Describe Lipoma in detail.

The Concept

A lipoma is a benign tumour of mature fat cells (adipocytes), and it is the commonest benign soft-tissue tumour. Because fat is present almost everywhere in the body, a lipoma can occur at almost any site — earning it the nickname the 'universal tumour' — though it is most often found in the subcutaneous tissue.

Clinical Features

A lipoma is characteristically a soft, lobulated, well-defined, mobile, painless swelling. Two signs are useful: it has a 'slip sign' (the edge slips away from the examining finger, because it is soft and encapsulated), and it may feel pseudo-fluctuant. Most are solitary; multiple painful lipomas occur in Dercum's disease (adiposis dolorosa).

Management & the Important Caveat

A small, typical lipoma can be reassured and observed; excision is done for large or symptomatic lesions, cosmetic reasons, or diagnostic doubt. The important caveat is that a lump which is large (> 5 cm), deep, rapidly growing or painful may be a liposarcoma rather than a benign lipoma, and warrants imaging and specialist assessment rather than simple excision.

Plane & Diagnosis

On examination a lipoma sits in the subcutaneous plane — it is free from the overlying skin (no punctum, unlike a sebaceous cyst) and mobile over deeper structures — which, with its soft lobulated feel and slip sign, usually makes the diagnosis clinical. Most subcutaneous lipomas need no investigation. It is the deep or unusually large lump where imaging (ultrasound or MRI) is used, precisely to distinguish a benign lipoma from a liposarcoma before deciding on treatment.

The Bottom Line

A lipoma is a benign, soft, mobile subcutaneous tumour of fat with a slip sign, usually diagnosed clinically and simply observed or excised — but a large, deep or growing 'lipoma' must be imaged to exclude a liposarcoma.

A Note on Variants & Sites

Lipomas have several recognised variants and sites worth a mention: an angiolipoma (containing blood vessels) can be tender; a subfascial or intramuscular lipoma lies deep and is harder to assess clinically; and lipomas occur at classic sites such as the neck, shoulders, back and limbs. Most remain small and stable for years. The practical rule stays the same — a benign-feeling, stable, superficial lipoma is reassured or excised for symptoms, while any deep, large or changing fatty lump prompts imaging to exclude malignancy.

The slip sign is characteristic of lipoma.

• Lipoma = benign tumour of mature fat cells; commonest benign soft-tissue tumour ('universal tumour').
• Soft, lobulated, well-defined, mobile, painless; positive 'slip sign'; pseudo-fluctuant.
• Multiple painful lipomas = Dercum's disease (adiposis dolorosa).
• Reassure/observe or excise if large/symptomatic/doubtful; beware liposarcoma (large, deep, growing, painful) → image and refer.