Giant middle cerebral aneurysm presenting as hemiathetosis in a child and its spontaneous thrombosis

A 10-year-old girl presented with a 6-week history of gradually increasing, abnormal movements and weakness of the right upper and lower limbs. There were no features of raised intracranial pressure. Computed tomography scan and magnetic resonance imaging (MRI) of the brain showed the features of a partially thrombosed giant middle cerebral artery aneurysm, located deep in the left lentiform region and compressing the basal ganglia and the mesencephalon. The angiogram confirmed the aneurysm and its origin from the main trunk of the artery with occlusion of all the branches. A direct approach was unsuitable for the treatment of the aneurysm, so an embolization procedure to occlude the neck of the aneurysm was considered. During the waiting period, the patient improved and became asymptomatic. Follow-up MRI showed complete thrombosis of the aneurysm and eventually, reduction in its size and mass effect. The hemiathetosis may have been the result of direct pressure on the basal ganglia by the aneurysm. The spontaneous intra-aneurysmal thrombosis may have been due to the massive size of the aneurysm and its narrow neck.