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.