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S. V. Ramana Reddy, William E. Karnes, Franklin Earnest IV and Thoralf M. Sundt Jr.

✓ A case of spontaneous vertebral arteriovenous fistula in association with fibromuscular dysplasia is reported. The patient presented with progressive cervical myelopathy and cervical bruit. The pathogenesis of the fistula development and the spinal cord symptoms is discussed. Symptoms subsided after obliteration of the fistula.

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Dudley H. Davis and Thoralf M. Sundt Jr.

✓ The relationship among cerebral blood flow (CBF), blood volume, cardiac output (CO), and mean arterial blood pressure (MABP) at varying levels of arterial CO2 tensions (PaCO2) were studied in 70 normal cats. The CBF was measured from the clearance curve of xenon−133 and CO with a thermal dilution catheter placed in the pulmonary artery. The CBF, CO, and MABP values varied appropriately with changes in PaCO2, confirming the reliability of the preparations and the presence of normal autoregulatory responses. Moderate hypovolemia that did not change MABP did, nevertheless, significantly decrease CO and CBF. In an effort to determine if this decrease in CO and CBF were coupled responses, the effects of beta stimulation, hypervolemia, and alpha and beta blockade were investigated. Propranolol, in a dosage insufficient to change MABP, decreased both CO and CBF. This agent abolished the CO response to elevations in PaCO2 but not the CBF response, making it unlikely that this CBF reduction resulted from impaired cerebral autoregulation. Isoproterenol, which, in contrast to propranolol, does not cross the normal blood-brain barrier, alone or in combination with phenoxybenzamine, produced a 38% and 72% increase in CO, respectively, without a change in CBF. Alpha blockade (no major change in CO) and beta blockade (major decrease in CO) did not significantly effect cerebral autoregulation to changes in MABP from angiotensin. The ability of the brain to resist increases in MABP and CO and maintain normal CBF is explained by normal cerebral autoregulation. However, its vulnerability to modest decreases in blood volume, which cannot be attributed to variations in perfusion pressure, is unexplained but obviously has important therapeutic implications. This may be related to reduction in CO, changes in autonomic activity, or a decrease in the size of the perfused capillary bed.

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Benjamin R. Gelber and Thoralf M. Sundt Jr.

✓ Ten patients with intracranial internal carotid artery (ICA) aneurysms were managed by combining ICA ligation with an extracranial to intracranial bypass procedure. Nine of these grafts were proven patent by angiogram. One patient was unable to return for postoperative angiograms; his graft had appeared patent on physical examination. Seven aneurysms were intracavernous, two were giant carotid-ophthalmic aneurysms, and one aneurysm was at the intracranial bifurcation of the ICA. Despite occlusion cerebral blood flow (CBF) measurements of 20 ml/100 gm/min or less in six patients, only one patient was unable to tolerate ICA ligation. Three patients developed transient aphasia, but there were no permanent neurological deficits associated with the carotid occlusion. Seven patients had improvement in pre-existing extraocular palsies or visual field defects. Others remained stable.

The combination of an extracranial to intracranial microvascular bypass procedure with ICA ligation seems to be an effective method of treatment for aneurysms near the base of the skull that cannot be obliterated by a direct intracranial approach. The addition of the bypass procedure permits ICA ligation in patients who would not otherwise have tolerated occlusion of that vessel. Intraoperative xenon CBF measurements are an important adjunct to the operation.

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Surgical approach to giant intracranial aneurysms

Operative experience with 80 cases

Thoralf M. Sundt Jr. and David G. Piepgras

✓ The authors report experience with the surgical management of 80 giant intracranial aneurysms (> 2.5cm in diameter) during a 10-year period in which they performed 594 operations for aneurysms. The overall incidence of giant aneurysms was 13% but varied according to location: 20% of aneurysms of the internal carotid artery (ICA); 13% of middle cerebral artery (MCA) aneurysms; 1% of anterior cerebral artery (ACA) aneurysms; 15% of aneurysms of the basilar artery caput (BAC); and 18% of vertebrobasilar trunk(VB) aneurysms. Twenty-five patients had a subarachnoid hemorrhage (SAH), 49 had mass effect from the aneurysm, and six had ischemic events. There was no apparent difference in results related to the presence or absence of an SAH. Poor results were attributable to the operation except in the two cases of ACA aneurysm in which preexisting dementia persisted. Mortality was 4% and morbidity was 14%, varying from a combined low morbidity-mortality of 8% for ICA lesions to a high of 50% for BAC aneurysms. During the period of the study, different techniques were developed in an attempt to lower the risks of surgery.Ultimately ICA aneurysms were monitored with cerebral blood flow measurements and electroencephalography before and after temporary ICA ligation, then approached following resection of the anterior clinoid or treated with bypass in combination with ICA ligation. Aneurysms of the MCA were either opened during temporary MCA occlusion or resected in combination with a bypass procedure. Bypass grafts and circulatory arrest with extracorporeal circulation may have a role in giant aneurysms of the posterior circulation.

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Thomas J. Rosenbaum and Thoralf M. Sundt Jr.

