In CT, the Hounsfield unit (HU) scale is defined with water as 0 HU and air as −1000 HU. A lesion in the liver measures +60 HU on non-contrast CT and shows minimal enhancement (+65 HU) on contrast-enhanced CT. An adjacent lesion measures −50 HU. The −50 HU lesion most likely contains:

• A Calcium
• B Simple fluid (water-density cyst)
• C Acute haemorrhage
• D Fat (lipid content, as in hepatic steatosis or angiomyolipoma) ✓

Explanation

Fat has characteristic negative HU values on CT, ranging from approximately −20 to −150 HU, corresponding to its lower electron density compared to water. A liver lesion measuring −50 HU indicates fat content, consistent with focal hepatic steatosis or a fat-containing tumour like hepatic angiomyolipoma or lipoma. Simple fluid cysts measure 0–15 HU. Calcium measures +100 to +400 HU. Acute haemorrhage measures +50 to +80 HU.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.