Lipoma

Benign tumour of mature adipocytes, the commonest soft tissue tumour. It occurs in about 1 to 2% of the population, mostly aged 40 to 60 years, and affects men and women.

• Typically a solitary, encapsulated, subcutaneous mass on the trunk, neck, shoulders, back, upper arms and thighs. Deeper lipomas may be intermuscular or intramuscular.
• Multiple lipomas (about 5 to 15% of patients) occur in:
  • Familial multiple lipomatosis (autosomal dominant).
  • Dercum disease (adiposis dolorosa: painful lipomas in obese women).
  • Madelung disease (benign symmetrical lipomatosis of the neck and shoulders, with alcohol misuse).
  • Gardner syndrome (APC mutation, with colonic polyps, osteomas and desmoid tumours).
  • Multiple endocrine neoplasia type 1, PTEN hamartoma tumour syndrome, and Proteus syndrome.
• Subtypes: angiolipoma (painful, multiple, young adults), spindle cell and pleomorphic lipoma (posterior neck and back of older men), hibernoma (brown fat), lipoma arborescens (joints), and intramuscular lipoma.
• Risks: obesity, alcohol, diabetes, hyperlipidaemia and trauma, although causation is unproven.
• The main concern is distinguishing a lipoma from an atypical lipomatous tumour (well differentiated liposarcoma), which is deep, large and often in the thigh, limb girdle or retroperitoneum. It is characterised by MDM2 gene amplification.

• Soft, rubbery, lobulated, doughy, mobile subcutaneous mass, usually painless, 1 to 10 cm, growing slowly over months to years. The overlying skin is normal. The edge slips away under a pressing finger (slip sign).
• Angiolipomas are small, multiple and tender, mostly on the forearms.
• Pain, numbness or weakness suggest pressure on a nerve, intramuscular growth, or an angiolipoma.
• Red flags for sarcoma or atypical tumour: size above 5 cm, deep location (beneath the fascia, in muscle, or retroperitoneal), rapid recent growth, firm or fixed consistency, pain, recurrence after excision, and location in the thigh.
• Differential diagnosis: epidermoid cyst, sebaceous cyst, ganglion, abscess, lymph node, haematoma, neurofibroma, hernia (abdominal wall), soft tissue sarcoma (liposarcoma, undifferentiated pleomorphic sarcoma), lymphangioma, and metastasis.
• Complications: pressure effects on nerves and vessels, cosmetic concern, rare malignant transformation (very low), and recurrence if incompletely excised.

• Clinical for a small, soft, mobile, subcutaneous lump that has been stable.
• Ultrasound: a well defined, homogeneous, hyperechoic mass parallel to the skin, with no internal vascularity. It confirms a typical superficial lipoma.
• MRI (the best test) for lesions above 5 cm, deep, fixed, growing, painful, or with atypical ultrasound. A lipoma is isointense to fat on all sequences, with fat suppression, and has few thin septa. Features suggesting an atypical lipomatous tumour include thick septa (above 2 mm), nodular or non-fatty areas, contrast enhancement, and large size.
• Core needle biopsy, with MDM2 amplification testing (fluorescence in situ hybridisation), is done for suspicious imaging, before any surgery, and in a sarcoma centre.
• For multiple lipomas, check glucose, lipids, liver tests, alcohol history and family history, and consider colonoscopy and genetic review where the features suggest Gardner syndrome.

• Observation: small, asymptomatic, stable lipomas need no treatment. Reassure the patient and advise review if the lump grows, hurts or changes.
• Indications for removal: pain, nerve compression, rapid growth, cosmetic or functional concern, uncertain diagnosis, or large size.
• Surgical excision (the definitive treatment):
  • Marginal excision under local anaesthesia (lidocaine 1% with adrenaline 1:200,000, maximum 7 mg/kg, about 500 mg or 50 mL in an adult) through a small incision over the mass, with blunt dissection to remove the lipoma with its capsule intact. Recurrence after complete excision is below 5%.
  • Close the dead space with absorbable sutures, and place a pressure dressing to reduce haematoma. Give no routine antibiotics. Tetanus status is not an issue for clean elective surgery.
  • Send every specimen for histology.
  • Larger or deep lesions need general or regional anaesthesia, in theatre.
• Liposuction (suction assisted lipectomy) for soft subcutaneous lipomas through a small incision gives a smaller scar but higher recurrence if the capsule is left, and no histology.
• Injection treatments (deoxycholic acid, phosphatidylcholine with deoxycholate, or triamcinolone with lidocaine) can shrink small lipomas but the evidence is limited and results are inconsistent.
• Atypical lipomatous tumour or suspected sarcoma: refer to a sarcoma service. Wide excision with a margin (about 1 cm or a fascial plane), no enucleation, with MRI follow up. Radiotherapy or chemotherapy is reserved for dedifferentiated tumours. Local recurrence is common (up to 10 to 50% depending on site).
• Dercum disease: analgesia (paracetamol, NSAIDs, gabapentin 300 mg increasing to 900 to 1800 mg daily in divided doses, or duloxetine 30 to 60 mg daily), lidocaine infusion in specialist care, weight loss, and liposuction for painful clusters.
• Gardner syndrome and other syndromes: genetic referral, colonoscopy surveillance and multidisciplinary care.
• Weight loss does not reliably shrink lipomas, but is advised for metabolic health and Dercum disease.
• Special groups:
  • Anticoagulation: small lipomas can be excised with local pressure and haemostasis. Plan larger excisions with the prescriber.
  • Children: lipomas are rare, so image any mass and consider lipoblastoma or syndromic disease.
  • Pregnancy: defer elective removal unless symptomatic.
  • Diabetes: control glucose before surgery, and watch for wound infection.
• Follow up: review at 1 to 2 weeks for the wound, and at 3 to 6 months for recurrence. Refer to a sarcoma team for any recurrence, rapid regrowth, or histology reporting atypia.