Basillar artery runs down the middle(in above image) and blockage is cause of this condition. Diagram of the arterial circulation at the base of the brain (inferior view).
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Silverman, IE; Liu, GT; Volpe, NJ; Galetta, SL (June 1995). "The crossed paralyses. The original brain-stem syndromes of Millard-Gubler, Foville, Weber, and Raymond-Cestan". Archives of Neurology. 52 (6): 635–8. doi:10.1001/archneur.1995.00540300117021. PMID7763214. {{cite journal}}: Cite journal requires |journal= (help)
Further reading
Kim, JS; Lee, JH; Im, JH; Lee, MC (Jun 1995). "Syndromes of pontine base infarction. A clinical-radiological correlation study". Stroke: A Journal of Cerebral Circulation. 26 (6): 950–5. doi:10.1161/01.STR.26.6.950. PMID7762044.
Krasnianski, M; Neudecker, S; Zierz, S (Aug 2004). "[Classical crossed pontine syndromes]". Fortschritte der Neurologie · Psychiatrie (in German). 72 (8): 460–8. doi:10.1055/s-2004-818392. PMID15305240. S2CID144167622.