Clinical and technical factors in endoscopic skull base surgery associated with reconstructive success.

BACKGROUND: In this study, we identified key discrete clinical and technical factors that may correlate with primary reconstructive success in endoscopic skull base surgery (ESBS). METHODS: ESBS cases with intraoperative cerebrospinal fluid (CSF) leaks at four tertiary academic rhinology programs were retrospectively reviewed. Logistic regression identified factors associated with surgical outcomes by defect subsite (anterior cranial fossa [ACF], suprasellar [SS], purely sellar, posterior cranial fossa [PCF]). RESULTS: Of 706 patients (50.4% female), 61.9% had pituitary adenomas, 73.4% had sellar or SS defects, and 20.5% had high-flow intraoperative CSF leaks. The postoperative CSF leak rate was 7.8%. Larger defect size predicted ACF postoperative leaks; use of rigid reconstruction and older age protected against sellar postoperative leaks; and use of dural sealants compared to fibrin glue protected against PCF postoperative leaks. SS postoperative leaks occurred less frequently with the use of dural onlay. Body-mass index, intraoperative CSF leak flow rate, and the use of lumbar drain were not significantly associated with postoperative CSF leak. Meningitis was associated with larger tumors in ACF defects, nondissolvable nasal packing in SS defects, and high-flow intraoperative leaks in PCF defects. Sinus infections were more common in sellar defects with synthetic grafts and nondissolvable nasal packing. CONCLUSIONS: Depending on defect subsite, reconstructive success following ESBS may be influenced by factors, such as age, defect size, and the use of rigid reconstruction, dural onlay, and tissue sealants.

Guidelines for management of idiopathic normal pressure hydrocephalus: progress to date.

The aim of this project was to develop evidenced based guidelines for the diagnosis and management of idiopathic normal pressure hydrocephalus (iNPH). An advisory panel consisting of the authors assisted by international experts met on several occasions and formulated preliminary guidelines for iNPH managemen. The authors developed evidentiary tables based on available literature from 1966 to the present. Additional meetings to refine the evidentiary tables and incorporate expert opinion when necessary resulted in the development the iNPH guidelines. Evidence based guidelines identifying the value of clinical examination, brain imaging, Tap Test, CSF drainage, ICP monitoring and Surgical Management in diagnosing and treating the iNPH patient were developed. These are the first international evidence based guidelines focused on iNPH. Class I data were scant and guidelines relied mostly on class II and III evidence. It became clear that more prospective randomized studies are needed to resolve some of the controversial issues such as iNPH classification and sensitivity of diagnostic tests for identifying shunt responsive iNPH.

PET investigation of post-traumatic cerebral blood volume and blood flow.

Hemodynamic changes following traumatic brain injury (TBI) may reflect cellular damage leading to secondary injury. The purpose of this study was to investigate the regional hemodynamic parameters acutely after TBI among regions in and around contusions. Sixteen patients (11 male, 5 female) showing evidence of contusion on CT and 18 normal volunteers (12 male, 6 female) underwent positron emission tomography (PET) with O-15 CO and O-15 H2O to estimate cerebral blood volume (CBV) and cerebral blood flow (CBF), respectively. A flow to volume ratio (FVR = CBF/CBV) was also calculated as an index of vasodilatation. The hemodynamic parameters were compared among contusion, pericontusion, and remote areas. Globally, hemodynamic parameters did not differ between patients and normal volunteers, and did not correlate with intracranial pressure (ICP). Regionally, contusional and pericontusional areas showed significantly lower CBF and FVR compared with normal volunteers, while CBV did not differ significantly. The correlation between CBF and CBV was significant (r = 0.37, p < 0.01). Remote areas did not show a significant difference in any of the PET parameters. In conclusion, regional brain edema is likely to occur in contusion and pericontusion areas, while some of the contusional tissue may show vascular engorgement.

Why valve opening pressure plays a relatively minor role in the postural ICP response to ventricular shunts in normal pressure hydrocephalus: modeling and implications.

