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Fredric B. Meyer, David G. Piepgras, and Nicolee C. Fode

✓ Ninety-two surgical procedures were performed in 82 patients for recurrent carotid artery stenosis. The etiology was recurrent atherosclerosis in 45 cases, myointimal hyperplasia in 20, organized thrombus without a significant underlying plaque in 20, and scarring along the proximal arteriotomy site in seven. The operations included a repeat endarterectomy in 66 cases and reconstruction with an interposition graft in 22. All five major neurological complications occurred in symptomatic patients, and included three instances of intraoperative embolization during exposure of the carotid artery. The majority of neurological complications occurred in symptomatic patients who had intraluminal thrombus confirmed at surgery. There were four perioperative deaths, due to cerebral hemorrhage in two patients and myocardial infarction in two.

In the patients whose original surgery was performed at the Mayo Clinic, the risk of recurrent carotid artery stenosis was 3.1% with a primary closure compared to 1.6% when a patch graft was used. These results indicate that surgery for recurrent carotid artery stenosis is technically more difficult and carries a significantly higher risk than surgery for primary disease. The difficulty is due to the friable recurrent plaque associated with intraluminal thrombus, which increases the risk of embolization during carotid artery exposure. In the majority of patients with recurrent atherosclerosis, a repeat endarterectomy can be achieved. However, in some patients, there is scarring without a definite plane of cleavage between the recurrent disease and the underlying media, making an endarterectomy difficult. In these cases, excision of the diseased segment and reconstruction with an interposition graft is the best treatment. The findings presented here also suggest that closure of the original arteriotomy with a patch graft decreases the risk of recurrent carotid artery stenosis.

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Fredric B. Meyer, John Huston III, and Stephen S. Riederer

✓ The internal flow dynamics were assessed in 16 cerebral aneurysms by cine phase-contrast magnetic resonance (MR) angiography. Six of the aneurysms were associated with subarachnoid hemorrhage and 10 were unruptured. The ruptured aneurysms demonstrated a 51% ± 10% increase in volume between systole and diastole, while the increase in volume of the unruptured aneurysms was 17.6% ± 8.9% (p < 0.005). The ruptured aneurysms demonstrated an approximate 1.0- to 1.5-mm increase in diameter in at least one dimension during systole. There was no relationship between aneurysm size and volumetric increases. These findings suggest that cine phase-contrast MR angiography can detect structural weakness in the aneurysmal wall. Imaging techniques that can evaluate aneurysmal wall dynamics may be useful in therapeutic planning.

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Marc S. Goldman, Robert E. Anderson, and Fredric B. Meyer

✓ There is controversy regarding the role of intermittent reperfusion employed as a cerebroprotective measure when temporary arterial occlusion is necessary during repair of difficult aneurysms. The intraluminal suture middle cerebral artery (MCA) occlusion technique was used in 23 Wistar rats under barbiturate anesthesia to induce 60, 90, or 120 minutes of uninterrupted MCA occlusion. The total infarcted areas obtained were compared to those occurring in 27 animals subjected to identical cumulative ischemic periods but with 5 minutes of reperfusion after every 10-minute ischemic period. The mean total infarcted areas in the groups with 60-minute (1.8 ± 0.89 sq mm), 90-minute (1.08 ± 1.02 sq mm), and 120-minute (8.72 ± 5.89 sq mm) intermittent reperfusion were significantly smaller than those occurring in the 60-minute (12.02 ± 3.10 sq mm), 90-minute (11.54 ± 2.68 sq mm), or 120-minute (30.43 ± 6.51 sq mm) control groups, respectively (p < 0.05). Furthermore, there was no difference in the occurrence of blood-brain barrier breakdown, intraparenchymal hemorrhage, hemispheric edema, or seizures between control and intermittent reperfusion groups. The results support the hypothesis that intermittent reperfusion is beneficial if vessel occlusion is required during aneurysm repair.

