Improvement of cerebral blood flow and/or CO2 reactivity after superficial temporal artery-middle cerebral artery bypass in patients with transient ischemic attacks and watershed-zone infarctions

Superficial temporal artery to middle cerebral artery bypass: past, present, and future

OBJECT

The aim of this study was to review the historical developments and current status of superficial temporal artery (STA) to middle cerebral artery (MCA) bypass.

METHOD

A literature review was performed to review the origins and current uses of the STA bypass procedure in neurosurgery.

RESULTS

The idea of providing additional blood supply to the brain to prevent stroke and maintain neurological function has been present in the mind of neurosurgeons for many decades. In 1967 the first STA-MCA bypass was done by M. G. Yaşargil, and an enormous step was made into the field of microneurosurgery and cerebral revascularization. During the decades that followed, this technique was used as an adjuvant or a definitive surgical treatment for occlusive disease of the extracranial and intracranial cerebral vessels, skull base tumors, aneurysms, carotid-cavernous fistulas, cerebral vasospasm, acute cerebral ischemia, and moyamoya disease. With the results of the first randomized extracranial-intracranial (EC-IC) bypass trial and the development of endovascular techniques such as angioplasty for intracranial atherosclerotic disease and cerebral vasospasm, the indications for STA-MCA bypass became limited. Neurosurgeons continued to perform EC-IC bypasses as an adjuvant to clipping of aneurysms and in the treatment of skull base tumors and moyamoya disease; the procedure is less commonly used for atherosclerotic carotid artery occlusion (CAO) with definite evidence of hemodynamic insufficiency. The evidence that patients with symptomatic CAO and "misery perfusion" have an increased stroke risk has prompted a second trial for evaluating EC-IC bypass for stroke prevention. The Carotid Occlusion Surgery Study is a new trial designed to determine whether STA-MCA bypass can reduce the incidence of stroke in these patients. New trials will also reveal the role of the STA-MCA bypass in the prevention of hemorrhages in moyamoya disease.

CONCLUSIONS

The role of STA-MCA bypass in the management of cerebrovascular disease continues to be refined and evaluated using advanced imaging techniques and by performing randomized trials for specific purposes, including symptomatic CAO.

Evaluation of extracranial-intracranial arterial bypass function with magnetic resonance angiography

Extracranial-intracranial (EC/IC) arterial bypass surgery is a valuable therapeutic modality in the field of cerebrovascular surgery. The assessment of bypass patency and its functional parameters are of utmost importance in the postoperative course. The present study examined the potential role of quantitative MR-based volume flow measurement techniques for the investigation of bypass patency. Forty-one patients with steno-occlusive cerebrovascular disease treated with EC/IC bypass surgery underwent conventional angiographic (CA) and two-dimensional cine-phase MR-based angiographic assessment (MRA) of bypass function. CA bypass function was evaluated as poor (grade I), moderate (grade II), or extensive (grade III) and was compared with quantitative volume flow measurements (BVF) obtained in MRA studies. Bypass filling was classified as grade I in 15% of the cases, grade II and grade III in 36% and 49% of the studies, respectively. Mean BVF differed significantly in the different grades: 31.94 +/- 9.8 ml/min in grade I, 73.6 +/- 16.7 ml/min in grade II, and 97.2 +/- 26.6 ml/min in grade III. BVF values of 48 ml/min or lower (n = 6) were specific for grade I bypass function, while only BVF values higher than 111 ml/min (3/20, 15%) are specific for extensive angiographic bypass function. The assessment of EC/IC bypass patency with quantitative BVF measurements provides exact, investigator-independent information under physiological conditions. MRA is well correlated with the angiographic bypass grading system.

CO2 reactivity in patients after subarachnoid haemorrhage

CO2 reactivity was tested in patients with transcranial Doppler sonography (TCD) and endtidal CO2 measurements after an average time interval of ten months after subarachnoid haemorrhage (SAH). After deliberately changing breathing there was a significant change in endtidal CO2 and in flow velocities in all three examination groups. Comparing 27 patients with SAH and 5 patients treated for incidental aneurysms and 20 patients without cerebrovascular disease there were no significant differences in CO2 reactivity. Furthermore, there were no right to left differences. In 12 patients with vasospasm, two of them treated by percutaneous transluminal angioplasty for delayed ischaemic deficits, CO2 reactivity was normal at the time of investigation. Furthermore, normal CO2 reactivity was found in patients after SAH and surgery for ruptured aneurysms regardless of the severity of the SAH.

