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Risk factors for hippocampal cavities in marginally-housed adults Cheng, Alex Yiu Ting


Reductions in hippocampal volume have been well established as a correlate of disease expression in a variety of psychiatric and neurological disorders such as Alzheimer’s dementia, major depressive disorder, schizophrenia, HIV infection, traumatic brain injury (TBI), and substance abuse. Although conventional neuroimaging studies focus on the measurement of total volume as a surrogate measure for integrity, abnormalities in hippocampal morphology are intuitively equally important yet less well-studied. Hippocampal cavities (HCs) are a common morphological variant found frequently on magnetic resonance imaging (MRI) examinations of the brain. Although they are common findings, their etiology and significance are unclear. We conducted a systematic review of the risk factors for the presence and severity of HCs visualized on MRI. We found that the vascular risk factors of age and hypertension were the most robust risk variables associated with HC, but limited associative evidence exists for a diverse set of other variables including apolipoprotein E (APOE) genotype, smoking, depression, transient global amnesia, mild cognitive impairment and dementia. Considerable methodological heterogeneity is a marked limitation of the current literature. Meta-analysis confirmed the presence of significant heterogeneity between studies (I²: 95% CI [94.3%, 94.0%], p < 0.0001). Meta-regression of age found no significant moderation of HC prevalence. Differences in study population and differences in how HC are rated contribute to heterogeneity. Future studies may benefit from using a standardized HC rating methodology. We then sought to characterize the prevalence and risk factors for HC in a sample of 375 marginally-housed persons living in Vancouver, BC. This cohort represents a population with a high severity of vascular risk factors, substance abuse, and viral infection and physical violence. Automated HC segmentation was used to characterize HC volumes. HCs were highly prevalent in this cohort, occurring in 71.6% of all participants. Age, hypertension, diabetes, smoking, and stimulant drug dependency were associated with larger HC volumes. No associations with HCs were found for alcohol abuse, HIV, and traumatic brain injury (TBI). This study provides a first look into the associations between HCs and substance abuse, HIV infection, and TBI. Drug-related factors may be a new avenue of research for HCs.

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