CSF SPACES IN IDIOPATHIC NORMAL-PRESSURE HYDROCEPHALUS - MORPHOLOGY AND VOLUMETRY

PURPOSE: Idiopathic normal pressure hydrocephalus (NPH) is an importan t cause of dementia in the elderly; however, idiopathic NPH is often d ifficult to differentiate from normal aging and vascular dementias in which brain atrophy with ventricular dilatation (hydrocephalus ex vacu o or central atrophy) is present. To elucidate the distinctive feature s of the distribution of CSF in idiopathic NPH, we used MR imaging to investigate the morphologic features and volume of the CSF space in pa tients with idiopathic NPH compared with those with other dementias. M ETHODS: We assessed the size of four CSF compartments (the ventricle, basal cistern, sylvian space, and suprasylvian subarachnoid space) in 11 shunt-responsive patients with idiopathic NPH by semiquantitative a nd volumetric analyses of coronal T1-weighted MR images. The results w ere compared with those in 11 age- and sex-matched patients with Alzhe imer disease and in 11 patients with vascular dementia. RESULTS: In pa tients with idiopathic NPH, the CSF volume was significantly increased in the ventricles and decreased in the superior convexity and medial subarachnoid spaces as compared with patients with other dementias. Th e sylvian CSF volume in patients with idiopathic NPH was significantly greater than in patients with Alzheimer disease. The volume of the ba sal cistern was comparable among the three groups. In several patients with idiopathic NPH, focally dilated sulci were observed over the con vexity or medial surface of the hemisphere. CONCLUSION: Our results in dicate that findings of enlarged basal cisterns and sylvian fissures a nd of focally dilated sulci support, rather than exclude, the diagnosi s of shunt-responsive idiopathic NPH and suggest that this condition i s caused by a suprasylvian subarachnoid block.