title: Investigation of the surgically treated and untreated unruptured cerebral aneurysms of the anterior circulation.
abstract: BACKGROUND
  The natural history of unruptured cerebral aneurysms and the surgical risks are modified by several factors including size, location, and presence of subarachnoid hemorrhage (SAH). The main confusion arises because the backgrounds of the past reports describing the natural history or the surgical complication of unruptured cerebral aneurysms were different. The present study aimed to adjust the backgrounds and investigate the surgical indication with close monitoring of both surgically treated and untreated unruptured cerebral aneurysms.
  
  
  METHODS
  In the past 9 years, 201 patients who had unruptured anterior circulation aneurysms were monitored. The decision of the operation was not randomized. The patients were divided into three subgroups by the size of the aneurysms (small group: below 5 mm, medium group: between 5 and 15 mm, large group: over 15 mm). In both surgically untreated and treated patients, overall mortality and morbidity corresponding to Rankin score II or worse was counted as unruptured aneurysm related event. The ratio of event free was compared between surgically treated and untreated patients using Log-rank test.
  
  
  RESULTS
  In untreated patients, SAH was noted in 1 in the small group and 4 in the medium group. The annual rupture rate of the medium group was 12 times higher than that of the small group. In surgically treated patients, overall mortality and morbidity of the surgery was 2.3% in the small group, 3.6% in the medium group, and 20% in the large group. One surgically treated patient had SAH because of regrowth of aneurysm. When ratio of event free was compared, no significant advantage of surgery was noted in the small group and in all of the patients. However, the benefit of surgery was significant in the medium group (Log-rank p = 0.0189).
  
  
  CONCLUSIONS
  The present results indicated that prophylactic surgery has a benefit for the medium-size aneurysms (5-15 mm) of the anterior circulation. For large aneurysms, individual investigation is necessary because of the variety of surgical difficulties, and the complex symptoms because of rupture and the mass effect as well as cerebral embolism. In small aneurysms, careful observation may be a reasonable choice unless the aneurysm is at a specially high risk of rupture.
authors.affiliation: Department of Neurosurgery, Stroke Center, Wakakusa Daiichi Hospital Higashi, Osaka, Japan
authors.forename: Katsumi
authors.initials: K
authors.lastname: Matsumoto
authors.forename: Katsuhio
authors.initials: K
authors.lastname: Akagi
authors.forename: Makoto
authors.initials: M
authors.lastname: Abekura
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Nakajima
authors.forename: Toshiki
authors.initials: T
authors.lastname: Yoshiminie
mesh_terms: D000368:Aged; D017542:Aneurysm, Ruptured / Q000209:etiology / Q000401:mortality / Q000517:prevention & control*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006801:Humans; D002532:Intracranial Aneurysm / Q000150:complications* / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications; D012307:Risk Factors; D015996:Survival Rate; D013997:Time Factors; D016896:Treatment Outcome