028 Delayed CT imaging leading to delays in acute stroke management in regional australia

Abstract

parallel to each other in the central arm of an 'H'. This study aimed to determine the population variance in chiasmal shape. Methods 68 MRI scans of healthy individuals without visual abnormality were randomly selected. A 2D image was created and images were analysed using AutoCAD software to determine the offset between lines drawn down the centres of the optic nerves and contralateral optic tracts. A positive offset would suggest an 'H' shape while an 'X'-shaped chiasm would have a offset of 0. Results The mean width of the chiasm was 12.0 mm, and the mean offset was 4.7 mm generating a mean offset:width ratio of 0.38. No chiasm had an offset of zero. Fibre crossings occurred approximately 2.35 mm lateral to the midline, and nasal (crossing) fibres travelled an average of 4.7 mm in the mediolateral plane before entering the contralateral optic tract. Conclusions The human optic chiasm is H-shaped, not Xshaped. This information will inform future models of chiasmal compression.