Occipital neuralgia treated by intradural dorsal nerve root sectioning

The term occipital neuralgia was first used in 1821 to describe a characteristic pain in the region innervated by the greater occipital nerve. Since that time numerous authors have failed to reach a consensus concerning the presentation, cause, and treatment of this entity. Review of these previous works reveals that the term occipital neuralgia encompasses a collection of signs and symptoms which develop secondary to a variety of different disease processes. We have treated nine patients suffering from severe occipital pain with associated C2 hypesthesia, unilateral retro-orbital pain, and occipital or C2 tubercle trigger points by intradurally sectioning the C1-C4 dorsal rootlets (C4 if shoulder pain existed). All patients had been treated previously with various modalities without success. This paper discusses the results obtained in these patients.

Increased stroke risk predicted by compromised cerebral blood flow reactivity

The authors sought to determine risk for stroke in individuals with symptomatic carotid stenosis or occlusion based upon an assessment of cerebral blood flow (CBF) reserves. Vascular reserve was assessed by two consecutive xenon/computerized tomography (Xe/CT) CBF studies with intravenous acetazolamide introduced 20 minutes prior to the second study. Patients were assigned to one of two vasoreactivity groups. Group 2 included individuals who experienced a CBF reduction of more than 5% in at least one vascular territory and had a baseline flow of 45 cc/100 gm/min or less. Group 1 included all other individuals. Any territory with volume loss on CT of more than 50% was eliminated from analysis. Sixty-eight individuals were followed at 6-month intervals for a mean of 24 months. In Group 1 two strokes were observed contralateral to the side with lowest reserve, for a stroke incidence of 4.4%; in Group 2 eight strokes were observed ipsilateral to the side with lowest reserve, for a stroke incidence of 36%. The latter group had a 12.6 times greater chance of stroke (p = 0.0007). History of stroke, history of transient ischemic attacks, baseline CBF, and degree of stenosis were not associated with an increased stroke rate. In this study, significantly compromised vascular reserves accompanied by relatively low initial flow identified individuals who subsequently demonstrated a significantly increased rate of ipsilateral stroke.

Local cerebral blood flow measured by xenon-enhanced CT during cryogenic brain edema and intracranial hypertension in monkeys

We developed a closed-skull model of freeze injury-induced brain edema, a model classically thought to produce vasogenic edema, and observed the natural course of changes in edema and blood flow using xenon-enhanced computed tomography (CT) in five rhesus monkeys before and for up to 6 h post insult. Intracranial pressure (ICP) gradually rose throughout the duration of the experiment. CT scans and CBF images permitted direct observation of the evolution of the lesion and revealed early ischemia in the periphery of the injury zone that progressed over time in association with edema. Frequency histogram analysis of local CBF (ICBF) demonstrated subtle but potentially important changes in distribution of ICBF between and within hemispheres at various times post insult. Changes in ICBF distribution were phasic and dissociated from increases in ICP in the latter stages of injury. The Xe/CT CBF method can be used to evaluate the effects of injury and therapy on CBF in this and other models of acute brain injury.

Xenon/CT cerebral blood flow studies during continuous depth electrode monitoring in epilepsy patients

PURPOSE

To observe and describe cerebral blood flow (CBF) alterations immediately following depth electrode stimulation of the temporal lobe in patients with medically intractable epilepsy.

MATERIALS AND METHODS

Five patients with partial epilepsy undergoing presurgical evaluation were chosen for xenon/CT cerebral blood flow (Xe/CT CBF) measurement immediately following electrically stimulated seizures via stereotactically placed temporal lobe depth electrodes. Each patient had a baseline Xe/CT CBF study. Four of the five patients had a total of seven temporal lobe stimulations each followed by a Xe/CT CBF study. The other patient had right temporal lobe electrical status epilepticus and was scanned without stimulation or electroencephalogram monitoring.

RESULTS

Of the four baseline or interictal scans, no areas of abnormally low flow were detected, but one baseline scan had elevated flows of 115 mL.100 g-1.min-1 in the left temporal lobe. One stimulation elicited 8 seconds of afterdischarge potentials, but no alteration of CBF was detected. One stimulation elicited an aura but no electrographic seizure was detected. This resulted, however, in bitemporal lobe elevation of CBF. The other five temporal lobe stimulations resulted in 17-63 seconds of afterdischarge potentials and all resulted in elevation of CBF to 69-118 mL.100 g-1.min-1. One of these five stimulations resulted in seizure and localized elevation of CBF. Following seizure activity, elevated CBF began to return to baseline levels by 20 minutes.

CONCLUSION

This study reveals a direct spatial and temporal relationship of elevated CBF with seizures. This study provides the most direct data to date in human subjects that focal seizure activity elevates CBF. Since seizures are known to increase metabolic activity in the activated tissue, this data also supports the assumption of coupling between CBF and metabolism during the pathologic process of a seizure.

Effects of Dobutamine and Dopamine on Whole Brain Blood Flow and Metabolism in Unanesthetized Monkeys

Dobutamine (DO) and dopamine (DA) are positive inotropic agents used clinically to improve cardiac output in patients in acute or chronic heart failure or to counteract intracranial vasospasm. These patients are also at risk for cerebrovascular disease, but studies on the effects of DA on cerebral blood flow (CBF) and metabolism are few and for DO nonexistent. We evaluated the effects on DO and DA on whole brain CBF and cerebral metabolic rates of oxygen (CMRO2) and glucose (CMRglc) in unanesthetized rhesus monkeys. Microelectrodes and catheters inserted in the superior sagittal sinus monitored H2 clearance and sampled cerebral venous blood. Studies were done at low and high doses with control measurements between doses. At 5.10, and 15 microg/kg/min (n = 6), neither systemic nor cerebral variables were affected by either drug. At doses of 50 and 100 microg/kg/min (n = 4), DO and DA increased arterial blood pressure and heart rate by 15 to 30%. Whereas CBF, CMRO2, and CMRglc were clearly unaffected by DO at high doses, they increased by 20-30% with DA, 100 microg/kg/min and although not significant (p >0.05), the consistency and magnitude of the increase along with the likelihood of a type II error led us to conclude that (a) both DO and DA are less effective in monkeys than in humans and (b) whereas DO at all doses tested showed no indication of affecting CBF and CMR, DA increased CBF and CMR by 20 to 30% at a dose of 100 microg/kg/min.

