Lipoma

Definition

A lipoma is a very common, benign, slow-growing tumour of mature fat cells (adipocytes). It usually lies in the subcutaneous fat, rarely deep to the fascia or within muscle. Malignant transformation is exceedingly rare.

Classification

• Variants: angiolipoma (often painful), spindle cell lipoma (especially on the neck of older people), pleomorphic lipoma, adenolipoma.
• Multiple lipomas (in about 5–10% of patients) are usually part of a syndrome or genetic disorder, e.g. familial multiple lipomatosis, Proteus syndrome, PTEN hamartoma syndrome, Gardner syndrome or MEN 2B; multiple painful lipomas occur in Dercum disease.

Occurrence & epidemiology

Lipomas typically appear between 40 and 60 years of age but can occur at any age. Both sexes are equally affected; they are more common in hyperlipidaemia, type 2 diabetes and obesity. The cause is unknown.

Clinical features

• Usually a solitary, painless, soft to rubbery, often lobulated and freely mobile nodule, 1 to more than 10 cm in diameter.
• The overlying skin is unchanged and not tethered to the nodule.
• Mainly on the trunk, neck and proximal limbs.
• Rarely, large lipomas compress nerves or adjacent structures and cause pain or numbness.

Histology

Mature adipose tissue with a few small capillaries in thin fibrous septa, often surrounded by a thin fibrous capsule. Distinguishing it from well-differentiated liposarcoma can be histologically difficult.

Diagnosis

• Usually a clinical diagnosis.
• Imaging and/or biopsy if the findings are uncertain.
• Rapidly growing nodules are examined histologically to exclude liposarcoma.

Differential diagnoses

• Epidermal cyst (atheroma)
• Lipoid proteinosis (Urbach–Wiethe disease)
• Dermatofibroma
• Fibrofolliculoma (Birt-Hogg-Dubé)
• Steatocystoma multiplex
• Abscess
• Haemangioma

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References (selection)

1. DermNet: Lipoma
2. DermNet: Lipoma pathology
3. MSD Manual Professional: Lipomas

Cross-references