Objective:Distal anterior cerebral artery(DACA) aneurysms represent about 6% of all intracranial aneurysms.So far,only small series on treatment of these aneurysms have been published.Our aim is to evaluate the anatomic features, treatment results,and long-term outcome of DACA aneurysms.In addition,we address the current techniques for microneurosurgical treatment of these lesions.Patients and methods:We analyzed the clinical and radiological data on 30 consecutive patients diagnosed with DACA aneurysm from Shandong Provincial Hospital.We used a defined subgroup of the whole study population in each part of the study.Detailed anatomic analysis was performed in 5 consecutive patients from 1997 to 2007.Treatment results were analyzed in 25 patients treated between 1985 to 2006,the era of CT imaging and microneurosurgery.With a median follow-up of 7 years we evaluated the long-term outcome of treatment in 17 patients with ruptured DACA aneurysm;no patients were lost to followup.Results:DACA aneurysms,found most often(80%) at the A3 segment of the anterior cerebral artery(ACA),were smaller(median 5mm vs.7mm),more frequently associated with multiple aneurysms(39%vs.20%),and presented more often with intracerebral hematomas(ICHs)(50%vs.25%) than ruptured aneurysms in general. They were associated with anomalies of the ACA in 26%of the patients. Microsurgical treatment showed similar complication rates(treatment morbidity 10%, treatment mortality 0.2%) as for other ruptured aneurysms.At one year after subarachnoid hemorrhage(SAH),DACA aneurysms had equally favorable outcome (GOS≥6) as other ruptured aneurysms(82%vs.71%) but their mortality was lower (11%vs.26%).Factors predicting unfavorable outcome for ruptured DACA aneurysms were advanced age,Hunt&Hess grade≥2,rebleeding before treatment, ICH,intraventricular hemorrhage,and severe preoperative hydrocephalus.The cumulative relative survival ratio showed 18%excess mortality in patients with ruptured DACA aneurysm during the first three years after SAH compared to the matched general population.From the fourth year onwards,there was no excess mortality during the followup.There were four episodes of recurrent SAH,only one due to treated DACA aneurysm,with a 7-year cumulative risk of 2.1%.Conclusions:The special neurovascular features and frequent association with anterior cerebral artery anomalies must be taken into account when planning occlusive treatment of DACA neurysms.With microneurosurgery,ruptured DACA aneurysms have equally favorable outcome but lower mortality at one year as ruptured aneurysms in general.Clipping of DACA aneurysms provides a long-lasting result,with very small rates of re-bleeding.After surviving three years from rupture of DACA aneurysm,the long-term survival of these patients becomes similar to that of the matched general population.