Objective: The goals of this investigation were to perform a detailed analysis of petroclival microanatomic features, to investigate the course of the abducens nerve in the petroclival region, and to identify potential causes of injury to neurovascular structures when anterior transpetrosal or transvenous endovascular approaches are used to treat pathological lesions in the petroclival region.
Methods: Petroclival microanatomic features were studied bilaterally in seven cadaveric head specimens, which were injected with colored silicone before microdissection. Another cadaveric head was used for histological section analyses.
Results: A lateral or medial location of the abducens nerve dural entrance porus, relative to the midline, was correlated with the course and angulation of the abducens nerve in the petroclival region. The angulation of the abducens nerve was greater and the nerve was closer to the petrous ridge in the lateral type, compared with the medial type. The abducens nerve exhibited three changes in direction, which represented the angulations in the petroclival region, at the dural entrance porus, the petrous apex, and the lateral wall of the internal carotid artery. The abducens nerve was covered by the dural sleeve and the arachnoid membrane, which became attenuated between the second and third angulation points. The abducens nerve was anastomosed with the sympathetic plexus and fixed by connective tissue extensions to the lateral wall of the internal carotid artery and the medial wall of Meckel's cave at the third angulation point. There were two types of trabeculations inside the sinuses around the petroclival region (tough and delicate).
Conclusion: The petroclival part of the abducens nerve was protected in a dural sleeve accompanied by the arachnoid membrane. Therefore, the risk of abducens nerve injury during petrous apex resection via the anterior transpetrosal approach, with the use of the transvenous route through the inferior petrosal sinus to the cavernous sinus, should be lower than expected. The presence of two anatomic variations in the course of the abducens nerve, in addition to findings regarding nerve angulation and tethering points, may explain the relationships between adjacent structures and the susceptibility to nerve injury with either surgical or endovascular approaches. Venous anatomic variations may account for previously reported cases of subarachnoid hemorrhage with the endovascular approach.