Lipoma

Section: Skin and soft tissue Sub-section: Benign skin and soft tissue] Curriculum: Curriculum, page 52

Definition

• Benign proliferation of adipocytes

Incidence

• Commonest benign soft tissue tumours
• Rare < 20yrs
• Consist of mature fat cells

Clinical

• Soft, mobile, painless lumps lump in the subcutis typically of proximal extremities & trunk
• Less frequently, lipomas are large, intramuscular & poorly circumscribed

Differential Diagnosis

• Sarcoma – usually deep to fascia
  • Increased risk if > 5cm
• Superficial; any part of body, Esp. H&N
• Deep; Limbs, Mediastinum, Retroperitoneum

Classification

• According to morphologic features
  • Conventional lipoma
  • Fibrolipoma
  • Angiolipoma
    • Young adult, limb, painful, vascular
  • Spindle Cell Lipoma
    • Shoulder
  • Myelolipoma
  • Intraneural
    • Most commonly median nerve at wrist
  • Pleomorphic lipoma
    • Fat cells, spindle cells, giant cells

Histology

• Multilobulated
  • Vary greatly in size
  • Thin encapsulated mature fat cells
• DDx
  • Liposarcoma
    • Well-differentiated (low grade)
      • Atypical lipomatous tumours (ALT)- If arising in extremity
        • Do not metastasise to other organs
      • Well differentiated lipomatous tumours - If arising in retroperitoneum
        • Have a very low risk of malignancy or spread to other sites
        • But have a propensity for local recurrence in the retroperioneum and can recur as dedifferentiated subtype
    • Have an amplification of MDM2/CDK4 gene which can tested for with FISH
    • Should be tested for as it will identify is lesion is low grade lipomatous tumour/well differentiated tumour/liposarcomas from benign lesions.

Investigations

• USS initially to gauge size and depth
  • Irregularity
• MRI if deep/atypical features
• Consider core biopsy if

  • 5cm size

  • Deep to fascia
  • Raise concern of sarcoma

Management

• Excision biopsy if:

  • 5cm

  • Growing
  • Tethered to deep fascia
  • Symptomatic
  • If concerns with DAL/WDLLLS
    • Excise with margins