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5 August 2015 - Case of the Week #360

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Case of the Week #360

Clinical History:
A 36 year old man presented with a history of right parotid swelling for five months, gradually increasing in size. Examination revealed a 10 x 5 x 4 cm irregular, firm to hard, non-expansile, non-translucent multinodular mass with irregular edges in the region of the parotid gland. USG, MRI and CT scan revealed a well defined soft tissue mass with an irregular outline involving the superficial and deep parotid gland, extending into the right retro-auricular space. No lymph node enlargement was seen. Frozen section revealed morphology of a spindle cell neoplasm. A total parotidectomy was performed.

Gross examination showed tan, firm tissue fragments weighing 77 g. The largest fragment measured 6 x 5 x 4 cm. They showed a vaguely lobulated appearance, and no foci of necrosis were seen.

Micro images:

H&E images



What is your diagnosis?































Diagnosis:
Deep "benign" fibrous histiocytoma

Discussion:

Immunostains were obtained:

CD34



Microscopically, a rim of normal parotid tissue surrounded an ill-defined, encapsulated spindled cell tumor with a well-marked storiform pattern and scattered mild lymphocytic infiltrate. No ramifying vessels with thickened or hyalinized walls were seen. The tumor showed pushing margins, entrapping normal salivary epithelium. The mitotic count was 4-5 / 10HPF.

Immunostains included were vimentin (positive), CD34 (positive), CD99 and BCL2 (focally positive). No reactivity for keratin, desmin, α-smooth muscle actin, EMA, S100 protein or CD117 was observed.

Very few cases of benign and malignant fibrous histiocytoma involving the salivary glands have been reported (Laryngoscope 1979;89:1808, J Clin Pathol 1982;35:946, Am J Clin Pathol 1992;97:512, Auris Nasus Larynx 2003;30:315). Deep benign fibrous histiocytoma is an uncommon and poorly recognized clinical subtype that arises in subcutaneous or deep soft tissue. Only a single series of these neoplasms have been published, and their clinical behavior is not well characterized (Am J Surg Pathol 2008;32:354). In this series, 22% arose in the head and neck region, and they ranged in size from 0.5 to 25 cm. Their morphology and immunostaining was as described in this case.

Differential diagnosis includes solitary fibrous tumor, dermatofibrosarcoma protuberans and soft tissue perineuroma. Solitary fibrous tumor has patternless sheets of cells with alternating hypo and hypercelluar areas, although it has an overlapping immunostaining profile with deep "benign" fibrous histiocytoma. Dermatofibrosarcoma protuberans have a dermal origin with infiltrative extension into the subcutis. Nuclei are small and slender. A lymphocytic infiltrate is usually absent (Semin Cutan Med Surg 1999;18:91, Am J Surg Pathol 1994;18:677). Soft tissue perineuroma has a whorled architecture. Cells have bipolar processes and very thin nuclei. EMA is positive, highlighting the cell processes.

To conclude, this neoplasm is a very rare in this site and must be distinguished from other spindle cell tumors of the parotid gland. A combination of light microscopy and immunostaining helps to differentiate it from other tumors. Recurrence is common after incomplete excision. Rarely, metastasis occurs. A careful follow up is advised.


Nat Pernick, M.D., President
and Shivani Thakore, Associate Medical Editor
PathologyOutlines.com, Inc.
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Bingham Farms, Michigan (USA) 48025
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