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Michael E. Ivan, Michael M. Safaee, Nikolay L. Martirosyan, Ana Rodríguez-Hernández, Barbara Sullinger, Priyanka Kuruppu, Julian Habdank-Kolaczkowski, and Michael T. Lawton

OBJECTIVE

Anterior communicating artery (ACoA) aneurysms are common intracranial aneurysms. Despite advances in endovascular therapy, microsurgical clipping remains an important treatment for aneurysms with broad necks, large size, intraluminal thrombus, complex branches, or previous coiling. Anatomical triangles identify safe corridors for aneurysm access. The authors introduce the A1-A2 junctional triangle and the A1-A1 precommunicating triangle and examine relationships between dome projection, triangular corridors of access, and surgical outcomes.

METHODS

Preoperative catheter and CT angiograms were evaluated to characterize aneurysm dome projection. Aneurysm projection was categorized into quadrants and octants. Preoperative, intraoperative, and postoperative factors were correlated to aneurysm dome projection and patient outcomes using univariate and multivariate analyses.

RESULTS

A total of 513 patients with microsurgically treated ACoA aneurysms were identified over a 13-year period, and 400 had adequate imaging and follow-up data for inclusion. Surgical clipping was performed on 271 ruptured and 129 unruptured aneurysms. Good outcomes were observed in 91% of patients with unruptured aneurysms and 86% of those with ruptured aneurysms, with a mortality rate < 1% among patients with unruptured aneurysms. Increasing age (p < 0.01), larger aneurysm size (p = 0.03), and worse preoperative modified Rankin Scale score (p < 0.01) affected outcomes adversely. Aneurysms projecting superiorly and posteriorly required dissection in the junctional triangle, and multivariate analysis demonstrated worse clinical outcomes in these patients (p < 0.01).

CONCLUSIONS

Anteriorly and inferiorly projecting aneurysms involve only the precommunicating triangle, are simpler to treat microsurgically, and have more favorable outcomes. Superior and posterior dome projections make ACoA aneurysms more difficult to visualize and require opening the junctional triangle. Added visualization through the junctional triangle is recommended for these aneurysms in order to facilitate dissection of efferent branch arteries, careful clip application, and perforator preservation. Dome projection can be determined preoperatively from images and can help anticipate dissection routes through the junctional triangle.

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Ramon Torné, Ana Rodríguez-Hernández, and Michael T. Lawton

Object

Intraoperative rupture can transform an arteriovenous malformation (AVM) resection. Blood suffuses the field and visualization is lost; suction must clear the field and the hand holding the suction device is immobilized; the resection stalls while hemostasis is being reestablished; the cause and site of the bleeding may be unclear; bleeding may force technical errors and morbidity from chasing the source into eloquent white matter; and AVM bleeding can be so brisk that it overwhelms the neurosurgeon. The authors reviewed their experience with this dangerous complication to examine its causes, management, and outcomes.

Methods

From a cohort of 591 patients with AVMs treated surgically during a 15-year period, 32 patients (5%) experienced intraoperative AVM rupture. Their prospective data and medical records were reviewed.

Results

Intraoperative AVM rupture was not correlated with presenting hemorrhage, but had a slightly higher incidence infratentorially (7%) than supratentorially (5%). Rupture was due to arterial bleeding in 18 patients (56%), premature occlusion of a major draining vein in 10 (31%), and nidal penetration in 4 (13%). In 14 cases (44%), bleeding control was abandoned and the AVM was removed immediately (“commando resection”). The incidence of intraoperative rupture was highest during the initial 5-year period (9%) and dropped to 3% and 4% in the second and third 5-year periods, respectively. Ruptures due to premature venous occlusion and nidal penetration diminished with experience, whereas those due to arterial bleeding remained steady. Despite intraoperative rupture, 90% of AVMs were completely resected initially and all of them ultimately. Intraoperative rupture negatively impacted outcome, with significantly higher final modified Rankin Scale scores (mean 2.8) than in the overall cohort (mean 1.5; p < 0.001).

