Fig 2. Partially thrombosed giant aneurysm of the P2-P3 segment of the left posterior cerebral artery in a 28-year-old woman presenting with headache and loss of consciousness.

A and B, CT scans with injection of contrast show a large lesion compatible with the diagnosis of a thrombosed aneurysm. C, Oblique view of the left vertebral artery angiography shows the circulating portion of the aneurysm associated with a slight stenosis of the parent artery. Slow filling of the parent artery beyond the aneurysm is noted (arrow). D, Intermediate step of the endovascular procedure. After occlusion of the P2-P3 segment of the posterior cerebral artery by using coils, anteroposterior (E) and lateral (F) views of the left internal carotid artery angiography show the retrograde vascularization of the PCA distal to the occlusion via the leptomeningeal anastomosis (arrows). Thirty-six hours after PAO, the patient presented with transient mild paresthesias and mild oculomotor paresis, which completely regressed in 3 days. Follow-up studies after 1 month (T1-weighted MR image, (G); and CT scan with injection of contrast, (H) show reduction of the aneurysmal thrombosed portion and reduction of the mass effect. Follow-up studies after 1 year (CT scan, (I) and after 4 years (fluid-attenuated inversion recovery MR image, (J); and CT scans, (K and L) show further shrinkage of the aneurysmal thrombosed compartment. The small left posterior thalamic infarct is well visualized (L). Findings of the neurologic examination were normal at 5-year follow-up.