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Fredric B. Meyer and Donald A. Muzzi

✓ A strategy for intraoperative cerebral protection is described in which intraoperative electroencephalography is used to titrate the level of inspired isoflurane given for anesthesia to obtain isoelectricity prior to temporary vessel occlusion during repair of difficult aneurysms. During temporary vessel occlusion, arterial blood pressure is maintained or increased with an inotropic or vasopressor agent. After clipping of the aneurysm, the concentration of isoflurane is reduced to allow the patient to awaken in the operating room for early postoperative neurological examination. The combination of a high concentration of isoflurane, temporary vessel occlusion, and maintenance of arterial blood pressure may be a useful protective regimen during neurovascular procedures.

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Daniela Lombardi, Bernd W. Scheithauer, David Piepgras, Fredric B. Meyer, and Glenn S. Forbes

✓ The term “angioglioma” denotes a highly vascular glioma, most of which are low-grade lesions associated with a favorable prognosis. The authors encountered an example of this pathology, a cystic oligodendroglioma associated with prominent vasculature which both clinically and histologically mimicked an occult arteriovenous malformation (AVM). This case and reports of the association of AVM and glioma prompted a histological review of 1034 surgically resected AVM's, both angiographically occult and visible, among which no oligodendroglial or astrocytic forms of “angioglioma” were found. Eight cases were observed, however, wherein oligodendroglial cells were increased in number within or about the malformation. Two basic histological patterns of oligodendroglial cell excess were seen; one appeared to be malformative in nature with abnormal disposition of oligodendroglial cells being an integral part of the AVM, whereas in the other an apparent increase in cellularity seemed the result of chronic ischemia with condensation of white matter. It appeared that the areas of increased oligodendrocyte content seen in association with AVM are non-neoplastic lesions that exhibit two rather distinct histological patterns of differing origin.

In an effort to determine the frequency of “angioglioma,” the authors examined Tissue Registry data for several glioma groups in which highly vascular examples are prone to occur. Tumors selected for study included 104 cerebellar-type (pilocytic) astrocytomas, 82 oligodendrogliomas, and 51 supratentorial pilocytic astrocytomas. Histological hypervascularity mimicking a vascular malformation (that is, an “angioglioma”) was encountered in 5%, 4%, and 12% of the cases, respectively. Based upon clinical, radiological, and pathological reviews of these cases, as well as a careful review of the literature, it was concluded that 1) “angiogliomas” are neither rare nor represent a distinct clinicopathological entity; 2) in histological but not necessarily angiographic surgical terms, they represent simply highly vascular gliomas, usually of low grade; and 3) the clinicopathological and angiographic features as well as the prognosis of such lesions do not differ from those of similar gliomas without angioma-like vasculature. Finally, “angiogliomas” must not be confused with gliomas of high-grade malignancy which, due to neovascularity, may be highly vascular at angiography and at surgery.

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Daniela Lombardi, Bernd W. Scheithauer, Fredric B. Meyer, Glenn S. Forbes, Edward G. Shaw, Donna J. Gibney, and Jerry A. Katzmann

✓ Twenty-one intracranial subependymomas were reviewed with regard to presentation, diagnosis, operative findings, and long-term follow-up data. The histopathological features were critically reviewed, and deoxyribunucleic acid analysis was performed by flow cytometry. The patients' mean age was 48.5 years (range 32 to 72 years). In 14 cases the tumor was located in the fourth ventricle, in six within a lateral ventricle, and in one in the third ventricle with extension into the lateral ventricle. Radiographic characteristics included isodensity with minimal enhancement on computerized tomography, frequent dystrophic calcification, and isointensity on T1-weighted or slight hyperintensity on T2-weighted magnetic resonance images. The predominant histological features in all cases were those of classic subependymoma. Nonetheless, pathological examination showed a minor (< 20%) ependymoma component in five cases, significant cytological atypia in seven, mitoses in 11, endothelial prominence in four, and focal hemorrhage-associated necrosis in two. Flow cytometry revealed a diploid pattern in 12 patients, tetraploidy in two, and aneuploidy in one.