Conclusions

Intraoperative AVM rupture is an uncommon complication caused by pathological arterial anatomy and by technical mistakes in judging the dissection distance from the AVM margin and in mishandling or misinterpreting the draining veins. The decrease in intraoperative rupture rate over time suggests the existence of a learning curve. In contrast, intraoperative rupture due to arterial bleeding reflects the difficulty with dysplastic feeding vessels and deep perforator anatomy rather than neurosurgeon experience. The results demonstrate that intraoperative AVM rupture negatively impacts patient outcome, and that skills in managing this catastrophe are critical.

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Ana Rodríguez-Hernández, Ahmed J. Awad, and Michael T. Lawton

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Andreu Gabarrós Canals, Ana Rodríguez-Hernández, William L. Young, Michael T. Lawton, and for the UCSF Brain AVM Study Project

Object

Descriptions of temporal lobe arteriovenous malformations (AVMs) are inconsistent. To standardize reporting, the authors blended existing descriptions in the literature into an intuitive classification with 5 anatomical subtypes: lateral, medial, basal, sylvian, and ventricular. The authors' surgical experience with temporal lobe AVMs was reviewed according to these subtypes.

Methods

Eighty-eight patients with temporal lobe AVMs were treated surgically.

Results

Lateral temporal lobe AVMs were the most common (58 AVMs, 66%). Thirteen AVMs (15%) were medial, 9 (10%) were basal, and 5 (6%) were sylvian. Ventricular AVMs were least common (3 AVMs, 3%). A temporal craniotomy based over the ear was used in 64%. Complete AVM resection was achieved in 82 patients (93%). Four patients (5%) died in the perioperative period (6 in all were lost to follow-up); 71 (87%) of the remaining 82 patients had good outcomes (modified Rankin Scale scores 0–2); and 68 (83%) were unchanged or improved after surgery.

Conclusions

Categorization of temporal AVMs into subtypes can assist with surgical planning and also standardize reporting. Lateral AVMs are the easiest to expose surgically, with circumferential access to feeding arteries and draining veins at the AVM margins. Basal AVMs require a subtemporal approach, often with some transcortical dissection through the inferior temporal gyrus. Medial AVMs are exposed tangentially with an orbitozygomatic craniotomy and transsylvian dissection of anterior choroidal artery and posterior cerebral artery feeders in the medial cisterns. Medial AVMs posterior to the cerebral peduncle require transcortical approaches through the temporo-occipital gyrus. Sylvian AVMs require a wide sylvian fissure split and differentiation of normal arteries, terminal feeding arteries, and transit arteries. Ventricular AVMs require a transcortical approach through the inferior temporal gyrus that avoids the Meyer loop. Surgical results with temporal lobe AVMs are generally good, and classifying them does not offer any prediction of surgical risk.

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Ana Rodríguez-Hernández, Christina Huang, and Michael T. Lawton

Iatrogenic pseudoaneurysms are rare but serious complications of transsphenoidal surgery, and an iatrogenic pseudoaneurysm of the posterior cerebral artery (PCA) has been reported just once in the literature. The authors encountered such a case with a new P1 segment PCA pseudoaneurysm after endoscopic transsphenoidal resection of a pituitary adenoma. The aneurysm proved ideal for a novel intracranial–intracranial bypass in which the superior cerebellar artery (SCA) was used as an in situ donor artery to revascularize the recipient P2 segment. The bypass allowed aneurysm trapping without causing ischemic stroke or neurological morbidity. This case represents the first reported surgical treatment of an iatrogenic PCA pseudoaneurysm. Endovascular occlusion with coils was an option, but dolichoectatic morphology requires sacrifice of the P1 segment, with associated risks to the thalamoperforators and circumflex perforators. The SCA-PCA bypass was ideal because of low-flow demands. Like other in situ bypasses, it requires no dissection of extracranial arteries, no second incision for harvesting interposition grafts, and has a high likelihood of long-term patency. The SCA-PCA bypass is also applicable to fusiform SCA aneurysms requiring revascularization with trapping. This case demonstrates a dangerous complication that results from the limited view of the posterolateral surgical field through the endoscope and the imprecision of endoscopic instruments.

