Variations of the 6th cranial nerve (nervus abducens) in the petroclival region: A microsurgical study.

The aim of this study is to present the variations of nervus abducens in localization and number as it pierces the clival dura mater. The calvaria of 16 cadaveric heads were removed by making horizontal incisions from Glabella to Inion in both sides of the head. The dura mater was dissected. Cerebrum and cerebellum were taken out by obtuse dissection. Dissections of cavernous sinus were made under the stereomicroscope and the findings were photographed. Out of 16 specimens, one of them was excluded. Fifteen heads were bilaterally analyzed. Analysis of these nerves presented four different variations. Variation types a classified CN VI as a single trunk and entering a single dural pore with 77% occurrence. Variation type b classified CN VI with two branches running in the petroclival region and entering a single dural pore with 10% occurrence. Variation type c classified CN VI as 2 trunks and entering 2 separate but close dural pores with 10% occurrence. Variation type d classified CN VI with 2 distinct trunks and 2 branches entering 2 separate but close dural pores with 3% occurrence. CN VI plays a major role in the clinic of the eye. Due to its intracranial and extracranial course, injuries to the head and to the nerve may result in malfunctioning of the lateral muscles of the eye. Therefore, the variations of branching, relations and its course were analyzed.