Surgical anatomy of the vertebrobasilar territory and posterior circle of Willis.

BACKGROUND: In the present era of microscopic and neuroendoscopic procedures, the surgical anatomy of the skull base vessels has gained increased significance. The pattern of the vertebrobasilar arterial complex and the posterior circle of Willis (COW) in Nigerians has not been previously reported despite various variants of these complexes existing in different populations. OBJECTIVE: To review and document the size, distribution and anomalies of the vertebrobasilar territory and posterior COW pattern in a Nigerian set of brains. METHODS: The target population for this study was a group of Nigerian adults 18 years and above. Specimens from patients with an ante-mortem or post-mortem evidence of meningitis or atherosclerosis were excluded. The size, distribution and anomalies of the vertebrobasilar artery, its branches, and the posterior COW were defined in 50 brains. RESULTS: The male: female ratio was 1.9:1 and a mean age of 44 years. Statistical analysis showed significant differences between the sizes of posterior inferior cerebellar arteries and anterior inferior cerebellar arteries (Student's t=-30.189; p-value= 0.000). Fifty-six percent of the brains had no anomalies. Thirty anomalies were noted in posterior COW compared with six in the vertebrobasilar territory. There were no aneurysms in all the specimens studied. CONCLUSION: Anomalies in the region of the posterior COW are commoner than the vertebrobasilar territory and the region of the posterior communicating artery is the most common site of anomalies in the posterior COW territory. These variations should be taken into account during skull base and carotid surgeries, and cerebral angiography.