Macrodystrophia lipomatosa

Rare, congenital, non-hereditary localised gigantism due to disproportionate fibrofatty overgrowth of soft tissues ± bone, typically along a nerve territory (e.g. median nerve in hand, plantar nerves in foot). Often presents as macrodactyly.

Key clinical points

• Present at birth or early childhood; progressive overgrowth.
• Common sites: 2nd–3rd digits of hand/foot, median or plantar nerve distribution.
• Usually unilateral, segmental; no systemic features (distinguish from overgrowth syndromes).

Imaging features

Radiograph

• Enlarged digits with:
  • Marked soft tissue overgrowth (predominantly radiolucent → fat).
  • Bony hypertrophy: enlarged, elongated phalanges/metacarpals/metatarsals.
  • Cortical thickening ± mild deformity.
• Joint spaces usually preserved.

Ultrasound

• Increased bulk of echogenic fat in subcutaneous and intermuscular planes.
• Enlarged nerve with hyperechoic epineurium and thickened fascicles if lipofibromatous hamartoma coexists.

MRI (most characteristic)

• Dominant component = fat signal:
  • High T1 / high T2, suppressed on fat-sat.
• Interspersed fibrous strands / septa: low T1, low–intermediate T2.
• Follows nerve distribution (e.g. along median nerve in the carpal tunnel).
• Bone:
  • Enlarged size, normal marrow signal.
• If associated fibrolipomatous hamartoma of nerve:
  • “Coaxial cable / spaghetti” appearance of enlarged nerve with fat interdigitating between fascicles.

CT is rarely needed but shows hypertrophic bone + low attenuation fat proliferation.

Differentials