Choroid plexus of third ventricle

The choroid plexus of third ventricle is formed when a structure called the tela choroidea intrudes into its cavity of the third ventricle from above. This structure hangs into the cavity on both sides of the midline. As this happens, the tela choroidea becomes tightly surrounded by the cuboidal ependymal lining of the third ventricle, giving rise to the choroid plexus. The choroid plexus is composed of three layers: the vascular endothelium, the pia mater, and the cuboidal ependyma. Together, these layers create a blood-cerebrospinal fluid barrier, filtering the blood to produce cerebrospinal fluid in the third ventricle.

The choroid plexus also produces growth factors that help maintain the stem cell pool in the subventricular zone. These functions are crucial for protection of brain against microbes and toxins. A tumor in the choroid plexus (papilloma) could lead to hydrocephalus due to overproduction of CSF.

The blood supply to the choroid plexus in the third and lateral ventricles is provided by the anterior and posterior choroidal branches of the internal carotid and posterior cerebral arteries, respectively.