Soft tissue

Adipose tissue tumors

Lipoma and variants

Lipoma


Resident / Fellow Advisory Board: Erna Forgó, M.D.
Deputy Editor-in-Chief: Borislav A. Alexiev, M.D.
Salvatore Lorenzo Renne, M.D.

Last author update: 13 December 2021
Last staff update: 24 January 2022

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PubMed Search: Lipoma [title] soft tissue pathology review [ptyp]

Salvatore Lorenzo Renne, M.D.
Page views in 2021: 38,341
Page views in 2022 to date: 34,733
Cite this page: Renne SL. Lipoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/softtissueadiposelipoma.html. Accessed August 14th, 2022.
Definition / general
  • Benign tumor composed of mature adipocytes
Essential features
  • Most common soft tissue tumor
  • Mostly subcutaneous, < 5 cm
  • Radiologically, grossly and microscopically same as normal fat
  • In large (> 10 cm) and deep seated / retroperitoneal tumors, exclusion of MDM2 amplification is required for diagnosis
ICD coding
  • ICD-O: 8850/0 - lipoma, NOS
  • ICD-11: 2E80.0Y - lipoma, other specified site
Epidemiology
Sites
  • Superficial (subcutaneous) soft tissue
  • Upper back, proximal extremities and abdominal region
  • Subset deep seated (intramuscular, parosteal, visceral)
Pathophysiology
Etiology
  • Unknown at this time
Clinical features
Diagnosis
Radiology description
Radiology images

Contributed by Salvatore Lorenzo Renne, M.D.
Isointense mass on MRI

Isointense mass on MRI

Discrete incapsulated mass on CT

Discrete incapsulated mass on CT

Prognostic factors
  • Recurrence < 5%
  • Incomplete surgery, higher local recurrence
Case reports
Treatment
  • Simple excision
Clinical images

Contributed by Mark R. Wick, M.D.

Superficial

Gross description
  • Well circumscribed
  • Nodular
  • Cut surface homogeneous
  • Fatty appearance
  • Usually small (< 5 cm)
  • Osteolipoma and chondrolipoma can be recognized grossly
Gross images

Contributed by Salvatore Lorenzo Renne, M.D. and AFIP images
Lipoma gross appearance

Lipoma gross appearance

Yellow adipose tissue within skeletal muscle

Microscopic (histologic) description
  • Proliferation of mature adipocytes
  • Paucicellular fibrous septa can be present
  • Fat necrosis is often found in larger tumor
  • Skeletal muscle fibers are infiltrated in intramuscular lipoma
  • Subtypes
    • Intramuscular lipoma
    • Chondrolipoma
  • Visceral sites
    • Submucosal lipoma of the colon
    • Endobronchial lipoma
Microscopic (histologic) images

Contributed by Salvatore Lorenzo Renne, M.D., Mark R. Wick, M.D., Charanjeet Singh, M.D. and AFIP images
Superficial, well circumscribed neoplasm

Superficial, well circumscribed neoplasm

Mature adipose tissue

Mature adipose tissue

Paucicellular fibrous septa

Paucicellular fibrous septa

Mature adipose proliferation

Mature adipose proliferation

Endobronchial lipoma

Endobronchial lipoma

Osteolipoma

Osteolipoma


Intramuscular type

Lipoma

Normal adult fat cells

Intramuscular lipoma

Adipocytes and atrophic muscle

Virtual slides

Images hosted on other servers:

Lipoma with fat necrosis

Intussusception by submucosa lipoma

Sigmoid polyp lipoma

Cytology description
  • Mature adipocytes with single lipid large droplet
  • Inconspicuous nucleus
Cytology images

Images hosted on other servers:

Adipocytes

Positive stains
Molecular / cytogenetics description
Molecular / cytogenetics images

Contributed by Salvatore Lorenzo Renne, M.D.
<i>MDM2</i> nonamplified

MDM2 nonamplified

Videos

Lipoma and its differential diagnosis

Sample pathology report
  • Soft tissue, subcutaneous trunk, excision:
    • Lipoma
  • Soft tissue, deep (deltoid), excision:
    • Lipoma, intramuscular (see comment)
    • Comment: Sections show a mature adipocytic neoplasm. No cytologic atypia or mitotic activity is identified. Immunohistochemical stain shows negativity for MDM2. Fluorescence in situ hybridization does not show amplification of MDM2 gene.
Differential diagnosis
  • Angiolipoma:
    • Typically composed of two elements: mature adipocytes and branching capillary sized vessels, which often contain fibrin thrombi
    • Relative proportions of adipocytes and vessels varies and some lesions are almost completely composed of vascular channels
  • Spindle cell / pleomorphic lipoma:
    • Head, neck, back
    • Male
    • Spindle and pleomorphic cells
    • Ropy collagen
    • CD34 strong IHC positivity
    • Rb loss by IHC (positive internal control of blood vessels)
  • Atypical lipomatous tumor / well differentiated liposarcoma:
    • Size > 10 cm
    • Deep seated
    • Atypical cells
    • MDM2 IHC positivity
    • MDM2 gene FISH cluster amplification
Board review style question #1

The tumor shown above is found in chest subcutis of a 58 year old woman. What is the most likely diagnosis?

  1. Angiolipoma
  2. Atypical lipomatous tumor
  3. Lipoma
  4. Normal fat
  5. Spindle cell lipoma
Board review style answer #1
C. Lipoma. The mass is in the subcutis, small (< 5 cm), well circumscribed and homogenously composed of adipocytes.

Comment Here

Reference: Lipoma
Board review style question #2
Which of the following is true about a lipoma?

  1. Diagnosis is often made without immunohistochemistry
  2. Highly infiltrative lesion, which leads the majority to recur
  3. It is the most common benign neoplasm
  4. It is usually large (> 10 cm) and located in deep soft tissue or retroperitoneum
  5. Patient always reports a history of trauma
Board review style answer #2
A. Diagnosis is often made without immunohistochemistry. Diagnosis can be done on H&E in most cases and in the appropriate clinicopathological setting (i.e. small, superficial, homogeneous lesion, composed of uniform adipocytic cells without atypia).

Comment Here

Reference: Lipoma
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