Soft Tissue Tumors

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Soft Tissue Tumors

Adipose tissue

Myolipoma

Reviewer: Vijay Shankar, M.D. (see Reviewers page)
Revised: 4 November 2012, last major update August 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

General
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● Benign tumor of mature adipocytes and mature smooth muscle
● First described in 1991 (Am J Surg Pathol 1991;15:121)

Terminology
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● Called lipoleiomyoma in uterus
● Note: myelolipoma is tumor with hematopoietic (including myeloid) elements, often in adrenal gland

Epidemiology
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● Very rare tumor of adults in abdomen, retroperitoneum or abdominal wall
● Other rare sites include eyelid, pericardium, base of tongue

Case reports
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● 4 year old boy presented with paraspinal tumor (Case Report Med 2009;2009:520126)
● 34 year old woman with tumor of iliac fossa (World J Surg Oncol 2005;3:72)
● 55 year old woman with tumor presenting as inguinal hernia (Radiology Case Reports 2006, Vol 1, No 1)

Treatment and prognosis
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● Excision
● Does not recur, metastasize or transform

Gross description
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● Often 9 cm or more, completely or partially encapsulated, yellow-white

Gross images
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Large lobulated mass with thick pseudocapsule

Fatty tissue with bands and nodules of firm white tissue

Micro description
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● Mature adipose tissue and mature (well differentiated) smooth muscle in short fascicles (Stanford University)
● Variable fibrosis and inflammation
● No floret cells, no thick walled vessels, no necrosis, no mitotic figures

Micro images
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Mature fat and smooth muscle fibers

Smooth muscle fibers are SMA+ (left), desmin+ (right two images)

Positive stains
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● Smooth muscle actin, desmin
● Occasionally ER, PR

Differential diagnosis
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● Angiomyolipoma: also thick walled vessels, HMB45+
● Liposarcoma with heterologous elements: has lipoblasts and atypia
● Low grade leiomyosarcoma infiltrating fat: smooth muscle component has atypia and mitotic figures, adipose tissue is not part of tumor

End of Soft Tissue Tumors > Adipose tissue > Myolipoma

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