Effect of stable xenon inhalation on internal carotid artery blood flow in unanesthetized monkeys

Stable xenon (Xe) gas, at inspired concentrations above 30%, reportedly increased cerebral blood flow (CBF) in animals and humans. An unpredictable Xe-induced elevation of CBF could result in erroneous CBF values being measured by Xe-enhanced computed tomography (Xe-CT). In order to detect a potentially rapid and transient effect of Xe on CBF, estimations of supratentorial CBF were obtained by Doppler flow probes chronically and bilaterally implanted on the internal carotid arteries of five adult monkeys. The unanesthetized monkeys with a clear plastic helmet were equilibrated for 15 min on a control gas (33% N2/67% O2) randomly exposed for 5 min to gas mixtures of either 33% Xe/67% O2 or 10% CO2/23% N2/67% O2. The mean control bilateral internal carotid artery blood flow (ICABF) was 23 +/- 10 ml/min (mean +/- SD), mean arterial pressure (MAP) was 101 +/- 13 mm Hg, and PaCO2 was 34 +/- 6 mm Hg. Inhalation of 33% Xe in O2 did not change the ICABF, MAP, or PaCO2. Inhalation of 10% CO2 in O2 increased the ICABF to 39 +/- 15 ml/min (p <0.001), MAP to 112 +/- 16 mm Hg (p <0.05), and PaCO2 to 54 +/- 5 mm Hg (p <0.001). The lack of change in ICABF and PaCO2 with 32% Xe inhalation suggests that a clinically relevant change in CBF is unlikely.

Effect of 80% Xe on Whole Brain Blood Flow and Metabolism in Awake Monkeys

We previously reported that 33% xenon (Xe) did not activate cerebral blood flow (CBF) and metabolism in monkeys as it appears to do in humans. However, monkeys may be less sensitive to Xe than humans are, which would explain the discrepancy in the results, but no one has studied the effects of higher concentrations of Xe on CBF and metabolism in monkeys. Therefore, we studied the effect of 80% Xe on whole-brain CBF, cerebral metabolic rate for oxygen (CMRO2) and glucose (CMRG) in five awake rhesus monkeys. Platinum microelectrodes and catheters inserted into the torcular Herophili were used to measure H2 clearance CBF, and to withdraw cerebral venous blood for O2 and glucose analysis. Cerebral variables were measured after 15 min exposure to 80% N2/20% O2 followed by 80% Xe/20% O2. Eighty percent Xe compared with 80% N2 increased (p <0.01) CBF by 52.7% from 74 +/- 16 to 113 +/- 25 (mean +/- SD) ml 100 g(-1)/min(-1), CBF/CMRO by 154% from 13 to 33, and decreased (p <0.05) CMRO2 by 39.3% from 6.1 +/- 0.9 to 3.7 +/- 0.8 ml 100 g(-1)/min(-1) and CMRG by 52.4% from 8.4 +/- 2.6 to 4.0 +/- 2.0 mg 100 g(-1)/min(-1). Electroencephalogram frequency decreased from a predominantly alpha to dagger rhythm in three of five monkeys. The 40 and 50% reduction in CMRO2 and CMRG, respectively, by 80% Xe suggests an anesthetic effect at this dose in the rhesus monkey but also activates CBF by 50%.

A partially thrombosed, fenestrated basilar artery mimicking an aneurysm of the vertebrobasilar junction: case report

We report a patient with a subarachnoid hemorrhage in whom a partially thrombosed, fenestrated basilar artery mimicked an aneurysm of the vertebrobasilar junction on preoperative angiography. Intraoperatively, no aneurysm was detected; instead, the patient was found to have partial thrombosis of one limb of the fenestrated basilar artery. The nodular appearance of the residual lumen of the vessel corresponded exactly to the angiographic findings. To our knowledge, no similar case has been reported.

Xe/CT cerebral blood flow evaluation of delayed symptomatic cerebral ischemia after subarachnoid hemorrhage

PURPOSE

We examined the xenon/CT method of measuring cerebral blood flow in assessing the location, pattern of onset, and severity of delayed cerebral ischemia.

PATIENTS AND METHODS

Fourteen patients with delayed neurologic deficits due to ischemia were selected from a group of 66 patients with subarachnoid hemorrhage. All blood flow studies were performed within 12 hours of deterioration and at regular intervals during medical management.

RESULTS

In 10 of the 14 patients, noncontrast CT did not identify a cause for deterioration, whereas the blood flow study revealed diminished flow values. Location of blood flow reduction was variable. In five of the 14 patients, blood flow reduction was closely related anatomically to the vessel of aneurysm origin. In another three, blood flow reduction was anatomically remote to the vessel of origin. The remaining six experienced local and remote cerebral blood flow reduction. Six of 14 patients suffered sudden, devastating deterioration, refractory to therapy and associated with blood flow of 15 cc/100 g.min or less, resulting in local or widespread infarction. The remaining eight had less severe blood flow reduction and did not infarct those territories.

CONCLUSIONS

Vasospasm can affect remote vessels as severely as local vessels and can affect remote vessels alone. Diminished cerebral blood flow correlated closely with clinical vasospasm in this group of patients. Xenon/CT cerebral blood flow studies can identify tissue at risk of infarction when CT is normal.

