Effects of neck position and head elevation on intracranial pressure in anaesthetized neurosurgical patients: preliminary results

This study reports the collective effect of the positions of the operating table, head, and neck on intracranial pressure (ICP) of 15 adult patients scheduled for elective intracerebral surgery. Patients were anesthetized with propofol, fentanyl, and maintained with a propofol infusion and fentanyl. Intracranial pressure was recorded following 20 minutes of stabilization after induction at different table positions (neutral, 30 degrees head up, 30 degrees head down) with the patient's neck either 1) straight in the axis of the body, 2) flexed, or 3) extended, and in the five following head positions: a) head straight, b) head angled at 45 degrees to the right, c) head angled at 45 degrees to the left, d) head rotated to the right, or e) head rotated the left. For ethical reasons, only patients with ICP < or = 20 mm Hg were included. Intracranial pressure increased every time the head was in a nonneutral position. The most important and statistically significant increases in ICP were recorded when the table was in a 30 degree Trendelenburg position with the head straight or rotated to the right or left, or every time the head was flexed and rotated to the right or left-whatever the position of the table was. These observations suggest that patients with known compromised cerebral compliance would benefit from monitoring ICP during positioning, if the use of a lumbar drainage is planed to improve venous return, cerebral blood volume, ICP, and overall operating conditions.     

Cerebrospinal fluid pressure monitoring after repair of cerebrospinal fluid leaks.

OBJECTIVE: To measure intracranial pressures (ICPs) via lumbar drains after surgical repair of cerebrospinal fluid (CSF) leaks. METHODS: We conducted a retrospective review of ICP measurements through lumbar drains during the immediate postoperative period after CSF leak repair. RESULTS: Eight patients with spontaneous CSF leaks underwent surgery and postoperative CSF pressures were measured via lumbar drains. ICP was elevated in 7/8 patients (mean, 32.5 cm H(2)O). Diuretics reduced ICP (mean, 10 cm H(2)O). Three traumatic CSF leaks patients served as controls (mean, ICP 14 cm H(2)O). CONCLUSION: Measurement of ICP through lumbar drains provides important information regarding the pathophysiology of CSF leaks that has an impact on subsequent medical and surgical treatment. Although the precise cause and mechanism of spontaneous CSF leaks are not fully understood, this study indicates that elevated ICP plays a role and that further medical or surgical treatment to correct the intracranial hypertension may be warranted.     

Positive end-expiratory pressure in supine and sitting positions: its effects on intrathoracic and intracranial pressures

The effects of positive end-expiratory pressure (PEEP) on central venous and intracranial (ICP) pressures were evaluated in 10 patients with posterior fossa tumors, in both supine and sitting positions. With patients in the supine position, intrathoracic PEEP-dependent venous hypertension was clearly transmitted to the intracranial compartment but without intracranial hypertension. On the contrary, with patients in the sitting position PEEP had no influence in almost half of our patients. In patients with radiological or clinical signs of increased ICP, however, the combination of head flexion and rotation with institution of PEEP caused a dangerous increase in ICP, even when the patients were in the sitting position. The need for early withdrawal of cerebrospinal fluid in these patients is stressed.     

Mechanical effects of leg position on vertebral structures examined by magnetic resonance imaging

BACKGROUND AND OBJECTIVES: Leg manipulation has been postulated to affect spinal curvature and position of the cauda equina within the dural sac. However, no evidence of such mechanical effects has been shown in living subjects. We used magnetic resonance imaging to evaluate the mechanical effects of leg position on these 2 parameters. METHODS: Sagittal and axial magnetic resonance images of the lumbosacral vertebral canal were obtained in 5 healthy, female volunteers with the subject in the supine position with knees straight, knees slightly flexed, and knees fully flexed. RESULTS: In the straight leg position, physiologic lumbar lordosis was evident in all subjects on midline sagittal slices, whereas lumbar lordosis disappeared in the fully flexed leg position. On the axial slices the cauda equina moved ventrally within the dural sac in all subjects in the fully flexed leg position. In 1 of the 5 subjects the cauda equina moved ventrally and also separated completely into right and left parts. CONCLUSIONS: Our findings indicate that 2 potential factors, flattening of the lumbar lordosis and some added tension on the lumbosacral nerve roots, may contribute to postoperative back and leg aching after spinal anesthesia in the lithotomy position.     

