Bifurcation of the trochlear nerve: cadaveric case report and literature review

The trochlear nerve [the fourth cranial nerve (IV CN)], one of the extraocular motor cranial nerves, exits the midbrain at its dorsal side, runs inside the lateral wall of the cavernous sinus (CS), and innervates the superior oblique muscle. In the wall of the CS, the IV CN travels in the vicinity of the oculomotor and ophthalmic nerves. These nerves border the infratrochlear and supratrochlear triangles (ST), which are part of a parasellar group of triangles of the CS, and provide safe entry zones to the inside of the CS.

During standard anatomical dissection, the unusual bifurcation of the trochlear nerve in the wall of the CS was found. The observed division of the IV CN clearly underscores that the traditional understanding of spatial relationships between structures that define the infratrochlear and ST may not always be adequate to represent the patient's anatomy.

Greater awareness of the possible variations in the trochlear nerve's course is essential for conducting surgeries with extremely limited surgical access, to minimize the risk of iatrogenic injury, and enable modified operative strategies.