✓ Various straight-jawed aneurysm clips were tested for occluding capabilities on a vascular tissue model. Occluding pressures varied markedly among the clip styles and were altered by changes in the lumen and tissue composition of the model. Mechanical characteristics are highly variable between clip styles, but fall within a narrow range for clips of a similar style. The complex interplay of the unique aspects of clip design and force generated by the spring in conjunction with tissue characteristics and precise clip placement upon the tissue are major variables in the apparent ability of a particular clip to occlude the neck of an aneurysm.

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Thoralf M. Sundt Jr. and David G. Piepgras

✓ The results, complications, and technical aspects of occipital to posterior inferior cerebellar artery (PICA) bypass surgery are reviewed. Patients were divided into two groups: those considered to be a high risk for posterior circulation infarct but not disabled by the symptoms or deficits (eight patients), and those moderately or severely disabled at the time of admission (eight patients). Postoperative angiography revealed that 15 of the 16 grafts were patent. In 10 of the 15 patent grafts, the bypass graft served as a sole or major blood supply of the vertebral basilar system; in five patients, flow was limited to the distribution of the PICA. Eight patients achieved full employment or normal activity, six were improved but did not return to full employment, and two patients were unchanged. Ataxia was the major residual deficit in these patients.

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Carotid endarterectomy

Temporal profile of the healing process and effects of anticoagulation therapy

Richard A. Dirrenberger and Thoralf M. Sundt Jr.

✓ The healing of the canine carotid endarterectomy was defined at intervals from 30 minutes to 3 months after surgery by means of angiography, light microscopy, and scanning electron microscopy. Immediately after flow was established, a fibrin-platelet carpet formed on the endarterectomized surface. A typical thrombus formed on this initial layer resulting in vessel occlusion in 52% of non-heparinized animals. By 48 hours after surgery, there was little evidence of active thrombus formation, and reendothelialization from existing endothelial cells was noted. One week later, most of the mural thrombus had disappeared and re-endothelialization was well underway; by 3 months after surgery, re-endothelialization was complete. Intraoperative heparinization resulted in a striking reduction in mural thrombus formation and 100% patency rate. Vessel closure with vein-patch grafts resulted in no improvement of vessel patency. However, the results of this aspect of the study cannot be totally extrapolated to human carotid endarterectomy for the reasons discussed. The survival of the vein-patch grafts was investigated.

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Marc R. Mayberg, O. Wayne Houser and Thoralf M. Sundt Jr.

✓ Scanning electron microscopy of feline basilar arterial endothelium 4 hours and 1, 3, 5, and 7 days after subarachnoid hemorrhage (SAH) showed longitudinal furrows that correlated with angiographically demonstrated vasospasm. These ridges persisted after fixation at physiological pressure, and probably reflected medial contraction with undulation of the underlying elastic lamina. No change in endothelial cell morphology or thrombogenesis was observed as long as 7 days after SAH. There is no evidence from this study to suggest that ischemia from vasospasm is a product of thromboembolism from damaged endothelial surfaces.

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Thomas J. Rosenbaum and Thoralf M. Sundt Jr.

✓ The sequential hematological and endothelial responses in the postoperative period after end-to-side arterial anastomosis in 1- to 1.3-mm vessels were assessed by scanning electron microscopy. Two minutes after restoration of flow, an amorphous coating covered the vessel lumen around the suture line, and oozing of blood from the suture line ceased. Within 15 minutes, a partially occluding thrombus was present, which was maximal at the anastomotic bifurcation point. The thrombus underwent partial lysis or embolization within 30 minutes, and gross intraluminal thrombi did not recur. The initial thrombi that formed within 2 minutes were composed of platelets and erythrocytes in a loose reticular fibrin network, but the intraluminal thrombi present at the branch point 15 minutes after flow restoration appeared to be composed solely of platelets. Thrombi that did not undergo complete dissolution had a loss of distinct cellular elements at later time intervals. The fibrin-platelet matrix coating the lumen remained unchanged during the initial 24 hours. When examined at 9 days, normal endothelium was present throughout the vessel with the exception of the suture line, which remained covered by a smooth coagulum. This sequence of events suggests that if surgical manipulation is to result in complete occlusion of the anastomosis, it will likely occur in the initial 30 minutes after resumption of blood flow.

Anticoagulant regimens were evaluated. Pretreatment with aspirin and intraoperative heparin irrigation of the vessel lumen were not beneficial in altering the quantity of thrombus. All systemic heparin regimes tested resulted in a quantitative decrease of thrombotic material. Five minutes of intravenous heparin therapy after resumption of blood flow was as effective as long-term heparin in decreasing the transient intraluminal thrombotic response.

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Thoralf M. Sundt Jr.

✓ The author reviews a form of management for patients deteriorating preoperatively or postoperatively from apparent ischemia attributed to progressive vasospasm after a subarachnoid hemorrhage. The clinical picture and relative frequency of this complication are considered in relationship to the status (grade) of the patient, location of the aneurysm, and ultimate neurological recovery. Experience suggests that the drug regimen reported is useful when instituted early after the onset of symptoms and is safe with proper monitoring techniques. The data do not justify early operative intervention after a subarachnoid hemorrhage, operation when there is angiographic evidence of severe spasm, or expectation of a dramatic effect in patients with a profound deficit or a fixed deficit several hours old.