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Prevalence and outcomes of incidental imaging findings: umbrella review

BMJ 2018; 361 doi: (Published 18 June 2018) Cite this as: BMJ 2018;361:k2387

Linked Editorial

Incidental findings on imaging


Incidental anarchy

  1. Jack W O’Sullivan, clinical researcher and DPhil candidate1,
  2. Tim Muntinga, honorary fellow1,
  3. Sam Grigg, medical student2,
  4. John P A Ioannidis, professor of medicine, health research and policy (epidemiology), biomedical data science, and statistics3 4 5 6 7
  1. 1Centre for Evidence-Based Medicine, Nuffield Department of Primary Care Health Sciences, University of Oxford, Oxford OX2 6GG, UK
  2. 2University of Melbourne, Victoria, Australia
  3. 3Stanford Prevention Research Center, Stanford University School of Medicine, Stanford, CA, USA
  4. 4Department of Health Research and Policy, Stanford University School of Medicine, Stanford, CA, USA
  5. 5Department of Biomedical Data Science, Stanford University School of Medicine, Stanford, CA, USA
  6. 6Department of Statistics, Stanford University School of Humanities and Sciences, Stanford, CA, USA
  7. 7Meta-Research Innovation Center at Stanford (METRICS), Stanford University, Stanford, CA, USA
  1. Correspondence to: J W O’Sullivan jack.osullivan{at} (or @DrJackOSullivan on Twitter)
  • Accepted 29 April 2018


Objective To provide an overview of the evidence on prevalence and outcomes of incidental imaging findings.

Design Umbrella review of systematic reviews.

Data sources Searches of MEDLINE, EMBASE up to August 2017; screening of references in included papers.

Eligibility criteria Criteria included systematic reviews and meta-analyses of observational studies that gave a prevalence of incidental abnormalities (“incidentalomas”). An incidental imaging finding was defined as an imaging abnormality in a healthy, asymptomatic patient or an imaging abnormality in a symptomatic patient, where the abnormality was not apparently 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.

Results 20 systematic reviews (240 primary studies) were identified from 7098 references from the database search. Fifteen systematic reviews provided data to quantify the prevalence of incidentalomas, whereas 18 provided data to quantify the outcomes of incidentalomas (13 provided both). The prevalence of incidentalomas varied substantially between imaging tests; it was less than 5% for chest computed tomography for incidental pulmonary embolism in patients with and without cancer and whole body positron emission tomography (PET) or PET/computed tomography (for patients with and without cancer). Conversely, incidentalomas occurred in more than a third of images in cardiac magnetic resonance imaging (MRI), chest computed tomography (for incidentalomas of thorax, abdomen, spine, or heart), and computed tomography colonoscopy (for extra-colonic incidentalomas). Intermediate rates occurred with MRI of the spine (22%) and brain (22%). The rate of malignancy in incidentalomas varied substantially between organs; the prevalence of malignancy was less than 5% in incidentalomas of the brain, parotid, and adrenal gland. Extra-colonic, prostatic, and colonic incidentalomas were malignant between 10% and 20% of the time, whereas renal, thyroid, and ovarian incidentalomas were malignant around a quarter of the time. Breast incidentalomas had the highest percentage of malignancy (42%, 95% confidence interval 31% to 54%). Many assessments had high between-study heterogeneity (15 of 20 meta-analyses with I2 >50%).

Conclusions There is large variability across different imaging techniques both in the prevalence of incidentalomas and in the prevalence of malignancy for specific organs. This umbrella review will aid clinicians and patients weigh up the pros and cons of requesting imaging scans and will help with management decisions after an incidentaloma diagnosis. Our results can underpin the creation of guidelines to assist these decisions.

Systematic review registration PROSPERO: CRD42017075679.


  • Contributors: JWOS and JI conceived and designed the study, and interpreted the results. TM, SG, and JWOS screened titles, abstracts, and full texts. JWOS and SG performed the data extraction. JWOS did the statistical analysis and JWOS is the study guarantor. All authors reviewed the manuscript. The corresponding author attests that all listed authors meet authorship criteria and that no others meeting the criteria have been omitted.

  • Funding: This study did not receive any specific funding. The Meta-Research Innovation Center at Stanford (METRICS) has been funded by the Laura and John Arnold Foundation.

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

  • Ethical approval: Not required.

  • Data sharing: We extracted data from published systematic reviews, all of which are available and accessible.

  • The manuscript’s guarantor affirms that the manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.

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