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Aneurysms of the posterior inferior cerebellar artery

A clinical and anatomical analysis

Rroger J. Hudgins, Arthur L. Day, Ronald G. Quisling, Albert L. Rhoton Jr, George W. Sypert and Francisco Garcia-Bengochea

✓ The clinical and anatomical features of 21 surgically treated saccular aneurysms of the posterior inferior cerebellar artery (PICA) are analyzed. Seventeen of these lesions originated from the PICA-vertebral junction, and four arose from distal PICA branching sites. Twelve lesions arose from the left PICA, nine were right-sided, and all were small (less than 12.5 mm). Most of these aneurysms occurred in females (16 of 21) and presented as classic subarachnoid hemorrhage. The lack of specific focal deficits prevented an accurate pre-angiographic determination of aneurysm location in most instances. Clinically significant vasospasm and aneurysm multiplicity occurred with approximately equal frequency as at other locations.

The angiographic and surgical features of these lesions are determined by the course of the vertebral artery and PICA; that is, they occur at branching sites and at curves in the parent vessel, and point in the direction in which flow would have continued if the curve at the aneurysm's origin had not been present. Aneurysms at the PICA-vertebral junction usually occur at least 1 cm above the foramen magnum level, arise distal to the PICA origin in the angle between the two vessels, and are best approached by a paramedian incision with the patient in the lateral recumbent position. Isolated clipping of the aneurysm neck is essential in this instance, as trapping may compromise vital perforating arteries of the brain stem. More distal (retromedullary) PICA aneurysms are sometimes associated with another vascular anomaly (two cases in this series), and are best handled through a bilateral suboccipital craniectomy. Clipping of the neck is the preferred treatment, but trapping is usually safe, if necessary.

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Arthur L. Day

✓ The clinical, angiographic, and surgical characteristics of 31 patients with high-grade middle cerebral artery (MCA) stenosis or occlusion (jointly termed “MCA obstructions”) referred for cerebral revascularization by extracranial-intracranial (EC-IC) bypass are reviewed. Overall, 12 (66%) of the 18 patients with stenosis and all 13 (100%) of those with complete occlusion experienced clinically evident infarctions. Twenty-five of these patients underwent arteriography at least twice during their clinical course. Eleven (44%) demonstrated significant improvement in flow or complete resolution of obstruction on their second study. Ten of these 11 were patients in whom the initial arteriography was done within 2 weeks of symptom onset. Five other patients with stenosis exhibited obstruction that was worse on serial arteriography without surgical intervention.

The high incidence of resolution of MCA obstructions indicates that surgery should not be contemplated in most instances until delayed arteriography has been performed, at least 6 weeks after the onset of symptoms. Proximal embolic sources, such as the cervical carotid bifurcation, should receive carotid endarterectomy and repeat arteriography in appropriate patients prior to consideration of EC-IC bypass. Persistent high-grade MCA obstructions are thereafter potential candidates for EC-IC bypass, since leptomeningeal collateral vessels are marginal in their protective ability. Overall, of 15 patients who underwent an EC-IC bypass procedure, 14 were either stable or improved postoperatively, and 13 have been free of any further ischemic events without the use of major anticoagulant agents.

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Patrick G. Ryan and Arthur L. Day

✓ A patient with known internal carotid artery occlusion developed transient ischemic attacks in the distribution of the occluded vessel. Arteriography demonstrated a thrombus clearly originating from the internal carotid artery stump, which was unassociated with significantly stenotic atherosclerotic disease of the ipsilateral common or external carotid arteries. Stump angioplasty and endarterectomy led to complete and sustained cessation of further symptoms.

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John Guy, Mark Sherwood and Arthur L. Day

✓ In two patients with traumatic optic neuropathy progressive visual loss was reversed by surgical decompression of the optic nerve sheath. The first patient with hemorrhage beneath the optic nerve sheath had progressive loss of vision from counting fingers to no light perception within 24 hours after the injury. Surgical evacuation of the hematoma improved visual acuity to 8/30. The second patient had progressive visual loss from 20/20 to 20/400 within the 1st week after injury. Drainage of an arachnoid cyst of the optic nerve sheath improved visual acuity to 20/25. Computerized axial tomography disclosed the hemorrhage in the first case and enlargement of the optic nerve sheath in the second. While the management of traumatic optic neuropathy is controversial, surgical intervention for an arachnoid cyst and hematoma involving the optic nerve is clearly beneficial.

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Aneurysms of the ophthalmic segment

A clinical and anatomical analysis

Arthur L. Day

✓ The clinical, radiographic, and anatomical features in 80 patients with ophthalmic segment aneurysms were reviewed, and were categorized according to a presumed origin related to the ophthalmic (41 cases) or superior hypophyseal (39 cases) arteries. There was a marked female predominance (7:1) and high incidence of multiple aneurysms (45%) within this population. Clinical presentations included subarachnoid hemorrhage in 23 cases (29%) and visual deficits in 24 (30%); five patients exhibited both hemorrhage and visual loss. Twenty-eight aneurysms were incidentally identified.

