Correlation between tap test and CSF aqueductal stroke volume in idiopathic normal pressure hydrocephalus.

ABSTRACT

INTRODUCTION: The diagnosis and management of idiopathic normal pressure hydrocephalus (INPH) remains unclear despite the development of guidelines. In addition, the role of cerebrospinal fluid (CSF) aqueductal stroke volume (ASV) remains unspecified. OBJECTIVES: The aim of this study was to compare the results of the tap test (TT) and ASV in patients with possible INPH. MATERIALS AND METHODS: Among 21 patients investigated with both TT and phase-contrast (PC) MRI, we identified two groups, with either (1) a positive TT (PTT) or (2) a negative one (NTT), and we compared their ASV as measured by PC-MRI. ASV cutoff value was set at 70 µL/cardiac cycle (mean value +2 standard deviations in age-matched healthy subjects). RESULTS: In the PTT group (n = 9), the mean ASV was 175 ± 71 µL. Among these patients, four were shunted, and improved after surgery. In the NTT group, two patients were finally diagnosed with aqueductal stenosis and excluded. Among the remaining patients (n = 10), the mean ASV was 96 ± 93 µL (p < 0.05). However, three of these patients presented with hyperdynamic ASV, and an associated neurodegenerative disorder was diagnosed. Two patients had ventriculoperitoneal shunting despite their NTT, and improved. DISCUSSION/CONCLUSIONS: In our patient population, the noninvasive measurement of hyperdynamic ASV correlated with PTT, suggesting PC-MRI could be utilized to select those patients who would benefit from shunting. ASV may therefore be an interesting supplemental diagnosis tool.