Quantitation of cerebrospinal fluid shunt flow

Noninvasive cerebrospinal fluid shunt flow measurement by Doppler ultrasound using ultrasonically excited bubbles: a feasibility study

Because normal cerebrospinal fluid (CSF) has almost no natural Doppler scatterers, patency testing of ventriculoperitoneal cerebrospinal fluid shunts (small silastic tubing with lumen diameter of approximately 1 mm draining excessive CSF from the brain) cannot be performed by Doppler ultrasound. We have developed a low-frequency bubble excitation system that generates microbubble scatterers in both distilled water and CSF. Doppler ultrasound can then be used for flow measurement in a ventriculoperitoneal shunt. By using low duty-cycle (approximately 10%), low-frequency (approximately 30 kHz), and low-amplitude (approximately 30 kPa) ultrasound, a population of microbubbles can be maintained for sufficiently long times (>10 min) for Doppler ultrasound measurement, although bubble initiation is inconsistent. The minimum pressure needed for bubble maintenance was found to decrease with increasing burst length and duty cycle. It has been possible to detect the presence of CSF shunt flow down to a mean flow rate of 3 mL/h (mean velocity approximately 0.6 mm/s). The bubble maintenance scheme developed satisfies the safety parameters specified by the American Institute of Ultrasound in Medicine (AIUM) and the US Food and Drug Administration (FDA). Results from both in vitro and in vivo (externalized shunts) experiments indicate the feasibility of this scheme for determining realistic CSF shunt flows, though some practical problems remain before the technique will be ready for clinical use.

Detection of CSF flow in the ventriculo-Peritoneal shunt using MRI

OBJECTIVE

A noninvasive test for shunt function would be beneficial in the management of patients with CSF shunting. We present our method to diagnose shunt function using MRI.

MATERIALS AND METHODS

We performed two experiments. In the first we simultaneously performed MRI of two tubes, one with water flowing inside at various flow speeds and the other with static water inside, and compared the signal intensity inside each lumen. In the second we took four MR images of the actual shunt tubes in three patients at different states of shunt function, each having a tube containing static water pasted side by side with the actual subcutaneous shunt tube.

RESULTS

In the first experiment we could detect the enhancement effect of slow flow. The minimal detectable flow speed using this method was approximately 1.7 ml/h. The result obtained in actual patients matched the clinical status of the shunt function.

CONCLUSION

This method would be useful as a qualitative test for shunt function.

Useful components of the shunt tap test for evaluation of shunt malfunction

Results of shunt tap were studied in 224 clinically or radiologically suspected instances of shunt malfunction. In 130 retrospectively studied patients the results of the tap had reported the opening pressure and ease of aspiration. In 94 prospectively studied instances the shunt tap parameters described were (i) the opening pressure, (ii) the drip interval, i.e., the interval between the drops of cerebrospinal fluid when the open end of the butterfly used for tapping was placed 5 cm below the level of the valve, and (iii) the closing pressure. The efficacy of the aspiration procedure for proximal malfunction was 40.3%, compared with the efficacy of drip interval which was 95.1%. For distal malfunction, the efficacy of measurement of opening pressure was 54.3% whereas that of closing pressure was 60.6%. An in vitro model of a functioning shunt showed that the opening and the closing pressures were related to the flow rate and the level of the distal catheter tip with respect to the valve, whereas the drip interval was linearly related to the flow through the proximal catheter and was independent of the distal catheter position. The opening pressure, closing pressure, and the drip interval recorded at surgery were not significantly different from the values obtained by shunt tap. The results suggested that shunt tap accurately provides information otherwise obtained at surgery and the drip interval is most useful for evaluating a proximal malfunction. The subjective impression of the distal flow may be more helpful in diagnosing distal malfunction rather than the absolute level of opening or closing pressures.

Evaluation of cerebrospinal fluid shunt function in hydrocephalic children using 99mTc-DTPA

The increasing numbers and survival of children with shunt-treated hydrocephalus make it mandatory to refine the methods for cerebrospinal fluid (CSF) shunt function evaluation. Radionuclide shuntography with 99mTc-DTPA, which has proved to be a safe and effective method, was performed in eight children with suspected CSF-shunt dysfunction. Characteristic shuntography patterns were found for proximal and distal CSF-shunt catheter obstruction as well as for overdrainage and normal CSF-shunt function. Shuntography contributed to the explanation of suspected CSF-shunt dysfunction in all children investigated.

