A new segment of the trochlear nerve: cadaveric study with application to skull base surgery

Area of Science:

• Neurosurgery
• Anatomy
• Skull Base Surgery

Background:

• The trochlear nerve (CN IV) is critical for skull base surgical approaches.
• Traditional anatomical descriptions divide the trochlear nerve into cisternal, cavernous, and orbital segments.
• Anecdotal observations suggested an additional segment requiring further investigation.

Purpose of the Study:

• To identify and characterize a potentially new segment of the trochlear nerve.
• To elucidate the microanatomy of the distal cisternal and precavernous trochlear nerve segments.
• To provide anatomical knowledge beneficial for skull base surgeons.

Main Methods:

• Microdissection of 20 latex-injected cadaveric sides using an operating microscope.
• Examination of the distal cisternal and precavernous segments of the trochlear nerve.
• Measurement of anatomical structures using a microcaliper and digital imaging.

Main Results:

• A previously undescribed segment of the trochlear nerve was identified in all specimens.
• This segment, named the trigonal segment, courses from the oculomotor trigone to the posterior cavernous sinus wall.
• The average length of this newly identified trigonal segment was 4 mm.

Conclusions:

• A novel trigonal segment of the trochlear nerve has been identified.
• This anatomical finding expands the current understanding of trochlear nerve microanatomy.
• Awareness of the trigonal segment is valuable for skull base surgeons to improve nerve preservation.