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15 August 2013 - Case of the Week #283
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Thanks to Dr. Saroona Haroon, The Aga Khan University Hospital (Pakistan), 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 #283
A 48 year old man presented with a mass / swelling on the back of his shoulder for the past 3 months, with no pain or tenderness. The clinical diagnosis was lipoma. The mass was biopsied.
What is your diagnosis?
Immunostains were performed:
Left to right: alpha smooth muscle actin, HMB45 (low and high power)
Angiomyolipoma (AML) most commonly occurs in the kidney and liver, but has also been described at many other sites. However, angiomyolipoma of soft tissue is very uncommon.
As in this case, the clinical impression is often a routine lipoma (Arch Anat Cytol Pathol 1997;45:221), but histology demonstrates a triphasic tumor with myoid spindle cells, islands of mature adipose tissue and dysmorphic thick walled blood vessels without elastic lamina. The smooth muscle component appears to originate from vessel walls and may be hypercellular, atypical, pleomorphic or epithelioid. It is variably HMB45+.
AML is a perivascular epithelioid cell tumor (PEComa), associated with tuberous sclerosis complex. Other PEComas include pulmonary lymphangiomyomatosis, clear cell “sugar” tumor and clear cell myomelanocytic tumors of the falciform ligament/ligamentum teres. These tumors are typically benign, but epithelioid tumors, at least in the kidney, tend to have more aggressive behavior.
Nat Pernick, M.D., President
and Palak Thakore, Associate Medical Editor
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