|Brain: Choroid plexus|
Scheme of roof of fourth ventricle. The arrow is in the foramen of Magendie.
1: inferior medullary velum
2: Choroid plexus
3: Cerebellomedullary cistern of subarachnoid cavity
4: Central canal
5: Corpora quadrigemina
6: Cerebral peduncle
7: Superior medullary velum
8: Ependymal lining of ventricle
9: Pontine cistern of subarachnoid cavity
The choroid plexus (CP) (from Greek khorion "membrane enclosing the fetus, afterbirth"; plexus: Mod.L., lit. "braid, network") is a plexus in the ventricles of the brain where cerebrospinal fluid (CSF) is produced. The choroid plexus consists of modified ependymal cells. CSF is recycled (flushed) 4 times per day in order to clean out metabolites and toxins like beta amyloid. Hence the choroid plexus must produce about 500 milliliters of CSF daily (or 21 mL per hour).
- 1 Structure
- 2 Function
- 3 Clinical relevance
- 4 Etymology
- 5 Additional images
- 6 See also
- 7 References
- 8 External links
There are four choroid plexuses in the brain, one in each of the ventricles. The CP consists of a layer of cuboidal epithelial cells surrounding a core of capillaries and loose connective tissue. The CP epithelial layer is continuous with the ependymal cell layer that lines the ventricles, but unlike the ependyma, the epithelial layer has tight gap junctions between the cells on the side facing the ventricle (apical surface). These gap junctions prevent the majority of substances from crossing the cell layer into the CSF; thus the CP acts as a blood-CSF barrier. The CP folds into many villi around each capillary, creating frond-like processes that project into the ventricles. The villi, along with a brush border of microvilli, greatly increases the surface area of the CP. CSF is formed as plasma is filtered from the blood through the epithelial cells. CP epithelial cells actively transport sodium, chloride and bicarbonate ions into the ventricles and water follows the resulting osmotic gradient.
Choroid plexus is found in the superior part of the inferior horn of the lateral ventricles. It follows up along this boundary, continuous with the inferior of the body of the lateral ventricles. It passes into the interventricular foramen, and is present at the top of the third ventricle.
The choroid plexus consists of many capillaries, separated from the ventricles by choroid epithelial cells. Fluid filters through these cells from blood to become cerebrospinal fluid. There is also much active transport of substances into, and out of, the CSF as it is made.
In addition to CSF production, the CP act as a filtration system, removing metabolic waste, foreign substances, and excess neurotransmitters from the CSF. In this way the CP has a very important role in helping to maintain the delicate extracellular environment required by the brain to function optimally.
Choroid plexus cysts
During embryological development, some fetuses may form choroid plexus cysts. These fluid-filled cysts can be detected by a level II ultrasound (18–20 weeks gestation). The finding is relatively common, with a prevalence of ~1%. Choroid plexus cysts (CPC) can be an isolated finding, which confers a 1-12% (variable based on population studied) risk of fetal aneuploidy. The risk of aneuploidy increases to 10.5-12% if other risk factors or ultrasound findings are noted. The particular size, bilaterality, disappearance/progression or the position of the CPC, do not have any effect on the risk of aneuploidy. 44-50% of Edwards syndrome (trisomy 18) cases will present with CPC, and 1.4% of Down syndrome (trisomy 21) cases will present with CPC. ~75% of abnormal karyotypes (obtained by chorionic villus sampling or amniocentesis) associated with CPCs are trisomy 18, while the remainder are trisomy 21.
CPCs typically disappear later during pregnancy, and are considered soft markers. They are usually harmless, and studies have shown that they have no effect on infant and early childhood development.
Ancient Greek origins of the expression choroid plexus
English choroid plexus  can be considered as a translation of Latin plexus chorioides. This Latin name mirrors Ancient Greek χοριοειδές πλέγμα, attested in the writings of Greek physician Galen. Both Classical Latin plexus and Ancient Greek πλέγμα refer to a twining, a braid or anything twined. Plexus is derived from the Classical Latin verb plectere, and πλέγμα from the Ancient Greek verb πλέκειν. Both verbs mean to pleat, to braid or to twine.
