, desmin, focal CD68; negative for CD21, CD35, S100 and EBV.


Histiocytic tumors: positive for CD68 and lysozyme.



Additional references:

Follicular dendritic cell tumor: oral cavity - AJSP 1994;18:148, AJSP 1996;20:944, Mod Path 2001;14:354

Fibroblastic reticulum cell tumor: Hum Path 2003;34:954

Interdigitating dendritic cell tumor: AJSP 2002;26:530, AJSP 1999;23:1141



Nat Pernick, M.D.
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