Soft tissue mass

What it means

The term covers any lump that sits in the body's soft tissues — muscle, fat, tendon, nerve, blood vessel, lymphatic tissue, or fibrous connective tissue — as distinct from a lump arising in bone or inside a solid organ. They are common, can appear anywhere, and range from harmless fatty bumps to less common tumours. The radiologist's job is to describe what the lump looks like in enough detail that the clinical team can decide whether it can be left alone, watched, or biopsied.

Why it appears on a CT or MRI report

Reports name the location (which limb, which compartment, which muscle), size in three dimensions, shape (well-defined, lobulated, infiltrative), what it is made of where this can be inferred (fat density, fluid, mixed), how it enhances with contrast, and how it relates to nearby nerves and vessels. MRI is usually better than CT for characterising soft-tissue lumps because it shows fat, fluid, and fibrous tissue more clearly. The report may suggest a likely diagnosis or note that the appearance is indeterminate and recommend specialist review.

What it usually means

Most soft-tissue lumps are benign. The single most common is a lipoma — a slow-growing collection of mature fat that often sits just beneath the skin or within a muscle. Other common benign lumps include simple cysts, ganglion cysts near joints, fibrous nodules, scar tissue, post-injection collections, vascular malformations, and nerve sheath tumours. Some lumps reflect inflammation or infection rather than a true growth — an abscess, an inflamed bursa, or a haematoma after injury can all look mass-like. A smaller proportion of soft-tissue masses are sarcomas, a family of tumours that need specialist management. Features that lower the suspicion for sarcoma include small size, very long history without growth, classic fatty signal, and a clear capsule. Features that raise suspicion include size over about five centimetres, growth, deep location, irregular borders, and unusual enhancement. When in doubt, soft-tissue masses with any worrying features are referred to a sarcoma centre before any biopsy is done.

When to follow up

Talk to your doctor about the report. Many benign-appearing lumps are watched or removed only if they bother you. Talk to your doctor sooner if the lump is described as deep, larger than about five centimetres, growing, painful at rest or at night, or if the report recommends specialist referral or biopsy. Seek prompt review for a rapidly enlarging lump, new neurological symptoms in the limb (numbness, weakness), or skin changes over the lump.

A plain-language way to picture it

Imagine a knot inside a pile of laundry. Most knots are loose folds you can shake out — the equivalent of harmless fatty lumps. Some are stuck together by something sticky from a spill, like an old inflammation. A few are a foreign object that fell in the basket and got wrapped up. You can usually tell by feeling and looking, but a few need to be unfolded carefully to know for sure. The radiologist is describing the knot in enough detail to decide which kind it is.