OBJECTIVES: In normal pressure hydrocephalus, there is no clear evidence that the opening pressure of differential pressure valves influences outcome. In this study, the objective was to determine whether the relationship between valve opening pressure and post-operative postural ICP changes was predictable. METHODS: Eight adult-onset hydrocephalus patients were evaluated using an intraparenchymal ICP microsensor. Postural ICP measurements were obtained before and after placement of a ventricular shunt (VP or VA) with a Codman Hakim programmable valve. RESULTS: Valve opening pressure had a poor correlation with ICP at any head-of-bed elevation across subjects (best r = 0.25). The degree of negative ICP encountered for any given patient did not appear to be determined by the valve pressure, and varied significantly between patients at the same valve pressure. Each individual's ICP correlated well to opening pressure (r > 0.76), but the response is more sigmoidal than linear, and the opening pressure at which ICP changed most was markedly different between patients. CONCLUSIONS: The hydrodynamic pressures generated by shunts with different pressure valves are unpredictable. Our data supports the use of programmable valves in patients with adult onset hydrocephalus and suggests that ICP be measured post-operatively to achieve an optimal clinical outcome.

Delayed increase in extracellular glycerol with post-traumatic electrographic epileptic activity: support for the theory that seizures induce secondary injury.

Early post-traumatic seizures occur commonly and may have adverse clinical consequences. In order to determine the significance of post-traumatic seizures, we performed a prospective assessment of the consequences of epileptic activity by assessing the change in extracellular glycerol levels. Glycerol is a marker of cellular membrane breakdown. Thirteen patients underwent combined electroencephalography (EEG) and cerebral microdialysis monitoring. Two patients had seizures on EEG with associated delayed elevations of glycerol associated with the seizure activity. Higher mean levels of glycerol were present in those patients with seizures compared to those without seizures (p < 0.001). Preliminary evidence suggests that post-traumatic seizures lead to additional membrane injury as reflected by elevated extracellular glycerol levels.

Evolving concepts of cerebrospinal fluid physiology.

This article reviews the basic known functions of cerebrospinal fluid (CSF). The traditional concepts of CSF production and absorption are reviewed and recent challenges to these concepts are discussed. MR imaging studies have begun to elucidate the complex interaction between pulsatile CSF movement, bulk CSF flow, and intracranial compliance. An understanding of a variety of disorders, including hydrocephalus and Chiari malformations, continue to evolve as knowledge of CSF physiology is increased.

Metabolic recovery following human traumatic brain injury based on FDG-PET: time course and relationship to neurological disability.

OBJECTIVE: Utilizing [(18)F]fluorodeoxyglucose positron emission tomography (FDG-PET), we assessed the temporal pattern and the correlation of functional and metabolic recovery following human traumatic brain injury. DESIGN AND SUBJECTS: Fifty-four patients with injury severity ranging from mild to severe were studied. Thirteen of these patients underwent both an acute and delayed FDG-PET study. RESULTS: Analysis of the pooled global cerebral metabolic rate of glucose (CMRglc) values revealed that the intermediate metabolic reduction phase begins to resolve approximately one month following injury, regardless of injury severity. The correlation, in the 13 patients studied twice, between the extent of change in neurologic disability, assessed by the Disability Rating Scale (DRS), and the change in CMRglc from the early to late period was modest (r = -0.42). Potential explanations for this rather poor correlation are discussed. A review of the pertinent literature regarding the use of PET and related imaging modalities, including single photon emission tomography (SPECT) for the assessment of patients following traumatic brain injury is given. CONCLUSION: The dynamic profile of CMRglc that changes following traumatic brain injury is seemingly stereotypic across a broad range and severity of injury types. Quantitative FDG-PET cannot be used as a surrogate technique for estimating degree of global functional recovery following traumatic brain injury.

Dissociation of cerebral glucose metabolism and level of consciousness during the period of metabolic depression following human traumatic brain injury.

Utilizing [18F]fluorodeoxyglucose positron emission tomography (FDG-PET), we studied the correlation between CMRglc and the level of consciousness within the first month following human traumatic brain injury. Forty-three FDG-PET scans obtained on 42 mild to severely head-injured patients were quantitatively analyzed for the determination of regional cerebral metabolic rate of glucose (CMRglc). Reduction of cerebral glucose utilization, defined as a CMRglc of < or =4.9 mg/100 g/min, was present regionally in 88% of the studies. The prevalence of global cortical CMRglc reduction was higher in severely head-injured patients (86% versus 67% mild-moderate), although the absolute magnitude was similar across the injury severity spectrum (mean CMRglc 3.9 +/- 0.6 mg/100 g/min). The level of consciousness, as measured by the Glasgow Coma Scale, correlated poorly with the global cortical CMRglc value (r = 0.08; p = 0.63). With regards to severity of head injury, this correlation was worst for the severely injured (r = -0.11; p = 0.58) and better for the mildly injured patients (r = 0.50; p = 0.07). In most cases, intraparenchymal hemorrhagic lesions were associated with either focal CMRglc reduction or elevation. It is concluded that the etiologies of CMRglc reduction are likely multifactorial given the complex nature of traumatic brain injury and that the reduction of CMRglc represents a fundamental pathobiologic state following head injury that is not tightly coupled to level of consciousness.