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Ana Rodríguez-Hernández, Albert L. Rhoton Jr., and Michael T. Lawton

Object

The conceptual division of intracranial arteries into segments provides a better understanding of their courses and a useful working vocabulary. Segmental anatomy of cerebral arteries is commonly cited by a numerical nomenclature, but an analogous nomenclature for cerebellar arteries has not been described. In this report, the microsurgical anatomy of the cerebellar arteries is reviewed, and a numbering system for cerebellar arteries is proposed.

Methods

Cerebellar arteries were designated by the first letter of the artery's name in lowercase letters, distinguishing them from cerebral arteries with the same first letter of the artery's name. Segmental anatomy was numbered in ascending order from proximal to distal segments.

Results

The superior cerebellar artery was divided into 4 segments: s1, anterior pontomesencephalic segment; s2, lateral pontomesencephalic segment; s3, cerebellomesencephalic segment; and s4, cortical segment. The anterior inferior cerebellar artery was divided into 4 segments: a1, anterior pontine segment; a2, lateral pontine segment; a3, flocculopeduncular segment; and a4, cortical segment. The posterior inferior cerebellar artery was divided into 5 segments: p1, anterior medullary segment; p2, lateral medullary segment; p3, tonsillomedullary segment; p4, telovelotonsillar segment; and p5, cortical segment.

Conclusions

The proposed nomenclature for segmental anatomy of cerebellar artery complements established nomenclature for segmental anatomy of cerebral arteries. This nomenclature is simple, easy to learn, and practical. The nomenclature localizes distal cerebellar artery aneurysms and also localizes an anastomosis or describes a graft's connections to donor and recipient arteries. These applications of the proposed nomenclature with cerebellar arteries mimic the applications of the established nomenclature with cerebral arteries.

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Ana Rodríguez-Hernández and Michael T. Lawton

Object

Surgical routes to posterior inferior cerebellar artery (PICA) aneurysms are opened between the vagus (cranial nerve [CN] X), accessory (CN XI), and hypoglossal (CN XII) nerves for safe clipping, but these routes have not been systematically defined. The authors describe 3 anatomical triangles and their relationships with PICA aneurysms, routes for surgical clipping, outcomes, and angiographically demonstrated anatomy.

Methods

The vagoaccesory triangle is defined by CN X superiorly, CN XI laterally, and the medulla medially. It is divided by CN XII into the suprahypoglossal triangle (above CN XII) and the infrahypoglossal triangle (below CN XII). From a consecutive surgical series of 71 PICA aneurysms in 70 patients, 51 aneurysms were analyzed using intraoperative photographs.

Results

Forty-three PICA aneurysms were located inside the vagoaccessory triangle and 8 were outside. Of the aneurysms inside the vagoaccessory triangle, 22 (51%) were exposed through the suprahypoglossal triangle and 19 (44%) through the infrahypoglossal triangle; 2 were between triangles. The lesions were evenly distributed between the anterior medullary (16 aneurysms), lateral medullary (19 aneurysms), and tonsillomedullary zones (16 aneurysms). Neurological and CN morbidity linked to aneurysms in the suprahypoglossal triangle was similar to that associated with aneurysms in the infrahypoglossal triangle, but no morbidity was associated with PICA aneurysms outside the vagoaccessory triangle. A distal PICA origin on angiography localized the aneurysm to the suprahypoglossal triangle in 71% of patients, and distal PICA aneurysms were localized to the infrahypoglossal triangle or outside the vagoaccessory triangle in 78% of patients.

Conclusions

The anatomical triangles and zones clarify the borders of operative corridors to PICA aneurysms and define the depth of dissection through the CNs. Deep dissection to aneurysms in the anterior medullary zone traverses CNs X, XI, and XII, whereas shallow dissection to aneurysms in the lateral medullary zone traverses CNs X and XI. Posterior inferior cerebellar artery aneurysms outside the vagoaccessory triangle are frequently distal and superficial to the lower CNs, and associated surgical morbidity is minimal. Angiography may preoperatively localize a PICA aneurysm's triangular anatomy based on the distal PICA origin or distal aneurysm location.