The orbitomeatal line, also known as the canthomeatal line, was the traditional axial plane used for CT of the brain. It was easily identified on the inspection of the patient's head when tilting the gantry or patient's head to achieve a standard axial plane.
The orbitomeatal line was defined as running from the outer canthus of the eye to the midpoint of the external auditory meatus 1,2.
This plane fell out of favour for CT of the brain as it generated significantly elevated doses to the lens compared to planes that avoid the orbit 1. Until recently the standard plane for CT of the brain in most departments was along the roof of the orbit, seen easily on the CT scout. This had the advantage of including the posterior fossa but avoiding the lens.
More recently, with volumetric scans becoming standard, and many CT scanners no longer being able to tilt, the whole head is scanned and then axial images are reconstructed at any desired angle. As such many departments are switching the standard axial CT brain plane to be aligned with the AC-PC line which is standard in MRI 2,3. Interestingly, this plane is quite close to the original orbitometal line and to the plane of the planum sphenoidale and hard palate.
- 1. Yeoman LJ, Howarth L, Britten A, Cotterill A, Adam EJ. Gantry angulation in brain CT: dosage implications, effect on posterior fossa artifacts, and current international practice. Radiology. 184 (1): 113-6. doi:10.1148/radiology.184.1.1609066 - Pubmed
- 2. Y.I. Kim, K.J. Ahn, Y.A. Chung, B.S. Kim. A New Reference Line for the Brain CT: The Tuberculum Sellae-Occipital Protuberance Line is Parallel to the Anterior/Posterior Commissure Line. American Journal of Neuroradiology. 30 (9): 1704. doi:10.3174/ajnr.A1676 - Pubmed
- 3. Kenneth L. Weiss, Judd Storrs, Jane L. Weiss, William Strub. CT Brain Prescriptions in Talairach Space: A New Clinical Standard. American Journal of Neuroradiology. 25 (2): 233. Pubmed