Endoscopic management of cysticercal cysts within the lateral and third ventricles.

OBJECT: In this report the authors review their 3-year experience with the endoscopic management of patients with hydrocephalus who harbored cysticercal cysts within the third and lateral ventricles. The management plan was to utilize an endoscopic approach to remove the cysts and to incorporate techniques useful in treating obstructive hydrocephalus. The ultimate goals were to avoid having to place a complication-prone cerebrospinal fluid shunt and to eliminate the risk of complications related to cyst degeneration. METHODS: A retrospective analysis of 10 patients with hydrocephalus and cysticercal cysts within the third or lateral ventricles who were endoscopically managed was performed. A general description of the instrumentation and technique used for removal of the intraventricular cysts is given. At presentation, neuroimaging revealed findings suggestive of obstructive hydrocephalus in eight patients. Seven of the 10 patients treated endoscopically were spared the necessity of shunt placement. Three successful third ventriculostomies and one therapeutic septum pellucidotomy were performed. Despite frequent rupture of the cyst walls during removal of the cysts, there were no cases of ventriculitis. The endoscopic approach allowed successful removal of a cyst situated in the roof of the anterior third ventricle. One patient suffered from recurrent shunt obstructions secondary to a shunt-induced migration of cysts from the posterior fossa to the lateral ventricles. CONCLUSIONS: The endoscopic removal of third and lateral ventricle cysticercal cysts, combined with a third ventriculostomy or septum pellucidotomy in selected cases, is an effective treatment in patients with hydrocephalus and should be considered the primary treatment for this condition.

Management of hydrocephalus with programmable valves after traumatic brain injury and subarachnoid hemorrhage.

Programmable shunt valves are a recent technological advance that enhance the management of most patients with hydrocephalus secondary to subarachnoid hemorrhage or traumatic brain injury. An improved understanding of the intracranial pressure dynamics occurring both before and after a cerebrospinal fluid diversionary shunt has provided a more scientific basis for the application of these valves.

Increased incidence and impact of nonconvulsive and convulsive seizures after traumatic brain injury as detected by continuous electroencephalographic monitoring.

OBJECT: The early pathophysiological features of traumatic brain injury observed in the intensive care unit (ICU) have been described in terms of altered cerebral blood flow, altered brain metabolism, and neurochemical excitotoxicity. Seizures occur in animal models of brain injury and in human brain injury. Previous studies of posttraumatic seizures in humans have been based principally on clinical observations without a systematic approach to electroencephalographic (EEG) recording of seizures. The purpose of this study was to determine prospectively the incidence of convulsive and nonconvulsive seizures by using continuous EEG monitoring in patients in the ICU during the initial 14 days post-injury. METHODS: Ninety-four patients with moderate-to-severe brain injuries underwent continuous EEG monitoring begin-ning at admission to the ICU (mean delay 9.6+/-5.4 hours) and extending up to 14 days postinjury. Convulsive and nonconvulsive seizures occurred in 21 (22%) of the 94 patients, with six of them displaying status epilepticus. In more than half of the patients (52%) the seizures were nonconvulsive and were diagnosed on the basis of EEG studies alone. All six patients with status epilepticus died, compared with a mortality rate of 24% (18 of 73) in the nonseizure group (p<0.001). The patients with status epilepticus had a shorter mean length of stay (9.14+/-5.9 days compared with 14+/-9 days [t-test, p<0.031). Seizures occurred despite initiation of prophylactic phenytoin on admission to the emergency room, with maintenance at mean levels of 16.6+/-2.8 mg/dl. No differences in key prognostic factors (such as the Glasgow Coma Scale score, early hypoxemia, early hypotension, or 1-month Glasgow Outcome Scale score) were found between the patients with seizures and those without. CONCLUSIONS: Seizures occur in more than one in five patients during the 1st week after moderate-to-severe brain injury and may play a role in the pathobiological conditions associated with brain injury.

