A CT scan of the abdomen shows a well-defined right renal cortical lesion with a thin wall, uniform internal attenuation of 4 Hounsfield units, and no measurable increase in attenuation after IV contrast administration. This lesion should be classified as:
- A A haemorrhagic cyst
- B A simple renal cyst ✓
- C A hypoenhancing renal cell carcinoma
- D An angiomyolipoma
Correct answer: B. A simple renal cyst
Explanation
Water is defined as 0 Hounsfield units and simple fluid ranges from about 0 to 20 HU. A thin-walled lesion measuring 4 HU that shows no enhancement fulfils all criteria for a simple cyst (Bosniak I). Haemorrhagic cysts measure above 20 HU, renal cell carcinoma shows perceptible enhancement (usually a rise greater than 10 to 20 HU), and angiomyolipoma contains fat, typically below minus 20 HU. The absence of enhancement is the single most reassuring feature here.
Reference: Grainger and Allison's Diagnostic Radiology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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