Origins of choroid and chorion
Ancient Greek χοριοειδές is composed of Ancient Greek χόριον and εἶδος. The Greeks used εἶδος, form or shape, in compounds to refer to the resemblance with the first part of the word, in this case like the χόριον. The Greek physician Galen used the name χόριον to refer to the outer membrane that encloses the fetus in the womb. The Greek philosopher Aristotle referred with χόριον to the membrane round the inside of the egg. In present-day anatomy the two aforementioned meanings are still covered by the technical term chorion.
An important feature of the χόριον in the aforementioned meanings is its strongly vascularized nature. Numerous other vascular membranes are named after the χόριον due to their strongly vascularized nature, like the choroid coat of the eye as χοριοειδής χιτών in Galen’s writings, and the pia mater as χοριοειδής μῆνιγξ in the writings of Greek physician Herophilos.
Besides choroid plexus (without -i after chor-) in medical works of the last decades the spelling chorioid plexus (with -i after chor-) can be found in older reference works as preferred spelling or as the only form strictly allowed.
Inclusion/Exclusion of -I in chorioideus
In Latin anatomic nomenclature similar orthographic changes over time can be seen. The most recent edition of the official Latin anatomic nomenclature of 1998 (Terminologia Anatomica) mirrors current English orthography by excluding the -i after chor- in plexus choroideus. This spelling revision can be traced back to the so-called 2nd edition of 1961 of the (Paris) Nomina Anatomica, that was actually based on modifications accepted at the International Anatomical Congress in New York in 1960. The subsequent editions from the Nomina Anatomica from 1966, 1977, 1983 and 1989 all wrote plexus choroideus without the letter -i.
An important part of the nomenclature development of the Nomina Anatomica represents orthographic changes over time. Eliminating vowels like -i from chorioideus is similarily seen in other words like thyreoideus that have three vowels in direct contact. In the latter case the elimination of the e could be explained as some kind of gesture to English-speaking anatomists, as they have difficulties in pronouncing that specific combination of letters, thereby forcing a greater resemblance between Latin and English orthography, in line with Nomina Anatomica's policy to simplify Latin nomenclature and to create a larger resemblance between anatomic Latin and its vernacular equivalents.
The real first edition of the Nomina Anatomica, also known as the Basle Nomina Anatomica, wrote plexus chorioideus (with -i after chor-) just like its successor the Jena Nomina Anatomica established in Jena in 1935. It must be noted that the American Dorland's medical dictionary allready simplified plexus chorioideus to plexus choroideus in 1948 with erroneously referring to the Basle Nomina Anatomica of 1895 even before the nomenclature committtee of the Nomina Anatomica executed this revision, as published in 1961.
The –i is clearly part of the adjective chorioideus as Ancient Greek χοριοειδής clearly bears this letter, that is part of the stem of the noun χόριον of which the adjective is derived. Leaving out –i could confound the actual derivation of the adjective as its seems that choroideus could be derived from χορός, dance, instead of χόριον, falsly indicating that the plexus choroideus is a dance-like braid. The term χοροειδής is however found in several manuscripts of the classics, but this form is seen as false reading of χοριοειδής.
Chorioideus versus Chorioides
Besides the spelling plexus chorioideus as used in the first few editions of the Nomina Anatomica the áforementioned alternative spelling plexus chorioides  is attested. It was brought forward as a possible revision for future editions of the Nomina Anatomica. On the first sight, the anatomic Latin adjective ‘’chorioides’’ seems to resemble χοριοειδής to a larger extent, with similarly –es and –ής, than Nomina Anatomica’s chorioideus, with the different ending -eus. The Latin adjective chorioideus can indeed be considered as a faulty redering of Greek χοριοειδής. Greek compounds ending on -ειδής, when imported into Latin as loanword, ended on -ides in Classical Latin. In the 17th-century the non-classical Latin form on -ideus/-idea/ideum for Greek -ειδής/-ειδές became into use, mostly by French anatomist Jean Riolan the Younger. No Greek loanwords (originally on -ειδής/-ειδές) ending on -ideus/-idea/-ideum exist in classical Latin, thereby making the form on -ideus/-idea/-ideum non-Latinate in character.
This article uses anatomical terminology; for an overview, see anatomical terminology.
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|Wikimedia Commons has media related to Choroid plexus.|
- 3-Dimensional images of choroid plexus (marked red)
- Anatomy diagram: 13048.000-3 at Roche Lexicon - illustrated navigator, Elsevier
- MedPix Images of Choroid Plexus
- More info at BrainInfo