Lesion

What it means

A lesion is any patch of tissue that doesn't look like the tissue around it. The word covers an enormous range — from a tiny harmless cyst, to a scar from an old injury, to a benign growth, to something that needs urgent attention. Radiologists use it as a placeholder when they need to name a finding without committing to a diagnosis on imaging alone.

Why it appears on a CT or MRI report

Because "lesion" is so broad, reports almost always pair it with descriptors. You may see size in millimetres, the organ it sits in (a liver lesion, a brain lesion), shape (well-defined, ill-defined, lobulated), density or signal (hyperdense, T2-bright), enhancement (whether it lights up with contrast), and a clinical impression (benign-appearing, indeterminate, suspicious). Those descriptors do the real diagnostic work — the word "lesion" on its own is just the headline.

What it usually means

Most lesions found incidentally on CT or MRI turn out to be harmless: simple cysts, scars, small benign tumours, vascular variants, or normal anatomical quirks. A radiologist's job is to sort them. When the descriptors are reassuring — small, well-defined, fat-containing, calcified, stable on prior scans — the lesion is usually filed away as benign. When descriptors are less reassuring — irregular borders, rapid enhancement, restricted diffusion, growth over time — the radiologist may use words like "indeterminate" or "suspicious" and recommend more imaging, a biopsy, or specialist follow-up. The same word "lesion" can therefore range from clinically irrelevant to the most important finding on the scan, depending entirely on what comes after it.

When to follow up

Read the rest of the sentence before reacting to the word. If the report uses "benign-appearing", "likely benign", "stable", or "no follow-up needed", the lesion is reassurance, not alarm. If you see "indeterminate", "suspicious", "needs further evaluation", or a recommendation for a specific follow-up scan or biopsy, book that conversation with your doctor promptly. Even when a lesion sounds benign, asking your clinician what it means for your own history (family cancer history, prior conditions, age) is reasonable.

A plain-language way to picture it

Think of a freshly mown lawn. A lesion is just a patch of grass that looks different — maybe yellower, maybe a different texture. The patch alone doesn't tell you whether it's a footprint, a dropped coin, a mushroom, or something growing under the surface. The gardener has to walk over and look closer before deciding whether to leave it alone, photograph it for next week, or dig it up.