Hibernoma

Definition

A benign tumour composed at least in part of brown fat.

Clinical features

This is a rare tumour occurring on the thigh, trunk, arm, head or neck. Myxoid and spindle cell variants occur on the shoulder,k as for spindle cell lipoma. A minority are intramuscular.

Macroscopic appearances

Tumours vary form yellow to brown. The cut surface is greasy or spongy.

Histopathology

Variants:

• granular or eosinophilic is the most common. There is a high proportion of multivacuolated cells

• pale variant: pure pale brown fat cells

• mixed: admixed of the granular and pale variants

• lipoma like; clusters of brown fat cells within an otherwise typical white fat lipoma

• myxoid

• spindle cell

Immunohistochemistry

• S-100 positivity in the brown fat cells is of variable strength.

• CD34 positivity occurs only in the spindle cells of the spindle cell variant.

Differential diagnosis

Management

All variants are adequately managed by local excision.

References

World Health Organization Classification of Tumours, Tumours of Soft Tissues and Bone, IARC Press 2002.

This page last revised 29.6.2004.

©SMUHT/PW Bishop