Focus on the Lateral Incisural Space: Where is the Trochlear Nerve?

Abstract

Objective To define the entrance point of the trochlear nerve in the free edge of the tentorium, giving a topographical description in relation to supratentorial and infratentorial reference points.

Method The study was performed on seven formaldehyde-fixed specimens (14 sides). The distance from supratentorial and infratentorial reference points to the entrance point of the trochlear nerve into the free tentorial edge was measured.

Results The cisternal segment of the trochlear nerve, the tentorial entry point, and the reference points could be clearly identified in all specimens. The assessed distances measured from the tentorial entry point of the trochlear nerve to the anterior clinoid process was 14 to 28 mm, to the posterior clinoid process was 9 to 19 mm, to the posterior lip of the inner auditory canal was 25 to 29 mm, to the posterior border of the Meckel cave was 9 to 14 mm, and to the oculomotor triangle was 5 to 16 mm.

Conclusions The cisternal length of the trochlear nerve shows a marked variability and may be further distorted by tumors, whereas the entry point into the tentorium is a stable landmark. Therefore, it might be an important reference point for identifying the nerve before cutting the tentorium.

Keywords

trochlear nerve - cranial nerve IV - tentorial notch - lateral incisural space

• References

• 1 Rhoton Jr AL. Tentorial incisura. Neurosurgery 2000; 47 (Suppl. 01) 131-153
• 2 Lang J. Skull Base and Related Structures. 2nd ed. Stuttgart: Schattauer; 2001
• 3 Ammirati M, Musumeci A, Bernardo A, Bricolo A. The microsurgical anatomy of the cisternal segment of the trochlear nerve, as seen through different neurosurgical operative windows. Acta Neurochir (Wien) 2002; 144 (12) 1323-1327
• 4 Tubbs RS, Oakes WJ. Relationships of the cisternal segment of the trochlear nerve. J Neurosurg 1998; 89 (6) 1015-1019
• 5 Yousry I, Moriggl B, Dieterich M, Naidich TP, Schmid UD, Yousry TA. MR anatomy of the proximal cisternal segment of the trochlear nerve: neurovascular relationships and landmarks. Radiology 2002; 223 (1) 31-38
• 6 Samii M, Carvalho GA, Tatagiba M, Matthies C, Vorkapic P. Meningiomas of the tentorial notch: surgical anatomy and management. J Neurosurg 1996; 84 (3) 375-381
• 7 Koerbel A, Kirschniak A, Ebner FH, Tatagiba M, Gharabaghi A. The retrosigmoid intradural suprameatal approach to posterior cavernous sinus: microsurgical anatomy. Eur J Surg Oncol 2009; 35 (4) 368-372