Cortical blood flow and cognition after extracranial-intracranial bypass in a patient with severe carotid occlusive lesions. A three-year follow-up study

The long-term effect of extra-intracranial arterial bypass on cerebral circulation was examined. Cortical blood flow and cognitive ability were evaluated pre- and up to 3 years post-bypass in a 58-years-old man with severe carotid occlusive lesions, who presented with 3 transient cerebral ischaemic attacks which resulted in mental deterioration over 3 years. Regional cerebral blood flow (rCBF) was evaluated pre- and up to 33 months post-bypass by 123Iodine N-isopropyl-p-iodoamphetamine (IMP) single-photon emission CT (SPECT). Mental abilities were evaluated before and up to 33 months after surgery by the Hasegawa's dementia rating scale (HDRS). Pre-operatively, cerebral angiography showed left carotid siphon occlusion and hypoplastic stenosis of left anterior cerebral artery with collaterals from the anterior communicating artery. CT and MRI showed left temporo-parietal borderzone infarction and an enhanced T 1 lesion by gadolinium-DTPA at left periventriculum. rCBF showed extensive hypoperfusion in left anterior-parieto-temporal-cortex. HDRS scores deteriorated apparently on days 3, 5, which recovered gradually on days 8, 10, 75 after onset of mental deterioration. A bypass was performed 4 months after onset. rCBF showed gradual recovery in the left anterior-parietal cortex up to 33 months after bypass. Semiquantitative rCBF showed gradual decreases of regional asymmetry after the bypass. HDRS scores returned to their maximum up to 37 months after onset. Three-year follow-up shows improved cortical rCBF and cognition after the bypass.

Magnetic resonance angiography and selective angiography following extra-intracranial bypass operations

Magnetic resonance angiography (MRA) was compared with conventional angiography in 14 patients following extra-intracranial arterial anastomosis. In 13 patients the bypass was shown by MRA and confirmed by conventional angiography. In five of these, the anastomosed vessels, in particular the superficial temporal artery, was of the same calibre or smaller than the same vessels on the contralateral, healthy side. In one patient no anastomosis could be shown by MRA, and occlusion of the bypass was confirmed by conventional angiography. Absence of dilatation of the anastomotic vessels may indicate insufficient bypass function due to stenosis or an incorrect indication for surgery.

A simple test to assess cerebrovascular reserve capacity using transcranial Doppler sonography and acetazolamide

The goal of this study was the development of a simple bedside test to assess cerebrovascular reserve capacity using transcranial Doppler sonography. We studied 33 normal persons at rest and after stimulation of cerebral blood flow with 1 g acetazolamide. Their mean +/- SD increase in blood flow velocity in 54 middle cerebral arteries 10 minutes after stimulation was 24.4 +/- 9.2 cm/sec. We tried to validate the increase in blood flow velocity as cerebrovascular reserve capacity in 21 patients with obstructive carotid artery disease and symptoms of cerebral ischemia. The patients were studied using transcranial Doppler sonography and xenon-133 dynamic single-photon emission computed tomography after acetazolamide stimulation. Their increases in blood flow velocity (delta FV) and increases in cerebral blood flow (delta CBF) correlated significantly in both hemispheres (asymptomatic: Y = 0.32X + 10.65, r = 0.45, p = 0.04; symptomatic: Y = 0.36X + 2.28, r = 0.59, p = 0.004). There was no significant difference between the slopes of the regression lines. Blood flow velocity and cerebral blood flow at rest were not correlated. The increase in blood flow velocity after acetazolamide stimulation offers a simple and reliable method for assessing cerebrovascular reserve capacity.

Changes in hyperfrontality of cerebral blood flow and carbon dioxide reactivity with age

We evaluated the topographic distributions of regional cerebral blood flow in 51 normal subjects (mean age 41 years) by the xenon-133 inhalation technique. Forty-five of these subjects were divided by age into young normals less than 30 years old (mean age 24 years), middle-aged normals 30-50 years old (mean age 40 years), and elderly normals greater than 50 years old (mean age 62 years); there were 15 subjects in each group. The distributions of vascular CO2 reactivity to hypocapnia were also evaluated in 20 of the normal subjects (mean age 34 years), including 11 younger normals less than 30 years old (mean age 24 years) and nine older (middle-aged or elderly) normals greater than or equal to 30 years old (mean age 45 years). The hyperfrontal distribution of regional cerebral blood flow observed in the young and middle-aged normals was not observed in the elderly normals. The hyperfrontal distribution of vascular CO2 reactivity observed in the younger normals was absent in the older normals. In addition, the correlation between regional cerebral blood flow and vascular CO2 reactivity observed in the younger normals was disturbed in the older normals. The data show a hyperfrontal distribution of regional cerebral blood flow in normal subjects that diminishes during the fifth and sixth decades, along with a distribution of vascular CO2 reactivity in younger normal subjects that is not homogeneous throughout the frontoparietal regions.(ABSTRACT TRUNCATED AT 250 WORDS)

