Ting Lei, M.D, Laura Snyder, M.D, Evgenii Belykh, M.D, Kaan Yagmurlu, M.D, Guozhu Sun, M.D, PhD, Kashif Malik, BS, David Malekooti, BS, Robert F. Spetzler, M.D, Mark C. Preul, M.D, Peter Nakaji, M.D

Introduction

•Resection of the inferior temporal and occipital lesions is challenging due to proximity of visual tracts, Wernicke’s area, and the vein of Labbé. Seeking to mitigate these risks, we have explored SCTTKA and correlated an anatomical and clinical study.

Methods

•Three variations SCTTKA (2.5x2.0cm craniotomy) studied on cadavers: 1) median, 2) paramedian, 3) lateral. Surgical exposure area and anatomical targets indicated with 0°endoscopes by stereotactic navigation. Bone and soft tissues thicknesses for different SCTTKA were measured on patient CT images (n=20). Similar surgical planning performed on patients.

•Comparative cases included 2 tentorial meningiomas and 1 hippocampal cavernous malformation using paramedian SCTTKA; 1 occipital glioblastoma using lateral SCTTKA. Gross total resection was achieved without deficit in all cases.

Results

•In cadavers,

•Median SCTTKA allows adequate surgical view only to posterior part of inferior occipital region.

•Paramedian SCTTKA provides a surgical view for inferior occipital region except for tentorial incisura. After tentorium cutting, the access yields sufficient angles for resecting petrous region lesion and mediobasal temporal lobe lesion.

•Lateral SCTTKA gives access to lesions located close to the tentorial incisura. A favorable access to mediobasal temporal region can be achieved also after incising tentorium.

Fig 1: Posterolateral view of anatomical specimen and neuronavigation illustrating the surgical exposure area under the 0o endoscope through the median(A), paramedian(B), and lateral(C) SCTT keyhole approach respectively.

Fig 2: A. Coordinates of maximal distal reachable points were recorded on the tentorial surface to calculate the area of surgical exposure through the median SCTT keyhole approach
B. and C. Maximal distal reachable points that were selected on the tentorial surface (white line area) and on the petrous surface (yellow line area) to calculate the area of surgical exposure through the paramedian and lateral SCTT keyhole approaches

Results
•In cadavers, median SCTTKA traversed the thickest bone and soft tissues, narrowing the range of bilateral surgical view.
•CT imaging showed that the thickness of bone and soft tissues dissected in median, paramedian, and lateral STTKA were: 17±4mm/7±2mm/7±2mm and 29±6mm/26±6mm/20±5mm respectively.
•Clinical data confirmed findings of cadaveric dissection study.

•A. The thickness of soft tissue in median (M) and paramedian (PM) approaches wassignificantly thicker than in lateral approach (both P<0.01).
•B. The median (M) SCTT keyhole approach traversed the thickest bone comparison tothe paramedian (PM) (P<0.01) and lateral (L) (P<0.01) approaches.

Results
•Four patients undervent SCTTKA procedure. Two patients with tentorial meningiomas and one with a hippocampal cavernous malformation had lesions removed using the paramedian SCTT keyhole approach. One patient had an occipital glioblastoma removed using the lateral SCTT keyhole approach. All patients underwent preoperative assessments before surgery.

Discussion
•In all exposures, the surgical field may relate to the shape of the cerebellum and tentorium. A tentori- um with a greater incline may require more retraction on the cerebellum and more difficulty in opening the tentorium for access.

•The crucial structures, such as occipital sinus, vermian veins, the vein of Labbé, the trochlear nerve, and so on, may limit the surgical exposure area in these three approaches. Some anatomical struc- tures can be sacrificed without severe surgical complications; but some anatomical structures should be protected intact, given ensuing serious complications if occluded or resected during the surgical procedure.

•Figures A and B show the occipital sinus and vermian veins that obstruct the entry of median SCTT keyhole approach.
•Figure C shows the vein of Labbé and the bridging veins to the tentorial sinus. These veins may limit the surgical expo-sure of paramedian SCTT keyhole approach.
•Figure D shows the trochlear nerve that runs anteriorly between the attached and free borders of the tentorium after it comes out of brainstem. It should be protected when the tentorium is cut during the paramedian and lateral SCTT keyhole approaches.

Summary Points
•The paramedian SCTT keyhole approach provides an adequate surgical angle and exposure to most of the inferior occipital region and the petrous part of the temporal bone.
•The lateral endoscopic SCTT keyhole approach accesses the middle fossa and tentorial incisura region directly.
•The median SCTT keyhole approach accesses the bilateral inferior occipital region and can be the alternate choice for paramedian SCTT keyhole approach.
•A carefully selected keyhole SCTT approach in combination with endoscopic technique may provide crucial surgical advantages and allow the surgeon to minimize approach-associated morbidity while accessing difficult supracerebellar lesions.

雷霆

主治医师、神经外科硕士、美国巴洛神经外科研究所研究员
专业特长：擅长烟雾病、颈动脉狭窄、动脉瘤、海绵状血管瘤、动静脉畸形、动静脉瘘等出血性和缺血性脑血管疾病的诊疗、手术和围手术期管理。擅长颅咽管瘤、脑膜瘤、胶质瘤、神经鞘瘤、转移瘤等各种颅内肿瘤的诊疗、手术和围手术期管理。