Communicating Hydrocephalus. Normal Pressure Hydrocephalus

Abstract

Communicating hydrocephalus is defined as a CSF flow circulation abnormality outside the ventricular system that produces an increase in the ventricular size. Most cases are secondary to obstruction of CSF flow between the basal cisterns and brain convexity and include common conditions such as subarachnoid hemorrhage and meningitis (infectious and neoplastic). In a subset of communicating hydrocephalus, no CSF obstruction can be demonstrated as occurs in normal pressure hydrocephalus (NPH), a complex entity with poorly understood CSF dynamics. Clinical neuroradiology plays an essential role in the diagnosis of communicating hydrocephalus and in distinguishing this condition from other causes of ventriculomegaly (central atrophy, non-communicating hydrocephalus).

NPH is a syndrome characterized by the triad of gait disturbance, mental deterioration, and urinary incontinence, associated with ventriculomegaly and normal cerebrospinal fluid (CSF) pressure. Although NPH represents a major cause for reversible and treatable dementia, this syndrome is frequently underdiagnosed. The clinical presentation (triad) may be atypical or incomplete or mimicked by other diseases, hence the need for supplementary tests, particularly to predict postsurgical outcome, including different radiological techniques such as computed tomography (CT) or magnetic resonance imaging (MRI). According to international guidelines, CT or MRI is decisive for NPH diagnosis and selection of shunt-responsive patients. These techniques provide essential morphological findings: ventricular enlargement associated with tight high convexity and medial subarachnoid sulci and enlarged Sylvian fissures (disproportionally enlarged subarachnoid space hydrocephalus [DESH]), ballooning of frontal horns, reduction of the callosal angle, corpus callosum thinning, and widening of temporal horns not explained by hippocampal atrophy. Other imaging methods such as radionuclide cisternography or cardiac-gated flow-sensitive phase-contrast cine MRI, although suitable for NPH diagnosis, do not yet provide improved accuracy for identifying shunt-responsive cases. In summary, morphological MRI features still play an essential role in the diagnosis of NPH and also in predicting a positive clinical outcome after shunting.

This publication is endorsed by: European Society of Neuroradiology (www.esnr.org).