Effects on intracranial pressure of dural puncture in supine and head-elevated positions. A study on the cat

BACKGROUND: Lumbar dural puncture may reduce intracranial pressure (ICP) due to a hydrostatic pressure gradient created by distal opening of the spinal fluid column towards the atmosphere. The magnitude of the reduction in hydrostatic force on the brain should depend on the vertical distance between the brain and the dural opening, and thus will increase by head elevation. No studies have analyzed ICP after dural puncture in supine and upright positions. METHODS: This study on the cat records ICP, mean arterial pressure, and central venous pressure before and after dural puncture in supine and head-elevated positions. The dural puncture was performed at a level corresponding to the lumbar region. Results: Initially ICP was 10.9 +/- 1.9 mmHg (mean +/- SD), which decreased to 5.1 +/- 2.0 mmHg after 24.5 cm (18 mmHg) of head elevation (n = 7). Intracranial pressure decreased to 5.2 +/-3.5 mmHg following dural puncture in the supine position and to -11.3 +/- 4.2 mmHg after the head elevation (n = 7). Active drainage of CSF fluid in the supine position in a volume similar to that spontaneously drained after head elevation reduced ICP by 2.0 +/- 0.5 mmHg (n = 3). CONCLUSIONS: The results show that a significant ICP reduction may occur following opening of the spinal canal. The reduction can be explained more by hydrostatic forces than by loss of CSF; also explaining why it is more significant when upright than supine. The decrease in ICP increases transvascular pressure, which may induce the disappearance of the normally present subdural venous collapse with an increase in venous blood volume.     

Effects of enflurane and isoflurane on resistance to reabsorption of cerebrospinal fluid in dogs

Using the technique of ventriculocisternal perfusion, resistance to reabsorption of cerebrospinal fluid (Ra) was calculated from determinations of the rate of reabsorption of cerebrospinal fluid (Va) at differing cerebrospinal fluid pressures in dogs. Ra was examined during prolonged anesthesia (5.0-6.0 h) with enflurane (2.2%, end expired) or isoflurane (1.4%, end expired). Compared with previously reported normal values for Ra in dogs (220-224 cmH2O . ml-1 . min), enflurane increased Ra to 274 +/- 4 cmH2O . ml-1 . min (mean +/- SEM), and isoflurane decreased Ra to 104 +/- 1 cmH2O . ml-1 . min. The alterations of cerebrospinal fluid (CSF) dynamics caused by enflurane, namely increase of both Ra and the rate of production of cerebrospinal fluid (Vf), may contribute to the sustained increase of intracranial pressure observed during prolonged anesthesia with enflurane. In contrast, the different alterations of CSF dynamics caused by isoflurane, namely decrease of Ra with no change in Vf, may explain, in part, why minimal increase of intracranial pressure is observed during prolonged anesthesia with isoflurane. Because decreased Ra improves spatial compensation by cerebrospinal fluid volume for increased intracranial pressure, isoflurane may offer an advantage over enflurane in patients at risk because of increased intracranial pressure.     

The effect of cerebrospinal fluid drainage on cerebral perfusion in traumatic brain injured adults

Cerebrospinal fluid drainage is a first line treatment used to manage severely elevated intracranial pressure (> or = 20 mm Hg) and improve outcomes in patients with acute head injury. There is no consensus regarding the optimal method of cerebrospinal fluid removal. The purpose of this investigation was to determine whether cerebrospinal fluid drainage decreases intracranial pressure and improves cerebral perfusion and to identify factors that impact treatment effectiveness. This study involved 31 severely head injured patients. Intracranial pressure and other indices of cerebral perfusion (cerebral perfusion pressure, cerebral blood flow velocity, and regional cerebral oximetry) were measured before, during, and after cerebrospinal fluid drainage. Arterial and jugular venous oxygen content was measured before and after cerebrospinal fluid drainage. Patients underwent three randomly ordered cerebrospinal fluid drainage protocols that varied in the volume of cerebrospinal fluid removed (1 mL, 2 mL, and 3 mL) for a total of 6 mL of cerebrospinal fluid removed. There was a significant change in the intracranial pressure from a mean at baseline of 26.1 mm Hg (SD = 4.4) to 22.1 mm Hg immediately after drainage. One third of patients experienced a decrease in the intracranial pressure below 20 mm Hg; in two patients the intracranial pressure dropped less than 1 mm Hg. The following factors predicted 61.5% of the variance in the responsiveness of intracranial pressure to drainage: vecuronium hypothermia, baseline cerebral perfusion pressure and acuity of illness. Cerebrospinal fluid drainage provides a transient decrease in intracranial pressure without a measurable improvement in other indices of cerebral perfusion.     

