Linear vs volume measures of ventricle size in hydrocephalus: relation to present and future gait and cognition

Objective To compare the clinical utility of volume-based ratios with the standard linear ratio of Evans index (EI) by examining their associations with gait, cognition, and other patient and imaging variables. 
 Methods From MRI scans of 1,774 participants in the Mayo Clinic Study of Aging, we calculated 3 ventricle size measures: Evan index (frontal horn width divided by widest width of skull inner table), total ventricular volume, and frontal horn volume as ratios of total intracranial volume. Gait was measured by a timed 25-foot walk and cognition by a composite of psychometric tests. We also evaluated variables associated with the measures of ventricular size. Further, we evaluated gait and cognition associations with MRI of extraventricular findings seen in normal-pressure hydrocephalus: disproportionate enlargement of subarachnoid space (DESH) and focal sulcal dilations (FSD). 
 Results Ventricular volume measures had stronger association with gait and cognition measures than EI. In decreasing order of strength of association with ventricle size were DESH, FSD, white matter hyperintensity volume ratio, age, male sex, cortical thickness, and education. Modest evidence was observed that FSD was associated with future decline in gait and cognition. 
 Conclusion Ventricular volume measures are clinically more useful than EI in indicating current and future gait and cognition. Multiple factors are associated with ventricle volume size, including FSD and DESH, suggesting that changes in CSF dynamics may go beyond simple ventriculomegaly. 


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