What Does Hypodense Mean on a CT Scan?

What it means

A CT scanner builds pictures from X-rays passing through the body. Things that block a lot of X-rays, like bone, look bright white. Things that let more X-rays through, like fluid, fat or air, look darker. Hypodense simply means one area looks darker than the tissue right next to it.

Radiologists use the word to describe what they see before they say what they think it is. When a report calls a spot hypodense, the writer is telling your doctor how it looked on the pictures. Size, shape, edges, how it changes after contrast dye and how it compares with older scans all help them decide what the spot probably is, or whether another test would help.

Hypodense is often confused with hypoechoic. Both mean darker than the surroundings, but hypodense is used for CT and hypoechoic for ultrasound. The opposite of hypodense is hyperdense, which means brighter on CT.

Where you may see it

• The 'Findings' section of CT scan reports of the abdomen and pelvis, often describing the liver or kidneys
• Head CT reports, describing areas of the brain that look darker than normal brain tissue
• Chest CT reports describing lymph nodes, fluid or the thyroid at the base of the neck
• The 'Impression' summary, sometimes with advice such as follow-up imaging or an MRI