Eldon L. Foltz

Hydrocephalus: Overdrainage by ventricular shunts. A review and recommendations

Selected literature review of the clinical course of patients with ventricular shunts for hydrocephalus shows that the effects of cerebrospinal fluid overdrainage are subdural hematoma, craniosynostosis, slit ventricle syndrome, and low intracranial pressure syndrome. These occur sequentially at different age groups, but approximate averages of incidence and time of occurrence after first shunt reveal an overall incidence of 10%-12% for at least one of these appearing at 6.5 years after shunting. The basic etiology, diagnosis, and variety of treatment modalities available are reviewed, including the need for shunt closing intracranial pressure control. Included is a hydrocephalus program designed to minimize the need for long-term extracranial shunts and to maximize therapeutic intracranial procedures for hydrocephalus.

Diagnosis of hydrocephalus by CSF pulse-wave analysis: A clinical study*

Pulsatility of the cerebrospinal fluid (CSF) is augmented in hydrocephalus. Analysis of pulsatility, including the CSF waveform, may be a more valid criterion for the diagnosis of hydrocephalus than mean CSF pressure. To test this possibility, CSF pressures were measured in 118 patients with presumed hydrocephalus. The pressure measurements included baseline mean pressure and pulse pressure, responses to jugular compression, and CSF wave analysis (amplitude and peak latency). Four groups of pressure recordings were identified and matched with four clinical groups: normal, arrested hydrocephalus, communicating hydrocephalus, and aqueduct stenosis hydrocephalus. The CSF pulse pressure and systolic slope form were highly reliable in the diagnosis of hydrocephalus, whereas mean CSF pressure was not reliable.

CSF pulsatility in hydrocephalus: respiratory effect on pulse wave slope as an indicator of intracranial compliance

The effect of inspiration and expiration on the systolic slope of the cerebrospinal fluid (CSF) pulse wave has been studied in 83 shunted and non-shunted patients undergoing diagnostic tests for suspected hydrocephalus. A ratio of the systolic CSF pulse slope on inspiration to the same in expiration (I/E ratio or index) has proved statistically valid in identifying non-hydrocephalic patients from hydrocephalic patients and in separating hydrocephalic patients into arrested, communicating and aqueductal stenosis hydrocephalus. The I/E ratio depends on the comparative damping effect of intracranial venous venting on the systolic CSF pulse slope during inspiration (I) when venous volume is evacuated from the cranium by negative mediastinal pressure, and during expiration (E) when cranial venous volume flow to heart is minimal due to positive mediastinal pressure. The low cranial venous outflow on expiration produces little effect on the normal damping of the systolic CSF pulse slope. The high venous outflow on inspiration produces a loss of damping, causing a high systolic CSF pulse slope. Therefore, exhausted cranial venous volume, or exhausted intracranial compliance, produces an I/E ratio approaching 1.0, whereas a normal I/E ratio is between 2.0 and 3.0. The I/E ratio can presumably be used to assess intracranial compliance changes occurring before the dangerous late intracranial pressure (ICP) upward surge related to the volume-pressure curve in all clinical problems of increasing ICP. The I/E ratio may be used likewise to assess the urgency of treatment for any hydrocephalus and increased intracranial pressure problem, i.e. the closer to unity the greater the urgency.

Hydrocephalus : slit ventricles, shunt obstructions, and third ventricle shunts : a clinical study

In a retrospective 5 year study of patients with ventricle shunts for hydrocephalus (N = 88), studies were developed on slit ventricles in teenagers and in young adults. These studies presented here are (1) time to slit ventricles from first shunt and average upright ICP associated (N = 24); (2) upright ICP in asymptomatic long-term ventricle shunt patients without slit ventricles (N = 21), (3) clinical course of patients with uncorrected slit ventricles and lateral ventricles or third ventricle shunts (N = 31), (4) resolution of slit ventricles by Zero ICP Shunt with normal upright ICP (N = 28), (5) no resolution of slit or large ventricles in shunted patients with normal upright ICP (N = 23), and (6) unreliability of CT ventricle size (slit or enlarged) after normal upright ICP achieved (N = 28; 23). Surprisingly, slit ventricle patients with the ventricular catheter in collapsed lateral ventricles develop shunt obstruction within 20 months (21/31; 71%; 10/31 29%) patients with ventricle catheters incidentally in the third ventricle did not obstruct during the 4 1/2 year follow-up.