Physiologic implications of adding small amounts of carbon dioxide to the gas mixture during inhalation of xenon

In addition to being a physiologically active tracer of CBF, xenon (Xe) in subanesthetic concentrations produces a relatively mild lowering of carbon dioxide (CO2) in the blood and elevation of transcranial Doppler (TCD) velocity. The addition of small concentrations of CO2 (0.4-1.2%) to the inhaled mixture produced no measurable effect on end tidal (P(et)) CO2 or TCD velocity. Cerebral blood flow (CBF) alterations induced by Xe are minimized by allowing P(et)CO2 to fall, permitting quantitative measurement of CBF by the Xe/CT CBF method.

Effect of 33% xenon inhalation on whole-brain blood flow and metabolism in awake and fentanyl-anesthetized monkeys

BACKGROUND AND PURPOSE

Despite the documented diagnostic value of local cerebral blood flow maps by xenon-enhanced computed tomography, reports of cerebral blood flow activation by inhaled 33% Xe raised concerns about the method's safety and accuracy. We evaluated the effect of 33% Xe inhalation on cerebral blood flow and cerebral metabolic rates for oxygen and glucose in four awake and six fentanyl-anesthetized rhesus monkeys.

METHODS

Platinum microelectrodes and catheters in the torcular Herophili were used to measure cerebral blood flow by hydrogen clearance, and oxygen and glucose concentrations. Cerebral variables were measured after 5 and 35 minutes of exposure to room air followed randomly by 67% O2 in 33% N2 or Xe. Five- and 35-minute measurements were combined because the duration of exposure had no effect.

RESULTS

In awake monkeys, 33% Xe compared with 33% N2 reduced (p less than 0.05) cerebral blood flow from 75 +/- 12 to 66 +/- 9 (mean +/- SD) ml.100 g-1.min-1 and oxygen consumption from 6.1 +/- 0.7 to 5.1 +/- 0.6 ml.100 g-1.min-1. In fentanyl-anesthetized monkeys, cerebral variables during 33% N2 versus 33% Xe were cerebral blood flow, 84 +/- 26 versus 79 +/- 23 ml.100 g-1.min-1; oxygen consumption, 5.0 +/- 0.7 versus 4.9 +/- 0.5 ml.100 g-1.min-1; and glucose consumption, 8.4 +/- 1.9 versus 7.9 +/- 2.0 mg.100 g-1.min-1.

CONCLUSIONS

In awake monkeys, 33% Xe reduced rather than activated cerebral blood flow and oxygen consumption by 12% and 16%, respectively; it had no effect in fentanyl-anesthetized monkeys.

Aneurysms of the intracavernous carotid artery: a multidisciplinary approach to treatment

Of 43 cavernous sinus aneurysms diagnosed over 6 1/2 years, 23 fulfilled indications for treatment; of these 19 were treated, eight surgically and 11 with interventional radiological techniques. Six small and two giant aneurysms were treated surgically: four were clipped, two were repaired primarily, and two were trapped with placement of a saphenous-vein bypass graft. Seven large and four giant aneurysms were treated with interventional radiological techniques: in five cases the proximal internal carotid artery (ICA) was sacrificed; one aneurysm was trapped with detachable balloons; and five were embolized with preservation of the ICA lumen. The mean follow-up period was 25 months. At follow-up examination, three patients in the surgical group were asymptomatic, two had improved, and three had worsened. Three of these patients had asymptomatic infarctions apparent on computerized tomography (CT) scans. At follow-up examination, four radiologically treated patients were asymptomatic, five had improved, two were unchanged, and none had worsened. One patient had asymptomatic and one minimally symptomatic infarction apparent on CT scans; both lesions were embolic foci after aneurysm embolization with preservation of the ICA. It is concluded that treatment risk depends more on the adequacy of collateral circulation than on the size of the aneurysm. A multidisciplinary treatment protocol for these aneurysms is described, dividing patients into high-, moderate-, and low-risk groups based on pretreatment evaluation of the risk of temporary or permanent ICA occlusion using a clinical balloon test occlusion coupled with an ICA-occluded stable xenon/CT cerebral blood flow study. Radiological techniques are suggested for most low-risk patients, while direct surgical techniques are proposed for most moderate- and high-risk patients.

CBF measured by Xe-CT: approach to analysis and normal values

Normal reference values and a practical approach to CBF analysis are needed for routine clinical analysis and interpretation of xenon-enhanced computed tomography (CT) CBF studies. We measured CBF in 67 normal individuals with the GE 9800 CT scanner adapted for CBF imaging with stable Xe. CBF values for vascular territories were systematically analyzed using the clustering of contiguous 2-cm circular regions of interest (ROIs) placed within the cortical mantle and basal ganglia. Mixed cortical flows averaged 51 +/- 10ml.100g-1.min-1. High and low flow compartments, sampled by placing 5-mm circular ROIs in regions containing the highest and lowest flow values in each hemisphere, averaged 84 +/- 14 and 20 +/- 5 ml.100 g-1.min-1, respectively. Mixed cortical flow values as well as values within the high flow compartment demonstrated significant decline with age; however, there were no significant age-related changes in the low flow compartment. The clustering of systematically placed cortical and subcortical ROIs has provided a normative data base for Xe-CT CBF and a flexible and uncomplicated method for the analysis of CBF maps generated by Xe-enhanced CT.

