CSF Dynamics and Pressure-volume Relationships in Communicating Hydrocephalus
Normal-pressure hydrocephalus or communicating hydrocephalus are more or less synonymous designations of a potentially treatable condition. Twenty-nine patients with this diagnosis were studied. In 17 cases the etiology was unknown. In 3 patients etiology was subarachnoid hemorrhage. The following studies were undertaken. 1) continuous intracranial pressure (ICP) monitoring by means of an intraventricular catheter; 2) pressure-volume studies; and 3) measurement of resistance to outflow of cerebrospinal fluid (Rout)- The two latter were studied by the bolus injection or pressure-volume index (PVI) technique. In 19 patients mean ICP never exceeded 15 mmHg. In the other 10 patients varying degrees of mildly raised ICP was noted. The frequency of 1/2 to 2/min. waves varied from 3% to 58%. PVI ranged from 4.6 to 18.2 ml, which is below what is considered normal limits. No explanation for this highly abnormal pressure-volume condition could be offered.