New insights into the anatomic dissection of the temporal stem with special emphasis on the inferior fronto-occipital fasciculus: implications in surgical approach to left mesiotemporal and temporoinsular structures.

Objective: To analyze the 3-dimensional relationships of the inferior fronto-occipital fasciculus (IFOF) within the temporal stem using anatomic dissection and to study the surgical application.

Methods: Ten postmortem human hemispheres (5 right, 5 left) were dissected using the Klingler fiber dissection technique. The 3-dimensional relationships of the IFOF with different landmarks of the temporal stem, insula, and temporal lobe were analyzed and measured.

Results: An average distance of 10.9 mm (range, 8-15 mm) was observed between the limen insulae and the anterior edge of the IFOF under the inferior limiting sulcus of the insula. This anterior one-third of the temporal stem is crossed by the uncinate fasciculus. The IFOF crosses the posterior two-thirds of the temporal stem, in the space between the posterior limit of the uncinate fasciculus and the lateral geniculate body. The average superoinferior distance between the IFOF and the inferior limiting sulcus was 3.8 mm. The auditory radiations and the claustro-opercular and insulo-opercular fibers of the external and extreme capsules pass through the temporal stem above the IFOF, whereas the optic radiations pass below.

Conclusion: In the transsylvian approach to the mesiotemporal structures in the left dominant hemisphere, an incision within the posterior 8 mm from the limen insulae is less likely to damage the IFOF than more posterior incisions along the inferior limiting sulcus. In the temporal transopercular approach to left temporo-insular gliomas, the IFOF constitutes the deep functional limit of the resection within the temporal stem.