Introduction: The oculomotor nerve exits the brainstem from the interpeduncular fossa of the midbrain, passes through the lateral wall of the cavernous sinus, and enters the orbit via the superior orbital fissure.
Methods: Ten cadaveric heads were examined using ×3 to ×40 magnification after the arteries and veins were injected with colored silicone. Both sides of each cadaveric head were dissected using different skull base approaches
Results: The petroclinoid segment is located between the cisternal and trigonal segment. This segment is proximal to the oculomotor porus, located in the roof of the cavernous sinus near the center of the oculomotor triangle. This segment of the oculomotor nerve is limited posteriorly by the posterior petroclinoid fold and anteriorly by the oculomotor porus of the roof of the cavernous sinus. The length and diameter of this segment average 4.9 mm (range, 3.6 – 6.2 mm) and 2.3 mm (range, 1.7 – 2.9 mm), respectively. The petroclinoid segment may be especially susceptible to damage when the brainstem shifts downward at the moment of head injury. The mechanisms of damage could be ascribed to the partial tearing of the parasympathetic fibers contused against the posterior clinoid or the interclinoid ligament
Conclusions: Care should be taken to preserve this segment during the posterior clinoid drilling procedure to have more room for entering the posterior fossa and clival areas.
Patient Care: A precise knowledge of the relationship between the oculomotor nerve and surrounding structures has allowed neurosurgeon to approach the clivus, petroclival area, cavernous sinus, and superior orbital fissure without surgical complications.
Learning Objectives: To know the detailed microsurgical anatomy of the petroclinoid segment of the oculomotor nerve.