GENERAL INFORMATION
Hibernoma is a benign neoplasm made up of multivacuolated brown fat cells. It is a type of lipoma.
CLINICAL DATA
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Rare, represents less than 2% of all types of lipomas
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Made of brown fat
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Affects ages between second and third decade of life
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Male preference
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May produce steroid hormones
DIFFERENTIAL DIAGNOSIS
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Lipoma
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Liposarcoma (well-differentiated)
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Rhabdomyosarcoma
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Hematoma
CLINICAL PRESENTATION
Sign/Symptoms
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Slow-growing mass
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Painless
Prevalence
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Preference for males (60%)
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May occur in other age groups as well, but usually arises between 20 and 30 years of age
Site
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Most commonly scapular and intrascapular region
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Thigh, chest wall, back, axilla and groin
RADIOGRAPHIC PRESENTATION
Plain x-ray
• No specific radiological features
CT
• Well-defined lesion
• Tissue attenuation intermediate between fat and skeletal muscle
MRI
• Well-defined mass
• High signal intensity similar to fat on T1W and T2W (Fig. 1 and 2)
• T1W shows areas of low signal intensity between that of fat skeletal muscle
• On fat suppression sequences show incomplete fat suppression.
Fig. 1-2 MRI of lower extremity hibernoma (Fig. 1 and Fig. 2) shows similar signal intensity to subcutaneous fat fat on different sequences .
PATHOLOGY
Gross
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Soft
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Well-circumscribed
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Tan to red-brown on cut section
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Usually 5 to 10 cm Ø
Microscopic
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Well-differentiated tumors, with lobulated pattern (Fig. 3)
Cells are uniform, round to oval cells
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May have central nuclei
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Granular to multivacuolated eosinophilic cytoplasm
Univacoulated fat cells are often admixed
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Sometimes numerous enough to produce an appearance intermediate between hibernoma and ordinary lipoma
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Poorly differentiated tumors
Endothelial cells are more atypical, close-packed, and often spindle-shaped
Progressive loss of evident vascular channels
Fig. 3 High power photograph shows a well differentiated tumor, with uniform cells. Note the nuclei is small with no atypia. There are multivacuolated cells and a cell with a central nucleus
IMMUNOHISTOCHEMISTRY
Positive
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S100
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Oil red O
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Sudan black
Negative
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CD 34
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P53
PROGNOSIS
BIOLOGICAL BEHAVIOR
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Hibernoma is benign and does not metastasize or convert to a malignancy
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It can grow to a large size
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Non-invasive
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Rare risk of recurrence after removal
TREATMENT
• Excision (Fig. 4 and 5)
Fig. 4-5 Intraoperative photograph of a resection of a hibernoma (Fig. 4 and 5)
