(A) Posterior inferior cerebellar artery > In unilateral infarcts there is always a sharp delineation in the midline because the superior vermian branches do not cross the midline, but have a sagittal course.> This sharp delineation may not be evident until the late phase of infarction.> In the early phase, edema may cross the midline and create diagnostic difficulties.> Infarctions at pontine level are usually paramedian and sharply defined because the branches of the basilar artery have a sagittal course and do not cross the midline.> Bilateral infarcts are rarely observed because these patients do not survive long enough to be studied, but sometimes small bilateral infarcts can be seen.# Embolic occlusion or thrombosis of a V4 segment causes ischemia of the lateral medulla.> Constellation of vertigo, numbness of the ipsilateral face and contralateral limbs, diplopia, hoarseness, dysarthria, dysphagia, and ipsilateral Horner's syndrome is called the Lateral medullary (or Wallenberg's) syndrome.> Most cases result from ipsilateral vertebral artery occlusion; in the remainder, PICA occlusion is responsible.> Occlusion of the medullary penetrating branches of the vertebral artery or PICA results in partial syndromes.> Hemiparesis is not a feature of vertebral artery occlusion.> Rarely, a medial medullary syndrome occurs with infarction of the pyramid and contralateral hemiparesis of the arm and leg, sparing the face.> If the medial lemniscus and emerging hypoglossal nerve fibers are involved, contralateral loss of joint position sense and ipsilateral tongue weakness occur.> Cerebellar infarction with edema can lead to sudden respiratory arrest due to raised ICP in the posterior fossa.> Drowsiness, Babinski signs, dysarthria, and bifacial weakness may be absent, or present only briefly, before respiratory arrest ensues.> Gait unsteadiness, headache, dizziness, nausea, and vomiting maybe the only early symptoms and signs and should arouse suspicion of this impending complication,which mayrequire neurosurgical decompression, often with an excellent outcome.> Separating these symptoms from those of viral labyrinthitis can be a challenge, but headache, neck stiffness, and unilateral dysmetria favor stroke.