10 August 2005 – Case of the Week #16
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We thank Professor D. Y. Cohen, Department of Pathology, Herzliyah Medical Center, Israel, for contributing this case. We invite you to contribute a Case of the Week by emailing [email protected] with microscopic images (any size, we will shrink if necessary) in JPG or GIF format, a short clinical history and any other images (gross, immunostains, EM, etc.) that you have and that may be helpful or interesting. We will write the discussion (unless you want to contribute to it), list you as the contributor, and send you a check for $35 (US) for your time if we use the case. Please only send cases with a definitive diagnosis.
Case of the Week #16
A 56 year old man had a retroperitoneal mass behind the pancreas and in front of the inferior vena cava. The clinical impression was schwannoma versus sarcoma.
Gross: The specimen consisted of three irregular fibrofatty fragments, the largest 5 cm and the others being very small. Sectioning revealed a well circumscribed yellow-gray myxoid mass measuring 3 x 2 x 2 cm.
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Diagnosis: Lipomatous hemangiopericytoma
Lipomatous hemangiopericytoma was first described in 1990 by Theunissen et. al. (Pathologe. 1990;11:346), and later by Nielsen et. al. (AJSP 1995;19:748). In 1999, it was described in detail by Weiss et. al. as a histologically benign hemangiopericytoma containing a variable amount of mature fat as an intrinsic part of the tumor (AJSP 1999;23:1201). These tumors occur primarily in men, with a mean age of 54 years (range 33-74 years), usually in the deep soft tissue of the retroperitoneum or leg. Grossly, they average 10 cm in size, are tan-yellow, and have a well circumscribed border. Microscopically, they have typical features of hemangiopericytoma, including round/oval cells, a sinusoidal or staghorn vasculature, and often perivascular hyalinization. The tumors contain 25-75% admixed fat. There is usually no/low mitotic activity, and variable nuclear atypia, ranging from none to moderate. No lipoblasts or atypical hyperchromatic cells are present. These tumors are positive for vimentin and CD99, usually positive for CD34+, positive for bcl2 in half of cases, and negative for keratin, inhibin, CD117/c-kit, CD31, and desmin. Clinically, they have benign behavior, without recurrence or metastatic spread.
The differential diagnosis includes well differentiated liposarcoma, spindle cell lipoma and solitary fibrous tumor. Well differentiated liposarcoma also occurs in the retroperitoneum and deep soft tissue. It is composed of variably sized cells with large, deep staining nuclei and atypia. In a small biopsy, it may resemble areas of lipomatous hemangiopericytoma with focal atypia. Spindle cell lipoma occurs almost exclusively in the head and neck in subcutaneous tissue. It typically has bland spindle cells in short packets or fascicles between dense collagen bundles in a background of mature adipose tissue. It may have a hemangiopericytoma-like vascular pattern, and also has similar immunohistochemistry as lipomatous hemangiopericytoma. Since both have benign behavior, the distinction is not critical. Solitary fibrous tumor has areas resembling classic hemangiopericytoma, but also has areas of haphazard growth, distinct fascicles of spindle cells, hyalinized stroma with a cracking artifact, and growth of single cells or short chains of cells. Some authors consider lipomatous hemangiopericytoma to represent a fat containing variant of solitary fibrous tumor (Hum Path 2000;31:1108)
Additional references: Archives 1999;123:941 (case report of thigh tumor with images)
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