颈椎手术并发脑脊液漏的处理

目的 探讨颈椎手术并发脑脊液漏（CSFL）的处理方法及其疗效。方法 对11例颈椎手术并发CSFL的患者,后路手术采用自体筋膜修补2例,前路手术采用自体筋膜明胶海绵堵塞9例,手术后仍存在CSFL患者采取去枕头高足低位、延长脱水剂应用时间、行腰穿蛛网膜下腔引流。结果 2例后路手术CSFL患者修补成功。9例前路行硬膜堵塞患者4例仍有CSFL,行腰穿蛛网膜下腔引流,切口引流或漏出0—3d停止．切口在引流后7d拆线均愈合。结论 CSFL术中采用修补或堵塞硬膜破口术后采用头高足低位、延长脱水剂应用时间可减少手术后CSFL的发生;术后持续腰穿蛛网膜下腔引流,能有效终止切口内CSFL,有利于切口愈合,避免感染发生。     

Cerebrospinal fluid and plasma vasopressin during short-time induced intracranial hypertension

Summary The response of plasma and ventricular cerebrospinal fluid vasopressin concentration to short-time induced intracranial hypertension was studied in 8 patients with hydrocephalus, defined as ventricular enlargement on computerized tomography. In connection with measurement of conductance to cerebrospinal fluid outflow, the concentration of vasopressin in plasma and cerebrospinal fluid was measured during perfusion at a low (20 mmHg) intraventricular pressure level. Mean plasma vasopressin concentration was increased from 2.4±0.4pg/ml (SEM) during perfusion at the low pressure level to 4.2±0.8 pg/ml (p<0.01) at the high pressure level. The cerebrospinal fluid concentrations of vasopressin at the low and high intraventricular pressure were 1.2 ±0.1pg/ml and 1.7±0.2 pg/ml (p<0.05), respectively. However, only half of the patients responded to the increase in intraventricular pressure with an increase in cerebrospinal fluid vasopressin concentration exceeding 50%. The results of the present study suggest that an increase in the intracranial pressure might be a stimulus for vasopressin release in both the blood and the cerebrospinal fluid.     

Effect of hydrocephalus on prostaglandins and thromboxane B2 in ventricular cerebrospinal fluid

The concentrations of prostaglandin F2 alpha, prostaglandin E2, 6-ketoprostaglandin F1 alpha (prostacyclin metabolite), and thromboxane B2 were assayed in ventricular cerebrospinal fluid obtained from 28 patients with hydrocephalus (17 obstructive, 11 communicating). Seven patients received dexamethasone or hydrocortisone on the day of sampling. No patient received nonsteroidal anti-inflammatory compounds for 48 hours before sampling. The median values did not differ significantly between the two types of hydrocephalus or from the concentrations in lumbar cerebrospinal fluid obtained from patients without intracranial pathology during lumbar myelography for possible lumbar disc disease. Hence, there is no evidence that eicosanoids accumulate in the ventricles in hydrocephalus, and it is unlikely that they have a significant role in its symptomatology.     

Intraoperative jugular bulb desaturation during acute aneurysmal rupture

PURPOSE: To describe an episode of acute jugular venous desaturation during intraoperative rupture of a cerebral aneurysm. CLINICAL FEATURES: A 57-yr-old patient was scheduled for clipping of a large unruptured basilar tip aneurysm. Abrupt bulging of the brain was observed after bone flap removal, but before dura was opened. This was associated with concurrent development of systemic hypertension to 200/120 mmHg and jugular venous bulb (S(jv)O(2)) desaturation to 13%. Rupture of aneurysm was confirmed by frank blood in cerebrospinal fluid drainage from the lumbar subarachnoid catheter. CONCLUSIONS: Abrupt S(jv)O(2) desaturation prior to dural opening may suggest an acute increase in intracranial pressure, which in our case followed aneurysmal rupture; the systemic response to increased intracranial pressure (Cushing's response) may be ineffective in maintaining cerebral perfusion.     

