UCAS Japan was conducted to clarify the natural course of unruptured cerebral aneurysms. Method: According to a pre-specified protocol, 5,720 patients with 6,697 aneurysms were prospectively registered and rupture risks were analyzed. Results: During 11,660 aneurysm-years of follow-up, 111 aneurysms ruptured. The total annual rupture rate was 0.95%. A multivariate Cox regression model showed that size, location, and shape (association with bleb formation) were significantly associated with rupture. UCAS data were included in the meta-analysis used to develop the PHASES scoring system. In this scoring system, aneurysm rupture risks for the first 5 years can be estimated according to population, hypertension, age, size, earlier subarachnoid hemorrhage history, and aneurysm site. Discussion: To conduct and publish large-scale cohort studies, it is important to: 1) never publish main results before the final paper, 2) fix the protocol and analysis plan prior to the study, 3) establish good collaboration with a statistician, and 4) raise a simple but important research question.

Acute sensorineural hearing loss with vertigo due to vascular events in the vertebrobasilar system is diagnostically challenging, especially if signs of central nervous system involvement are minimal. We report herein on the clinical course and diagnostic process of a 60-year-old woman who presented with acute sensorineural hearing loss and vertigo caused by a dissecting aneurysm in the vertebral artery. Brain magnetic resonance imaging (MRI), magnetic resonance angiography (MRA), single-photon emission computed tomography (SPECT), and a lumbar puncture revealed a dissecting aneurysm in the left vertebral artery with no evidence of ischemic lesions or subarachnoid hemorrhage. Dysfunction in the cerebellum was suggested by saccadic pursuit and truncal ataxia. The patient underwent anticoagulant therapy for 1 year, following which the isolated cavity of the dissecting aneurysm reduced in size as observed on brain MRI. In addition, significant improvements were seen in her gait and hearing level. The patient can now walk normally and has suffered no relapse of symptoms. (152 words)

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