Is it possible to make a diagnosis of idiopathic normal pressure hydrocephalus on MRI/CT?

Abstract

In 2004, Japanese guidelines for idiopathic normal pressure hydrocephalus (iNPH) were created to diagnose it more precisely and treat it more effectively. The guidelines suggested the importance of a tight cerebrospinal fluid (CSF) space at the high convexity area. We reviewed MRI/CT findings in 38 cases of probable iNPH during Jan. 1998 to Dec. 2003. We noted the tightness in the interhemispheric fissure on axial MRI/CT view. Thirty-three cases were shunt-responsive among 38 cases (shunt effectiveness: 86.8%). MRI/CT findings of iNPH on axial view were classified into typical, almost typical and atypical. Major findings of typical cases showed: 1) ventricular dilatation, 2) tight interhemispheric fissure, 3) dilated Sylvian fissure. Almost all of the typical cases were a little bit questionable on findings for 2) and/or 3). Atypical cases showed an absence of finding 2) or showed aqueductal stenosis. Among 33 the shunt-responding cases, ten cases (30%) were typical, 16 cases (49%) were almost typical and seven cases were atypical. Among the 5 cases of non-responders, they were divided into 2, 2 and 1 cases, respectively. Atypical cases included 2 cases of aqueductal stenosis and 5 cases of open interhemispheric fissure; the latter were difficult to differentiate form brain atrophy. Thus, about 80% of iNPH cases could be diagnosed or highly suspected on axial MRI/CT findings. Although MRI/CT findings were not definitive for making a diagnosis of iNPH, they were highly useful to idenitify patients for a CSF tap test.