Fatal rupture of the intracranial carotid artery during transluminal angioplasty for vasospasm induced by subarachnoid hemorrhage. Case report

The authors report the clinical course, radiographic findings, and gross and microscopic pathology of a patient with fatal rupture of the supraclinoid segment of the left internal carotid artery during transluminal angioplasty for subarachnoid hemorrhage-induced vasospasm. The rupture most likely resulted from a small portion of aneurysm neck which remained unclipped, thereby leaving an area of structural weakness in the arterial wall at the site of clipping. The area of structural weakness predisposed the artery to rupture upon the addition of transmural pressure induced by balloon inflation during transluminal angioplasty. Caution is advised when performing transluminal angioplasty in the region of aneurysm clipping since the vessel lumen "recreated" during the clipping procedure may contain some residual and structurally incomplete aneurysm neck in the vessel wall.

Stable xenon does not increase intracranial pressure in primates with freeze-injury-induced intracranial hypertension

Stable xenon (Xe)-enhanced computed tomography is a potentially valuable tool for high resolution, three-dimensional measurement of CBF in patients. However, reports that Xe causes cerebrovascular dilation and increases intracranial pressure (ICP) have tempered enthusiasm for its use. The effects of 5 min of 33% Xe inhalation on ICP (right and left hemispheres) were studied in eight fentanyl-anesthetized Rhesus monkeys after right-sided cortical freeze injury. ICP, CBF, and physiological variables were monitored for up to 6 h postinsult. The preinjury (control) right hemispheric ICP was 8 +/- 5 mm Hg (mean +/- SD) and left hemispheric ICP was 5 +/- 2 mm Hg. Postinjury observations were classified into low (less than 15 mm Hg) and high ICP (greater than or equal to 15 mm Hg) groups. Both right and left ICP values averaged 9 +/- 3 mm Hg in the low ICP group. In the high ICP group, the right ICP was 20 +/- 4 mm Hg and left ICP was 21 +/- 6 mm Hg. ICP was unchanged by Xe inhalation under control conditions as well as in both low and high ICP groups postinjury. Postinjury, the MABP decreased 10-15 mm Hg in the low ICP group and 10-17 mm Hg in the high ICP group 2-3 min after the start of Xe inhalation (p less than 0.05). These results show that 33% Xe inhalation does not increase ICP in fentanyl-anesthetized monkeys but could decrease MABP in stressed states, presumably because of the anesthetic effects of Xe.

Acute regional cerebral blood flow changes caused by severe head injuries

To evaluate the changes in cerebral blood flow (CBF) that occur immediately after head injury and the effects of different posttraumatic lesions on CBF, 61 CBF studies were obtained using the xenon-computerized tomography method in 32 severely head-injured adults (Glasgow Coma Scale score (GCS) less than or equal to 7). The measurements were made within 7 days after injury, 43% in the first 24 hours. During the 1st day, patients with an initial GCS score of 3 or 4 and no surgical mass had significantly lower flows than did those with a higher GCS score or mass lesions (p less than 0.05): in the first 1 to 4 hours, those without surgical mass lesions had a mean CBF of 27 cc/100 gm/min, which rose to 44 cc/100 gm/min by 24 hours. Patients without surgical mass lesions who died tended to have a lower global CBF than did those with better outcomes. Mass lesions were associated with a high global CBF and bihemispheric contusions with the lowest flows. By 24 hours after injury, global blood flow increased in groups that originally had low flows and decreased in those with very high initial flows, such that by 36 to 48 hours, most patients had CBF values between 32 and 55 cc/100 gm/min. Lobar, basal ganglion, and brain-stem blood flow values frequently differed by 25% or more from global averages. Brain-stem CBF varied the most but did not correlate with clinical signs of brain-stem dysfunction. Double studies were performed at two different pCO2 values in 10 patients with various posttraumatic lesions, and the CO2 vasoresponsivity was calculated. Abnormal CO2 vasoresponsivity was found with acute subdural hematomas and defuse cerebral swelling but not with epidural hematomas. In patients without surgical mass lesions, the findings suggest that CBF in the first few hours after injury is often low, followed by a hyperemic phase that peaks at 24 hours. Global CBF values vary widely depending on the type of traumatic brain injury, and brain-stem flow is often not accurately reflected by global CBF values. These findings underscore the need to define regional CBF abnormalities in victims of severe head injury if treatment is intended to prevent regional ischemia.

The role of xenon CT measurements of cerebral blood flow in the clinical determination of brain death

The demonstration of absent blood flow to the brain is often used as a confirmatory test of brain death. Traditionally, cerebral angiography and dynamic radionuclide brain scanning have been used for this purpose. Recently, xenon CT cerebral blood flow techniques have been developed and applied to a wide variety of clinical problems, including the confirmation of brain death. We report our experience with xenon CT studies performed over a 7-year period (1983-1989) in 30 patients with brain injuries. These patients met clinical criteria for brain death within 24 hr of the study. Twenty patients had average global flow values of less than 5 ml/100 ml/min. Seven patients demonstrated mixed flow patterns, whereby large areas of brain showed flow values of less than 5 ml/100 ml/min and residual pockets of flow greater than 5 ml/100/ml/min. Globally symmetric normal to hyperemic flows were seen in three patients. Our study suggests that the demonstration of average global flows of less than 5/ml/100 ml/min is confirmatory of brain death. Demonstration of persistent flow to the entire brain or regions of the brain is not diagnostic of brain death but also does not exclude such an outcome in patients with severe brain injuries. Xenon-derived flow information may be clinically useful in determining the patient's prognosis and in counseling the patient's family.

