Arachnoid cysts are space-occupying lesions filled with CSF-like content and surrounded by a membrane resembling arachnoid matter. They are regarded as a development abnormality of the arachnoid, originating from a splitting or duplication of this membrane. However, precise etiology and natural history remain controversial. Different hypotheses have been developed including agenesis of brain structures, arachnoiditis, active fluid secretion, and pulsatile pump. We present a review of the literature concerning these items and report one case of a suprasellar arachnoid cyst in which a slit-valve mechanism was observed by means of cine-mode MRI preoperatively and confirmed during the endoscopic intervention.

In addition to age and histologic grade, abnormalities of chromosome 14 contribute to a better prognostic stratification of meningioma patients at diagnosis. Additional prospective studies in larger series of patients, also including larger numbers of patients who experienced relapse, are necessary to confirm the utility of the proposed predictive model.

Objectives-The fibreoptic device is a type of intracranial pressure monitor which seems to oVer certain advantages over conventional monitoring systems. This study was undertaken to analyse the accuracy, drift characteristics, and complications of the Camino® fibreoptic device. Methods-One hundred and eight Camino® intracranial pressure (ICP) devices, in their three modalities, were implanted during 1997. The most frequent indication for monitoring was severe head injury due to road traYc accidents. Results-Sixty eight probe tips were cultured; 13.2% of the cases had a positive culture without clinical signs of infection, and 2.9% had a positive culture with clinical signs of ventriculitis. The most common isolated pathogen was Staphylococcus epidermidis. All patients were under cephalosporin prophylaxis during monitoring. Haemorrhage rate in patients without coagulation disorders was 2.1% and 15.3% in patients with coagulation abnormalities. Drift characteristics were studied in 56 cases; there was no drifting from the values expected according to the manufacturer's specifications in 34 probes. There was no relation between direction of the drift and duration of placement, nor between drift and time. Conclusions-Although the complication and drift rates were similar to those reported elsewhere, there was no correlation between the direction of the drift and long term monitoring despite the fact that some published papers refer to overestimation of values with time with this type of device. (J Neurol Neurosurg Psychiatry 2000;69:82-86)

PURPOSE: Nonlinear dynamics has enhanced the diagnostic abilities of some physiological signals. Recent studies have shown that the complexity of the intracranial pressure (ICP) waveform decreases during periods of intracranial hypertension in paediatric patients with acute brain injury. We wanted to assess changes in the complexity of the cerebrospinal fluid (CSF) pressure signal over the large range covered during the study of CSF circulation with infusion studies. METHODS:We performed 37 infusion studies in patients with hydrocephalus of various types and origin (median age 71 years; interquartile range 60-77 years). After 5 minutes of baseline measurement, infusion was started at a rate of 1.5 ml/minute until a plateau was reached. Once the infusion finished, CSF pressure was recorded until it returned to baseline. We analyzed CSF pressure signals using the LempelZiv (LZ) complexity measure. To characterize more accurately the behaviour of LZ complexity, the study was segmented into four periods: basal, early infusion, plateau and recovery. RESULTS:The LZ complexity of the CSF pressure decreased in the plateau of the infusion study compared to the basal complexity (p=0.0018). This indicates loss of complexity of the CSF pulse waveform with intracranial hypertension. We also noted that the level of complexity begins to increase when the infusion is interrupted and CSF pressure drops towards the initial values. CONCLUSIONS:The LZ complexity decreases when CSF pressure reaches the range of intracranial hypertension during infusion studies. This finding provides further evidence of a phenomenon of decomplexification in the pulsatile component of the pressure signal during intracranial hypertension.