Determination of cerebrospinal fluid shunt obstruction with magnetic resonance phase imaging

The cerebrospinal fluid (CSF) flow rates in 12 patients with symptoms suggestive of CSF shunt obstruction were measured with magnetic resonance (MR) phase imaging. The shunts were imaged over the skull, just distal to any reservoir, using a curved surface coil. Images perpendicular to the direction of flow were made on a 1.5-tesla clinical unit with a flow-sensitive pulse sequence. The patients' ages ranged from 2 months to 28 years. All patients had ancillary investigations to determine the functional status of the shunt. No flow was detected in seven patients with blocked shunts. Flow rates between 3 and 40 cc/hr were found in three patients with functioning shunts. Two patients, one with a blocked shunt and one with a functioning shunt, could not be imaged due to motion artifact. Magnetic resonance phase imaging is a promising technique in the determination of CSF shunt obstruction.

Scintigraphic study of cerebrospinal fluid shunts

This paper deals with experience gained in the study of patency of different types of shunt. Results of subsequent surgery are considered. Findings of 79 scintigraphic studies with radiotechnetium on 68 patients are presented. The method is simple, quick, easy to reproduce and means only moderate radiation load for the patient. Results obtained suggest that this study is a reliable diagnostic tool which can be used in a routine way.

Dynamic changes of cerebrospinal fluid shunt flow in patient's daily life

The shunt flow rate will be greatly influenced by the changing posture of the patient. A newly designed method of assessing shunt flow rate by isotope clearance is described and the results of phantom experiments and clinical data are presented. This method makes it possible to assess shunt flow rates in a variety of postures, such as recumbent, or head raised or as posture changes from recumbent to sitting and eventually to upright. As patients changed from the recumbent to the sitting position, shunt flow rates ceased in some cases. In cases with low flow rates in the recumbent position, shunt flow rate increased with any elevation of the upper half of the body. In many cases, flow rates increased as the patient's position changed from recumbent to sitting and then to the upright position. The results suggest that shunt flow rates vary substantially as postures alter in a patient's daily life.

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 Ringer's solution.

The use of shunting devices for cerebrospinal fluid in Canada

The use of diversionary CSF shunting devices for the treatment of hydrocephalus has been surveyed in Canada. Various factors influencing the operation of shunting devices, the characteristics of commercial shunts and the causes of shunt malfunction are described. Suggestions are made as to how to reduce the incidence of shunt malfunction.

In vitro evaluation of CSF shunt function by radionuclides

An in vitro study of clearance of a radiolabeled marker was conducted on nine commonly used shunting devices. Clearance of 0.5 ml of 113mIn-diethylenetriamine-pentaacetic acid (DTPA) injected into the chamber, by water infused through the system at constant rate (0.034-0.46 ml/min), was measured by monitoring activity over the chamber and accumulating counts at 5-s intervals on a multichannel analyzer. Each flow rate was triplicated, and a graph of log value of counts versus time made. A mean t1/2 was computed for each flow rate and a new graph constructed. A best-fit curve constructed for the graph of each shunt system allows determination of flow rate for a known half time of isotope clearance.

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.

The false fontanel

In the neonate, palpation of the anterior fontanel is recognized as a simple and reliable means for estimating intracranial pressure. With closure of the fontanel this aspect of the clinical examination is lost. The authors report a series of 15 shunted infants and children in whom a false fontanel was created by making a 2-cm craniectomy in the right parietal region and excising the underlying internal pericranium. This produces a cranial opening which, like the anterior fontanel, can be used for palpation and real-time ultrasound imaging of the brain. By removing the internal pericranium, reossification of the defect is delayed by more than 12 months. Sparing the dura propria avoids the risks of cerebrospinal fluid leak or brain herniation into the cranial window. This procedure is reported to be simple, reliable, and of value in assessing shunt function in hydrocephalic infants and young children. An illustrative case report is presented.

Radionuclide estimation of cerebrospinal fluid shunt flow. Evidence supporting an alternative theoretical model

Flow of cerebrospinal fluid through a surgically implanted valve may be estimated by analyzing the disappearance curve resulting from the injection of a radiotracer into the valve. The standard method for estimating flow assumes an exponential disappearance of the tracer from the valve. This method models the valve as a single well-mixed compartment. Experimental evidence, showing that estimates of flow were dependent upon the site of injection, is at variance with this assumption. An alternative method of analyzing the disappearance curves, based on the area to height ratio (A/H) of the curves, was found to be more consistent with the experimental evidence and resulted in greater precision than the exponential method. It was concluded that optimal results are obtained using the A/H method with a fixed injection technique.