Auditory brainstem response in infant hydrocephalus

Fifteen infants with hydrocephalus ranging in age from 32 to 43 weeks from conception were studied. The auditory brainstem response (ABR) was measured 48 h prior to the placement of a CSF shunt and within 5 days following shunt insertion. Results of this study showed a general improvement in the ABR following placement of the shunt. No consistent patterns were observed that allowed a clear explanation of the cause and effect of the abnormal ABR. However, the changes seen in the ABR are caused by increased CSF pressure, which may compress the transmission fibers, and generators of the ABR producing a type of neuropraxis. Early shunting appears to have a better outcome on the ABR than later shunting.

Hydrocephalus: increased intracranial pressure and brain stem auditory evoked responses in the hydrocephalic rabbit.

The auditory evoked response (AER) was used to study the effect of increased intracranial pressure (ICP) on the auditory pathway in normal New Zealand rabbits and in those made hydrocephalic by intracisternal injections of kaolin. AERs were studied: (a) in the normal and then in the hydrocephalic animal; and (b) in the hydrocephalic animal during further ICP elevation by cerebrospinal fluid infusion. The AER was obtained from ongoing electroencephalographic activity after rarefaction auditory clicks presented at 90 dB sound pressure equivalent. In comparing base line normal AERs to those found in hydrocephalic conditions, a statistically significant increase in latency for AER components N2, P2, and P5 was noted in hydrocephalic rabbits. Increased ICP in the hydrocephalic model showed an increase in the latencies of AER components for P0 and P1 at 250 mm H2O, and a prolongation of P3-P5 central conduction time at 700 mm H2O above base line cerebrospinal fluid pressure. In addition, a decrease in the P4/N5 amplitude and an increase in P1-P3 central conduction times at 700 mm H2O was observed. The differences between normal and hydrocephalic rabbit AER base lines may be the result of the chronically increased ICP and presumed chronic anatomical changes within the auditory pathway due to kaolin itself. The differences in the AER from base line hydrocephalus to acute increased ICP may indicate that the hydrocephalic system is more sensitive to acute neuropraxic pressure effects on the brain stem auditory structures than is the normal brain.

Hydrocephalus: the zero ICP ventricle shunt (ZIPS) to control gravity shunt flow

Significant morbidity from ventricle shunt overdrainage at 6–7 years after initial shunt placement for hydrocephalus is increasingly recognized as due to excessive gravity-flow of shunted CSF when upright. Shunts are designed primarily to control high ICP. Shunts should also mimic normal upright ICP. Normal upright ICP is -65 mm of water (vertex reference), indicating that a level of zero ICP exists at 65 mm below the brain vertex, with negative ICP above and positive ICP below that level. This normal zero ICP level must be maintained by CSF shunts to mimic normal upright ICP. This will prevent and correct CSF shunt overdrainage. The zero ICP shunt (ZIPS) by design controls this zero level with a zero pressure device (ZPD; siphon control device) installed at the normal vertical level of zero ICP (cm/mm) below the vertex (65 mm). The shunt thus prevents excessive gravity-induced CSF shunt flow. Successful use of ZIPS in 56 patients is reported (low ICP group: n = 42; high ICP group: n = 14). Follow-up is up to 4.5 years. Results show that: (1) adjustability of ZPD level can achieve the desired clinical results; (2) the level of ZPD installed correlates within 4 mm of upright ICP attained; (3) the optimal level of ZPD installation to produce normal upright ICP is 65 mm below the vertex; (4) CT ventricle size, both slit ventricles and large ventricles, may or may not normalize when normal upright ICP is attained in this group of complex, previously shunted patients.

Head trauma and nonsurvival—a sample survey

A retrospective survivor study of 42 patients with severe brain and multisystem injury is presented. All patients were treated with vigorous trauma/neurosurgical techniques. Thirty-seven patients in this series had a Glasgow Coma Score of 3 at the initial examination, and none survived. Since all 37 patients at initial emergency room evaluation showed persistent apnea at 40-60 minutes after injury, a diagnosis of dead on arrival (DOA) might have been appropriate. Cost analysis shows that the direct cost for the 37 cases was

Symptomatic low intracranial pressure in shunted hydrocephalus

27,000 per patient, or

Double compartment hydrocephalus--a new clinical entity.

990,000 for the 37 patients with no survivors. A diagnosis of DOA would have been