Ophthalmic artery aneurysms arose from the internal carotid artery (ICA) just distal to the ophthalmic artery, pointed superiorly or superomedially, and (when large) deflected the carotid artery posteriorly and inferiorly, closing the siphon. Abnormalities relating to vision were not identified until the aneurysm realized giant proportions. The optic nerve was typically displaced superomedially, which restricted contralateral extension until late in the clinical course; unilateral nasal field loss was seen in 12 patients. Nine patients had bilateral ophthalmic artery aneurysms which were often clipped via a unilateral craniotomy.

Superior hypophyseal artery aneurysms arose just above the dural ring from the medial bend of the ICA, at the site of perforator origin to the superior aspect of the hypophysis, and had no direct association with the ophthalmic artery. The carotid artery was usually located lateral or superolateral relative to the aneurysm. These lesions could extend medially beneath the chiasm (suprasellar variant), producing a clinical and computerized tomography picture similar to a pituitary adenoma, or they could extend ventrally to burrow beneath the anterior clinoid process (paraclinoid variant).

Preoperative categorization of these lesions according to their likely branch of origin provides excellent correlation with visual deficits and operative findings, and has allowed the author to clip 52 of 54 lesions, with very low operative or visual morbidity.

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James W. Simpkins, Gopal Rajakumar, Yu-Qi Zhang, Christopher E. Simpkins, David Greenwald, Chun J. Yu, Nicholas Bodor and Arthur L. Day

✓ The present study was undertaken to determine if estrogens protect female rats from the neurodegenerative effects of middle cerebral artery (MCA) occlusion. The rats were ovariectomized and 7 or 8 days later various estrogen preparations were administered before or after MCA occlusion. Pretreatment with 17β-estradiol (17β-E2) or a brain-targeted 17β-E2 chemical delivery system (CDS) decreased mortality from 65% in ovariectomized rats to 22% in 17β-E2—treated and 16% in 17β-E2 CDS—treated rats. This marked reduction in mortality was accompanied by a reduction in the ischemic area of the brain from 25.6 ± 5.7% in the ovariectomized rats to 9.8 ± 4% and 9.1 ± 4.2% in the 17β-E2—implanted and the 17β-E2 CDS—treated rats, respectively. Similarly, pretreatment with the presumed inactive estrogen, 17α-estradiol, reduced mortality from 36 to 0% and reduced the ischemic area by 55 to 81%. When administered 40 or 90 minutes after MCA occlusion, 17β-E2 CDS reduced the area of ischemia by 45 to 90% or 31%, respectively. In summary, the present study provides the first evidence that estrogens exert neuroprotective effects in an animal model of ischemia and suggests that estrogens may be a useful therapy to protect neurons against the neurodegenerative effects of stroke.

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Stephen B. Lewis, Dongwoo John Chang, David A. Peace, Pamela J. Lafrentz and Arthur L. Day

Object. Aneurysms located on the distal portion of the posterior inferior cerebellar artery (PICA) are uncommon, and their underlying pathology, natural history, and clinical management are poorly understood. To clarify these lesions more fully, the authors undertook a retrospective analysis of the clinical features and management results of 22 distal PICA aneurysms in 20 consecutive patients treated at one institution by the same surgeon during the past decade.

Methods. The series included 10 men and 10 women (mean age at presentation 51 years). Nine patients presented with only subarachnoid and/or intraventricular hemorrhage (median Hunt and Hess Grade II). In seven patients intracerebellar hemorrhage was also found; two patients presented with pressure effects and two hemorrhages were incidentally discovered. Prominent comorbidities included cigarette smoking (50%) and hypertension (50%). The 13 saccular and nine fusiform distal PICA aneurysms were distributed on the following segments of the PICA: lateral medullary (seven lesions), tonsillomedullary (five lesions), telovelotonsillar (five lesions), and cortical (five lesions). Six cases were associated with cerebellar arteriovenous malformations. Skull-base and far-lateral transcondylar surgical approaches were used to secure the aneurysms in 86% of cases, either by direct clipping (13 lesions), vessel sacrifice (four lesions), or vessel sacrifice plus bypass (two lesions). Two aneurysms were treated using endovascular PICA ablation. Overall outcome at hospital discharge was excellent or good in 70% of cases. At long-term follow up (100% of patients, mean 123 days), an excellent or good outcome had been achieved in 85% of cases.

Conclusions. Depending on the PICA segment that was affected, variations in clipping strategies and surgical exposures aimed at the PICA branch and main trunk preservation were major contributors to good long-term results.

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Roberto C. Heros

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Roberto C. Heros