Dual Origin of Extradural Posterior Inferior Cerebellar Artery From Vertebral and Occipital Arteries

BACKGROUND: Small anastomotic channels exist between the occipital artery (OA) and muscular branches of the vertebral artery; however, no direct connection has been reported between an extradural origin of the posterior inferior cerebellar artery (PICA) and the OA. OBJECTIVE: To describe a rare anatomic connection between the extradural PICA and the OA. METHODS: A far lateral exposure was completed on a cadaveric head prepared for surgical simulation. The course and branches of the OA were followed, and the relations to their immediate anatomic structures were studied. RESULTS: The origin of the PICA was found at the second segment of the vertebral artery, between the C1 and C2 transverse foramina. There was a large anastomotic connection between the superficial descending branch of the occipital artery and the PICA 12 mm proximal to the dural entrance of the artery. CONCLUSION: Awareness of the angioarchitecture of the suboccipital region and the existence of patent vertebrocarotid anastomotic connections is important to avoid complications during surgical or endovascular interventions. When present, a pre-existing OA-PICA anastomosis can be exploited to facilitate treatment in certain vascular pathologies (eg, vertebral artery aneurysms). Awareness of the existence of both an extradural origin of the PICA and a direct connection of this vessel with the OA is of great relevance to the muscular stage of surgical approaches to the posterior craniovertebral junction.