Lumbar cerebrospinal fluid pressure waves versus intracranial pressure waves in idiopathic normal pressure hydrocephalus

The aim of this study was to explore how the lumbar cerebrospinal fluid pressure (CSFP) waves recorded during lumbar infusion compared with the intracranial pressure (ICP) waves recorded, either during lumbar infusion or during long-term, overnight monitoring. For this purpose, we assessed 27 simultaneous lumbar CSFP/ICP recordings made during lumbar infusion and 27 long-term, overnight ICP recordings in 27 consecutive idiopathic normal pressure hydrocephalus (iNPH) patients. Pressure waves during lumbar infusion were explored by computing pulse pressure amplitude and mean single wave pressure of every corresponding CSFP/ICP wave pair; among our 27 lumbar CSFP/ICP recordings a total of 35,532 CSFP/ICP wave pairs were available for analysis. We as well computed mean values of pulse pressure amplitude (i.e. mean CSFP wave amplitude or mean ICP wave amplitude) and mean values of mean single wave pressure (i.e. mean CSFP or mean ICP) during consecutive 6-s time windows, as well as average values for the individual recordings. During lumbar infusion, the cerebrospinal fluid pulse pressure amplitudes were about 2 mmHg smaller than the corresponding intracranial pulse pressure amplitudes. The mean CSFP wave amplitudes recorded during lumbar infusion correlated significantly with the mean ICP wave amplitudes recorded either during lumbar infusion or during long-term, overnight ICP monitoring. In 21 of 27 lumbar infusion tests (78%), the presence of elevated lumbar mean CSFP waves was related to presence of elevated mean ICP wave amplitudes during long-term, overnight ICP monitoring. Hence, the lumbar cerebrospinal fluid pulse pressure amplitudes recorded during lumbar infusion could be used to predict the intracranial pulse pressure amplitudes recorded during long-term, overnight ICP monitoring.     

Effet de la position sur la pression intracrânienne

The question as to whether the head and trunk of neurosurgery patients should be elevated remains controversial. This question is particularly important when intracranial hypertension is present. Head up position may have beneficial effects on intracranial pressure (ICP) via changes in mean arterial pressure (MAP), airway pressure, central venous pressure and cerebro spinal fluid displacement. However, in some circumstances, head up position may decrease MAP which in turn will result in a paradoxical rise in ICP through autoregulation mechanisms. Therefore, the degree of head elevation has to be titrated by evaluating the most adequate cerebral perfusion pressure (CPP) for each patient by means of transcranial Doppler or measurement of jugular venous blood oxygen saturation. Head elevation above 30° should be avoided in all cases. In most patients with intracranial hypertension, head and trunk elevation up to 30° is useful in helping to decrease ICP, providest that a safe CPP of at least 70 mmHg or even 80 mmHg is maintained. Patients in poor haemodynamic conditions are best nursed flat. CPP is thus the most important factor in assessment and monitoring when considering head elevation in patients with increased ICP.     

The role of arterial and venous pressure for volume regulation of an organ enclosed in a rigid compartment with application to the injured brain

BACKGROUND: Treatment of increased intracranial pressure often includes an active change in arterial and venous pressure, sometimes with draining of cerebrospinal fluid. We evaluated tissue and perfusion pressure during corresponding interventions in an organ enclosed in a rigid compartment with capillaries permeable for electrolytes and impaired autoregulation, conditions comparable to those present in the injured brain. METHOD: An isolated cat skeletal muscle enclosed in a closed fluid-filled plethysmograph served as a model for the injured brain surrounded by cerebrospinal fluid and the cranium. Tissue pressure and blood flow were measured during variation in arterial and venous pressures and in intraplethysmographic fluid volume. Autoregulation was depressed by papaverine. RESULTS: 1) Tissue pressure was not influenced by the venous pressure when this was below the tissue pressure, hereby generating venous collapse and a venous outflow resistance. When venous pressure was higher than the tissue pressure (no venous outflow resistance), these two parameters changed in parallel. 2) A change in arterial pressure induced a similar large change in tissue pressure at steady state, whereas blood flow remained unchanged. 3) Variation in tissue pressure induced by a change in the intraplethysmographic fluid volume was transient. CONCLUSIONS: If applicable to the injured brain, the results indicate that 1) a venous pressure change has a small influence on the intracranial pressure when a venous outflow resistance is present, 2) brain oedema can be reduced by lowering of the arterial inflow pressure, and blood flow will be maintained, 3) the decrease in intracranial pressure obtained by draining cerebrospinal fluid will be transient.     

