Sarcopedia

BenignSoft tissue

Hibernoma

Synonyms: Brown fat tumour

High FDG uptake on PET-CT can be mistaken for malignancy - awareness is critical

Quick Facts

Behaviour

Benign

Category

Soft tissue

Grade

Not set

Synonyms

Brown fat tumour

Category

Soft tissue

Behaviour

Benign

Gender

Both equally

Tissue of Origin

Adipose

Epidemiology

  • Rare Benign lipomatous tumour
  • Peak incidence in young adults (2nd–4th decades)
  • Comprises <1% of all lipomatous tumours

Clinical Features

  • Slow-growing painless soft tissue mass
  • Often incidentally found on imaging
  • May have prominent Vascularity clinically
  • No systemic symptoms

Location

  • Interscapular region / posterior neck (most common)
  • Axilla
  • Mediastinum
  • THigh and retroperitoneum

Imaging

  • CT: mixed density fat-containing mass (less dense than normal fat - brown fat)
  • MRI: heterogeneous with areas slightly hypointense to subcutaneous fat on all sequences
  • Avid FDG uptake on PET-CT (brown fat metabolically active - can mimic malignancy)
  • Prominent Vascularity

Pathology

  • Brown adipocytes with multivacuolated granular cytoplasm and central nucleus
  • Admixed with univacuolated white fat cells
  • Mitochondria-rich cytoplasm (granular appearance)
  • S100 positive, vimentin positive

Genetics

  • Chromosome 11q13 rearrangements most common
  • AIP, GARP, MEN1 gene region affected
  • Benign karyotype

Treatment

  • Simple excision curative
  • No wide margins needed

Prognosis

  • Excellent - no Malignant potential
  • Recurrence after complete excision extremely rare

Key Points

  • High FDG uptake on PET-CT can be mistaken for malignancy - awareness is critical
  • Multivacuolated granular cytoplasm of brown fat is pathognomonic
  • Often in 'brown fat depots': interscapular, axilla, mediastinum, neck
  • Simple excision is curative - no oncological resection needed

Workup - Blood Tests

No tests required

Workup - Local Imaging

  • CT or MRI - mixed-density fat mass; brown fat less dense than white fat
  • Ultrasound - initial assessment; hypervascular

Workup - Biopsy

  • Biopsy NOT routinely required if imaging typical
  • Core needle biopsy - if imaging atypical
  • Histology: multivacuolated brown adipocytes with granular mitochondria-rich cytoplasm
  • S100+, vimentin+

Workup - Staging

No staging required