Formation of a Large Fusiform Aneurysm near a Medullary Infarction Caused by Dissection of the Posterior Inferior Cerebellar Artery.

Infarction of the posterior inferior cerebellar artery (PICA) can lead to ischemic stroke in the lateral medullary oblongata. PICA dissection can also elicit an ischemic event in this region, but its detection on radiological images is difficult because of the small diameter of the vessel. We report a case of Wallenberg syndrome due to PICA dissection in a 48-year-old man, which was difficult to diagnose on first admission. He reported sudden onset of 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. Magnetic resonance angiography (MRA) performed at the time of his admission showed no cerebral vessel abnormalities. An MRI study 18 months after the event revealed a fusiform aneurysm on the lateral medullary segment of the PICA, which was extremely close to the cerebral infarct. We concluded that the infarct was due to PICA dissection because of the sudden onset of symptoms and because the infarcted territory of the occluded penetrating branch of the dissecting aneurysm was consistent with Wallenberg syndrome. The aneurysm was trapped and an occipital artery-PICA bypass was placed. At the latest follow-up, 1 year after the procedure, he had no neurological symptoms. Imaging findings at the time of his first admission indicated that the PICA was intact. However, 18 months later, MRI revealed enlargement of an aneurysm at the site of the dissection. A cerebral infarct with headache may indicate PICA dissection.