Prevalence of incidental intracranial findings on magnetic resonance imaging: a systematic review and meta-analysis

Background As the volume and fidelity of magnetic resonance imaging (MRI) of the brain increase, observation of incidental findings may also increase. We performed a systematic review and meta-analysis to determine the prevalence of various incidental findings. Methods PubMed/MEDLINE, EMBASE and SCOPUS were searched from inception to May 24, 2021. We identified 6536 citations and included 35 reports of 34 studies, comprising 40,777 participants. A meta-analysis of proportions was performed, and age-stratified estimates for each finding were derived from age-adjusted non-linear models. Results Vascular abnormalities were observed in 423/35,706 participants (9.1/1000 scans, 95%CI 5.2-14.2), ranging from 2/1000 scans (95%CI 0-7) in 1-year-olds to 16/1000 scans (95%CI 1-43) in 80-year-olds. Of these, 204/34,306 were aneurysms (3.1/1000 scans, 95%CI 1-6.3), which ranged from 0/1000 scans (95%CI 0-5) at 1 year of age to 6/1000 scans (95%CI 3-9) at 60 years. Neoplastic abnormalities were observed in 456/39,040 participants (11.9/1000 scans, 95%CI 7.5-17.2), ranging from 0.2/1000 scans (95%CI 0-10) in 1-year-olds to 34/1000 scans (95%CI 12-66) in 80-year-olds. Meningiomas were the most common, in 246/38,076 participants (5.3/1000 scans, 95%CI 2.3-9.5), ranging from 0/1000 scans (95%CI 0-2) in 1-year-olds to 17/1000 scans (95%CI 4-37) in 80-year-olds. Chiari malformations were observed in 109/27,408 participants (3.7/1000 scans, 95%CI 1.8-6.3), pineal cysts in 1176/32,170 (9/1000 scans, 95%CI 1.8-21.4) and arachnoid cysts in 414/36,367 (8.5/1000 scans, 95%CI 5.8-11.8). Conclusion Incidental findings are common on brain MRI and may result in substantial resource expenditure and patient anxiety but are often of little clinical significance.