Evaluation of mechanism of increased intracranial pressure with insufflation

Background: Previous studies have documented an increase in intracranial pressure with abdominal insufflation, but the mechanism has not been explained. Methods: Nine 30–35-kg domestic pigs underwent carbon dioxide insufflation at 1.5 l/min. Intracranial pressure (ICP), lumbar spinal pressure (LP), central venous pressure (CVP), inferior vena cava pressure (IVCP), heart rate, systemic arterial blood pressure, pulmonary arterial pressure, cardiac output, heart rate, respiratory rate, temperature, and end-tidal CO₂ were continuously measured. Mechanical ventilation was used to maintain a constant pCO₂. Measurements were recorded at 0, 5, 10, and 15 mmHg of abdominal pressure with animals in supine, Trendelenburg (T), and reverse Trendelenburg (RT) positions. Prior to recording measurements, the animals were allowed to stabilize for 40 min after each increase in abdominal pressure and for 20 min after each position change. Results: The animals showed a significant increase in ICP (mmHg) with each 5-mmHg increase in abdominal pressure (0 mmHg: 14 ± 1.7; 5 mmHg: 19.8 ± 2.3, p < 0.001; 10 mmHg: 24.8 ± 2.5, p < 0.001; 15 mmHg: 29.8 ± 4.7, p < 0.01). The ICP at 15 mmHg abdominal pressure increased further in the T position (39 ± 4, p < 0.01). Insufflating in the RT position did not significantly reduce the increase in ICP. The IVCP (mmHg) increased with increased abdominal pressure (0 mmHg: 11.5 ± 6.2, 15 mmHg: 22.1 ± 3.5, p < 0.01). This increase correlated with the increase in ICP and LP (r of mean pressures ≥0.95). There was no significant change in CVP. Conclusions: This study suggests that care may be needed with laparoscopy in patients at risk for increased ICP due to head injury or a space occupying lesion. The mechanism of increased ICP associated with insufflation is most likely impaired venous drainage of the lumbar venous plexus at increased intraabdominal pressure. Further studies of cerebral spinal fluid movement during insufflation are currently underway to confirm this hypothesis. Received: 28 March 1997/Accepted: 5 August 1997     

Cerebral perfusion pressure, intracranial pressure, and head elevation

Previous investigations have suggested that intracranial pressure waves may be induced by reduction of cerebral perfusion pressure (CPP). Since pressure waves were noted to be more common in patients with their head elevated at a standard 20 degrees to 30 degrees, CPP was studied as a function of head position and its effect upon intracranial pressure (ICP). In 18 patients with varying degrees of intracranial hypertension, systemic arterial blood pressure (SABP) was monitored at the level of both the head and the heart. Intracranial pressure and central venous pressure were assessed at every 10 degrees of head elevation from 0 degree to 50 degrees. For every 10 degrees of head elevation, the average ICP decreased by 1 mm Hg associated with a reduction of 2 to 3 mm Hg CPP. The CPP was not beneficially affected by any degree of head elevation. Maximal CPP (73 +/- 3.4 mm Hg (mean +/- standard error of the mean] always occurred with the head in a horizontal position. Cerebrospinal fluid pressure waves occurred in four of the 18 patients studied as a function of reduced CPP caused by head elevation alone. Thus, elevation of the head of the bed was associated with the development of CPP decrements in all cases, and it precipitated pressure waves in some. In 15 of the 18 patients, CPP was maintained by spontaneous 10- to 20-mm Hg increases in SABP, and pressure waves did not occur if CPP was maintained at 70 to 75 mm Hg or above. It is concluded that 0 degree head elevation maximizes CPP and reduces the severity and frequency of pressure-wave occurrence. If the head of the bed is to be elevated, then adequate hydration and avoidance of pharmacological agents that reduce SABP or prevent its rise are required to maximize CPP.     