Beneficial effect of siphoning in treatment of adult hydrocephalus.

OBJECTIVE: To increase awareness about the treatment of adult patients with shunt-nonresponsive hydrocephalus--a state characterized by marked ventriculomegaly, low intracranial pressure, and a patent cerebrospinal fluid diversionary shunt. DESIGN: Retrospective analysis of hospital and outpatient records. PATIENTS: Four patients with symptomatic ventriculomegaly and patent ventriculoperitoneal shunts treated with a protocol of progressive ventricular hypotension induced by external cerebrospinal fluid drainage. RESULTS: Severe clinical manifestations exhibited by the patients, including parkinsonian features, Parinaud syndrome, and extensor posturing, completely reversed once a normalization of ventricular size was achieved. External ventricular drainage pressures as low as -30 cm H2O were required to reduce ventricular size. All patients finally received a shunt incorporating a standard medium differential pressure valve with no antisiphon device. CONCLUSIONS: Shunt siphoning may be an essential mechanism by which cerebrospinal fluid shunting is effective in many patients with adult hydrocephalus. Cerebrospinal fluid shunts that contain an antisiphon device are ineffective in these patients, despite the attainment of "physiologic" intracranial pressures. Based on reported experimental and clinical evidence, it seems that the cause of this condition may be related to abnormally high intracranial compliance.

Endoscopic removal of cysticercal cysts within the fourth ventricle. Technical note.

There is no consensus as to the optimum management of patients who harbor cysticercal cysts within the fourth ventricle. Compared with the alternative treatment options of anthelmintic medication and/or cerebrospinal fluid shunt placement, the surgical removal of the cyst has the advantage of eliminating the inflammatory nidus and potentially obviating the need for a complication-prone shunt. Here, an endoscopic surgical approach is described and proposed as an alternative to the standard suboccipital craniectomy for removal of cysticercal cysts within the fourth ventricle. A retrospective analysis of five consecutive endoscopic cases was performed. Endoscopic removal of all cysts within the fourth ventricle was successful in each case. The mean length of operative time was short and blood loss was insignificant. The endoscopic procedure was safe and associated with minimal postoperative discomfort in most patients. In properly selected patients, the endoscopic removal of cysticercal cysts located within the fourth ventricle should be considered as the primary treatment for this condition.

Endoscopic resection of colloid cysts: surgical considerations using the rigid endoscope.

OBJECTIVE: Colloid cysts of the third and lateral ventricles have traditionally been treated by transfrontal and transcallosal microsurgical resection or by stereotactic aspiration. Recently, rigid and flexible ventricular endoscopic techniques have been used to treat these lesions. Our study was undertaken to examine the efficacy of rigid endoscopy in the resection of colloid cysts. METHODS: Fifteen patients with a radiological diagnosis of colloid cysts were given the option of undergoing either endoscopic surgery or craniotomy. The average tumor size was 1.43 cm. Fourteen patients underwent planned endoscopic resections, and a craniotomy was performed initially in one patient. RESULTS: Entire tumor resection was achieved with the endoscope in 12 patients (86%). A craniotomy was required for two colloid cysts that could not be resected endoscopically. In total, complete radiographic resections were achieved in 14 patients (93%). There were no permanent complications, although postoperative deficits included short-term memory loss and hemiparesis, each in one patient. CONCLUSION: Rigid endoscopy affords good optical resolution, high magnification, and excellent illumination. Total or near total resection of colloid cysts should be the goal for all patients and can be achieved using the rigid endoscope, with little morbidity, shortened operative time, reduced length of stay, and resolution of symptoms. Although long-term follow-up is needed, we think that endoscopy should be considered as a primary treatment for most patients.

Endoscopic management of cysticercal cysts within the lateral and third ventricles.

