Soft tissue
Adipose tissue
Lipoma

Author: Vijay Shankar, M.D. (see Authors page)

Revised: 28 July 2016, last major update August 2012

Copyright: (c) 2002-2016, PathologyOutlines.com, Inc.

PubMed Search: Lipoma [title] soft tissue

Definition / General
  • 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
  • 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
  • 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
  • Relatively static growth after initial growth period
  • Does not regress even with starvation
  • Becomes hard after application of ice
Case Reports
Treatment
  • Benign, but 1 - 4% recur
  • Excision is adequate treatment
Clinical Images

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Superficial, courtesy of Mark R. Wick, M.D.



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Right breast mass

Gross Description
  • 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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Atypical, courtesy of Mark R. Wick, M.D.

Chondriod, courtesy of Mark R. Wick, M.D.

Spindle cell type, courtesy of Mark R. Wick, M.D.

Fatty mass with surgery-related hemorrhage



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After resection

Chest wall giant lipoma

Encapsulated cardiac mass

Micro Description
  • 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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Images courtesy of Mark R. Wick, M.D.:

Atypical type

Chondroid type

Fibrohistiocytic tyoe



Intramuscular type

Lipoma

Pleomorphic superficial type



Spindle cell type, CD34

Spindle cell type

Normal adult fat cells



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Endobronchial lipoma

Scapula

Thorax

Cytology Images

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Adipocytes

Positive Stains
Electron Microscopy Description
  • Univacuolar mature adipocytes that compress peripheral nuclei (Cancer 1982;50:102), pinocytotic vessels, cells are surrounded by external lamina
Molecular / Cytogenetics Description
  • 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