Neurocognitive and affective dysfunction in Chiari malformation type I

Chiari malformation type I (CM-I) is traditionally conceptualized as a structural disorder of the posterior cranial fossa characterized by cerebellar tonsillar herniation. However, increasing clinical and experimental evidence suggests that CM-I may be associated with distributed neurocognitive and affective sequelae consistent with cerebellar network dysfunction.

The authors conducted a PRISMA-compliant systematic review of the MEDLINE and Embase databases from database inception through November 2025 to identify studies reporting standardized neuropsychological outcomes in pediatric and adult patients with CM-I. Given substantial heterogeneity in study design, cognitive instruments, and outcome reporting, findings were synthesized using a structured narrative approach. Methodological quality was assessed using an adapted Newcastle-Ottawa Scale and mapped to Agency for Healthcare Research and Quality criteria.

Thirty-four studies comprising 2113 individuals with CM-I met inclusion criteria. Across pediatric and adult cohorts, selective cognitive vulnerabilities were most consistently observed in complex attention, executive function, visuospatial processing, learning and memory, language, and higher-order social cognition. These profiles closely resembled features of cerebellar cognitive affective syndrome. Cognitive deficits varied by developmental stage and were modulated by chronic pain, psychiatric comorbidity, and neurodevelopmental factors. Advanced neuroimaging studies demonstrated widespread disruption of cerebello-thalamo-cortical and cortico-ponto-cerebellar networks. Reported effects of posterior fossa decompression on neurocognitive outcomes were heterogeneous and inconsistent across domains and study designs.

The available evidence supports reconceptualizing CM-I as a heterogeneous, large-scale brain network disorder with clinically meaningful cognitive and affective consequences in a subset of patients. Integration of domain-specific neuropsychological assessment into routine clinical evaluation may improve prognostication and guide future mechanism-based interventions.