The posterior inferior cerebellar artery (PICA) is the largest branch of the vertebral artery, arising just before the two vertebral arteries unite to form the basilar artery. It winds around the brainstem, loops down around the cerebellar tonsil (forming the characteristic tonsillar loop used in surgical planning), and supplies the posteroinferior cerebellum, the choroid plexus of the fourth ventricle, and the lateral medulla via perforating branches.
PICA occlusion produces the lateral medullary syndrome (Wallenberg syndrome): ipsilateral facial pain and numbness, Horner syndrome, palatal and vocal cord palsy, and ataxia, combined with contralateral spinothalamic sensory loss. The characteristic dissociated sensory loss (ipsilateral face, contralateral body) reflects the crossing pattern of the spinothalamic tract in the medulla. The PICA tonsillar loop is a key surgical landmark in posterior fossa and Chiari decompression surgery.
Occlusion of PICA or the parent vertebral artery produces lateral medullary ischaemia with the classic syndrome of ipsilateral facial numbness, Horner syndrome, hoarseness, dysphagia, and ataxia, combined with contralateral body pain and temperature loss, managed with antithrombotic therapy and dysphagia rehabilitation.
Aneurysms at the vertebral artery-PICA junction produce subarachnoid haemorrhage into the posterior fossa, often presenting with severe occipital headache and neck stiffness, requiring neurosurgical or endovascular treatment.
