Mitsuo Numoto

Cine magnetic resonance imaging of aqueductal stenosis

Cerebral aqueductal stenosis is one of the most common causes of congenital and acquired hydrocephalus, but the etiology, pathophysiology and cerebrospinal fluid (CSF) dynamics of aqueductal stenosis have yet to be clarified. Utilizing cardiac gated cine magnetic resonance (MR) imaging, we evaluated aqueductal configuration and pulsatile motion of brain and CSF flow stimulated by cardiac pulsation in five patients with nontumoral aqueductal stenosis. Cine MR of four cases revealed obliteration of the aqueduct by thickening mesencephalic tectum, turbulent CSF flow in the III ventricle, and absence of flow-related signal void, which in all normal cases indicates CSF movement within the aqueduct. In the remaining fifth case, with proximal dilation of the aqueduct resulting from thinning of the tectum, distortion of caudal (distal) tectum related to pulsatile motion of the brain caused funnel-like narrowing of the aqueduct, leading to incomplete obstruction and the absence of upward CSF flow during diastole.

CSF shunt physics: factors influencing inshunt CSF flow

Cerebrospinal fluid (CSF) in a shunt does not have a constant flow rate. The flow fluctuates from 0.01 ml/min to 1.93 ml/min according to each patients own daily supine rhythmic pattern. We determined and evaluated the factors influencing CSF flow in a shunt in 19 cases of hydrocephalus. Postural changes, such as head elevation, led to increases by over 0.04 ml/min in inshunt CSF flow, while inshunt CSF flow in the supine position was less than 0.04 ml/min. Respiratory changes, such as coughing and apnea-hyperventilation, also influenced inshunt CSF flow. Changes in intracranial pressure (ICP) corresponded to changes in inshunt CSF flow. Inshunt CSF flows were higher than average during the night, the flows being stimulated by increases in ICP especially during REM sleep.

Factors Affecting Cerebrospinal Fluid Flow in a Shunt

Nineteen hydrocephalic patients were studied to determine factors affecting cerebrospinal fluid (CSF) flow through shunts. This study was based on our previously reported method by which fluctuations in CSF flow through a shunt of from 0.01 ml min-1 to 1.93 ml min-1 were identified, each having its own rhythmic pattern. While CSF flow in a supine position was less than 0.01 ml min-1, head elevation to 60 degrees led to increases in CSF flow from 0.12 ml min-1 to 0.17 ml min-1. Sudden respiratory changes such as coughing also affected CSF flow. CSF flows were higher than average between 10 pm and 7 am, and changes in CSF flow were related to slight increases in ICP during REM sleep. There is no relationship between CSF flow in a shunt and daily fluid intake which varied from 27 ml kg-1 to 103 ml kg-1, and no significant changes in CSF flow resulting from rapid intravenous injection of Glycerol and Ringers solution.

A non-invasive CSF flowmeter

A new non-invasive method for quantitative measurement of cerebrospinal fluid (CSF) flow in the ventriculo-peritoneal shunt tubing, used in hydrocephalus, has been developed. It is an implantable device which produces a bubble in the shunt tubing by electrolysis. This bubble is then detected in the tubing by an electrode arrangement using electric impedance or ultrasonically using a Doppler probe. The energy for electrolysis is supplied by extracorporeal high-frequency transmission. The CSF flow rate is calculated by the velocity of bubble flow in the tubing. CSF flow rates, ranging from 0.01 to 1.00 ml/min, have been measured in animal experiments with statistically good accuracy. In 11 clinical cases a flow range of between 0.01 and 1.93 ml/min have been observed.

Hydrodynamics and CSF Flow Through a Shunt in Hydrocephalus

It is difficult to predict the benefits of a shunt undergone in normal pressure hydrocephalus [NPH] showing disturbance in CSF dynamics. Therefore, hydrodynamic studies of cerebrospinal fluid [CSF] were evaluated with respect to any improvements in neurological status in eight adult communicating hydrocephalus. CSF flow through a shunt, measured with an inshunt flowmeter developed by the authors, radioisotope [RI] cisternography, clearance of dye (phenolsulfonphthalein, PSP) administered intrathecally, and intracranial pressure [ICP] were compared with changes in clinical features and changes in CT findings. Six of the 8 cases had clinical improvements in neurological symptoms and signs after shunt. Ventricular sizes on serial CT reduced postoperatively to an average 30% (range 23–35) in 7 cases. Scans of RI cisternography of all cases yielded definitely positive results; ventricular reflux in 7, ventricular stasis in 6, convexity stasis in 3, and 6 patients favorably responded to shunt. Dye clearance test revealed that 4 of the 5 cases had disturbed absorption within 70% secretion into urine within 24 hours. Four responded favorably. Mean ICP values in all cases studied were lower than 15 mmHg, 4 of them showed frequent B waves and none showed A wave. Only 3 of the 4 cases with B wave responded to shunt. Daily volumes of CSF flowing in shunt were 42 ml-278 ml with peaks of 0.06 ml/min to 0.46 ml/min. Cases with an average less than 120 ml/day showed improvements in neurological findings after shunt. However, in cases of disturbed CSF absorption with 50% or less dye clearance, daily volume of CSF flowing in shunt tended to exceed 120 ml.

CSF Circulation in Hydrocephalus. A Study of CSF Flow in a Shunt System

A hydrodynamic study of cerebrospinal fluid (CSF) circulation in the presence of hydrocephalus requires measurement of the flow rate of CSF in the ventriculo-peritoneal shunt tube. Although a variety of methods for such measurement have been reported, most are not capable of continuous or intermittent monitoring without the use of injection or other surgical procedures.

A Simple Clinical ICP Meter

Since the importance of monitoring the intracranial pressure (ICP) was pointed out by Lundberg et al. in 1965 (2), a number of papers have been published on the methods of measuring the ICP. They could be classified into two major categories. One is a group of simple, practical and non-electronic devices and the other is a group of more elaborate electronic instruments. Each has its own advantages and disadvantages over others. Unfortunately, no ideal perfect device has yet been seen on the market. Therefore, one has to chose a device by compromising with its performances and one’s specific requirements.

Dynamic Response of Subdural Screw Bolt for Intracranial Pressure Measuring

The subdural screw bolt, with all its variations [1, 2, 3], remains a common method for ICP monitoring in clinical practice and experimental studies [2, 4, 5, 6]. Since the first report by Vries et al. [1], many authors have tried to improve the static performance of this device. When the lumen is occluded by brain tissue, or a blood clot, the ICP tends to be underestimated when the pressure is high [7]. Regardless of the occlussion and the resulting falsely low pressure reading, the CSF pulsations are preserved. Some workers have produced modified versions of the original screw [2, 3]. Dearden et al. [2] and Shields et al. [9] have designed infusion and flush techniques to solve this problem.

The Application of ICP Monitoring in Deciding Surgical Management

Patients are often encountered who do not require immediate surgery but for whom strict follow-up of intracranial pathophysiology is necessary for fear of an enlarging hematoma, the occurrence of a delayed hematoma, and the development of herniation. In such cases, the ideal procedure during the pre-surgery period is for intracranial pressure (ICP) monitoring, and neurological and CT follow-ups and so on to be performed in conjunction with medical treatment.

Estimation of Intracranial Pressure in Acute Subarachnoid Hemorrhage Based on CT

The predictive values of certain features of computed tomography (CT) scans in estimating intracranial pressure (ICP) were investigated during the acute stage of subarachnoid hemorrhage (SAH) to determine if noninvasive CT can be useful for the identification of patients not requiring ICP monitoring.