Formation of a large fusiform aneurysm next to a medullary infarction due to posterior inferior cerebellar artery dissection.

Posterior inferior cerebellar artery (PICA) infarction can lead to ischemic stroke at the lateral part of the medullary oblongata. PICA dissection can also elicit an ischemic event in this region but its detection on radiological images is difficult due to the small diameter of the vessel. We report a 48-year-old male with Wallenberg syndrome due to PICA dissection, which was difficult to diagnose on first admission. He reported sudden-onset sensory disturbance on the right side of his face, ataxic gait, and headache. Brain magnetic resonance imaging (MRI) revealed a fresh cerebral infarct in the right lateral medulla oblongata. Serial MRI and magnetic resonance angiography (MRA) performed at the time of his admission failed to demonstrate cerebral vessel abnormalities. MRI study performed 18 months after the attack revealed a fusiform aneurysm on the lateral medullary segment of the PICA; its site was extremely close to the cerebral infarct. We concluded that the infarct was due to PICA dissection because it was sudden onset of the symptom at the event and the lesion enlarged dissecting aneurysm located to be coincident with symptoms of Wallenberg syndrome. The aneurysm was trapped, and an occipital artery-PICA bypass was placed. At the latest follow-up, one year after the operation, he manifested no neurological symptoms.Imaging findings at the time of his first admission indicated that the PICA was intact in this patient with Wallenberg syndrome attributable to PICA dissection, which obscured on imaging studies performed at symptom onset and was diagnosed later. However,18 months later, MRI revealed enlargement of an aneurysm at the site of the dissection. A cerebral infarct in the PICA territory in patients with headache may be indicative of PICA dissection.