baholzer - Endoscopic Spine

21 www.baholzer.de transitional anatomy. For example, a high ilium or a sacralized lumbar segment may dictate a more acute distal approach angle. The neuroforaminal access should be planned and conceptualized on preoperative plain film studies and be reproduced during surgery on intraoperative anterior-posterior and lateral fluoroscopy images. The entry point to the lumbar neuroforamen can be determined on axial and sagittal views. 1.2.1 AXIAL IMAGING Entry point can be chosen from the median line depending on the location (of the herniation) either in the entry, mid or exit zone of the neuroforamen (IMG 1 , 2, 3). Assessing the pathology on axial views allows to determine the distance of the entry point from the midline. 1.2.2 SAGITTAL IMAGING The assessment of cranial-caudal localization of pathology such as a herniated disc dictates whether the sur- geon should choose a steep or shallow cranio-caudal angle. Lee et al. [1] published a radiographic classifi- cation system of herniated discs to direct surgical intervention. This classification is based on pre-operative sagittal MRIs and classifies the discmigration into four zones, depending on the direction and distance from the disc space (see Table and Scheme 1). IMG 1 Extraforaminal Scheme 1 Radiological classification of migrated disc herniation according to Lee et al. (1) IMG 2 Intraforaminal IMG 3 Medical, Mediolateral entry Zone Direction Range of Distance 1 Far-Upward From the inferior margin of the upper pedicle to 3 mm below of the inferior margin of the upper pedicle 2 Near-Upward From 3 mm below the inferior margin of the upper pedicle to the inferior margin of upper vertebral body 3 Near-Downward From the superior margin of the lower vertebral body to the centre of lower pedicle 4 Far-Downward From the centre of lower pedicle of lower vertebral body to the inferior margin of lower pedicle