Cerebral blood flow in frontal lesions of aneurysms of the anterior communicating artery

Cerebral microdialysis and positron emission tomography after surgery for aneurysmal subarachnoid hemorrhage in grade I patients

BACKGROUND

Using cerebral microdialysis, baseline values for energy-related chemical markers have been reported in awake patients. Radionuclide studies have demonstrated a locally decreased metabolism, thought to be the result of brain retraction. These baseline values, however, may not be applicable to patients after surgical aneurysm repair following a subarachnoid hemorrhage (SAH). We assessed metabolic chemical marker levels in World Federation of Neurological Surgeons Committee (WFNS) grade I SAH patients after aneurysm surgery and compared them with previously reported baseline values.

METHODS

In 5 WFNS grade I SAH patients, energy-related chemical marker levels were obtained using microdialysis in the area of brain retraction after aneurysm surgery. In addition, an [(18)F]2-deoxy-d-glucose positron emission tomography (FDG-PET) was performed.

RESULTS

The FDG-PET showed a decrease of glucose metabolism in the frontotemporal area. Comparing the mean values for chemical markers of this study with reported baseline values, the most striking difference was a mild decrease of pyruvate and an increase of the lactate/pyruvate ratio. In individual patients, some markers indicated possible ischemia. A consistent pattern or ischemic profile for all markers, however, was not found.

CONCLUSION

FDG-PET scanning confirmed postoperative metabolic changes found in previous studies. Mean interstitial chemical marker levels ranged from normal to mildly deviant compared with reference chemical marker levels for awake patients and are likely to be applicable in SAH patients after aneurysm repair.

Intraoperative Mild Hypothermia Ameliorates Postoperative Cerebral Blood Flow Impairment in Patients with Aneurysmal Subarachnoid Hemorrhage

OBJECTIVE

Intraoperative mild hypothermia has been used during cerebral aneurysm surgery to reduce ischemic injury induced by temporary vessel occlusion and brain retraction. However, the clinical effects on cerebral hemodynamics are unclear. This study investigated the effects of intraoperative mild hypothermia on cerebral blood flow (CBF) after surgery to treat aneurysmal subarachnoid hemorrhage.

METHODS

Twenty-four patients with ruptured internal carotid or middle cerebral artery aneurysms, of preoperative Hunt and Hess Grade II or III, underwent aneurysm clipping within 72 hours after the onset of subarachnoid hemorrhage. During surgery, patients were randomly assigned to either intraoperative mild hypothermia (33.5°C, n = 12) or normothermia (37°C, n = 12). Brain single photon emission computed tomography with 99m Tc-hexamethylpropylenamine oxime or 99m Tc-l,l-ethylcysteinate dimer was performed on Days 4, 7, and 14 after subarachnoid hemorrhage. Regional CBF was determined in the basal ganglia and cingulate, frontal, and frontoparietal cortices, using a semiquantitative method.

RESULTS

CBF in the frontal cortex ipsilateral to the aneurysm was significantly higher in the hypothermia group than in the normothermia group on Day 4 (P < 0.01) but not Day 7 or 14. There was a similar trend in the ipsilateral frontoparietal cortex, but it was not significant. There were no differences in regional CBF in the ipsilateral cingulate cortex or basal ganglia or in any contralateral region during the study period.

CONCLUSION

Intraoperative mild hypothermia may reduce the severity of ischemia induced by intraoperative temporary vessel occlusion and brain retraction, thus ameliorating postoperative CBF impairment. (47;601;2000)

Cerebral hemodynamic and metabolic changes caused by brain retraction after aneurysmal subarachnoid hemorrhage

OBJECTIVE

The cerebral hemodynamic and metabolic effects of aneurysmal subarachnoid hemorrhage are complex. To investigate the impact of surgical retraction, we analyzed position emission tomography (PET) studies that measured the regional cerebral metabolic rate for oxygen, regional oxygen extraction fraction, and regional cerebral blood flow in four patients before and after right frontotemporal craniotomies for clipping of ruptured anterior circulation aneurysms.

METHODS

Preoperative studies were conducted 1 day before surgery and postoperative studies 6 to 17 days after surgery. No patient had hydrocephalus or intracerebral hematoma. At the time of the second PET study, none of the patients had signs of clinical vasospasm. Regional measurements were obtained from the right ventrolateral frontal and anterior temporal regions corresponding to the area of retraction and compared to the same regions in the opposite hemisphere. To establish a quantitative means to differentiate between hemodynamic and metabolic changes related to arterial vasospasm and those caused by brain retraction, we studied a second group of preoperative patients, who had undergone PET during angiographic and clinical vasospasm.

RESULTS

There was a 45% reduction in regional cerebral metabolic rate for oxygen (1.87 +/- 0.22 to 1.04 +/- 0.28 ml 100 g-1 min-1) and 32% reduction in regional oxygen extraction fraction (0.41 +/- 0.04 to 0.28 +/- 0.03) in the region of retraction but no change in the opposite hemisphere (paired t test; P = 0.042 and 0.003, respectively). There was no change in regional cerebral blood flow in any region. Brain retraction produced a focal area of tissue injury at the site of retractor blade placement, as compared to more diffuse vascular territory changes produced by vasospasm.

CONCLUSION

This reduction in the cerebral metabolic rate of oxygen and the oxygen extraction fraction indicates a primary reduction in metabolism and uncoupling of flow and metabolism (luxury perfusion). Similar findings of luxury perfusion have been reported after ischemic stroke and traumatic brain injury. Further studies will be necessary to fully understand the clinical and pathophysiological significance of these observations.

Aneurysm of the anterior communicating artery: a review of neuroanatomical and neuropsychological sequelae

For over 100 years, the study of amnesia in humans has been limited primarily to subjects with either diencephalic or mesial temporal lobe lesions. However, over the last 30 years, it has been reported that individuals who survived aneurysms of the anterior communicating artery (ACoA) often displayed an amnestic syndrome, despite the fact that diencephalic and mesial temporal structures were intact. This article presents a comprehensive review of the ACoA literature concerning the neurobehavioral and neuroanatomical substrates of what has been termed the "ACoA syndrome". Various theoretical models regarding the neural substrates of amnesia are discussed. Possible directions for future research are outlined.