The Doppler CO2 test to exclude patients not in need of extracranial/intracranial bypass surgery

In patients with an internal carotid artery (ICA) occlusion who suffer from ipsilateral transient ischaemic attacks or minor stroke extra/intracranial (EC/IC) bypass surgery may be useful only where there is insufficient collateral supply. The transcranial Doppler CO2 test offers a simple method of investigating the residual autoregulatory capacity which gives quantitative information about the efficiency of the collaterals. In 155 patients with 162 ICA occlusions there was a significant correlation between a markedly decreased or exhausted autoregulatory capacity and a recent ipsilateral ischaemic event (p less than 0.001). The Doppler CO2 test may enable the exclusion of patients not in need of EC/IC bypass surgery. In the reported series this affected more than 80% of all ICA occlusions.

Measurements of regional cerebral blood flow in patients following superficial temporal artery-middle cerebral artery anastomosis

Regional cerebral blood flow (rCBF) was measured using the inhalation xenon 133 technique in 25 patients undergoing superficial temporal artery-middle cerebral artery anastomotic surgery. rCBF was measured once before and 3 times after operation, up to one year. Data were compared to rCBF-measurement in 16 patients with similar diagnosis, age distribution and medical treatment except that they were not operated on. Mean rCBF increased in some patients 4-8 weeks after surgery on the ipsilateral side. Compared to the non-surgical patients mean rCBF at this time was higher over both hemipheres. However, taking a flow increase of at least 15% as being significant only one third of all patients presented with a significant flow increase. Regional flow data indicated that the amount of hypoaemic areas in the operated side decreased significantly. Areas with normal flow increased in number from CBF 1 to the 4-8th week. There were no significant changes in flow distribution over the contralateral side. It was concluded that extracranial-intracranial bypass improves flow in patients with TIA or PRIND respectively only in some cases. Also a return to normal flow distribution can be achieved in only a few cases.

Neurological improvement in chronic ischemic stroke following surgical brain revascularization

50 patients suffering from completed ischemic stroke in the carotid territory for at least two months (17 mild, 31 moderate, 2 severe strokes) underwent extra-intracranial arterial bypass surgery. Neurological improvement was obtained in 43 cases; it persisted in time in 40 cases. Quantitative evaluation of motor performance in 21 patients showed that the degree of improvement was highly significant. Several factors strongly indicate a causal relation between surgical revascularization and neurological restoration. The positive surgical result is strictly dependent on correct patient selection and, in particular: i) on the documentation of local hemodynamic insufficiency; ii) on the occurrence of transient neurological (and to a certain extent EEG) improvement following hyperbaric oxygenation. The latter can also provide reliable information on the minimum degree of improvement to be expected from surgery.

Cerebral haemodynamic changes after extracranial-intracranial bypass surgery

Regional cerebral blood flow, oxygen utilisation, fractional oxygen extraction, and cerebral blood volume were measured by positron emission tomography in twelve patients with carotid artery occlusion. Follow-up studies were carried out at a mean interval of eleven weeks after extracranial-intracranial bypass surgery. Clinical improvement was observed in three patients who had presented with frequent transient ischaemic attacks. One patient with multiple vascular occlusions suffered a stroke at the time of surgery. Follow-up studies showed an increase of regional cerebral blood flow in only two of the twelve patients. In the group as a whole, there was no significant change of cerebral blood flow, oxygen consumption or fractional oxygen extraction after bypass surgery. The most consistent post-operative change, observed in eleven of the twelve patients, was a fall of cerebral blood volume in the cortical territory of the bypassed carotid artery (p less than 0.01). This effect was most marked in patients with bilateral carotid occlusion, in whom there was often an accompanying fall of blood volume in the contralateral hemisphere. The post-operative findings were consistent with an increase of regional cerebral perfusion pressure as a result of the bypass procedure. Although this effect is potentially of value, those patients with most to gain from bypass surgery may also run the highest risk of peri-operative cerebral ischaemia.