Impaired cerebral vasoreactivity after embolization of arteriovenous malformations: assessment with serial acetazolamide challenge xenon CT

Embolization of a portion of the nidus of an arteriovenous malformation not only may alter hemodynamics within the nidus, but also may change blood flow dynamics in adjacent normal vessels. Sequential acetazolamide-challenge xenon CT cerebral blood flow studies were performed in eight patients before and after embolization of arteriovenous malformations to assess the hemodynamic effects on the major vascular territories supplying the malformation. Acetazolamide is a potent cerebral vasodilator, and its administration combined with cerebral blood flow studies allows assessment of cerebral vasoreactivity. In seven of the eight patients, one or more parenchymal areas exhibited a normal cerebral blood flow augmentation response to acetazolamide before embolization, but diminished acetazolamide flow augmentation was seen after embolization, indicating abnormal vasoreactivity. We found that the decrease in vasoreactivity peaked 6-10 days after embolization. In one of the eight patients, a temporary delayed neurologic deficit developed during a period of impaired cerebral vasoreactivity following embolization. Our results suggest that embolization of an arteriovenous malformation can induce vasoreactivity changes in adjacent normal vessels. Because these changes appear to be somewhat time-dependent, an appropriate interval should be observed between embolization stages or before surgical resection of an arteriovenous malformation following embolization to allow hemodynamic equilibration to occur. Acetazolamide challenge combined with serial cerebral blood flow studies following embolization enables determination of this hemodynamic equilibration.

Stable xenon CT cerebral blood flow imaging: rationale for and role in clinical decision making

The stable xenon CT method of measuring cerebral blood flow has been investigated in research studies for over 10 years. Recently, it has been gaining clinical acceptance, primarily owing to a combination of several unique advantages it holds over other cerebral blood flow measurement techniques. The accuracy of this technique in quantifying low cerebral blood flow gives it a unique application in cases of brain death and acute stroke and it can be repeated after an interval of 20 min. making it possible to evaluate autoregulation and cerebrovascular reserve. Furthermore, cerebral blood flow information is directly coupled to CT anatomy. Although it is more difficult to administer than a standard CT scan, careful monitoring can ensure patient safety during the examination. In this article we review the physiologic and technical bases for the clinical application of xenon CT-derived quantitative cerebral blood flow information and discuss the advantages and disadvantages of the technique. We also describe its current clinical applications, including its usefulness in the evaluation of acute stroke, occlusive vascular disease, carotid occlusion testing, vasospasm, arteriovenous malformations, and head trauma management.

Stable xenon-enhanced CT measurement of cerebral blood flow in reversible focal ischemia in baboons

When the lateral striate arteries of the baboon are temporarily occluded for either 20 or 60 minutes, a near-cessation of blood flow is followed by a dramatic, transient local increase in blood flow values. These findings are evident from serial xenon (Xe)-computerized tomography (CT) measurement of cerebral blood flow (CBF). In this study, 20 minutes of vessel occlusion resulted in brief (less than 1 hour) hyperemia, with no subsequent CT alteration and minimal random neuronal injury. Sixty minutes of occlusion resulted in a more prolonged hyperemia, a low-density area on CT images within 3 hours of reperfusion, and infarction of all cellular elements within the anterior lentiform nucleus. The Xe-CT method provides a sensitive, noninvasive technique for examining sequential alterations of CBF in small regions deep within the brain. This method of recording CBF also permits correlative studies of cerebral infarction, both clinically and experimentally, and allows reasonable inference about the probabilities of neuronal tissue damage with or without reperfusion.

Aneurysms of the Intracavernous Carotid Artery: Natural History and Indications for Treatment

Of 37 patients with 44 intracavernous carotid artery aneurysms (ICCAAns) diagnosed between 1976 and 1988. patients with 20 aneurysms were followed without treatment for 5 months to 13 years (median, 2.4 years). Ten of the 20 ICCAAns were asymptomatic at diagnosis, and 10 were symptomatic. Three of the asymptomatic ICCAAns were symptomatic at follow-up. One of these required clipping because of a progressing cavernous sinus syndrome; the other 2 were minimally symptomatic and have not required treatment. Of the 10 initially symptomatic ICCAAns, 2 had not changed, 4 became more symptomatic, and 4 had symptomatically improved by follow-up. One patient with an ICCAAn that had not changed clinically was lost to follow-up 6 months after diagnosis. Of the 4 ICCAAns that became more symptomatic, 2 continue to be monitored, and 2 required intervention; one with detachable balloon occlusion of the aneurysm with preservation of the internal carotid artery lumen, and the other with gradual cervical internal carotid artery occlusion. The clinical course of this selected group of patients with ICCAAns suggests that the natural history of ICCAAns can be quite variable. Although clinical progression does occur, symptomatic ICCAAns also can improve spontaneously. Therapeutic intervention for asymptomatic ICCAAns should be reserved for patients with aneurysms arising at the anterior genu of the carotid siphon and/or extending into the subarachnoid space, where subarachnoid hemorrhage is most likely. Intervention for symptomatic ICCAAns should be reserved for patients with subarachnoid hemorrhage, epistaxis, severe facial or orbital pain, evidence of radiographic enlargement, progressive ophthalmoplegia, or progressive visual loss.

Aneurysms of the intracavernous carotid artery: natural history and indications for treatment

Of 37 patients with 44 intracavernous carotid artery aneurysms (ICCAAns) diagnosed between 1976 and 1988, patients with 20 aneurysms were followed without treatment for 5 months to 13 years (median, 2.4 years). Ten of the 20 ICCAAns were asymptomatic at diagnosis, and 10 were symptomatic. Three of the asymptomatic ICCAAns were symptomatic at follow-up. One of these required clipping because of a progressing cavernous sinus syndrome; the other 2 were minimally symptomatic and have not required treatment. Of the 10 initially symptomatic ICCAAns, 2 had not changed, 4 became more symptomatic, and 4 had symptomatically improved by follow-up. One patient with an ICCAAn that had not changed clinically was lost to follow-up 6 months after diagnosis. Of the 4 ICCAAns that became more symptomatic, 2 continue to be monitored, and 2 required intervention: one with detachable balloon occlusion of the aneurysm with preservation of the internal carotid artery lumen, and the other with gradual cervical internal carotid artery occlusion. The clinical course of this selected group of patients with ICCAAns suggests that the natural history of ICCAAns can be quite variable. Although clinical progression does occur, symptomatic ICCAAns also can improve spontaneously. Therapeutic intervention for asymptomatic ICCAAns should be reserved for patients with aneurysms arising at the anterior genu of the carotid siphon and/or extending into the subarachnoid space, where subarachnoid hemorrhage is most likely. Intervention for symptomatic ICCAAns should be reserved for patients with subarachnoid hemorrhage, epistaxis, severe facial or orbital pain, evidence of radiographic enlargement, progressive ophthalmoplegia, or progressive visual loss.

