Spontaneous resolution of an aneurysm arising from a penetrating branch of the middle cerebral artery.

Aneurysms of the penetrating branches of the middle cerebral artery are rare. Previous reports have concentrated on aneurysms that arise from the distal lenticulostriate artery where the natural history is unclear. Here, we report a case of a ruptured aneurysm located at the insular penetrating branch of the right middle cerebral artery, which was associated with an external capsular haematoma. The aneurysm persisted as shown by angiography at one month and the patient refused surgical treatment at that stage. Follow-up angiography two years later showed resolution of the aneurysm. The aetiologies and treatment options are reviewed.