Lateral medullary syndrome is due to?

Veebral aery REF: Harrison's Internal Medicine 17th ed Chapter 364. Cerebrovascular Diseases, Brainstem disorders by Peter P Urban, Louis R Caplan page 205-207. See previous question for table of Brainstem syndromes Embolic occlusion or thrombosis of a V4 segment causes ischemia of the lateral medulla. The constellation of veigo, numbness of the ipsilateral face and contralateral limbs, diplopia, hoarseness, dysahria, dysphagia, and ipsilateral Horner's syndrome is called the lateral medullary (or Wallenberg's) syndrome. Most cases result from ipsilateral veebral aery occlusion; in the remainder, PICA occlusion is responsible. Note: Although lateral medullary syndrome is also known as "Posterior inferior cerebellar aery syndrome, veebral aery is most commonly involved.