Mass

What it means

Radiologists use this word for a defined lump of tissue that is larger and more substantial than a small spot. The usual cut-off is roughly three centimetres across — anything smaller tends to be called a nodule. The label says nothing about what the lump is made of; that requires the descriptors that follow, and sometimes more tests.

Why it appears on a CT or MRI report

When radiologists spot a lump that stands out from its surroundings, they describe it carefully: where it sits (which organ, which lobe), how big it is in millimetres, the shape of its borders (smooth, lobulated, irregular), what it looks like inside (solid, fluid-filled, fat-containing, calcified), and how it behaves when contrast dye is given. Each of those details narrows the list of possible causes and helps the clinical team decide what to do next.

What it usually means

The range is wide. Many lumps in this size category turn out to be benign — a fibroid in the uterus, a lipoma made of fat, an adenoma in the adrenal gland, an old healed scar, or a long-standing cyst that grew quietly. Others are inflammatory or infectious. A smaller share are tumours that need treatment, and a smaller share again are malignant. Reassuring descriptors include smooth borders, fat or calcium inside, stability on prior scans, and a typical appearance for a known benign entity. Worrying descriptors include irregular or spiculated borders, rapid growth, heterogeneous enhancement, restricted diffusion on MRI, or invasion into nearby tissues. The radiologist will often suggest the most likely diagnoses and recommend the next step — additional imaging, a specialist referral, or sometimes a biopsy.

When to follow up

Take the recommended next step seriously, but try not to read the worst into the word itself. Book a conversation with your doctor to go through the full description, your symptoms, and your personal history. If the report recommends a specific follow-up scan, a referral, or a biopsy, schedule it promptly rather than waiting. If the description is reassuring and stability is noted, your clinician may simply plan a check-up scan in a few months.

A plain-language way to picture it

Imagine running your hand under a smooth bedsheet and feeling a tennis ball underneath. You know something is there, you can feel its rough shape, but you can't tell from the touch alone whether it's a soft toy, a piece of fruit, or something harder. That's what the radiologist sees — a defined bulge that needs more information before anyone can say what it is.