Question
A 51 year old man has a soft, painless lump in the thenar eminence that has grown slowly.
- Describe the MRI.
- Which features of a soft tissue mass need referral to a sarcoma service?
- How do you distinguish a lipoma from an atypical lipomatous tumour, and how is each treated?
Answer
MRI
- Well defined mass in the thenar muscles
- High T1 signal identical to subcutaneous fat
- Suppresses on fat saturated sequences
- Benign lipoma
Referral criteria
- Size over 5 cm
- Deep to the deep fascia
- Growing
- Painful
- Recurrence after excision
Lipoma versus atypical lipomatous tumour
| Feature | Lipoma | Atypical lipomatous tumour |
|---|---|---|
| Size | Small | Often over 10 cm |
| Septa | Thin | Thick, nodular, enhancing |
| Non fatty areas | None | Present |
| MDM2 | Not amplified | Amplified (FISH) |
Treatment
- Lipoma, marginal excision for symptoms
- Atypical lipomatous tumour in the limbs, marginal excision, local recurrence about 10%
- Dedifferentiation is rare in the limbs and more common in the retroperitoneum
- Liposarcoma (myxoid, pleomorphic), wide excision and radiotherapy
Related pages
Author Contributions
Orthofracs team
Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.