Baseline radiological parameters associated with good neurological outcome following ventriculoperitoneal shunt in normal pressure hydrocephalus: A single-center study on 82 patients

Background: Idiopathic normal pressure hydrocephalus (iNPH) is a benign neurologic condition with treatment response rates ranging only between 30 and 50%. Several studies have attempted to identify clinical or radiological predictive factors of a favorable and sustained response to shunting, with conflicting and inconclusive results. With this report, we aimed to define the role of the Evans index (EI), enlargement of temporal horns, lateral ventricular bulges, and isolated elements of disproportionally enlarged subarachnoid spaces (high-convexity tightness and sulcal focal dilation) in predicting outcomes following ventriculoperitoneal shunt (VPS) placement. Methods: All patients referred to Ospedali Riuniti of Ancona, Italy, from 2010 to 2021 were retrospectively examined for evaluation of iNPH. Clinical notes and neuroimaging were reviewed. After screening, 82 patients undergoing VPS procedures for iNPH were included in this series. Most (82.9%) patients were aged >65, with a male-to-female ratio of 1.92:1. Results: Small baseline EI was associated with a significant improvement in gait apraxia scores (0.36 ± 0.04 vs. 0.40 ± 0.05, P = 0.04) and urinary incontinence episodes (0.38 ± 0.03 vs. 0.40 ± 0.05, P = 0.04). An EI > 0.40 was associated with a reduced likelihood of gait improvement (30.2%) in contrast to symptom stability or worsening (53%, P = 0.03). Similarly, an EI > 0.40 was associated with a reduced likelihood of continence improvement compared to stability or worsening of episode frequency (21.8% vs. 54%, P = 0.004). The presence of moderately compressed or obliterated cortical sulci was associated with a significant improvement of modified Rankin scale (mRS) functional status following surgery compared to patients with no convexity tightness (78% vs. 49.1%, P = 0.02 and 39.1% vs. 16.9%, P = 0.03, respectively). A large preoperative EI was predictive of poor response in the domains of gait apraxia (odds ratio [OR] = 0.001, 95% confidence interval [CI]: 0.001-0.4, P = 0.004) and urinary continence (OR = 0.001, 95% CI: 0.001-0.3, P = 0.003). The strongest predictors of improved mRS performance status were moderately (OR= 3.72, 95% CI: 1.22-11.35, P = 0.02) or severely compressed cortical sulci (OR= 3.15, 95% CI: 1.07-9.26, P = 0.03). Conclusion: The EI is a significant parameter predictive of enhanced gait function and urinary continence postsurgery. Furthermore, noteworthy evidence supports the association of high-convexity tightness with improved overall functional scores following surgical intervention.