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Yuto Shingai, Hiroyuki Sakata, Toshiki Endo, Shinsuke Suzuki, Masayuki Ezura, and Teiji Tominaga

BACKGROUND

Bow hunter’s syndrome (BHS) is an uncommon cause of vertebrobasilar ischemic stroke, which results from occlusion or injury to the vertebral artery (VA) during neck rotation. Although hemodynamic insufficiency is the predominant underlying mechanism of this entity, BHS due to embolic mechanisms is rare. The authors report a case of BHS characterized by repeated posterior circulation embolism and present some considerations of BHS with an embolic mechanism.

OBSERVATIONS

A 57-year-old man suffered from repeated embolic stroke in the posterior circulation. Digital subtraction angiography revealed caliber irregularity of the V3 segment of the left nondominant-side VA, which occluded when the neck rotated to the right side. The patient was diagnosed with BHS with an embolic mechanism due to endothelial damage caused by osteophytes at the C1 foramen transversarium. After C1–C2 fusion surgery, the patient never experienced the recurrence of stroke. According to a literature review, BHS due to embolic mechanisms tends to occur in young male adults, manifesting as recurrent stroke in the posterior circulation. Involvement of the nondominant-side VA can cause BHS with an underlying embolic mechanism.

LESSONS

BHS due to an embolic mechanism should be considered as a differential diagnosis if patients have repeated embolic strokes in the posterior circulation.

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Miki Fujimura, Naoto Kimura, Masayuki Ezura, Kuniyasu Niizuma, Hiroshi Uenohara, and Teiji Tominaga

The development of a de novo arteriovenous malformation (AVM) in patients with moyamoya disease is extremely rare. A 14-year-old girl developed an AVM in the right occipital lobe during the 4-year postoperative period following successful bilateral revascularization surgeries. She suffered a transient ischemic attack with hemodynamic compromise of the bilateral hemispheres at the age of 10 years. Results of an initial examination by 1.5-T MRI and MR angiography satisfied the diagnostic criteria of moyamoya disease but failed to detect any vascular malformation. Bilateral direct and indirect revascularization surgeries in the anterior circulation relieved her symptoms, and she underwent MRI and MR angiography follow-up every year after surgery. Serial T2-weighted MRI revealed the gradual appearance of flow voids in the right occipital lobe during the follow-up period. Magnetic resonance angiography ultimately indicated the development of an AVM 4 years after these surgeries when catheter angiography confirmed the diagnosis of an AVM in the right occipital lobe. The AVM remained asymptomatic, and the patient remained free of cerebrovascular events during the time she was observed by the authors. Acquired AVM in moyamoya disease is extremely rare, with only 3 pediatric cases including the present case being reported in the literature. The development of a de novo AVM in a postoperative patient with moyamoya disease appears to be unique, and this case may provide insight into the dynamic pathology of AVMs.

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Tamer Hassan, Eugene V. Timofeev, Tsutomu Saito, Hiroaki Shimizu, Masayuki Ezura, Yasushi Matsumoto, Kazuyoshi Takayama, Teiji Tominaga, and Akira Takahashi

Object. The authors created a simple, broadly applicable classification of saccular intracranial aneurysms into three categories: sidewall (SW), sidewall with branching vessel (SWBV), and endwall (EW) according to the angiographically documented patterns of their parent arteries. Using computational flow dynamics analysis (CFDA) of simple models representing the three aneurysm categories, the authors analyzed geometry-related risk factors such as neck width, parent artery curvature, and angulation of the branching vessels.

Methods. The authors performed CFDAs of 68 aneurysmal geometric formations documented on angiograms that had been obtained in patients with 45 ruptured and 23 unruptured lesions. In successfully studied CFDA cases, the wall shear stress, blood velocity, and pressure maps were examined and correlated with aneurysm rupture points. Statistical analysis of the cases involving aneurysm rupture revealed a statistically significant correlation between aneurysm depth and both neck size (p < 0.0001) and caliber of draining arteries (p < 0.0001).

Wider-necked aneurysms or those with wider-caliber draining vessels were found to be high-flow lesions that tended to rupture at larger sizes. Smaller-necked aneurysms or those with smaller-caliber draining vessels were found to be low-flow lesions that tended to rupture at smaller sizes. The incidence of ruptured aneurysms with an aspect ratio (depth/neck) exceeding 1.6 was 100% in the SW and SWBV categories, whereas the incidence was only 28.75% for the EW aneurysms.

Conclusions. The application of standardized categories enables the comparison of results for various aneurysms' geometric formations, thus assisting in their management. The proposed classification system may provide a promising means of understanding the natural history of saccular intracranial aneurysms.

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Toshiyuki Takahashi, Teiji Tominaga, Masayuki Ezura, Kiyotaka Sato, and Takashi Yoshimoto

✓ The authors report on a 38-year-old woman with a dislocated hangman fracture associated with unilateral vertebral artery (VA) occlusion. The patient presented with a mild central cord syndrome, as well as anterior subluxation of the C-2 vertebral body upon C-3, bilateral neural arch fractures, and a unilateral locked facet joint. Digital subtraction angiography revealed occlusion of the right VA, with the posterior cerebral circulation entirely dependent on the left VA. Intraoperative angiography demonstrated that complete reduction of the dislocation would have caused severe stenosis of the left VA; partial reduction and anterior fixation were performed instead, with excellent neurological outcome. In this case, intraoperative angiography was particularly useful for preventing brain-related ischemic complications during reduction.