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Soft Tissue Tumors

Adipose tissue

Lipoma


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 composed of mature white adipocytes with uniform nuclei resembling normal white fat
● Most common mesenchymal and soft tissue tumor (100x more common than liposarcoma)

Epidemiology
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● Most common soft tissue tumor - 16% of all mesenchymal neoplasms
● Adults, age 40+
● No gender or ethnic preference
● Rare in children
● Associated with obesity
Multiple lipomas: 5%, more common in women, often familial, associated with neurofibromatosis, multiple endocrine neoplasia syndromes, Bannayan syndrome (macrocephaly, hemangiomas and lipomas, Wikipedia)

Sites
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● Usually trunk, back, shoulder, neck, proximal extremities
● Rare on hands, feet, face, lower leg, retroperitoneum
● Usually subcutaneous (liposarcomas are usually deep seated)
● Unusual sites include oral cavity, pancreas, breast, intestines

Clinical features
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● Relatively static growth after initial growth period
● Does not regress even with starvation
● Becomes hard after application of ice

Case reports
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● 38 year old man with breast swelling (Eur J Plast Surg 2012;35:407)
● 52 year old man with mass in buccal mucosa (Dent Res J (Isfahan) 2011;8:48)
● 68 year old man with giant chest wall mass for 30 years (Interact Cardiovasc Thorac Surg 2012;15:323)

Treatment and prognosis
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● Benign, but 1-4% recur
● Excision is adequate treatment

Clinical images
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Right breast mass

Gross description
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● Bright yellow homogeneous fat with fine fibrous capsule (superficial lesions only) and trabeculae
● May be very large (particularly if deep)
● Greasy cut surface

Gross images
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Fatty mass with surgery-related hemorrhage


Various images


Encapsulated cardiac mass

Other images: encapsulated mass

Micro description
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● Mature white adipose tissue without atypia
● 2-5x variation in cell size (more than normal white adipose tissue), with obvious large cells up to 300 microns
● Cytoplasmic vacuoles are relatively uniform
● May have intranuclear vacuoles, thickened fibrous septa in buttocks, foot or hand
● May contain areas of fat necrosis with histiocytes, infarct or calcification
● Rarely contains bone or cartilage
● No mitotic figures
Note: diagnosis of lipoma requires presence of a mass

Micro images
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Unencapsulated subcutaneous lipoma


Mass has normal adult fat cells


Endobronchial lipoma

Other images: scapula, thorax

Virtual slides
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Left: site unspecified; right: retroperitoneal

Cytology images
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Adipocytes

Positive stains
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● Vimentin, S100, CD34 (slender spindle cells)
● Leptin, PAS (highlights capillaries), reticulin (surrounds each adipocyte)

Electron microscopy description
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● Univacuolar mature adipocytes that compress peripheral nuclei (Cancer 1982;50:102), pinocytotic vessels, cells are surrounded by external lamina

Molecular/cytogenetics description
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● 55%-75% of solitary lipomas with cytogenetic abnormalities have rearrangements of HMGA2/HMGIC at 12q13-15, although no associated clinicopathologic features are associated with the resulting fusion transcripts (Anticancer Res 2008;28:535, J Biomed Biotechnol 2011;2011:524067)
● Marker ring or giant chromosomes are extremely rare
● Multiple lipomas usually have normal phenotype

Molecular/cytogenetics images
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Schematic of HMGA2 and LPP

Differential diagnosis
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Normal fat: not circumscribed or encapsulated, not a mass
Pneumatosis cystoides intestinalis in small bowel: not actually adipocytes
● Mesenchymal cells producing acid mucopolysaccharide - vacuoles contain fluid and are not clear, nuclei are not deformed

Additional references
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eMedicine #1, #2, Atlas of Genetics and Cytogenetics, Stanford University

End of Soft Tissue Tumors > Adipose tissue > Lipoma


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