Association of Disproportionately Enlarged Subarachnoid Space Hydrocephalus Features at MRI with Cognitive Decline.

Background The prevalence of incomplete disproportionately enlarged subarachnoid space hydrocephalus (DESH) and its cognitive relevance remain unclear. Purpose To determine the prevalence of complete and incomplete DESH and their associations with baseline cognitive impairment and follow-up cognitive decline. Materials and Methods This prospective community-based cohort (age ≥ 65 years) included participants who underwent baseline brain MRI and were followed for 5-7 years. Two radiologists assessed baseline MRI scans for core DESH features: Evans index greater than 0.3, enlargement of the Sylvian fissures (ESF), and tightness of the high-convexity sulci (THC). Complete DESH was defined as all three core features, incomplete DESH as one or two core features, and no DESH as zero core features. Feature combinations were modeled as single binary indicators of copresence (eg, THC plus ESF was 1 if both were present and 0 otherwise). Separate cross-sectional and longitudinal logistic regression models were used to evaluate associations of baseline imaging features with concurrent cognitive impairment and follow-up cognitive decline, respectively. Longitudinal models were fitted separately in participants with normal cognition and in a combined cohort of participants with normal cognition or mild cognitive impairment at baseline. Results Among 2133 participants (median age, 69 years [IQR, 67-73 years]; 1304 female participants), complete DESH, incomplete DESH, and no DESH were present in 37 (1.7%), 988 (46.3%), and 1108 (51.9%), respectively. There was no evidence of an association between baseline imaging features and baseline cognitive impairment (all Holm-adjusted P > .05). Baseline THC was associated with follow-up cognitive decline in the cognitively normal cohort (odds ratio [OR], 2.95 [95% CI: 1.95, 4.45]; Holm-adjusted P < .001) and in the combined cohort (OR, 2.87 [95% CI: 1.96, 4.21]; Holm-adjusted P < .001). THC plus ESF was associated with decline only in the combined cohort (OR, 1.83 [95% CI: 1.16, 2.87]; Holm-adjusted P = .04). Conclusion Incomplete DESH was more prevalent than complete DESH. Baseline THC was associated with subsequent cognitive decline. © RSNA, 2026 Supplemental material is available for this article. See also the editorial by Haller in this issue.