Xenon-enhanced computed tomography compared with [14C]iodoantipyrine for normal and low cerebral blood flow states in baboons

The correlation between the acute, invasive diffusible [14C]iodoantipyrine technique for cerebral blood flow and the noninvasive xenon-enhanced computed tomographic method has been assessed by simultaneous measurements in the baboon. Blood flows in small tissue volumes (about 0.125 cm3) were directly compared in normal and low flow states. These studies demonstrate a statistically significant association between the two methods (p less than 0.001). Similar correlations were obtained by both the Kendall (tau) and the Spearman (r) methods (r = 0.67 to 0.92, n greater than or equal to 19 for each study). The problems and limitations of such correlations are discussed.

Use of acetazolamide-challenge xenon CT in the assessment of cerebral blood flow dynamics in patients with arteriovenous malformations

Arteriovenous malformations (AVMs) may cause symptoms related to a reduction of cerebral blood flow (CBF) to surrounding brain parenchyma. To evaluate this compromise of hemodynamic reserve (commonly referred to as steal phenomenon), we used acetazolamide challenge and stable-xenon CT (Xe/CT). Baseline Xe/CT studies in 13 patients with AVMs were followed by an acetazolamide challenge to the vascular reserve. Blood flow maps were quantitated by using region-of-interest (ROI) software. ROI findings were categorized into four groups on the basis of the presence or absence of normal baseline CBF and presence or absence of normal augmentation of CBF. ROIs were designated as near site (within the vascular territory supplying the AVM) or far site (outside the vascular territory supplying the AVM). One patient had a normal baseline and normal augmentation of CBF (group 1). The other patients had a combination of one or more of the other three categories. Ten patients had parenchymal areas that exhibited either a normal or low baseline CBF with decreased augmentation; both conditions were interpreted as decreased vascular reserve (groups 2 and 3). Eleven patients had parenchymal areas that showed a low baseline CBF and normal augmentation with acetazolamide (group 4), interpreted as having a decreased demand for CBF but having a normal vascular reserve. Decreased vascular reserve was found in 27% of the nearsite areas and 17% of the far-site areas. No patients had only far-site abnormal vascular reserve. We believe that compromised vascular reserve can best be evaluated with a challenge study, such as this acetazolamide-challenge Xe/CT study.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral blood measurements in vasospasm

Although vasospasm remains a common cause for morbidity and mortality following subarachnoid hemorrhage, new therapeutic approaches and diagnostic studies offer the hope that injury caused by this disorder can be further lessened. Current CBF technologies can help to determine whether new symptoms are caused by ischemia, as well as define the often unpredictable manner in which ischemia occurs in this disorder. The CBF measurements may also help identify the best time for surgical intervention following subarachnoid hemorrhage. In addition, CBF studies may delineate when aggressive medical therapies are indicated and when they are potentially harmful. Despite the inherent limitations, as new technologies for CBF determination become more widely available, they should play an important role in the management of patients with aneurysmal subarachnoid hemorrhage.

Selective occlusion of blood supply to the anterior perforated substance of the dog: a highly reproducible stroke model

We created a highly reproducible stroke model in dogs by the selective occlusion of middle and anterior cerebral artery branches that penetrate the anterior perforated substance and supply much of the basal forebrain. We also analyzed the anatomic organization of the arterial supply to this region in this animal. Perforators came from anterior communicating artery branches similar to the recurrent artery of Heubner in humans and from the middle cerebral artery at several sites distal to the bifurcation of the internal carotid artery. Although some animals had a single source of the perforating arteries, most had two or more. In 50% of our specimens, the anterior communicating artery was the dominant source of arterial supply, in 21% the middle cerebral artery was dominant, and in 24% neither source dominated. Occlusion of all microscopically visible perforators to the anterior perforated substance reliably resulted in infarction of the internal capsule (100%), caudate nucleus (91%-100%), putamen or globus pallidus (82%-91%), and anterior commissure (73%). Structures involved less frequently in infarctions include the external capsule, claustrum, anterior commissure, and septal nuclei. We believe this anatomic information is useful for understanding why previous focal ischemia lesions in the distribution of the middle cerebral artery in the dog have been highly variable as well as for planning and interpreting future studies in this species. The proposed model of focal ischemia may be of use for the study of stroke.

A new method to predict safe resection of the internal carotid artery

A patent internal carotid artery (ICA) is essential in most patients. Management of skull base lesions often requires translocation, balloon embolization, or resection of this vessel. Preoperative tests to assess the availability of collateral flow have not been uniformly accurate. A new test that significantly increases the safety of surgical removal of the ICA is described. One hundred thirty-six patients were studied with temporary balloon occlusion (TBO) of the ICA and determination of stable xenon-enhanced computed tomography cerebral blood flow (Xe/CT CBF) measurements. Eleven patients failed TBO and were determined to be at very high risk of stroke with loss of the ICA. Ninety-six of the patients were predicted to be at minimal risk with permanent loss of the ICA by Xe/CT CBF studies. Twenty-one patients in this group had either permanent balloon occlusion (PBO) or surgical resection of the ICA with no permanent neurologic sequelae. Our studies show that the combination of preoperative TBO and Xe/CT CBF studies significantly increases the safety of ICA resection.