In this report the authors review their 3-year experience with the endoscopic management of patients with hydrocephalus who harbored cysticercal cysts within the third and lateral ventricles. The management plan was to utilize an endoscopic approach to remove the cysts and to incorporate techniques useful in treating obstructive hydrocephalus. The ultimate goals were to avoid having to place a complication-prone cerebrospinal fluid shunt and to eliminate the risk of complications related to cyst degeneration. A retrospective analysis of 10 endoscopically managed patients with hydrocephalus and cysticercal cysts within the third or lateral ventricles was performed. A general description of the instrumentation and the technique used for removal of the intraventricular cysts is given. At presention, neuroimaging revealed findings suggestive of obstructive hydrocephalus in eight patients. Seven of the 10 patients treated endoscopically were spared the necessity of shunt placement. Three successful third ventriculostomies and one therapeutic septum pellucidotomy were performed. Despite frequent rupture of the cyst walls during removal of the cyst, there were no cases of ventriculitis. The endoscopic approach successfully allowed removal of a cyst situated in the roof of the anterior third ventricle. One patient suffered from recurrent shunt obstructions secondary to a shunt-induced migration of cysts from the posterior fossa to the lateral ventricles. The endoscopic removal of third and lateral ventricle cysticercal cysts, combined with a third ventriculostomy or septum pellucidotomy in selected cases, is an effective treatment in patients with hydrocephalus and should be considered the primary treatment for this condition.

Endoscopic removal of cysticercal cysts within the fourth ventricle: technique and results.

There is no consensus as to the optimum management of patients who harbor cysticercal cysts within the fourth ventricle. Compared with the alternative treatment options of anthelmintic medication and/or cerebrospinal fluid shunting, the surgical removal of the cyst has the advantage of eliminating the inflammatory nidus and potentially obviating the need for a complication-prone shunt. Here, an endoscopic surgical approach is described and proposed as a superior alternative to the suboccipital craniotomy for removal of a fourth ventricle cyst. A retrospective analysis was conducted to compare five consecutive endoscopic cases with eight previous consecutive cases in which a suboccipital craniotomy was performed to remove fourth ventricle cysticercal cysts. Comparisons are made with regards to success in removing the cyst, length of operation, surgical blood loss, postoperative discomfort, and complications. A detailed description of the endoscopic technique is given. Endoscopic removal of all cysts within the fourth ventricle was successful in each case. The mean length of operative times was shorter and the blood loss was reduced with the endoscopic procedure compared with the suboccipital craniotomy (2.5 +/- 0.8 hours and 5.3 +/- 2.2 hours [p = 0.02], 19 +/- 4ml and 269 +/- 203 ml [p = 0.02], respectively). The endoscopic procedure was safe and associated with less postoperative discomfort in most patients. In properly selected patients, the endoscopic removal of cysticercal cysts located within the fourth ventricle is superior to the suboccipital craniotomy and should be considered as the primary treatment for this condition.

The relationship of pulsatile cerebrospinal fluid flow to cerebral blood flow and intracranial pressure: a new theoretical model.

An electrical-equivalent circuit model of the cerebrovascular system is proposed, components of which directly relate to cerebrospinal fluid (CSF) compartment compliance and the determination of intracranial pressure (ICP). The model is based on three premises: 1) Under normal, physiologic conditions, the conversion of pulsatile arterial to nonpulsatile venous flow occurs primarily as a result of arterial compliance. Nonpulsatile venous flow is advantageous because less energy is required to maintain constant flow through the venous system, which comprises 75-80% of total blood volume. 2) Dynamic CSF movement across the foramen magnum is the primary facilitator by which intracranial arterial expansion occurs. Interference of the displacement of CSF during systole results in pulsatile venous flow and increased venous flow impedance. 3) Tissue hydrostatic pressure (here defined as ICP) is a dependent variable which is a function of capillary hydrostatic pressure and the osmotic/oncotic pressure gradient created by the blood-brain-barrier (BBB). An interference of transcranial CSF movement results in a decrease in cerebral blood flow (CBF) due to inertial effects impeding pulsatile venous flow. Feedback regulation in response to this decreased CBF leads to arteriolar vasodilatation (decreased resistance), thereby lowering the pressure difference between internal carotid and capillary pressures. Assuming no changes in the BBB potential, ICP increases linearly as capillary pressure increases.

Depression, cognition, and functional correlates of recovery outcome after traumatic brain injury.

The present study investigated the prevalence and magnitude of depressive symptomatology in a sample of patients who had sustained traumatic brain injury (TBI) six months earlier. Depression was examined as a function of recovery outcome status, and its association with neuropsychological functioning, personal competency, and employability was also explored. Subjects were 100 patients who had previously sustained moderate-to-severe TBI who were enrolled as research subjects in the UCLA Brain Injury Research Center, and 30 matched control subjects who had sustained traumatic injuries other than to the head six months prior to evaluation. The results showed a significant association between depression and recovery status as measured by the Glasgow Outcome Scale (GOS). A significant majority of depressed subjects were found in the poorer GOS outcome groups (severe and moderate disability), compared to TBI subjects who had good GOS outcomes, and control subjects. This association was also reflected in the magnitude of the mean depression scores on two self-report measures of depression. However, no association was found between depression status and performance on the neuropsychological measures. Effects of depression were found only on an examiner-rated Patient Competency scale, and a metacognition measure based on self-report. These results are discussed in terms of brain injury severity, recovery status, and metacognition issues in TBI and other disorders.

