Posteromedial central arteries

The posteromedial central arteries or paramedian arteries (also (also posteromedial perforating arteries, or posteromedial ganglionic arteries ) are branches of the posterior cerebral artery, and posterior communicating artery. They entering the substance of the brain through the posterior perforated substance. They supply a large portion of the diencephalon as well as some subcortical telencephalic structures.

Origin
PMCAs arise from the proximal (pre-communicating (P1) ) segment of the posterior cerebral artery (PCA), and along the entire length of the posterior communicating artery   (though branches arising from the latter may be considered as a distinct anatomical entity ). The PMCAs thus arise at and near the bifurcation of the basilar artery. The PMCAs are the very first branches of the PCA.

Course
PMCAs intermingle to form an extensive venous plexus in the interpeduncular fossa before entering the substance of the brain through the posterior perforated substance, then also passing through the posterior part of the internal capsule along their path. 

Distribution
The PMCAs supply a substantial part of the diencephalon.

The PMCAs are distributed to:


 * globus pallidus,
 * (lateral wall of) third ventricle,
 * (parts of the) thalamus (partially via the thalamoperforating artery )
 * subthalamus
 * hypothalamus
 * mammillary bodies
 * pituitary gland
 * optic chiasm and tracts
 * tuber cinereum
 * posterior limb of internal capsule
 * mesencephalon (midbrain)
 * basis pedunculi
 * substantia nigra
 * mesencephalic tegmentum

Clinical significance
An embolus passing along a vertebral artery will typically continue into the basilar artery before finally lodging at the bifurcation of the basilar artery, thus bilaterally obstructing the PMCAs (as well as the superior cerebellar artery); such occlusion of the PMCAs will swiftly result in infarction of the reticular formation at the level of the mesencephalon-pons junction (resulting in coma) as well as destruction of the fibers of both oculomotor nerve (CN III) (resulting in divergence of both eyes, and fixed mydriasis).

An embolism of a single PMCA at mesencephalic levels may result in a small infarction of the mesencephalon, causing Weber's syndrome.

Uncal herniation can cause compression of the PMCAs, which may result in Duret haemorrhages.