Lipoma
Summary
A Lipoma is a benign mesenchymal tumour composed of mature adipose tissue. It is the most common soft tissue tumour in adults. They are typically slow-growing, painless, mobile, and soft ("doughy") subcutaneous masses. While benign, the critical clinical task is to distinguish large or deep lipomas from Liposarcomas. [1,2]
Clinical Pearls
The "Slip Sign": A classic clinical sign. If you press gently on the edge of a lipoma, the tumour "slips" out from under your finger. This is because it is encapsulated and relatively mobile within the subcutaneous fat.
Lipoma vs Sebaceous Cyst: The two most common lumps.
- Lipoma: Soft, Mobile, Slip sign positive, No Punctum, Not tethered to skin.
- Cyst: Firm, Tethered to skin (cannot move skin over it), Punctum (black dot) present.
The "Golf Ball" Rule: Any soft tissue lump that is >5cm (size of a golf ball) or deep to the fascia (cannot wobble it) requires an Urgent Ultrasound/MRI to exclude Soft Tissue Sarcoma. Do not just reassure.
Demographics
- Prevalence: 1% of the population.
- Age: 40-60 years. Rare in children.
- Gender: No significant difference (though rare variants like Dercum's disease are female predominant).
Syndromes
- Familial Multiple Lipomatosis: Autosomal dominant. Multiple small lipomas on arms/trunk. Sparing of head/shoulders.
- Dercum's Disease (Adiposis Dolorosa): Multiple painful lipomas in obese post-menopausal women.
- Gardner Syndrome: FAP (Colon polyps) + Osteomas + Lipomas.
Histology
- Composed of mature adipocytes that are morphologically identical to normal fat cells.
- Enclosed in a thin fibrous capsule (unlike normal fat which is not encapsulated).
- Angiolipoma: A variant with excessive vascular proliferation. Often painful.
Symptoms
Sites
- Inspection: Smooth, lobulated contour.
- Palpation:
- Soft (feels like dough).
- Mobile.
- Slip Sign: Positive.
- Temperature: Normal (sarcomas may be warm due to vascularity).
Imaging
- Ultrasound:
- Lipoma: Homogeneous, hyperechoic (or isoechoic to fat), compressible.
- Sarcoma: Heterogeneous, vascular flow, deep invasion.
- MRI: Gold standard for >5cm or deep lesions. "Fat suppression sequences" confirm it is fat.
Biopsy
- Warning: Do not perform a verified core biopsy or excision of a suspected sarcoma in primary care. Referral to a sarcoma centre is required to plan the biopsy tract (which gets excised with the tumour).
Management Algorithm
SOFT TISSUE LUMP
↓
CLINICAL FEATURES SUSPICIOUS?
(>5cm, Deep, Rapid Growth, Pain)
┌─────────┴─────────┐
YES NO
↓ ↓
URGENT US/MRI CLINICAL DIAGNOSIS
(Sarcoma Pathway) (Lipoma)
↓ ↓
CONFIRMED? SYMPTOMATIC?
┌───┴───┐
YES NO
↓ ↓
EXCISION LEAVE ALONE
(Observe)
Techniques
- Observation: Appropriate for the vast majority.
- Surgical Excision:
- Indication: Cosmesis, Pressure symptoms, Diagnosis uncertain.
- Procedure: Incision over lump -> Blunt dissection of capsule ("Shelling out") -> Closure.
- Liposuction: Can be used for large or multiple lipomas to minimize scarring, but high recurrence rate as capsule remains.
- Compression: Of nerves (e.g., radial nerve).
- Cosmesis: Disfigurement.
- Malignant Change: Lipomas do not turn into Liposarcomas (mostly). Liposarcomas arise de novo.
- Recurrence: Rare (less than 5%) if completely excised with capsule.
- Malignancy: Benign.
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| Sarcoma Referral | NICE NG12 | Urgent US for soft tissue lump >5cm, deep, or painful. |
| Excision | NHS | Lipoma removal is usually considered a "Procedure of Low Clinical Value" (PLCV) and not funded for purely cosmetic reasons. |
Landmark Evidence
1. The "Golf Ball" Study
- Studies validating the NICE guidelines show that size >5cm is the single most sensitive predictor of malignancy in soft tissue tumours.
What is a Lipoma?
It is a harmless "fatty lump". It is just a collection of normal fat cells that have grown inside a thin skin (capsule).
Is it cancer?
No. It is a benign tumour. It does not spread.
Will it turn into cancer?
No. It stays as fat.
Do I need it removed?
Only if it bothers you. If it involves a nerve, rubs on your belt, or looks unsightly, we can pop it out. Otherwise, it is perfectly safe to leave it.
How is it removed?
A small cut under local anaesthetic. It usually pops out easily like a grape from its skin.
Primary Sources
- NICE. Suspected cancer: recognition and referral [NG12]. 2015.
- Rydholm A, et al. Size, site and clinical incidence of lipoma. Factors in the differential diagnosis of lipoma and sarcoma. Acta Orthop Scand. 1983.
Common Exam Questions
- Sign: "Slip Sign?"
- Answer: Lipoma.
- Differential: "Punctum present?"
- Answer: Epidermoid Cyst.
- Red Flag: "Lump size trigger for referral?"
- Answer: >5cm.
- Syndrome: "Multiple painful lipomas in obese lady?"
- Answer: Dercum's Disease.
Viva Points
- Hibernoma: A rare benign tumour of Brown Fat.
- Liposarcoma Types: Well-differentiated, Myxoid, Pleomorphic (worst).
- Sub-fascial Lipoma: These are rarer. Because they are trapped under the fascia, they feel firm (not soft) when the muscle contracts, mimicking a solid tumour. Always image these.
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.