Variation in the Anatomy of the Normal Human Optic Chiasm: An MRI Study

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Title Variation in the Anatomy of the Normal Human Optic Chiasm: An MRI Study
Creator Nicholas S. I. Bosler; David Ashton; Andrew J. Neely; Christian J. Lueck
Affiliation Australian National University Medical School (NSIB, DA, CJL), Canberra, Australia; Departments of Neurology (NSIB, CJL) and Radiology (DA), The Canberra Hospital, Canberra, Australia; and School of Engineering and Information Technology (AJN), University of New South Wales, Canberra, Australia
Abstract Background: Compression of the optic chiasm typically leads to bitemporal hemianopia. This implies that decussating nasal fibers are selectively affected, but the precise mechanism is unclear. Stress on nasal fibers has been investigated using finite element modeling but requires accurate anatomical data to generate a meaningful output. The precise shape of the chiasm is unclear: A recent photomicrographic study suggested that nasal fibers decussate paracentrally and run parallel to each other in the central arm of an 'H.' This study aimed to determine the population variation in chiasmal shape to inform future models. Methods: Sequential MRI scans of 68 healthy individuals were selected. 2D images of each chiasm were created and analyzed to determine the angle of elevation of the chiasm, the width of the chiasm, and the offset between the points of intersection of lines drawn down the centers of the optic nerves and contralateral optic tracts. Results: The mean width of the chiasm was 12.0 ± 1.5 mm (SD), and the mean offset was 4.7 ± 1.4 mm generating a mean offset:width ratio of 0.38 ± 0.09. No chiasm had an offset of zero. The mean incident angle of optic nerves was 56 ± 7°, and for optic tracts, it was 51 ± 7°. Conclusions: The human optic chiasm is 'H' shaped, not 'X' shaped. The findings are consistent with nasal fibers decussating an average of 2.4 mm lateral to the midline before travelling in parallel across the midline. This information will inform future models of chiasmal compression.
Subject Magnetic Resonance Imaging; Optic Chiasm; Optic Nerve; Photomicrography
OCR Text Show
Date 2021-06
Language eng
Format application/pdf
Type Text
Publication Type Journal Article
Source Journal of Neuro-Ophthalmology, June 2021, Volume 41, Issue 2
Collection Neuro-Ophthalmology Virtual Education Library: Journal of Neuro-Ophthalmology Archives: https://novel.utah.edu/jno/
Publisher Lippincott, Williams & Wilkins
Holding Institution Spencer S. Eccles Health Sciences Library, University of Utah
Rights Management © North American Neuro-Ophthalmology Society
ARK ark:/87278/s6b6n1tk
Setname ehsl_novel_jno
ID 1996646
Reference URL https://collections.lib.utah.edu/ark:/87278/s6b6n1tk
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