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17 October 2013 - Case of the Week #289

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Case of the Week #289

Clinical History:
A 42 year old man presented with a painful nodular forearm mass.

Micro images:

What is your diagnosis?


Glomangiomas are a type of glomus tumor that resembles a capillary hemangioma. They occur in a wide age range, and are exquisitely painful due to abundant nerve fibers.

Glomus tumors arise from modified smooth muscle cells of the glomus body, a specialized arteriovenous anastomosis involved in thermoregulation. They are usually found under fingernails, but also in the skin, flexor arm/knee and GI tract.

Histologically, glomus tumors have nests or aggregates of glomus cells arranged around vessels. The glomus cells are distinctively homogeneous, with bland nuclei and small, regular and indistinct nucleoli. There is no / minimal atypia or mitotic activity. All glomus tumors should have at least focal areas of typical glomus tumor, usually at the periphery (
Am J Surg Pathol 2001;25:1).

Glomus tumors are immunoreactive for smooth muscle actin (as in this case), type 4 collagen and vimentin. There is variable expression of CD34, h-caldesmon and calponin, and no expression of keratin, desmin, S100 and chromogranin. CD31 highlights the vasculature, but tumor cells are CD31-.

Left: alpha-smooth muscle actin; right: CD31

The differential diagnosis of glomangioma includes capillary hemangioma, which lacks the alpha smooth muscle actin+ cells seen in this case. Eccrine spiradenoma is often painful, but is not arranged around vessels, has two cell types, and is also CEA+ (Br J Dermatol 1984;111:175). Glomus tumors with 5+ mitotic figures/50 HPF, atypical mitotic figures, large size (2 cm+), or location deep to the muscular fascia may be designated as glomangiosarcoma, with possible metastatic behavior (Appl Immunohistochem Mol Morphol 2009;17:264).

Glomus tumors without atypia and without mitotic activity typically have a benign clinical course, and excision is curative.

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and Palak Thakore, Associate Medical Editor
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