Jeppe Praetorius - Role of the Choroid Plexus in Health and Disease

The human choroid plexus (CP) is a highly vascularized epithelial structure, weighing approximately 1 g and residing inside the brain ventricles. The CP secretes the majority of the daily production of 500 ml cerebrospinal fluid (CSF) with a transport rate, which is unsurpassed by other human epithelia. The CP is a key structure for (1) providing the CSF for buoyancy decreasing the effective weight of the brain from 1.5 kg to only 50 g, (2) delivering local mediators and hormones to the brain parenchyma via the CSF, (3) maintaining a suitable ionic microenvironment, and (4) forming a barrier against toxins, drugs, microorganisms, and immune cells. Choroid plexus dysfunctions are described in a wide range of clinical conditions such as aging, Alzheimers disease, brain edema, stroke, neoplasms, and several types of hydrocephalus. Knowledge on the structure and ultrastructure of the choroid plexus is essential for generating hypotheses on the mechanisms involved in the normal function of the CP and in diseases and conditions with deranged CSF secretion, in inflammation, or in drug delivery.

1.1 Development of the Choroid Plexus

The choroid plexus (CP) is a highly vascularized epithelial structure that protrudes into the brain ventricles. The development of the CP is initiated after neural tube closure in the fourth week of gestation in humans. The CP in the fourth brain ventricle is the first to appear from an invagination of the dorsal roof plate in the midline of the neural tube (Fig. ). Also, the CP in the third ventricle develops as an individual structure but eventually it bifurcates and merges into one continuous structure with the lateral ventricle CP.

Fig. 1.1

Development of the choroid plexus. Initially following closure of the neural tube the brain is divided into the rhombencephalon (hindbrain), the mesencephalon (midbrain) and the prosencephalon (forebrain) (a: sagittal section and c: frontal section). At 5 weeks the prosencephalon consists of the telencephalon and the diencephalon; the rhombencephalon develops into the metencephalon and the myelencephalon (b and d). The fourth ventricle CP is the first to appear in the hindbrain (b). The lateral ventricle CP arises next in the telencephalon and finally the third ventricle CP in the diencephalon. The mesencephalon contains the aquaduct which connects the third and fourth ventricle. As the telencephalon expands the lateral ventricle elongates but remains in contact with the third ventricle through the foramen of Monroe (e). The third ventricle CP initially develops as a separate structure but eventually comes into contact with the lateral ventricle CP through the foramen of Monroe (