Unexpected findings on medical imaging are usually harmless

Brain MRIImagine you go for an MRI or an x ray and the radiologist spots something they didn’t anticipate on your scan – you would be worried, right?

Well, maybe you don’t need to be. A study of more than 1,400 scan found that almost 40% showed at least one such “incidental finding” but only 2.5% were thought to show a genuine medical problem and required further clinical action.

Although spotting something by accident on a medical scan can mean that a disease or disorder is detected and treated early, the extra scans and tests that follow might be painful or dangerous if the incidental finding turns out to be clinically harmless. As such, it’s important that radiologists have some kind of idea which findings are worth acting on and which represent innocuous anatomical quirks.

The authors of this study raked through the medical records of patients at Mayo Clinic in Minnesota who had taken part in imaging research between January and March 2004.

Of the 1,426 scans for which three years of follow-up was reported, 567 (38.9%) had at least one incidental finding. Out of these people whose scan had an incidental finding, 35 (6.2%) underwent further clinical action such as follow-up imaging or invasive diagnostic tests like broncoscopy.

Four people turned out to have diseases or disorders that were medically serious or even life threatening, which would have gone undetected had they not been in an imaging study. Only one person was found to have minimal or trivial disease, which presumably would not have merited the further investigations conducted.

Six (1.1%) people with an incidental finding had treatment that resolved or improved the newly detected disorder or disease, whereas only three underwent medical or surgical treatment that resulted in lack of improvement. In the rest of the participants with an incidental finding the medical benefit or burden of the subsequent treatment was unclear.

The likelihood of an incidental finding varied considerably depending on the type of scan used – nearly two thirds (61%) of people who had computed tomography of the abdomen and pelvis had an incidental finding on their scan, compared with only 4% of people who underwent some sort of nuclear medicine procedure. However, only computed tomography and MRI of the head yielded incidental findings that received further investigation.

It seems that people whose incidental finding does represent serious disease are being checked out and few people whose odd findings on imaging are harmless are being pursued. However, the authors say: “the clinical investigation of a suspicious incidental finding that results in a benign diagnosis is not necessarily without clinical value or avoidable when presented with potentially life-threatening consequences (e.g. a solid renal mass).”

Orme N et al. (2010) Incidental Findings in Imaging Research: Evaluating Incidence, Benefit, and Burden. Archives of Internal Medicine 170:1525-1532. DOI: 10.1001/archinternmed.2010.317

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