Any soft-tissue mass that is deep to the fascia, larger than 5 cm, growing or painful needs MRI before biopsy — the report gives the compartment, size, relation to the neurovascular bundle and bone, and the features that a lipoma would not have.
Orient first
- Red flags: > 5 cm, deep to fascia, increasing size, pain (verify local referral criteria).
- Most sarcomas are well-defined and can look deceptively benign.
- Biopsy at a sarcoma centre along the planned resection tract.
Acquire the study
- Axial and longitudinal T1, STIR or T2 fat-saturated, DWI, post-gadolinium T1 with subtraction; skin marker over the lump.
The manoeuvre
- Compartment and depth relative to the deep fascia on axial images.
- Size in cm in three planes.
- T1: fat content (lipomatous tumour) vs none.
- Post-contrast subtraction: nodular enhancing solid tissue, necrosis.
- Relation to vessels, nerves and bone (encasement, cortical involvement).
What confirms it
- Histology at a sarcoma centre.
What licenses you to exclude it
- A superficial, small mass with a classic benign pattern (lipoma, ganglion, epidermoid) needs no MRI.
The classic misread
- Calling a myxoid sarcoma a cyst — it enhances.