Choroidplexus

The choroid plexus is a highly vascularized, secretory structure within the brain’s ventricular system. It consists of a single layer of modified ependymal cells encasing a core of capillaries and connective tissue. Choroid plexus tissue is located in the roofs of the lateral ventricles, the third ventricle, and the fourth ventricle.

Anatomically, the capillaries are fenestrated and reside in a connective tissue stroma; the epithelial layer forms the blood–CSF barrier through tight junctions. The apical surfaces have microvilli and cilia to aid secretion and absorption. The plexus is supplied by branches of the choroidal arteries and enveloped by pia mater.

Primary function is the production and regulation of cerebrospinal fluid (CSF). In adults, about 500 milliliters of CSF are produced daily, with continuous turnover. The choroid plexus actively transports ions and solutes to determine CSF composition, supporting CNS homeostasis. CSF circulates through the ventricular system and is drained primarily via arachnoid granulations.

Developmentally, choroid plexus epithelium forms early in embryogenesis from neuroepithelial tissue and differentiates to establish early CSF production. CSF composition and plexus activity vary with age and disease, and regional differences exist among the ventricles.

Clinical significance includes choroid plexus tumors, such as papillary carcinomas and less commonly benign papillomas, which can cause hydrocephalus through increased CSF production or obstruction. Diagnosis relies on imaging and CSF analysis; treatment is usually surgical resection, with adjuvant therapy as indicated. Congenital choroid plexus cysts may be incidental findings and rarely require intervention.