Transcranial Doppler CO2 test for the detection of hemodynamically critical carotid artery stenoses and occlusions

Cerebral CO2-reactivity was tested by transcranial Doppler sonography (Doppler CO2 test) in 232 patients. Time averaged flow velocity in the middle cerebral artery at the 40 mm Hg blood pCO2 level was taken as a reference point, and the relative increase of flow in hypercapnia of 46.5 mm Hg pCO2 was defined as "Normalized Autoregulatory Response" (NAR). A total of 82 patients with no evidence of cerebrovascular disease gave "normal" values for NAR (23.2 +/- 5.2 SD). In 150 patients with 233 stenoses and occlusions of the internal carotid artery NAR was significantly decreased in higher-grade stenoses (P = 0.01 for 80% diameter reduction, P less than 10(-6) for 90% or more). In such stenoses, patients with NAR less than 14 had suffered more frequently (P less than 0.01) from ipsilateral transient ischemic attacks and/or stroke during the previous 6 months than patients with "normal" NAR. Preoperative NAR less than 14 always improved to "normal" values following carotid surgery, while preoperative NAR greater than 19 remained unchanged (60 cases). The transcranial Doppler CO2 test is thought to be a reliable noninvasive method to detect hemodynamically critical carotid stenoses and occlusions. This may be of interest in selecting patients for superficial temporal artery-middle cerebral artery bypass and carotid surgery. For practical use 4 categories of NAR are suggested.

T.I.A. revisited: new wine--old bottle

TIA has been accepted as a concept of transient cerebral ischemia. There is an ever enlarging body of literature sparking controversies considering its natural history, prognosis, outcomes of clinical trials and usefulness of the concept. Much of the controversy is related to the diverse pathophysiology of TIAs, the selection of patients for clinical trials and the associated risk factor in the studied population. The advantages of the concept are a warning of the possibility of future irreversible pathology an opportunity to treat and/or remove risk factors an opportunity to establish a basis for monitoring the patient and making interim decisions concerning intervention. The risks of the concept are: administering a specific therapy to all patients, failure to fully evaluate the patient once the diagnosis is made, tendency to rely on "experts" for guidance. TIA is a useful concept if one recognizes: the pathophysiology is polymorphous and multiplex, the concept is a signal for diligent search for the underlying cause or causes, it is more important to treat the risk factors than to give a specific therapy.

Failure of extracranial-intracranial arterial bypass to reduce the risk of ischemic stroke. Results of an international randomized trial

To determine whether bypass surgery would benefit patients with symptomatic atherosclerotic disease of the internal carotid artery, we studied 1377 patients with recent hemisphere strokes, retinal infarction, or transient ischemic attacks who had atherosclerotic narrowing or occlusion of the ipsilateral internal carotid or middle cerebral artery. Of these, 714 were randomly assigned to the best medical care, and 663 to the same regimen with the addition of bypass surgery joining the superficial temporal artery and the middle cerebral artery. The patients were followed for an average of 55.8 months. Thirty-day surgical mortality and major stroke morbidity rates were 0.6 and 2.5 per cent, respectively. The postoperative bypass patency rate was 96 per cent. Nonfatal and fatal stroke occurred both more frequently and earlier in the patients operated on. Secondary survival analyses comparing the two groups for major strokes and all deaths, for all strokes and all deaths, and for ipsilateral ischemic strokes demonstrated a similar lack of benefit from surgery. Separate analyses in patients with different angiographic lesions did not identify a subgroup with any benefit from surgery. Two important subgroups of patients fared substantially worse in the surgical group: those with severe middle-cerebral-artery stenosis (n = 109, Mantel-Haenszel chi-square = 4.74), and those with persistence of ischemic symptoms after an internal-carotid-artery occlusion had been demonstrated (n = 287, chi-square = 4.04). This study thus failed to confirm the hypothesis that extracranial-intracranial anastomosis is effective in preventing cerebral ischemia in patients with atherosclerotic arterial disease in the carotid and middle cerebral arteries.

Computer-analyzed EEG before and after bypass surgery. Quantification by a computerized wave form recognition method

Chronological changes of the EEG before and after extracranial-intracranial arterial bypass surgery were studied on 12 patients with minor completed stroke of the carotid circulation. Instead of a power spectrum used in the conventional computer analysis, a wave form recognition method, which well correlated with visual assessment of the EEG, was applied to the present computer analysis of the EEG. The EEG changed mainly in the parietal, occipital, anterior and middle temporal records of the affected cerebral hemisphere. Deterioration of the EEG continued until 1 month, and improved gradually during 3 and 6 months after the operation. However, it was difficult to conclude that the EEG improved by surgery.