Computed tomography of the optic chiasm.

Using a CT/T 8800 scanner, axial and coronal images of the optic chiasm were obtained in a cadaver, 41 normal individuals, and six patients with symptoms of chiasmal glioma. The size and shape of each chiasm were determined. The normal chiasm appeared to be U- or boomerang-shaped in axial sections, and U- or dumbell-shaped in coronal sections. The average normal chiasm diameters were 1.8 cm (transverse) by 0.8 cm (anteroposterior) by 0.4 cm (vertical). The chiasm was globular and larger than 0.6 cm (vertical dimension) in all cases of chiasmal glioma. The abnormal chiasm can be distinguished accurately from the normal chiasm by computed tomography.