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Surgical Pathology Criteria

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  • Tumor of cells with features of brown fat

Diagnostic Criteria

  • Circumscribed, lobulated mass
    • Grossly yellow-brown
  • Cellular features of brown fat
    • Numerous small cytoplasmic vacuoles
    • Pale to intensely eosinophilic granular cytoplasm
    • Normal fat cells may be admixed
      • 7% of cases are predominantly mature fat
  • Cytologically bland
    • Small central nuclei
      • Prominent nucleoli
    • Mitotic figures and cytologic atypia rare
      • No clinical significance if present
  • May have myxoid stroma (9% of cases)
  • Rarely combined with spindle cell lipoma
  • Malignant neoplasms with brown fat differentiation are controversial

Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting : July 29, 2007
Updates: May 25, 2009

Supplemental studies


S100 85%, may be focal
CD68 Positive
CD34 Negative unless combined with spindle cell lipoma

Immunohistochemistry of lipomatous tumors
  MDM2 CDK4 p16
Atypical lipomatous tumor 45-100% 84-92% 78-97%
Dedifferentiated liposarcoma 55-95 90-100 90
Myxoid / round cell liposarcoma 0-4 0-4 0
Pleomorphic liposarcoma 0 0 0
Lipoma 0-4 0-2 0
Spindle cell and pleomorphic lipoma 0-25 0-6 20
Angiomyolipoma 0 0  
Hibernoma 0 0 positive, variable
Lipoblastoma 0 (1 case) 0 (1 case) positive (1 case)

Genetic Study

  • Frequent rearrangements of 11q13-21 region

Differential Diagnosis

Fat Necrosis Hibernoma
Poorly circumscribed Circumscribed
Foamy cytoplasm, few vacuoles Multiple small vacuoles
Variable pattern from normal fat to necrotic fat to histiocytes Uniform pattern

Lipoblastoma Hibernoma
Restricted to children at presentation Rare in children
Immature cells and lipoblasts Microvesicular brown fat
8q11-13 abnormalities 11q13 abnormalities

Hibernoma with predominant mature fat Atypical Lipomatous Tumor
Small, central bland nuclei in vacuolated cells Lipoblasts, if present, have atypical nuclei
Lacks atypical nuclei Contains atypical nuclei
Frequently superifcial Rarely superficial
MDM2, CDK4, p16 negative MDM2, CDK4, p16 most positive

Myxoid Liposarcoma Hibernoma with Myxoid Stroma
Rarely superficial Frequently superficial
Prominent "chicken wire" vascular pattern Lacks "chicken wire" vascular pattern
t(12;16) or t(12;22) 11q13 rearrangement


  • Predominantly young adults
    • Range 2-72, mean 38
  • Most near scapula or thigh
    • Most others on trunk
    • 10% intramuscular
    • 6% in abdomen or retroperitoneum
    • Rare locations: breast, mediastinum, uterus
  • Benign, recurrence is very rare


Lipogenic tumors


  • Kempson RL, Fletcher CDM, Evans HL, Henrickson MR, Sibley RS. Tumors of the Soft Tissues, Atlas of Tumor Pathology, AFIP Third Series, Fascicle 30, 2001
  • Fletcher CDM, Unni KK, Mertens F. Pathology and Genetics of Tumours of Soft Tissue and Bone, World Health Organization Classification of Tumours 2002
  • Weiss SW, Goldblum JR. Enzinger and Weiss's Soft Tissue Tumors, 4th edition, 2001
  • Furlong MA, Fanburg-Smith JC, Miettinen M. The morphologic spectrum of hibernoma: a clinicopathologic study of 170 cases. Am J Surg Pathol. 2001 Jun;25(6):809-14.
  • Gaffney EF, Hargreaves HK, Semple E, Vellios F. Hibernoma: distinctive light and electron microscopic features and relationship to brown adipose tissue. Hum Pathol. 1983 Aug;14(8):677-87.
  • Kindblom LG, Angervall L, Stener B, Wickbom I. Intermuscular and intramuscular lipomas and hibernomas. A clinical, roentgenologic, histologic, and prognostic study of 46 cases. Cancer. 1974 Mar;33(3):754-62.
  • Gisselsson D, Hoglund M, Mertens F, Dal Cin P, Mandahl N. Hibernomas are characterized by homozygous deletions in the multiple endocrine neoplasia type I region. Metaphase fluorescence in situ hybridization reveals complex rearrangements not detected by conventional cytogenetics. Am J Pathol. 1999 Jul;155(1):61-6.
  • Mertens F, Rydholm A, Brosjo O, Willen H, Mitelman F, Mandahl N. Hibernomas are characterized by rearrangements of chromosome bands 11q13-21. Int J Cancer. 1994 Aug 15;58(4):503-5.
  • Rubin BP, Dal Cin P. The genetics of lipomatous tumors. Semin Diagn Pathol. 2001 Nov;18(4):286-93.
  • Lele SM, Chundru S, Chaljub G, Adegboyega P, Haque AK. Hibernoma: a report of 2 unusual cases with a review of the literature. Arch Pathol Lab Med. 2002 Aug;126(8):975-8.
  • Enterline HT, Lowry LD, Richman AV. Does malignant hibernoma exist? Am J Surg Pathol. 1979 Jun;3(3):265-71.
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