Aneurysms of the intracavernous carotid artery: clinical presentation, radiographic features, and pathogenesis

Thirty-seven patients with 44 intracavernous carotid artery aneurysms (ICCAAns) were seen at one institution from 1976 through 1988. Fifteen patients had multiple intracranial aneurysms and 7 had bilateral ICCAAns. Age at diagnosis ranged from 15 to 80 (median 61). Thirty patients were women. Sixteen had a history of hypertension. In 34% of patients the ICCAAns were asymptomatic at diagnosis, 36% were associated with headache, and 57% had associated signs or symptoms of mass effect including sixth nerve paresis (43%), trigeminal pain or sensory loss (32%), third nerve paresis (20%), decreased vision or visual field cut (18%), fourth nerve paresis (16%), and Horner's syndrome (7%). In 4 patients the ICCAAns ruptured, leading to subarachnoid hemorrhage in 3 and epistaxis in 1. Two patients with ICCAAns were seen with spontaneous thrombosis of the ipsilateral internal carotid artery leading to distal ischemic symptoms in 1. More than 90% of the ICCAAns were saccular. Thirty-four percent were small (less than 1 cm), 48% were large (1 to 2.5 cm), and 16% were giant (greater than 2.5 cm). The majority arose from the anterior genu of the intracavernous internal carotid artery, followed in frequency by the horizontal segment, and then the posterior genu. Magnetic resonance imaging is superior to computed tomography for diagnosing ICCAAns and is the screening procedure of choice. Angiography remains the "gold standard" for diagnosis and determining specific anatomic details necessary to plan therapy. Analyzing the radiographic anatomy of 44 ICCAAns. we conclude that theories attributing the origin of aneurysms to arterial bifurcations may be inadequate to explain the point of origin and direction of take off of up to one-fourth of ICCAAns.

Clinical observations on the effect of carotid artery occlusion on cerebral blood flow mapped by xenon computed tomography and its correlation with carotid artery back pressure

Xenon computed tomographic cerebral blood flow mapping was correlated with internal carotid artery stump pressures and clinical neurologic assessment during temporary internal carotid artery occlusion. One hundred fourteen patients with skull base tumors or intracranial aneurysms potentially requiring carotid resection or ligation underwent angiography, xenon CT cerebral blood flow mapping, and internal carotid artery blood pressure monitoring. The internal carotid artery was then temporarily occluded with a balloon catheter, stump pressure was measured through the catheter, and the xenon CT cerebral blood flow mapping was repeated. Adequate xenon CT cerebral blood flow was defined as greater than 30 cc/100 gm/min. All patients had normal xenon CT cerebral blood flow before internal carotid artery occlusion. During internal carotid artery occlusion, xenon CT cerebral blood flow was found to be normal (group I, 40 patients), globally reduced but still within the normal range (group II, 50 patients), or low in the distribution of the ipsilateral middle cerebral artery (group III, 13 patients). With balloon occlusion, an immediate neurologic deficit developed in 11 patients (9%) requiring deflation of the balloon preceding xenon CT cerebral blood flow measurement (group IV). In group I internal carotid artery blood pressure was 128 mm Hg. (range 85 to 171 mm Hg) with stump pressure 86 mm Hg (range 46 to 125 mm Hg). In group II internal carotid artery blood pressure was 130 mm Hg. (range 78 to 199 mm Hg), with stump pressure 86 mm Hg (range 31 to 150 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)

Autoregulation remains intact during stable xenon inhalation in the baboon

To test the possible effect of 32% end-tidal Xe concentration upon autoregulation, 5 baboons, Papio anubis/cynocephalus, were anesthetized/paralyzed with propranolol 0.02, diazepam 0.1, morphine sulfate 0.1, and pancuronium 0.2 (mg/(h.kg)). The animals were subjected to a servocontrolled blood infusion-withdrawal program to control central aortic blood pressure (CAP). PaCO2 was held to 30 to 35 torr, with individual variation less than 3 torr by control of ventilation and by including CO2 in the Xe/O2 mixture. Three to six CBF measurements were made in each subject over the above range. In four animals the CAP was varied between 18 and 150 torr, with corresponding CBF measurements. The CAP range was extended to 196 torr in the 5th animal by IV administration of phenylephrine. Significant lowering of global blood flow did not occur above 40 torr mean CAP. While regulated flow persists to about 150 torr at the high end, there is a breakaway between 150 and 190 torr where flow increased 90%. A 4th order polynomial fit of the data has the characteristic appearance of the familiar autoregulation curve. We conclude that autoregulation is preserved even in the presence of FIXe of 32% in the breathing mixture.

Intracranial pressure response to stable xenon inhalation in patients with head injury

Cerebral blood flow measured by xenon-enhanced computed tomography may provide useful information in victims of severe head injury. To assess the effect of stable xenon inhalation on intracranial pressure, intracranial pressure was measured in 17 mechanically ventilated patients with severe head injury undergoing cerebral blood flow studies with xenon-enhanced computed tomography. Under hypocapnic conditions, mean intracranial pressure increased by less than 1 mm Hg (p less than 0.05) late in the inhalation period only in patients whose baseline intracranial pressure was less than 20 mm Hg. It was concluded that under hypocapnic conditions, the magnitude of this increase in intracranial pressure does not prohibit the safe evaluation of cerebral blood flow in victims of head injury using xenon-enhanced computed tomography.