Conjunctival oedema as a potential objective sign of intracranial hypertension: a short illustrated review and three case reports

Periorbital and conjunctival oedema has been reported anecdotally by patients with raised intracranial pressure states. We present three clinical cases of this phenomenon and discuss the current evidence for pathways by which cerebrospinal fluid (CSF) drains in relation to conjunctival oedema. We reviewed the available literature using PubMed, in regards to conjunctival oedema as it relates to intracranial hypertension, and present the clinical history, radiology and orbital photographs of three cases we have observed. Only one previous publication has linked raised intracranial pressure (ICP) to conjuctival oedema. The weight of evidence supports the observation that the majority of CSF drains along the cranial nerves as opposed to via the arachnoid projections. Conjunctival oedema may be a clinical manifestation of CSF draining via the optic nerve in elevated ICP states.     

A combined spinal-epidural technique for labor analgesia and symptomatic relief in two parturients with idiopathic intracranial hypertension

Idiopathic intracranial hypertension is a condition consisting of increased intracranial pressure of unknown etiology, predominantly affecting obese women of childbearing age. Symptomatic relief can be provided by lumbar puncture and withdrawal of cerebrospinal fluid, and the technique has been described in laboring women using an intrathecal catheter. We present two patients who achieved both labor analgesia and symptomatic relief via a combined spinal-epidural technique with small volume cerebrospinal fluid withdrawal. Both women complained of headache of at least a 5 on a 10-point pain scale at the time of labor induction. Between 5 and 6 mL of cerebrospinal fluid were withdrawn at the time of combined spinal-epidural insertion and pain relief was successfully achieved with patient-controlled epidural anesthesia. One patient proceeded to cesarean delivery for fetal indications under epidural anesthesia. Both women described significant improvement in headache symptoms that persisted until discharge from hospital, and neither developed new neurologic symptoms. A combined spinal-epidural technique with a small volume of cerebrospinal fluid withdrawal may provide labor analgesia and symptomatic relief in the parturient with idiopathic intracranial hypertension.     

Effect of head-down tilt on intracranial pressure and sagittal sinus pressure during general anesthesia in cats.

The effect of head-down tilt during general anesthesia on intracranial pressure (ICP) dynamics was examined in eight cats. Changes in lateral ventricular pressure (LVP), sagittal sinus pressure (SSP), and effective CSF pressure (ECSFP), which is the driving pressure of cerebrospinal fluid (CSF) absorption, were studied in association with a shift from the horizontal prone position to the 20 degrees head-down tilt position. Both LVP and SSP values were significantly (P < 0.01) increased at 10 min in the head-down tilt position as compared with the control position, remained elevated during the next 110 min, and returned to baseline when the horizontal position was restored. However, ECSFP (expressed by LVP - SSP) was not significantly different from the control value, because changes in LVP and SSP were similar. These results suggest that head-down tilt does not impair CSF absorption.     

Appraisal of cerebrospinal fluid alterations during aortic surgery with intrathecal papaverine administration and cerebrospinal fluid drainage

We have previously described a technique for intrathecal administration of papaverine and cerebrospinal fluid drainage to prevent paraplegia after aortic surgery. Herein we report the cerebrospinal fluid and hemodynamic alterations that occurred in 11 patients who had 30 mg of a specially prepared papaverine hydrochloride 10% dextrose solution injected before aortic cross-clamping and also had cerebrospinal fluid drainage. A mean of 26.6 ml (SD +/- 7.1 ml) was drained before and 34.6 ml (SD +/- 24.1 ml) was drained during aortic cross-clamping. The cerebrospinal fluid pressure increased significantly with anesthetic induction (p less than 0.03), during the period between anesthetic induction and cerebrospinal fluid drainage (p less than 0.005), and with aortic cross-clamping (p less than 0.05). These cerebrospinal fluid pressure alterations were similar to central venous pressure increases with a significant linear correlation between cerebral spinal fluid pressure and central venous pressure before anesthetic induction (r2 = 0.81, p less than 0.005), and both before (r2 = 0.94, p less than 0.005) and after (r2 = 0.74, p less than 0.005) aortic cross-clamping. As expected, cerebrospinal fluid pressure was significantly reduced by cerebrospinal fluid drainage before aortic cross-clamping (p less than 0.001). The administration of intrathecal papaverine had no significant effect on mean arterial pressure, systemic vascular resistance, cerebrospinal fluid pressure, nor the pH of cerebrospinal fluid. Neither were there any complications noted related to the technique. All the patients survived, and no new immediate postoperative paraparesis or paraplegia occurred.(ABSTRACT TRUNCATED AT 250 WORDS)