Objectives The aim of this study was to assess the long-term outcomes of endovascular treatment of MCA aneurysms and identify factors associated with recurrence.

Subjects 161 aneurysms in 147 patients treated between January 2008 and August 2011.

Methods A retrospective case note review was performed. Aneurysm occlusion was assessed using the Raymond-Roy classification. Clinical outcome was graded using the mRS.

Results The minimum period of follow up was 65 months, with a maximum follow up period of 120 months. 49% of aneurysms were ruptured at the time of treatment. Morbidity was observed in 15% of the unruptured aneurysms (6% permanent neurological deficit), and in 33% of ruptured aneurysms (15% permanent neurological deficit). 84% of aneurysms were fully occluded following first treatment. Of these, 34% demonstrated angiographic recurrence and 10% required re-intervention. 25% of aneurysms≤7 mm in maximal diameter demonstrated angiographic recurrence, as compared with 50% of aneurysms>7 mm. Aneurysm size >7 mm was associated with a significantly shorter time to recurrence (log rank=9.655, p=0.002).

Conclusions This is a large series of MCA aneurysms with a long period of follow up. Our results demonstrate that endovascular treatment of MCA aneurysms is associated with a low morbidity and mortality. Given the increasing use of adjunctive devices (stents, web devices) full occlusion of ruptured aneurysms in the acute phase is not necessary, and deliberate staged treatment a reasonable strategy.