Neurovascular relationships of the root entry zone of lower cranial nerves: a microsurgical anatomic study in fresh cadavers.

The study describes the microsurgical neurovascular relationships of the root entry zone of lower cranial nerves in 23 cadavers. The vessel type, frequency of contact and site of contact on the root entry zone were analysed. Three types of vascular patterns (Types I-III) were found. Facial nerve: frequency of contact 31.8%; arterial contact 92.9%, Type I (lying across) 78.9%; anterior inferior cerebellar artery in 84.6%. Glossopharyngeal nerve: frequency of contact 23.9%; arteries 54.5%, veins 45.5%; posterior inferior cerebellar artery in 83.3% and Type II (loop) 50.1%. Vagus nerve: frequency of contact 26.1%, arteries 58.3%. Types II and III (passing through) formed 42.9% each. Hypoglossal nerve: frequency of contact 78.2%; vertebral artery 88.9%. No 'grooving' on any nerve was seen. Hence, 'contact' by a vessel at the root entry zone may not be significant in the etiology of lower cranial rhizopathies.