2026 Poster Presentations
P338: COUPLING THE SURGICAL CORRIDOR WITH INTRA-BRAINSTEM ANATOMY: PRELIMINARY MR MICROSCOPY STUDY ON SURGICAL FREEDOM WITH A FOCUS ON THE INFRA-TRIGEMINAL SAFE ENTRY ZONE
Yunjia Ni, MD1; Kivanc Yangi, MD2; Danielle VanBrabant, MS, CMI3; Alberto Fuentes1; Dakota Graham4; Philip Warren4; Jack Olson2; Jarett Prince2; Michael T Lawton, MD5; Mark C Preul, MD2; Richard D Dortch1; 1Barrow Neuroimaging Innovation Center, Department of Translational Neuroscience, Barrow Neurological Institute, St Joseph's Hospital and Medical Center, Phoenix, AZ; 2The Loyal & Edith Davis Neurosurgical Research Laboratory, Department of Neurosurgery, Barrow Neurological Institute, St Joseph's Hospital and Medical Center, Phoenix, AZ; 3Neuroscience Publications, Barrow Neurological Institute, St Joseph's Hospital and Medical Center, Phoenix, AZ; 4Thurston Innovation Center, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center; 5Department of Neurosurgery, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center
Quantitative cadaver studies of surgical “freedom” in brainstem safe entry zones (SEZs) are limited by a key disconnect: the intrinsic brainstem anatomy is often analyzed separately from surgical corridor. As a result, numerical estimates from these studies might be inflated. In vivo 3T MRI offers noninvasive visualization compared with conventional white matter dissections, but reliable diffusion MRI scan (e.g., DTI) is challenging in cadaver tissue, limiting tract-based assessment. Ex vivo MR microscopy (MRM) has gained interest due to superior resolution compared with 3T MRI, with white matter tracts directly visualized on T1-weighted imaging (T1WI) without diffusion sequences. However, most MRM studies require extraction of small specimens, severing the link between surgical trajectory and intrinsic anatomy unless complex registration is performed. Thus, the surgical value of MRM for SEZ remains largely unexplored. In this proof-of-concept study, we focus on the infra-trigeminal zone (ITZ) and demonstrate a novel MRM-based approach that integrates the extended retrosigmoid surgical corridor with intrinsic brainstem anatomy on the same cadaver, enabling quantitative assessment of surgical freedom.
An 83-year-old male cadaver (post-mortem interval 72h; 8% formalin fixation) underwent a clinical 3 T T1-weighted neuronavigation scan (Philips) and registration was performed on Medtronic StealthStation S8 for coordinate collections. An extended retrosigmoid craniotomy (35×34 mm bone window) was performed, followed by inverted T-shaped incision of the dura. Ten surgical corridor landmarks were collected – four bone window corners, four dura window points, the inferior point of the CN V root entry zone and the superior point of the CN VII root entry zone. The brainstem (retaining cerebellar tissue to fit) was rehydrated ex vivo in PBS doped with gadobutrol for two weeks, immersed in Fomblin and degassed within an airtight MR-compatible container, and imaged (T1WI, 0.3 mm isotropic, six averages) on a 7 T Bruker Biospec 70/30 system (0.1×0.1×0.8 mm resolution, scan time = 2h 32min). With manual and rigid registration, the 3T Stealth coordinates were converted to the 7T space. Corticospinal tract (CST), medial lemniscus/spinothalamic tract (MLSTM) and CN V nuclei were manually segmented. A computer algorithm searched for straight trajectories that traverse the bone window, the dura window and the ITZ line while remaining lateral or posterior to the CST or MLSTM, or anterior or lateral to the CN V nuclei. Surgical freedoms were reported in both intra-brainstem depth of freedom and angular freedom.
The area of bone window was 1178.48 mm2 and the area of the dura window was 680.21 mm2. The length of the ITZ was 12.76 mm. The algorithm detected 257 rigid lines that meet the restrictions stated above. Mean ± standard deviation (SD) of the intra-brainstem depth of freedom was 2.59±1.44 mm. The mean angular freedom was 21.0±8.1 degrees.
By registering 3T surgical coordinates to ex vivo 7T MRM from the same cadaver, we directly linked the external retrosigmoid corridor with intrinsic brainstem anatomy and quantified surgical freedom at the ITZ. This novel framework might potentially overcome key limitations of dissection-only or geometry-only approaches, reducing the risk of inflated feasibility estimates.
