The pterion is the region where the frontal, parietal, temporal, and sphenoid bone join together.
It is located on the side of the skull, just behind the temple.
At the cranial surface, the foramen of Monro is roughly 2 cm superior to the pterion, just behind the lower third of the coronal suture. At the cerebral surface, the foramen is located deep to the central portion of the pars opercularis. At the insular level, it is located deep to the central part of the second short insular gyrus. The thalamus is located at the center of the brain with the foramen of Monro at one end and the pineal gland at the other. Together, the surface landmarks of the foramen of Monro and pineal gland estimate the deep position of both the thalamus and third ventricle. The foramen of Monro approximates the anterosuperior thalamic margin, and the pineal gland defines its posterior edge.