PMC7775600_01
MRI T1 sequence (A) and time of flight acquisition (B). Centered within the midline of the posterior fossa, favored to lie just below the floor of the fourth ventricle, there is a 3.1 x 3.1 x 2.8 cm partially thrombosed aneurysm sac, which arises from the right PICA. There is a suspected patent lumen measuring ~8.5 x 5.5 mm. Aneurysm sac demonstrates a narrow neck, ~2 mm. There is no evidence of superficial siderosis or hemosiderin deposition.
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F1
An MRI of the brain, arranged by his family physician, demonstrated a partially thrombosed giant right PICA aneurysm filling the fourth ventricle (Figure 1).
Digital subtraction angiography. Injection of the dominant right vertebral artery lateral (A) and AP view (B). There is filling of the giant partially thrombosed aneurysm (asterisk), arising from a large right PICA distal to the caudal loop. Just proximal to the filling portion of the aneurysm there is a reduction in caliber of the PICA (black arrow on A). There appear to be 2 smaller aneurysms arising from the distal PICA (white arrows on A). The filling portion of the largest partially thrombosed aneurysm measures approximately 7.5 mm x 14 mm, the second aneurysm measuring approximately 4.0 x 2.6 mm and the most distal aneurysm measuring ~2.7 x 1.8 mm. A small arteriovenous malformation (white pentagon on A) is also seen with feeders from the right PICA and right SCA. Drainage of the AVM is via the torcula into the right transverse sinus (B).
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F2
In addition, the AVM is also supplied by the ipsilateral superior cerebellar artery (SCA) and drains superficially into the right transverse sinus through the torcula, Spetzler-Martin grade 1 (Figure 2).