[Spontaneous occlusion of PICA-involved dissecting aneurysm with development of a collateral channel from the posterior meningeal artery].

A 53-year-old man suffered severe headache, which continued for three days. No abnormality was shown on CT scan, and a dissecting aneurysm of the right vertebral artery was suspected on MRI. Cerebral angiography revealed a dissection aneurysm of the right vertebral artery involved with the posterior inferior cerebellar artery (PICA) as pearl and string sign. The patient was conservatively managed under careful blood pressure control, and was followed by serial MRI. He presented with Wallenberg syndrome three weeks later. Second angiography revealed the occlusion of the PICA-involved dissecting aneurysm and the lateral medullary segment of the PICA supplied by a newly arising vessel from the right posterior meningeal artery (PMA). For the conservative treatment of a vertebral dissection aneurysm involved with PICA presenting with only pain, observation of the course by MRI was effective, and the PMA could develop as the collateral channel to the PICA territory.