Two patients died in the perioperative period. Of the remaining 19, 12 underwent gross total resection (two of whom received postoperative irradiation) and seven underwent subtotal resection (five of whom received irradiation). None of the 12 non-irradiated patients developed tumor progression or died of direct tumor-related causes. Of the seven irradiated patients, follow-up imaging studies demonstrated their tumors to be radioresponsive, particularly with doses of 5000 cGy or greater. Despite the presence of cytological atypia and mitotic activity in the majority of cases, the prognostic effects of such factors as tumor location and the extent of surgical resection outweighed those of the standard histopathological parameters. Routine postoperative irradiation is not recommended, but should be reserved for cases with a symptomatic residual or recurrent subependymomas following surgery.

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Fredric B. Meyer, Daniela Lombardi, Bernd Scheithauer, and Douglas A. Nichols

✓ Extra-axial cavernous hemangiomas are rare lesions previously associated with unacceptable mortality and morbidity rates that precluded surgical resection. The authors analyze the clinical presentation, surgical results, and histology of eight intrasinus cavernous hemangiomas: six located in the cavernous sinus, one in the petrosal sinus, and one in the torcula. Magnetic resonance imaging is the best radiographic test for surgical planning. Successful tumor removal was achieved in six cases with no mortality and low morbidity. In the remaining two patients, only subtotal resection was achieved because of massive hemorrhage in one and the misdiagnosis of a pituitary adenoma leading to a transsphenoidal approach in the other. For hemangiomas arising within the cavernous sinus, extradural removal of the sphenoid bone facilitated preservation of the neurovascular structures. Since the clinical and histological characteristics of these lesions are distinct from intra-axial cavernous hemangiomas, a more appropriate term may be “sinus cavernoma” to indicate that these lesions are primarily intrasinus in origin.

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Fredric B. Meyer, Thoralf M. Sundt Jr., Nicolee C. Fode, Michael K. Morgan, Glen S. Forbes, and James F. Mellinger

✓ In this study, 24 aneurysms occurring in 23 patients under the age of 18 years (mean 12 years) are analyzed. The male:female ratio was 2.8:1, and the youngest patient was 3 months old. Mycotic lesions and those associated with other vascular malformations were excluded. Forty-two percent of the aneurysms were located in the posterior circulation, and 54% were giant aneurysms. Presenting symptoms included subarachnoid hemorrhage in 13 and mass effect in 11. Several of these aneurysms were documented to rapidly increase in size over a 3-month to 2-year period of observation. All aneurysms were surgically treated: direct clipping was performed in 14; trapping with bypass in four; trapping alone in four; and direct excision with end-to-end anastomosis in two. The postoperative results were excellent in 21 aneurysms (87%), good in two (8%), and poor in one. The pathogenesis of cerebral aneurysms is reviewed.

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Treatment of experimental focal cerebral ischemia with mannitol

Assessment by intracellular brain pH, cortical blood flow, and electroencephalography

Fredric B. Meyer, Robert E. Anderson, Thoralf M. Sundt Jr., and Tony L. Yaksh

✓ Intracellular brain pH, cortical blood flow (CBF), and electrocorticograms were recorded in regions of severe and moderate ischemia in 10 control rabbits and 10 rabbits given mannitol, 1 gm/kg, after occlusion of a major branch of the middle cerebral artery. Pooling the data from all 20 animals, preocclusion CBF was 46.4 ±3.6 ml/100 gm/min and intracellular brain pH was 7.01 ± 0.04 (means ± standard error of the means). Although mannitol administration mildly improved CBF in regions of severe ischemia, this increase was not sufficient to prevent metabolic deterioration as assessed by brain pH. However, in regions of moderate ischemia, CBF improved significantly with mannitol and the gradual decline in brain pH observed in control animals was prevented. For example, in the treated moderate ischemia sites 4-hour postocclusion CBF and pH values were 31.8 ml/100 gm/min and 6.89 ± 0.09, respectively, as compared to control values of 14.3 ml/ 100 gm/min and 6.75 ± 0.06. These results suggest that mannitol may be of benefit in stabilizing regions of moderate, but not severe, ischemia after vessel occlusion.