====== The Unruptured Cerebral Aneurysm Study Japan ======

[[The Unruptured Cerebral Aneurysm Study Japan]], is a project of the [[Japan Neurosurgical Society]],  designed to clarify the natural course of [[unruptured intracranial aneurysm]]s (UIAs). From January 2001 through March 2004, 6697 UIAs among 5720 patients were prospectively registered. At registration, 2839 patients (49.6%) had 3132 (46.8%) small UCAs of 3-4 mm. The registered, treated, and [[rupture]] numbers of these [[small intracranial aneurysm]]s and the annual [[rupture]] [[rate]] were investigated. The rate was assessed per aneurysm. The characteristics of patients and aneurysms were compared to those of unruptured [[large intracranial aneurysm]]s (≥ 5 mm). Cumulative rates of SAH were estimated per aneurysm. [[Risk factor]]s underwent [[univariate]] and [[multivariate]] analysis.

Treatment and rupture numbers of small UCAs were 1132 (37.1% of all treated aneurysms) and 23 (20.7% of all ruptured aneurysms), respectively. The registered, treated, rupture number, and annual rupture rates were 1658 (24.8%), 495 (16.2%), 11 (9.9%), and 0.30%, respectively, among 3-mm aneurysms, and 1474 (22.0%), 637 (20.9%), 12 (10.8%), and 0.45%, respectively, among 4-mm aneurysms. Multivariate risk-factor analysis revealed that a screening brain checkup (hazard ratio [HR] 4.1, 95% confidence interval [CI] 1.2-14.4), history of SAH (HR 10.8, 95% CI 2.3-51.1), uncontrolled hypertension (HR 5.2, 95% CI 1.8-15.3), and location on the anterior communicating artery (ACoA; HR 5.0, 95% CI 1.6-15.5) were independent predictors of rupture.

Although the annual rupture rate of small aneurysms was low, the actual number of ruptures was not low. Small aneurysms that ruptured during follow-up could be detected, screened, and managed based on each risk factor. Possible selection criteria for treating small UCAs include a history of [[SAH]], uncontrolled [[hypertension]], location on the [[ACoA]], and [[young]] patients. Further large prospective and longitudinal trials are needed.Clinical trial registration no.: C000000418 (https://www.umin.ac.jp/ctr)
((Ikawa F, Morita A, Tominari S, Nakayama T, Shiokawa Y, Date I, Nozaki K,
Miyamoto S, Kayama T, Arai H; Japan Neurosurgical Society for UCAS Japan
Investigators. Rupture risk of small unruptured cerebral aneurysms. J Neurosurg. 
2019 Jan 25:1-10. doi: 10.3171/2018.9.JNS181736. [Epub ahead of print] PubMed
PMID: 30684948.
)).