Neuropsychological, psychosocial and vocational correlates of the Glasgow Outcome Scale at 6 months post-injury: a study of moderate to severe traumatic brain injury patients.

Traumatic brain injury (TBI) subjects at Glasgow Outcome Scale levels 3 (severe disability), 4 (moderate disability), 5 (good recovery), and an other-injury control group (OIC) were compared in terms of neuropsychological, psychosocial, and vocational functioning 6 months after injury. Subjects were a sample of 100 patients with a moderate to severe traumatic brain injury (TBI) and a matched sample of 30 other-injury control subjects (OIC) enrolled in the UCLA Brain Injury Research Center study of TBI outcome. Overall, the results showed a systematic decrease in mean neuropsychological test performance as a function of increasing GOS severity, as well as an increased prevalence of symptoms of depression and lower ratings on measures assessing employability and capacity for self care. TBI patients in the 'severe' and 'moderate disability' groups were distinctly inferior to the 'good recovery' and 'OIC' groups, who were quite similar to each other in terms of cognitive, psychosocial, and vocational outcomes. The results demonstrate overall support for the predictive and concurrent validity of the GOS 6 months post injury. Despite these results, which strengthen the utility and appeal of the GOS for multicentre studies, concerns still remain regarding GOS category 4 (moderate disability), which was shown to lack sufficient discriminability in this study.

Cerebral blood flow as a predictor of outcome following traumatic brain injury.

As part of a prospective study of the cerebrovascular effects of head injury, 54 moderate and severely injured patients underwent 184 133Xe-cerebral blood flow (CBF) studies to determine the relationship between the period of maximum blood flow and outcome. The lowest blood flows were observed on the day of injury (Day 0) and the highest CBFs were documented on postinjury Days 1 to 5. Patients were divided into three groups based on CBF values obtained during this period of maximum flow: Group 1 (seven patients), CBF less than 33 ml/100 g/minute on all determinations; Group 2 (13 patients), CBF both less than and greater than or equal to 33 ml/100 g/minute; and Group 3 (34 patients), CBF greater than or equal to 33 ml/100 g/minute on all measurements. For Groups 1, 2, and 3, mean CBF during Days 1 to 5 postinjury was 25.7 +/- 4, 36.5 +/- 4.2, and 49.4 +/- 9.3 ml/100 g/minute, respectively, and PaCO2 at the time of the CBF study was 31.4 +/- 6, 32.7 +/- 2.9, and 33.4 +/- 4.7 mm Hg, respectively. There were significant differences across Groups 1, 2, and 3 regarding mean age, percentage of individuals younger than 35 years of age (42.9%, 23.1%, and 76.5%, respectively), incidence of patients requiring evacuation of intradural hematomas (57.1%, 38.5%, and 17.6%, respectively) and incidence of abnormal pupils (57.1%, 61.5%, and 32.4%, respectively). Favorable neurological outcome at 6 months postinjury in Groups 1, 2, and 3 was 0%, 46.2%, and 58.8%, respectively (p < 0.05). Further analysis of patients in Group 3 revealed that of 14 with poor outcomes, six had one or more episodes of hyperemia-associated intracranial hypertension (simultaneous CBF > 55 ml/100 g/minute and ICP > 20 mm Hg). These six patients were unique in having the highest CBFs for postinjury Days 1 to 5 (mean 59.8 ml/100 g/minute) and the most severe degree of intracranial hypertension and reduced cerebral perfusion pressure (p < 0.0001). These results indicate that a phasic elevation in CBF acutely after head injury is a necessary condition for achieving functional recovery. It is postulated that for the majority of patients, this rise in blood flow results from an increase in metabolic demands in the setting of intact vasoreactivity. In a minority of individuals, however, the constellation of supranormal CBF, severe intracranial hypertension, and poor outcome indicates a state of grossly impaired vasoreactivity with uncoupling between blood flow and metabolism.