An endoscope-assisted craniometric cadaveric study for the brain stem and the cisternal segment of the trochlear nerve.

BACKGROUND AND PURPOSE

This study analyzed the relationship of trochlear nerve with neurovascular structures using craniometric measurements. The study was aimed to understand the course of trochlear nerve and minimize the risk of injury during surgical procedures.

METHODS

Twenty trochlear nerves of 10 fresh cadavers were studied bilaterally using endoscopic assistance through the view afforded by the lateral infratentorial-supracerebellar, and the combined presigmoid-subtemporal transtentorial approaches. Trochlear nerves were exposed bilaterally taking seven parameters into consideration: the distance between the cisternal segment of trochlear nerve and vascular structures (superior cerebellar artery/SCA; posterior cerebral artery/PCA), the origin of the trochlear nerve in the brain stem, the angle in the level of tentorial junction, length, diameter, and length of nerve in the cisternal segment.

RESULTS

We identified the brain stem and cisternal segments of the trochlear nerve. The lateral infratentorial supracerebellar approach allowed the exposure of the cisternal segments (crural and ambient cisterns), including the origin of the nerve in the brain stem. The combined presigmoid-subtemporal transtentorial approaches provided visualization of the cisternal segment of the nerve and the free edge of the tentorium. In this study, the mean length and width of the trochlear nerve in the cisternal segment were 30.3 and 0.74 mm, respectively. Length of the trochlear nerve from its origin to its dural entrance was 37.2 mm, tentorial dural entrance angle of the trochlear nerve and exit angle of the trochlear nerve from the brain stem were 127.0 degrees and 54 degrees, PCA to trochlear nerve in mid ambient cistern and SCA to trochlear nerve in mid ambient cistern were 7.3 mm and 6.8mm.

CONCLUSION

Trochlear nerve is vulnerable to injury during the surgical procedures. Therefore, it is necessary to have a sufficient knowledge of the anatomy of cisternal segment and its relationship with adjacent neurovascular structures. The anatomical and craniometric data can be helpful in middle and posterior fossa surgery in minimizing the potential injury of the trochlear nerve.