The Vertebrobasilar Trunk and Its Anatomical Variants: A Microsurgical Anatomical Study

Abstract

Background: The trunk of the basilar artery has not been included in microanatomy studies. Anatomical variants of the perforant branches of the vertebrobasilar trunk and their relationship with neural structures are very important in surgical approaches. Surgical dissection for the treatment of vascular lesions requires a perfect knowledge of the microsurgical anatomy.

Methods: We conducted a descriptive analysis of 50 brains, which were fixed with formalin at 10% for 2 weeks, and the arterial system was injected with colored latex. After microsurgical dissection, it was divided into three segments: the lower portion went from the anterior spinal artery to the anteroinferior cerebellar artery, the middle segment was raised from the upper limit of the lower portion to the origin of the superior cerebellar artery, and the upper segment ranged from the previous portion until the origin of the posterior cerebral artery.

Results: The basilar artery had an average length of 30 mm. The average diameter at its junction with the vertebral arteries was 4.05 mm. The average middle segment was 3.4 mm in diameter and 15.2 mm in length. The diameter of the upper segment was 4.2 mm, and its average length was 3.6 mm. The average number of bulbar arteries was three, and their average diameter was 0. 66 mm. The number of caudal perforator arteries were five on average, with a diameter of 0.32 mm. We found three rare cases of anatomical variants in the vertebra-basilar junction.

Conclusions: The basilar artery emits penetrating branches in its lower, middle, and upper portions. The origin of penetrating branches was single or divided after forming a trunk. However, we observed long branches from perforant arteries.

Keywords: anatomy; arterial trunk; basilar artery; laboratory; neurosurgery; perforants; terminal branches; vertebral artery.

Figure 1

Vertebrobasilar arterial trunk: panoramic view. PCA, posterior cerebral artery; SCA, superior cerebellar artery; AICA, anterior inferior cerebellar artery; VA, vertebral artery; BA, basilar artery; ASA, anterior spinal artery; PICA, posterior inferior cerebellar artery; III, oculomotor nerve; VI, abducens nerve; VII, facial nerve; VIII, vestibulocochlearis nerve; X, vagus nerve.

Figure 2

Injection and washing technique. (A) Arterial system during its irrigation with physiological solution. (B) Perfused arterial system with colored latex.

Figure 3

Caudal segment of the BA.

Figure 4

Caudal segment of the BA and related perforating arteries. Anastomoses were observed in 38 (76%) of all the brains, which ranged from three to nine in number per brain, and with diameters ranging from 135 to 190 μm. Anastomotic bridges were observed in 8 (16%) of encephalons between the middle and CSs of the BA, and also between the caudal perforators and the perforators of the vertebral artery in 13 (26%) encephalons; however, anastomoses between the caudal perforators were observed in only 2 (4%) encephalons.

Figure 5

Brain stem, where the middle segment of the BA is observed.

Figure 6

Middle segment of the inferior BA, perforating groups in a single arrangement or trunks.

Figure 7

Rostral segment of the BA.

Figure 8

The upper segment of the BA and related perforating arteries.

Figure 9

A right persistent trigeminal artery (PTA) and its relationship with the right trigeminal nerve (V). BA, basilar artery; III, oculomotor nerve; VA, vertebral artery.

Figure 10

Fenestrated BA. It shows a widening and cleft of the right vertebrobasilar artery junction.

Figure 11

Vertebral communicating artery. The vascular bridge from which the spinal artery emerges is observed.