Variations in the anatomy of the vertebral artery cervical loop segment - a potential predisposing factor for traumatic basal subarachnoid hemorrhage?

Fatal traumatic basal subarachnoid hemorrhage (TBSAH) is a characteristic forensic pathological entity, the investigation of which requires special techniques. In Liverpool, post-mortem room angiography is undertaken, followed by complete removal of the vertebral arteries and histological examination. It has been observed that the arterial anatomy can be highly variable, particularly the length and course of the loop segments located between the C2 vertebra and the dura. In a number of cases of TBSAH the loop segments of torn vessels have appeared relatively short. Having observed this phenomenon subjectively in our case work, a radiological study was undertaken with the aim of quantifying vertebral artery loop anatomy variation in a 'normal' population. Multiphase post-mortem computed tomography angiography (MPMCTA) scans of 98 subjects were reviewed and the lengths of the different portions of the loop segments (foramen magnum to the upper border of C1, between C1 and C2, and the bony foramina themselves) of each vertebral artery were measured using semi-automated vessel analysis software. The measurements obtained provide objective evidence of marked anatomical variation, with some loop segments more than twice the length of others. These results are important because a short vertebral artery loop segment might be a significant factor in predisposing an individual to TBSAH following a blow to the head or neck.