Choroid plexus

The choroid plexus is a structure inside the ventricle(s) that produces cerebrospinal fluid. It is formed when the tela choroidea, which is a double fold of pia with a vascular core, infringes into the ventricular cavity. As it does so, it becomes tightly surrounded by the cuboidal ependymal lining of the ventricle, giving rise to the choroid plexus. These three layers of choroid plexus, namely the vascular endothelium, the pia mater, and cuboidal ependyma, together create a blood-cerebrospinal fluid barrier that filters the blood to produce cerebrospinal fluid in the ventricles.

The choroid plexus can be found in the lateral, third, and fourth ventricles of the brain. In the case of the third ventricle, the choroid plexus is formed when the tela choroidea on the roof of the ventricle intrudes into its cavity from above, hanging into the cavity of third ventricle on both sides of the midline.

The same tela choroidea on the roof of the third ventricle extends laterally through the choroid fissure and passes through the interventricular foramen of Monroe, entering the lateral ventricles on both sides and forming the choroid plexus there. Additionally, the tela choroidea enters into the temporal horn of the lateral ventricle by intruding into the ventricular cavity through the lower part of the choroid fissure situated between the stria terminalis and the fimbria of hippocampus.

As for the fourth ventricle, the tela choroidea extends between the anteroinferior cerebellum and the back of the medulla and fourth ventricle. Here, it intrudes into the cavity of the fourth ventricle surrounded by the ependyma, thereby forming the choroid plexus.

The blood supply to the vascular core of the choroid plexus in the fourth ventricle is provided by the posterior and anterior inferior cerebellar arteries, mainly the PICA. In the case of the third and lateral ventricles, the anterior and posterior choroidal branches of the internal carotid and posterior cerebral arteries supply them, respectively.