dr james c wittig, orthopedic oncologist, new york, new jersey
Patient Education
Hibernoma

GENERAL INFORMATION

Hibernoma is a benign neoplasm made up of multivacuolated brown fat cells. It is a type of lipoma.

CLINICAL DATA

Rare, represents less than 2% of all types of  lipomas
Made of brown fat
Affects ages between second and third decade of life 
Male preference
May produce steroid hormones

DIFFERENTIAL DIAGNOSIS
Lipoma
Liposarcoma (well-differentiated)
Rhabdomyosarcoma
Hematoma

CLINICAL PRESENTATION

Sign/Symptoms

Slow-growing mass
Painless

Prevalence

Preference for males (60%)
May occur in other age groups as well, but usually arises between 20 and 30 years of age

Site

Most commonly scapular and intrascapular region
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

Soft
Well-circumscribed
Tan to red-brown on cut section
Usually 5 to 10 cm Ø

Microscopic

Well-differentiated tumors, with lobulated pattern (Fig. 3)
Cells are uniform, round to oval cells
May have central nuclei
Granular to multivacuolated eosinophilic cytoplasm
Univacoulated fat cells are often admixed
Sometimes numerous enough to produce an appearance intermediate between hibernoma and ordinary lipoma
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
S100
Oil red O
Sudan black

Negative
CD 34
P53

PROGNOSIS

BIOLOGICAL BEHAVIOR

Hibernoma is benign and does not metastasize or convert to a malignancy
It can grow to a large size
Non-invasive
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)
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