Comparison of Anterior Lateral Ventricular Index with Evans Index, Callosal Angle, and Disproportionately Enlarged Subarachnoid-space Hydrocephalus in Postoperative Evaluation of Idiopathic Normal Pressure Hydrocephalus

This study aimed to compare the anterior lateral ventricular index with established radiological markers, including the Evans Index, callosal angle, and disproportionately enlarged subarachnoid-space hydrocephalus, in evaluating postoperative radiological improvement in patients with idiopathic normal pressure hydrocephalus. A retrospective analysis was conducted on 46 patients who underwent ventriculoperitoneal shunt surgery between January 2019 and February 2025. Pre- and postoperative cranial computed tomography and magnetic resonance imaging scans were used to measure Evans Index, anterior lateral ventricular index, callosal angle and the presence of disproportionately enlarged subarachnoid-space hydrocephalus was assessed. Clinical parameters, including gait performance (10-meter walking and 360° turning steps) and urinary continence, were compared with radiological changes. Both Evans Index and anterior lateral ventricular index significantly decreased postoperatively (Evans Index: 0.388→0.336, p < 0.001; anterior lateral ventricular index: 0.552→0.479, p < 0.001), while callosal angle significantly increased (85.3°→99.7°, p < 0.05). Anterior lateral ventricular index reduction correlated moderately with Evans Index reduction (r = 0.37, p = 0.011) and weakly with callosal angle increase (r = 0.26, p = 0.080). Gait performance improved significantly (p < 0.001), and urinary incontinence resolved in 40.9% of affected patients. Anterior lateral ventricular index reduction showed stronger correlations with gait improvement (r = -0.45, p = 0.002) and continence recovery (r = -0.33, p = 0.024) compared with Evans Index or callosal angle. Disproportionately enlarged subarachnoid-space hydrocephalus positivity was not significantly associated with postoperative outcomes. These findings suggest that anterior lateral ventricular index may provide a more sensitive and clinically relevant linear measure than traditional indices and can serve as a complementary parameter to Evans Index and callosal angle in the postoperative evaluation of idiopathic normal pressure hydrocephalus.