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‘Incidental’ Imaging Findings Unlikely to be Cancer

male doctor with female patient during a ct scan

Researchers from University of Oxford and Stanford University have reviewed hundreds of studies to learn how often incidental abnormal findings from imaging tests are found, how often those turn out to be malignant tumors, and how often they turn out to be harmless. The review defines an “incidentaloma” as something a radiologist spots on an imaging test while looking for something else, either because the patient’s symptoms were unrelated, or because the patient had no symptoms at all.

The review was published June 18, 2018 in BMJ.

Incidentalomas: an increasing problem

The demand for imaging tests – including PET scans, CT scans, and MRIs – has increased at the same time the tests have become more advanced, and better able to detect any abnormalities. This has led to an increase in incidentalomas. Risks associated with incidentalomas include patient anxiety as well as the potential for more testing and treatment. Additional procedures cost money and put more strain on the medical system.

The goal of the review is to help doctors and patients weigh the benefits and risks of imaging tests, as well as following up on incidentalomas when they occur.

The likelihood of finding cancer

The researchers actually reviewed 20 other reviews, consisting of 240 studies, to find out how often incidentalomas are found and how often they turn out to be cancer.

By imaging test, the highest rate of incidentalomas was found in chest CT (45%) followed by CT colonoscopy (38%) and cardiac MRI (34%). Spine and brain MRIs both had incidentaloma rates of 22%. The lowest rates were found in whole body PET or PET/CT and chest CT for incidental pulmonary embolism.

The frequency of cancerous tumors found in incidentalomas varied by body part. The highest percentage occurred in the breast (42%), followed by ovaries, thyroid, and kidney, where cancer was found about 25% of the time. Colon and prostate incidentalomas were malignant 10% to 20% of the time. Cancer was rarely found in incidentalomas of the brain, salivary gland, and adrenal gland.


According to the authors, these results can help doctors and patients weigh the pros and cons of requesting imaging scans and with the pros and cons of following up on a diagnosis of incidentaloma.

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Prevalence and outcomes of incidental imaging findings: umbrella review. Published June 18, 2018 in BMJ. First author Jack W. O’Sullivan, University of Oxford, United Kingdom.