Anterior perforated substance

The anterior perforated substance (APS) is a small, roughly rhomboid and depressed area on the basal surface of the forebrain. It lies immediately posterior to the olfactory trigone and has a perforated appearance to it.

Boundaries

The main anatomical boundaries of the anterior perforated substance include:

• Anteriorly; the olfactory trigone and olfactory striae,

• Medially; the optic tract and lateral border of the optic chiasm. The diagonal band of Broca is closely related to its posteromedial aspect.

• Laterally; the anterior parahippocampal region and uncus (containing the entorhinal cortex).

Why is it called “perforated”?

Its most important identifying feature is the large number of small perforating arteries entering through its surface. The internal carotid artery terminates and divides beneath this region, and perforating branches associated with the anterior cerebral artery, recurrent artery of Heubner, middle cerebral/lenticulostriate arteries, terminal internal carotid artery, and anterior choroidal artery enter through the anterior perforated substance. These vessels supply important deep structures, including parts of the caudate nucleus, lentiform nucleus and internal capsule.