Perichiasmal

Perichiasmal is an anatomical term describing structures surrounding the optic chiasm, the X-shaped crossing of the optic nerve fibers located at the base of the brain just above the pituitary gland. The perichiasmal region lies in the suprasellar space and includes adjacent optic nerve segments, the chiasm itself, proximal portions of the optic tracts, and nearby cisternal and vascular structures.

Anatomically, the perichiasmal area encompasses the proximal optic nerves, the optic chiasm, the nearby optic tracts, the pituitary stalk, and surrounding arachnoid cisterns. It is a term used in neuroanatomy and neuroradiology to describe the zone around the chiasm and to help characterize relationships during surgical planning or imaging assessment.

Clinical significance arises when lesions arise in or extend into the perichiasmal region. Tumors and vascular lesions in this area, such as pituitary macroadenomas, craniopharyngiomas, meningiomas near the tuberculum sellae, or aneurysms, can compress or distort the optic chiasm, leading to visual disturbances, most notably bitemporal hemianopia. Imaging modalities such as MRI or CT are used to evaluate perichiasmal involvement by assessing chiasmal displacement, thinning, or contrast enhancement of surrounding tissues. See also optic chiasm and suprasellar region for related context.