Intracranial cerebrospinal fluid measurement studies in suspected idiopathic normal pressure hydrocephalus, secondary normal pressure hydrocephalus, and brain atrophy.

Objective: To investigate intracranial cerebrospinal fluid (CSF) distribution in patients with a clinical diagnosis of idiopathic normal pressure hydrocephalus (INPH).

Methods: 24 patients with a clinical diagnosis of INPH were studied. Control groups comprised 17 patients with secondary normal pressure hydrocephalus (SNPH), 21 patients with brain atrophy, and 18 healthy volunteers. Ventricular volume (VV) and intracranial CSF volume (ICV) were measured using a magnetic resonance based method and the VV/ICV ratio was calculated.

Results: The SNPH group showed a marked increase in the VV/ICV ratio compared with the healthy volunteers (37.8% v 15.6%, p < 0.0001). The brain atrophy group showed a significant increase in ICV compared with the healthy volunteers (284.4 ml v 194.7 ml, p =0.0002). The INPH group showed an increase in ICV (281.2 ml, p = 0.0002) and an increase in the VV/ICV ratio (38.0%, p < 0.0001). Fifteen of 24 INPH patients underwent shunting; 11 improved and four did not.

Conclusions: The results suggest that INPH patients have brain atrophy in addition to hydrocephalic features. This may help to explain the difficulties encountered in the diagnosis and the unpredictable response rate to shunt surgery in INPH patients.