Incidentaloma rates vary by imaging methods, malignancy

In a review of literature through August 2017, incidentalomas occurred in more than a third of cardiac MRIs and chest CTs, and CT colonoscopy revealed extracolonic incidentalomas 38% of the time.


There is large variability across different imaging techniques in the prevalence of incidentaloma findings, as well as in how often these findings are malignant, a systematic review found.

To provide an overview of the evidence on prevalence and outcomes of incidental imaging findings, researchers reviewed the literature for systematic reviews and meta-analyses of observational studies that gave a prevalence of incidental abnormalities through August 2017. Results were published by The BMJ on June 18.

An incidentaloma was defined as an incidental imaging finding in a healthy, asymptomatic patient or an imaging abnormality in a symptomatic patient where the abnormality was not related to the patient's symptoms. Primary studies that measured the prevalence of incidentalomas in patients with a history of malignancy were also considered in sensitivity analyses. Twenty systematic reviews involving 240 primary studies were included in the meta-analysis. Fifteen systematic reviews provided data to quantify the prevalence of incidentalomas, 18 provided data to quantify the outcomes of incidentalomas, and 13 provided both.

Incidentalomas occurred in more than a third of cardiac MRIs and chest CTs. CT colonoscopy revealed extracolonic incidentalomas 38% of the time. Intermediate rates of incidentalomas occurred with MRI of the spine (22%) and brain (22%). Whole-body positron emission tomography (PET) or PET/CT found incidentalomas less than 5% of the time, and incidental pulmonary embolism was found in fewer than 5% of chest CTs.

The rate of malignancy in incidentalomas varied substantially by organ: less than 5% in incidentalomas of the brain, parotid, and adrenal gland and between 10% and 20% in extra-colonic, prostatic, and colonic incidentalomas. Renal, thyroid, and ovarian incidentalomas were malignant around a quarter of the time. The highest percentage of malignancy was noted in breast incidentalomas (42%; 95% CI, 31% to 54%).

“Our results—the quantification of the prevalence of incidental findings from different imaging tests—equips clinicians to appropriately inform patients about the risks of incidentalomas before the ordering of a scan,” the authors wrote. “Our study provides the data for clinicians to quantify the risk of incidentalomas for numerous different imaging tests and thus allow clinicians and patients to weigh up the risks and benefits of undergoing an imaging test.”

An editorial cautioned that clinicians and patients should be aware that malignant neoplasms in one organ system can sometimes confer better survival than benign neoplasms in another.

“Discussion about the prevalence of incidentalomas before an imaging test is likely to be beneficial in many scenarios, particularly where clinicians are under pressure to investigate,” the editorial stated. “However, there are many evidence based guidelines that recommend practical approaches to requesting imaging. Better adherence to this guidance would also reduce the harmful overdiagnosis of conditions that will never cause symptoms or shorten a patient's life.”