Hemorrhage

What it means

Bleeding describes blood that has escaped from a vessel and settled where it should not be. It can happen almost anywhere — inside a muscle after an injury, around the kidneys, in the lung, the abdomen, the pelvis, or the chest. On a fresh CT scan, recent blood looks bright. As days pass, the appearance fades and becomes harder to date. MRI shows blood differently depending on how old it is, which is one of the reasons radiologists choose between the two.

Why it appears on a CT or MRI report

Reports usually name the exact location and an estimated size. You may see terms such as retroperitoneal, intraperitoneal, intramuscular, pulmonary, pelvic, or perirenal. Words like acute, subacute, and chronic suggest how recent the bleed is. The report may mention whether the blood appears contained, whether contrast is leaking actively, and whether nearby structures are pushed aside. Bleeding inside the skull is described separately because the closed space changes how it behaves; see the intracranial-hemorrhage entry for that.

What it usually means

The significance depends almost entirely on where the blood is, how much there is, and whether it is still bleeding. Small collections from a known cause — a recent procedure, an injection site, a minor injury, or a known small vessel — are often watched and reabsorb on their own over weeks. Larger collections, active extravasation (contrast leaking on the scan), or bleeding in someone on blood thinners can be urgent and may need transfusion, embolization, or surgery. Common causes include trauma, blood-thinning medication, ruptured cysts, tumours that bleed, vascular abnormalities, and complications of recent procedures. Older, stable collections from a known event months ago are usually unconcerning. The care team weighs vital signs, blood counts, and the trajectory on repeat imaging rather than the word alone.

When to follow up

If this is a new finding on an emergency scan, the team is already responding. If you are reading the words on an outpatient report, contact your doctor the same day to plan next steps. Go to the emergency department for sudden severe pain, lightheadedness, fainting, a rapidly swelling area, vomiting blood, blood in stool or urine, shortness of breath, or unexplained pale and clammy skin, especially if you take blood thinners or had a recent procedure.

A plain-language way to picture it

Imagine a water pipe that has sprung a small leak inside a wall. A little dampness behind the plaster may dry on its own and never bother anyone. A steady drip into the cavity, though, will pool, spread, and eventually need a plumber. Bleeding inside the body works the same way — a small, stopped leak is often left to heal, while an active one needs someone to find the source and close it.