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Views And Reviews

The curse of the priors when interpreting scans

BMJ 2021; 373 doi: (Published 09 June 2021) Cite this as: BMJ 2021;373:n1438
  1. Giles Maskell, radiologist
  1. Truro
  1. gilesmaskell{at}

It’s a truism that the more we look the more we’ll find—but more imaging also means ever more opportunities to get things wrong, says Giles Maskell

I used to joke that radiology was getting easier because, as we carried out more and more imaging, soon everyone would have a previous scan to compare. The point is that detecting changes from a baseline set of appearances is always easier than interpreting de novo. And it’s much easier to dismiss an abnormal appearance if you can see that it looked the same a few years ago.

You might think that a CT scan of the abdomen, for example, is either normal or abnormal. Not so. Not only does normal anatomy vary to an astonishing degree between individuals, but all of us carry “abnormalities” that are usually harmless but can masquerade as significant pathology. Cysts in the liver …

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