[Continuous intracranial pressure monitoring in normal pressure hydrocephalus--with special reference to clinical significance of B wave and prognostic criteria for CSF shunting].

The authors investigated the hydrodynamics in normal pressure hydrocephalus (NPH) and suggested surgical indication for identifying cases suitable for shunt operation. 48 patients with presumed NPH who underwent CT scanning, CT cisternography, and continuous monitoring of intracranial pressure for 24 hours were studied for assessing the correlation of incidence of B wave with clinicopathological features of the normal pressure hydrocephalus syndromes. The causes of NPH consisted of idiopathic of primary origin in 24 patients, subarachnoid hemorrhage in 9, head injury in 8, cerebrovascular occlusion in 3, meningitis in 2, intracerebral hematoma in one and craniotomy in one. The incidence of B waves in term of percentage of time with B waves did not correlate with the age of the patients and presence or absence of CT evidence of brain atrophy. There was a good correlation between incidence of B waves and the degree of ventriculomegaly, the presence of periventricular lucency on CT, and the grade of CSF circulation disturbance as evaluated by CT cisternography. The pathogenesis of B waves may be related to increased malabsorption of CSF in the major pathways and episodic pressure response promoting CSF absorption in the lesser pathways. Those patients who exhibit the type IV or type V on CT cisternography and B waves for more than 20% of the time monitored on continuous monitoring of intracranial pressure (ICP) responded to shunting in more than 90%. Patients showing type III-b on CT cisternography and B waves for more than 5% on ICP monitoring benefited from a shunt in about 70%. On the other hand, patients with type III-a on CTC and B waves for less than 5% of the time monitored could not be expected to respond to shunting. Incidence of B waves on continuous ICP monitoring correlated closely with response to CSF shunting. Therefore continuous ICP monitoring, combined with CT cisternography, provide a reliable indication of the potential of a patient with NPH to recover after shunting.