Definition and Examination of the Brainstem Safe Entry Zones with 4.7T Magnetic Resonance Imaging and Diffusion Tractography

Background: Although safe entry zones of the brain stem have been described in clinical cases with various pathologies or very limited number of cadaveric studies, a comprehensive study that has tested these entry zones is lacking. Safe entry zones and surgical paths that have been previously described were simulated and relations between adjacent eloquent structures were tested with 4.7T magnetic resonance imaging (MRI) and fiber tractography (FT) in cadaveric brainstems.

Material and Methods: Twelve previously reported safe entry zones and surgical paths were simulated on 8 formalin-fixed adult cadaveric brainstems using wooden sticks (Figure 1). These brainstems were examined with T2-weighted MRI and FT before and after creating entrance into the brainstem and surgical paths (Figure 2).

Results: The most important anatomical structures that were identified with MRI were described in the pathway of the every single safe entry zone. Various measurements taken from entry zones and surgical paths to the adjacent nuclei or ascending and descending tracts were noted.

Conclusions: This is the first study utilizing 4.7 T MRI and FT to test already purposed safe entry zones of the brainstem.

In addition, relationship between these cranial nerve nuclei and fiber tracts were demonstrated comprehensively.