The acetazolamide challenge: imaging techniques designed to evaluate cerebral blood flow reserve

Cerebral blood flow was analyzed by the stable xenon (Xe)/CT scanning technique in 29 patients with significant vascular lesions before and after administration of an acetazolamide (Diamox) vasodilatory challenge. Three response types were identified: I, normal flow before Diamox with flow augmentation after Diamox; II, low flow before Diamox with flow augmentation after Diamox; and III, low or normal flow before Diamox with no augmentation or decreased flow after Diamox. Twenty-four percent of the patients studied qualified for category III. We believe that patients in this category represent a group of individuals without blood flow reserve whose clinical management should include careful consideration of their hemodynamic status. The Xe/CT scanning technique with the addition of Diamox flow challenge is a clinically accessible and effective method for assessing cerebral blood flow and blood flow reserve.

Cerebral blood flow determination within the first 8 hours of cerebral infarction using stable xenon-enhanced computed tomography

Cerebral blood flow mapping with stable xenon-enhanced computed tomography (Xe/CT) was performed in conjunction with conventional computed tomography (CT) within the first 8 hours after the onset of symptoms in seven patients with cerebral infarction. Six patients had hemispheric infarctions, and one had a progressive brainstem infarction. Three patients with very low (less than 10 ml/100 g/min) blood flow in an anatomic area appropriate for the neurologic deficit had no clinical improvement by the time of discharge from the hospital; follow-up CT scans of these three patients confirmed infarction in the area of very low blood flow. Three patients with moderate blood flow reductions (15-45 ml/100 g/min) in the appropriate anatomic area had significant clinical improvement from their initial deficits and had normal follow-up CT scans. One patient studied 8 hours after stroke had increased blood flow (hyperemia) in the appropriate anatomic area and made no clinical recovery.

Determination of irreversible ischemia by xenon-enhanced computed tomographic monitoring of cerebral blood flow in patients with symptomatic vasospasm

In patients with subarachnoid hemorrhage, delayed neurological deficits, often followed by infarction, are believed to result from ischemia caused by vasospasm. Cerebral blood flow (CBF) data have been useful in predicting the risk of vasospasm in these patients and in distinguishing those deficits caused by vasospasm. Although CBF thresholds for infarction have been established in animals, few clinical studies have correlated CBF values with neurological symptoms and infarction. To assess the sensitivity to ischemia provided by xenon-enhanced computed tomography (Xe/CT) of CBF and to define the clinical significance of specific values that it measures, we compared the clinical, CT, and Xe/CT findings on CBF in 51 patients with subarachnoid hemorrhage caused by ruptured aneurysms. Each patient had 1 to 6 Xe/CT studies. Fourteen patients had symptomatic vasospasm. In all 14, the first post deficit Xe/CT study found abruptly reduced CBF, either regionally or globally. In 9 of these 14 patients, flow values fell below 15 ml/100 g/min in 2 or more adjacent 2-cm cortical regions of interest, and in all 9, concurrent follow-up CT scans showed infarction in these regions. Eight of the 9 had paralysis and a severe sensory deficit. No patient whose CBF remained above 18 ml/100 g/min developed infarction. The blood flow studies caused neither significant complications nor neurological deterioration. The Xe/CT CBF method appears very sensitive to the early detection of symptomatic vasospasm. In most patients with subarachnoid hemorrhage, this noninvasive technique can replace angiography to delineate the location and severity of vasospasm, and may be useful in predicting the development of infarction.

Local "inverse steal" induced by hyperventilation in head injury

Hyperventilation is used routinely to reduce intracranial pressure in victims of severe head injury. In the clinical setting, the effects of hyperventilation on regional cerebral blood flow usually are not known. We describe a case in which hyperventilation resulted in local, paradoxic increases in cerebral blood flow (i.e., "inverse steal") associated with a reduction in intracranial pressure. Although the reduced intracranial pressure was thought to be beneficial, serial computed tomographic scans suggested that the inverse steal response could have promoted cerebral edema, resulting in secondary brain injury.

Value of transcranial Doppler examination in the diagnosis of cerebral vasospasm after subarachnoid hemorrhage

In 21 patients with subarachnoid hemorrhage secondary to ruptured intracranial aneurysms, we performed serial neurological evaluations, transcranial Doppler examinations, and cerebral blood flow (CBF) determinations. We classified 8 patients as having vasospasm (delayed neurological deterioration, appropriate reduction of CBF) and 13 patients as having no spasm on the basis of this information. Transcranial Doppler flow velocities in the middle cerebral artery and the anterior cerebral artery were significantly elevated for the group with vasospasm on posthemorrhage Days 4 through 12. Elevation of transcranial Doppler velocities preceded clinical signs of cerebral ischemia. The maximal transcranial Doppler flow velocities achieved were compared on the basis of the extent of clot on early computed tomographic (CT) scans. The mean anterior cerebral artery flow velocities were significantly different between CT Grades II and III. The initial transcranial Doppler flow velocities were compared on the basis of the patient's Hunt and Hess grade upon admission. The flow velocities for Grade V patients were significantly lower than those for Grade IV patients. Transcranial Doppler flow velocities were compared with arteriographically observed anterior cerebral artery and middle cerebral artery radii in 12 instances. The correlation was poor, but the data should be interpreted cautiously in view of the small number of arteriograms. We conclude that transcranial Doppler examination has considerable potential in the early diagnosis of delayed ischemic neurological deficit (clinical vasospasm) in patients with subarachnoid hemorrhage.

Stable xenon enhanced computed tomography in the study of clinical and pathologic correlates of focal ischemia in baboons

When the lateral striate arteries of baboons are occluded, an immediate cessation of blood flow followed by a transient, minimal restitution of flow occurs in that vascular distribution. These findings are evident from serial xenon/computed tomography cerebral blood flow imaging. In our study, infarction consistently accompanied arterial occlusion for 6 hours or more. The xenon/computed tomography method provides a sensitive, noninvasive technique for examining sequential alterations of cerebral blood flow in small regions deep within the brain. This methodology for recording cerebral blood flow permits correlative studies of cerebral infarction, clinically and experimentally, and allows reasonable inferences about the probabilities of neural tissue damage.