Question:medium
CT scan is least accurate for the diagnosis of which of the following?
CT scan is least accurate for the diagnosis of which of the following?
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Which of these lesions is often non-calcified and isodense to its surrounding fluid?
Updated On: Jun 24, 2026
- 1 cm aneurysm in the hepatic artery
- 1 cm lymph node in the para-aortic region
- 1 cm mass in the tail of the pancreas
- 1 cm gall stone
Show Solution
The Correct Option is D
Solution and Explanation
The trick here is to compare how each lesion behaves on CT density. CT discriminates structures by their X-ray attenuation, so it shines when a lesion differs sharply from its background.
A hepatic artery aneurysm enhances brightly with intravenous contrast and stands out. A para-aortic lymph node is a soft-tissue density nicely outlined against retroperitoneal fat. A pancreatic tail mass distorts the gland and alters its enhancement pattern, so it too is detectable. Each of these is well within CT's strengths.
A gallstone is the odd one out. Cholesterol stones are frequently isodense to bile and may show no calcium at all, so they blend into the gallbladder lumen and escape detection. This is exactly why ultrasound, which reveals the stone as an echogenic focus casting an acoustic shadow, is the first-line test for gallstones. CT is consequently the least reliable modality for a 1 cm stone.
\[\boxed{\text{1 cm gall stone}}\]
A hepatic artery aneurysm enhances brightly with intravenous contrast and stands out. A para-aortic lymph node is a soft-tissue density nicely outlined against retroperitoneal fat. A pancreatic tail mass distorts the gland and alters its enhancement pattern, so it too is detectable. Each of these is well within CT's strengths.
A gallstone is the odd one out. Cholesterol stones are frequently isodense to bile and may show no calcium at all, so they blend into the gallbladder lumen and escape detection. This is exactly why ultrasound, which reveals the stone as an echogenic focus casting an acoustic shadow, is the first-line test for gallstones. CT is consequently the least reliable modality for a 1 cm stone.
\[\boxed{\text{1 cm gall stone}}\]
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