Idiopathic normal pressure hydrocephalus: correlating magnetic resonance imaging biomarkers with clinical response.

Idiopathic Normal Pressure Hydrocephalus (NPH) is a debilitating condition of the elderly. The patient is typically "wet, wobbly and wonky", to different degrees of the triad. The diagnosis is supported by the radiologic finding of dilated ventricles, determined by an elevated Evan's Index (EI) without a demonstrable cause. Patients with newly diagnosed NPH typically respond to ventriculo-peritoneal shunting (VPS). NPH-related dementia is possibly the only surgically reversible dementia. An elevated cerebrospinal fluid (CSF) fl ow rate (FR) is associated with a positive response to shunting. However, post-shunting EI and FRs are unpredictable. Of late, intracranial apparent diffusion coefficient (ADC) quantification via Diffusion Weighted Imaging (DWI) has been emerging as a possible marker in NPH diagnosis. A local study, conducted on a national level, to study the relationship of EI, FR and ADC to pre- and post-shunt clinical measurements has just ended. This review seeks to reconcile the current thinking of NPH, magnetic resonance imaging (MRI) quantification and clinical evaluation, and in the process shed some light on major pathophysiological determinants of the disease.

Value of quantitative MRI biomarkers (Evans' index, aqueductal flow rate, and apparent diffusion coefficient) in idiopathic normal pressure hydrocephalus.

PURPOSE: To define the value of Evans' index (EI), aqueductal flow rate (FR), and apparent diffusion coefficient (ADC) in the diagnosis of normal pressure hydrocephalus (NPH) and to assess the ability of these markers preoperatively to predict shunt response. To shed some light as to the mechanisms responsible for the symptoms of NPH. MATERIALS AND METHODS: Preoperative EI, FR, and ADC readings in nine cases of clinically diagnosed NPH were compared with those of age- and gender-matched controls. Similar pre- and postoperative readings of responders and nonresponders were subsequently compared. RESULTS: Compared with the controls, all measurements were statistically significant except for peak systolic flow rate (pSfr), which was near statistical significance. Comparison of pre- and postoperative readings of responders and nonresponders revealed a decrease in ADC in all responders (P = 0.032). Subdural hemorrhage was found in all nonresponders (P = 0.012). CONCLUSION: For patients presenting with signs and symptoms of NPH, readings on MRI greater than 0.3, 10 mL/min, -9.0 mL/min, and 10.65 x 10(-4) mm(2)/s for EI, peak diastolic flow rate (pDfr), pSfr, and ADC, respectively, add further weight to the diagnosis. The strong correlation between shunt response and ADC decline support our hypothesis that water accumulation in the cerebrum is the major cause for the symptoms of NPH. The presence of subdural hemorrhage in all nonresponders raises suspicion of decreased compliance as the other major cause.