Reappraisal of the intracranial pressure and cerebrospinal fluid dynamics in patients with the so-called ?Normal pressure hydrocephalus? syndrome

Abstract

Fifty-four shunt-responsive patients were selected from a prospective protocol directed to study patients with suspected normal pressure hydrocephalus (NPH). Patients with gait disturbances, dementia, non-responsive L-Dopa Parkinsonism, urinary or faecal incontinence and an Evans ratio greater or equal to 0.30 on the CT scan were included in the study. As a part of their work-up all patients underwent intracranial pressure monitoring and hydrodynamic studies using Marmarou's bolus test. According to mean intracranial pressure (ICP) and the percentage of high amplitude B-waves, patients were subdivided in the following categories: 1) Active hydrocephalus (mean ICP above 15 mmHg), which is in fact no tone normal pressure hydrocephalus; 2) Compensated unstable hydrocephalus, when mean ICP was below 15 mmHg and B-waves were present in more than 25% of the total recording time and 3) Compensated stable hydrocephalus when ICP was lower or equal to 15 mmHg and beta waves were present in less than 25% of the total recording time. The majority of the patients in this study (70%) presented continuous high or intermittently raised ICP (active or unstable compensated hydrocephalus group). Mean resistance to outflow of CSF (Rout) was 38.8 mm Hg/ml/min in active hydrocephalus and 23.5 mm Hg/ml/min in the compensated group (Students t-test, p less than 0.05). Higher resistance to outflow was found in patients with obliterated cortical sulci and obliterated Sylvian cisterns in the CT scan. No statistically significant correlation was found when plotting the percentage of beta waves against pressure volume index (PVI), compliance or Rout. An exponential correlation was found when plotting beta waves against the sum of conductance to outflow and compliance calculated by PVI method (r = 0.79). Patients with the so-called normal pressure hydrocephalus syndrome have different ICP and CSF dynamic profiles. Additional studies taking into consideration these differences are necessary before defining the sensitivity, specificity and predictive value of ICP monitoring and CSF studies in selecting appropriate candidates for shunting.

Guidelines for Management of Idiopathic Normal Pressure Hydrocephalus: Second Edition

“…18,57,68,108,110) Lumbar subarachnoid pressure is the most frequently measured 8,10,18,25,31,57,68,96,108,141) ; however, there are also studies measuring parenchymal pressure, 34,35) intraventricular pressure, 110) and epidural pressure. 109,113,127,131) The following 3 items are examined during the measurement. 1) Baseline ICP: The shunt procedure is effective in cases with high baseline ICP, and the threshold is approximately 90-200 mmH 2 O.…”

“…1) Baseline ICP: The shunt procedure is effective in cases with high baseline ICP, and the threshold is approximately 90-200 mmH 2 O. 10,18,57,68,113) Many cases show pressure that is closer to the upper limit of normal pressure. Conversely, some studies report that there is no correlation between the baseline ICP and the efficacy of shunting.…”

“…68) The higher their incidence becomes (more than 15% of all records), the more effective is the shunt procedure. 18,57,113,131) Conversely, some studies report that there is no correlation between the appearance of B-waves and the efficacy of shunting. 31,108,109,141) 3) CSF pulse pressure: Increased amplitude together with decreased latency of the ICP pulse wave are noted in most of shunt-effective cases.…”

“…The values vary depending on the site of injection (lumbar site 19,22,59,88,113,131) ), speed of injection (at a constant injection speed 19,22,59,109,113) or bolus injection 131) ), and ICP measurement site (lumbar subarachnoid pressure 19,22,59,88) or epidural pressure 113,131) ); however, the values are not affected by lesions of the meninges or cerebral parenchyma.…”

“…1) CSF outflow resistance (R out ): In previous reports, R out was significantly elevated in shuntingeffective groups and its positive predictive rate was over 80%. 19,59,113,131) However, the absolute value of R out and the threshold between shunting-effective and -ineffective were reported as approximately 14-20 mmHg/ml/min (positive predictive rate 80-92%), 19,59,131) the value differs according to the method of injection. Moreover, many recent studies report that there is no correlation between R out and the efficacy of shunting.…”