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Soft Tissue Tumors

Adipose tissue

Intramuscular lipoma


Reviewer: Charanjeet Singh, M.D. (see Reviewerspage)
Revised: 10 November 2012, last major update June 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

General
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● Lipoma that infiltrates within muscle belly
● Called intermuscular lipoma if between muscle fascicles

Terminology
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● Also called invasive or infiltrative lipoma
● Not a WHO diagnosis

Sites
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Intramuscular: affects thigh, trunk, head and neck of middle-aged adults
Intermuscular: affects abdominal wall of middle-aged adults; doesn’t recur if completely excised

Clinical features
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● Benign, but 20% recur due to incomplete excision
● Infiltration may be due to muscular degeneration and endomysial fatty growth secondary to atrophy (BMC Musculoskelet Disord 2004;18:20)

Case reports
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● 37 year old woman with giant infiltrative tumor of face (AJNR Am J Neuroradiol 2003;24:283)
● 58 year old and 63 year old women with tumors of pectoralis major muscle simulating a breast mass (Ann Acad Med Singapore 2005;34:275, Arch Pathol Lab Med 2011;135:1061)
● Well circumscribed tumor of sternocleidomastoid muscle (Auris Nasus Larynx 2004;31:283)

Clinical images
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Tumor of face

Gross description
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Intramuscular - poorly circumscribed, extends between and around skeletal muscle fibers

Gross images
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Yellow adipose tissue within skeletal muscle


Irregular lobulated tumor without encapsulation


Deep tumor of calf

Other images: yellow adipose tissue within skeletal muscle

Micro description
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● Mature lipocytes that infiltrate skeletal muscle
● No atypia, no mitotic figures

Micro images
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Prominent muscular atrophy


Adipocytes and atrophic muscle


Intramuscular lipoma

Other images: intramuscular fat tissue covered by fibrous capsule

Differential diagnosis
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Intramuscular hemangioma: adolescents and young adults, usually head and neck, prominent vasculature, variable adipose tissue
Well differentiated liposarcoma: definite atypia present

End of Soft Tissue Tumors > Adipose tissue > Intramuscular lipoma


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