A NECROPSY AND HISTOMORPHOMETRIC STUDY OF ABNORMALITIES IN THE COURSEOF THE VERTEBRAL ARTERY ASSOCIATED WITH OSSIFIED STYLOHYOID LIGAMENTS

Aims-To establish whether abnormalities in the course of the vertebral artery occur and whether they are relevant to arterial injury associa ted with head and neck movements. Methods-Twenty vertebral arteries we re carefully dissected at necropsy and abnormalities in course were no ted, along with any other bony or cartilaginous cervical anomalies. Th e effect of head and neck movement on these vessels was studied before a detailed histomorphometric examination was undertaken on sections o f the excised arteries. Results-Five vessels had an abnormal course. O ne vessel entered the transverse foramina of the fifth cervical verteb ra rather than the sixth, but was otherwise normal. In two subjects bo th vertebral arteries were abnormal in the upper cervical portion with , in each case, a straight left vertebral artery and a right vertebral artery with a deficient loop, closely applied to the atlanto-axial jo int. Both of these subjects also had completely ossified stylohyoid li gaments and the arteries visibly stretched with modest head and neck m ovements. Histology revealed variable degrees of smooth muscle disarra y in the tunica media of two of the arteries with loop deficiencies. T he circumference of one of the straight arteries was smaller than expe cted but in all other measured histomorphometric parameters these vess els appeared normal. Conclusions-Vertebral artery loops are deficient in a number of subjects. This finding is important given the recently described biomechanical susceptibility of the vertebral artery to long itudinal extension and may explain the smooth muscle changes, in that this may represent attempts at arterial wall remodelling. Subjects wit h such loop deficiencies may be more susceptible to a variety of head and neck insults and such abnormalities should be sought at necropsy i n subjects who die as a result of fatal vertebral artery injury.