Fig 1. Partially thrombosed giant aneurysm of the superior branch of the right MCA bifurcation in a 64-year-old woman presenting with headache and paresis of the left arm.

A and B, CT scans with contrast injection show a giant heterogeneous right temporal lesion with a "cystic" compartment, calcifications, and severe mass effect. C, Coronal T2-weighted MR image shows an unusual aspect of a partially thrombosed giant aneurysm of a right MCA branch. The right internal carotid artery angiography, in anteroposterior (D) and lateral (E) views, depicts the patent compartment of the aneurysm. F, Occlusion test with a nondetachable balloon. On the angiographic venous phase in the lateral view, a retrograde filling of the arterial branches after the level of the occlusion (arrows) is observed via leptomeningeal anastomosis. G, Three days after the PAO was performed by using coils, a CT scan without injection of contrast shows shrinkage of the aneurysm and reduction of the mass effect. H, A CT scan with injection after 1.5 years shows persistent disappearance of the mass effect and reduction of the thrombosed compartment in relation to the CT examination performed after 6 months (not shown). I, Angiographic 1.5-year follow-up of the right internal carotid artery in the anteroposterior view shows persistent exclusion of the aneurysm and retrograde vascularization of the vessels beyond the occlusion via leptomeningeal anastomosis from ACA and MCA branches. Arterial supply from the PCA was also observed on the vertebral angiogram (not shown). In follow-up studies after 3.5 years, CT scans (J and K) and coronal T2-weighted MR image (L) show further shrinkage of the aneurysmal thrombosed compartment. Findings of the neurologic examination were normal.