Huge Fenestration of the Vertebral Artery and Fenestrated Basilar Artery

Background: Fenestrations, such as those of the vertebral artery (VA), are generally regarded as arterial slits. To the authors' knowledge, large fenestrations of the VA were reported twice previously, those morphological patterns being different. We hereby report a third pattern of such large fenestration of the VA. Methods: It was found serendipitously on the computed tomography angiograms of a 63 year-old male which were documented retrospectively. Results: The findings were as follows: 1. the right VA entered the posterior fossa, crossed to the left side and joined the opposite VA to form the basilar artery; 2. the right posterior inferior cerebellar artery was absent; 3. the left VA entered the posterior fossa then it had a huge fenestration with 2 limbs: an anterior one, appearing as the main trunk of the VA coursing to form the BA, and a posterior, coiled one, inserted at both ends into the VA; 4. that posterior limb of the left VA fenestration sent off 2 posterior inferior cerebellar branches; 5. a slit-like fenestration of the basilar artery was also found. Conclusions: Large fenestrations of the VA could result if, during embryogenesis, the proximal segment of the lateral basivertebral anastomosis and the distal segment of the proatlantal artery persist. Large fenestrations of the VA bring into a narrow neurosurgical field an additional arterial trunk that should be carefully documented preoperatively in order to avoid hemorrhagic events.