Sequential bilateral dissection of the posterior inferior cerebellar artery within 1 week in a young patient.

A man in the 40s presented with acute vertigo and occipital headache. He was diagnosed with right posterior inferior cerebellar artery (PICA) dissection, which resulted in right cerebellar and lateral medullary infarct. During antiplatelet therapy, the left cerebellum infarct recurred on the seventh hospital day. Subsequent CT angiography showed the pearl and string sign on the left PICA, and he was diagnosed with bilateral isolated PICA dissection. Besides, only two cases of bilateral isolated PICA dissection have been reported. Most had vascular risk factors, and unilateral dissection preceded shortly before the onset of contralateral dissection. We hypothesise that blood flow to the ipsilateral cerebellum diminished during unilateral PICA dissection, and the compensatory increase in blood flow through the contralateral PICA caused the haemodynamic stress on the contralateral PICA, leading to bilateral PICA dissection. Contralateral PICA dissection should be considered in patients with unilateral PICA dissection presenting with new neurological symptoms.