Radionuclide demonstration of ventriculoatrial shunt-cutaneous fistula with cerebrospinal fluid leak

Radionuclide techniques have commonly been used to assess ventriculovenous shunt function, cerebrospinal fluid dynamics, and for the diagnosis of cerebrospinal fluid leaks. All of these techniques were utilized in this unusual case of retrograde migration of a ventriculoatrial catheter into the neck, with cutaneous fistulization and CSF leak.

Determination of CSF shunt patency with a lumbar infusion test

✓ The authors report on the potential role of the lumbar infusion technique in the determination of cerebrospinal fluid (CSF) shunt patency. The test was performed in a series of 12 patients and reliably predicted shunt patency. This method of assessment proved to be superior to computerized tomography scanning because of its ability to demonstrate the CSF dynamics rather than the ventricular size.

A new method for measuring cerebrospinal fluid flow in shunts

An implantable device for measurement of cerebrospinal fluid (CSF) flow in a ventriculoperitoneal shunt tube has been developed. The unit is energized by an extracorporeal high-frequency generator (200 KHz), and electrolysis creates bubbles in the shunt tube. Velocity of bubble flow is detected by a pair of ultrasonic Doppler probes placed a certain distance apart on the skin surface and in parallel with the implanted tube. The CSF flow rate is calculated taking into account velocity and tube diameter, and is expressed in ml/min. The unit consists of a coil with a capacitor, a silicon diode to rectify the high frequency, and a Zener diode to regulate maximum output voltage of 20 V. The output is fed to a pair of platinum electrodes placed inside the unit's tunnel through which the CSF flows. These components are molded in epoxy resin and coated with medical-grade silicone rubber. In animal experiments, CSF flow rates ranging from 0.033 to 1.0 ml/min could be measured by this flowmeter. Clinically, CSF flow has been measured to date in several cases. In two cases of communicating hydrocephalus occurring after the onset of cerebrovascular disease, and in which the CSF flow was continuously monitored for 24 hours, the flow rate ranged between 0.05 and 0.78 ml/min. The CSF flow rate fluctuates in a 24-hour period, increasing in the morning, especially between 12 midnight and 6 a.m., which suggests a circadian rhythm.

A noninvasive approach to quantitative measurement of flow through CSF shunts. Technical note

A method of measuring flow rate through cerebrospinal fluid (CSF) shunts is reported. It consists of two thermistors in series applied to the skin over the shunt tubing. The thermistors respond by a drop in measured temperature following application of an ice cube placed on the skin overlying the proximal shunt tube. The time required for the thermal response to travel between the two thermistors is related to the velocity of flow through the shunt tubing. Flow rate can then be calculated using the internal diameter of the tubing. A series of animal experiments employing a constant infusion of mock CSF through subcutaneously implanted shunt tubing showed excellent correlation between calculated flow rates and actual infusion rates. The device is noninvasive and easily adapted to use in patients. The measurements are readily repeatable.

Quantitative cisternography

By quantitative cisternography using a stationary detector system with correction for tissue background, an exponential elimination of 131I-HSA from the basal cisterns was demonstrated, allowing calculation of a biologic half time (BHT) of the clearance curve of a satisfactory level of reproducibility. 'Normal' range of BHT was calculated. Demented patients had significantly longer BHT. In 4 patients with normal pressure hydrocephalus prolonged BHT turned normal after shunting, paralleled by marked clinical improvement, in contrast to previous findings in 4 patients with presenile dementia. The method is now being modified employing 111In-DTPA and a computer assisted gamma camera for regional dynamic analysis.

Determination of cerebrospinal fluid shunt function with water-soluble contrast medium

Determination of cerebrospinal fluid shunt patency with water-soluble contrast medium is a simple, rapid, reliable, and safe technique. Since September, 1974, the authors performed 113 examinations. With the Spitz-Holter valve, only the atrial catheter can be studied, but, with the Pudenz valve and with the shunting devices that have a double-dome reservoir, both the proximal and the distal catheter can be visualized. Through the ventricular catheter a full ventriculographic study can be made, demonstrating ventricular size, malposition of the catheter, and the lesion that caused the hydrocephalus, or its evolution. The problem of collapsed ventricules, in which clinical and "manual" evaluation of the flushing device can give misleading findings, is emphasized. The injection of the atrial or peritoneal catheter in the pathological cases demonstrated its blockage, level of disconnection, malposition, sleeve, or cyst formation. Computerized tomography has only slightly decreased the number of these studies: when the ventricles are large, the examination with water-soluble contrast medium is still needed to demonstrate the exact level of malfunction. This demonstration has decreased the number of the total revisions complete changes of shunting systems, eliminating some unnecessary changes of normally functioning catheters.