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Choroid plexus

Choroid plexus
Coronal section of lateral and third ventricles.
Latin Plexus chorioides
Gray's p.798
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Anatomical terms of neuroanatomy

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).[citation needed] When a "dangling choroid plexus" is seen located in a dilated lateral ventricle on ultrasound, the fetal anomaly spina bifida is suspected.


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.[citation needed]

Choroid plexus is present in all components of the ventricular system except for the cerebral aqueduct, frontal horn of the lateral ventricle,[1] and occipital horn of the lateral ventricle.[1]

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.

There is also choroid plexus in the fourth ventricle, in the section closest to the bottom half of the cerebellum.

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.

The blood–cerebrospinal fluid barrier is a pair of barriers that separates peripheral and cerebral blood flow from the cerebrospinal fluid (CSF);[2] it is composed of epithelial cells of the choroid plexus at the peripheral blood–CSF boundary and the arachnoid membrane at the cerebral blood–CSF boundary.[2] The blood–CSF barrier serves the same purpose as the blood–brain barrier, but facilitates the transport of different substances into the brain due to the distinct structural characteristics between the two barrier systems.[2]

Clinical significance

Choroid plexus cysts

Main article: 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% (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.[3]

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.[4]


Ancient Greek origins of the expression choroid plexus

English choroid plexus[5] can be considered as a translation of Latin plexus chorioides.[6] This Latin name mirrors Ancient Greek χοριοειδές πλέγμα,[7] attested in the writings of Greek physician Galen.[7] Both Classical Latin plexus and Ancient Greek πλέγμα refer to a twining, a braid or anything twined.[7][8] Plexus is derived from the Classical Latin verb plectere,[9] and πλέγμα from the Ancient Greek verb πλέκειν.[9] Both verbs mean to pleat, to braid or to twine.[7][8]

Origins of choroid and chorion

Ancient Greek χοριοειδές is composed of Ancient Greek χόριον and εἶδος.[9] The Greeks used εἶδος, form or shape,[7] in compounds to refer to the resemblance with the first part of the word,[9] in this case like the χόριον.[10] The Greek physician Galen used the name χόριον to refer to the outer membrane that encloses the fetus in the womb.[7] The Greek philosopher Aristotle referred with χόριον to the membrane round the inside of the egg.[7] In present-day anatomy the two aforementioned meanings are still covered by the technical term chorion.[5]

An important feature of the χόριον in the aforementioned meanings is its strongly vascularized nature.[11] Numerous other vascular membranes are named after the χόριον due to their strongly vascularized nature,[12] like the choroid coat of the eye as χοριοειδής χιτών in Galen’s writings,[7] and the pia mater as χοριοειδής μῆνιγξ in the writings of Greek physician Herophilos.[7]

English Spelling

Besides choroid plexus (without -i after chor-) in medical works of the last decades[5][13][14][15] the spelling chorioid plexus (with -i after chor-) can be found in older reference works as preferred spelling[16] or as the only form strictly allowed.[17]

Latin spelling

Inclusion or 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.[18] 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.[19] The subsequent editions from the Nomina Anatomica from 1966,[20] 1977,[21] 1983[22] and 1989[23] all wrote plexus choroideus without the letter -i.

An important part of the nomenclature development of the Nomina Anatomica represents orthographic changes over time.[24] Eliminating vowels like -i from chorioideus is similarly seen in other words like thyreoideus that have three vowels in direct contact.[24] 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,[25] thereby forcing a greater resemblance between Latin and English orthography, in line with Nomina Anatomica's policy to simplify Latin nomenclature[26] and to create a larger resemblance between anatomic Latin and its vernacular equivalents.[21]

The real first edition of the Nomina Anatomica,[27] 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.[6][28][29] It must be noted that the American Dorland's medical dictionary[13] already simplified plexus chorioideus to plexus choroideus in 1948 with erroneously referring to the Basle Nomina Anatomica of 1895 even before the nomenclature committee of the Nomina Anatomica executed this revision, as published in 1961.[19]

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 it seems that choroideus could be derived from χορός, "dance",[8] instead of χόριον, falsely 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.[7][11][15]

Chorioideus versus chorioides

Besides the spelling plexus chorioideus as used in the first few editions of the Nomina Anatomica the aforementioned alternative spelling plexus chorioides[6] is attested. It was brought forward as a possible revision for future editions of the Nomina Anatomica.[6] On 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 rendering of Greek χοριοειδής.[30] Greek compounds ending on -ειδής, when imported into Latin as loanword, ended on -ides in Classical Latin.[9][31] In the 17th century, the non-classical Latin form on -ideus/-idea/ideum for Greek -ειδής/-ειδές came into use, mostly by French anatomist Jean Riolan the Younger.[11] No Greek loanwords (originally on -ειδής/-ειδές) ending on -ideus/-idea/-ideum exist in classical Latin,[8][31] thereby making the form on -ideus/-idea/-ideum non-Latinate in character.[31]

Additional images

See also

This article uses anatomical terminology; for an overview, see anatomical terminology.


  1. ^ a b Young, Paul A. (2007). Basic clinical neuroscience (2nd ed.). Philadelphia, Pa.: Lippincott Williams & Wilkins. p. 292. ISBN 0-7817-5319-8. 
  2. ^ a b c Laterra J, Keep R, Betz LA et al. (1999). "Blood–Cerebrospinal Fluid Barrier". Basic Neurochemistry: Molecular, Cellular and Medical Aspects. (6th ed.). Philadelphia: Lippincott-Raven. 
  3. ^ Drugan et al., 2000, American Journal of Medical Genetics
  4. ^ Digiovanni et al., 1997, Obstetrics and Gynecology
  5. ^ a b c Anderson, D.M. (2000). Dorland’s illustrated medical dictionary (29th edition). Philadelphia/London/Toronto/Montreal/Sydney/Tokyo: W.B. Saunders Company.
  6. ^ a b c d Suzuki, S., Katsumata, T., Ura, R. Fujita, T., Niizima, M. & Suzuki, H. (1936). Über die Nomina Anatomica Nova. Folia Anatomica Japonica, 14, 507-536.
  7. ^ a b c d e f g h i j Liddell, H.G. & Scott, R. (1940). A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with the assistance of. Roderick McKenzie. Oxford: Clarendon Press.
  8. ^ a b c d Lewis, C.T. & Short, C. (1879). A Latin dictionary founded on Andrews' edition of Freund's Latin dictionary. Oxford: Clarendon Press.
  9. ^ a b c d e Triepel, H. (1927). Die anatomischen Namen. Ihre Ableitung und Aussprache. Anhang: Biographische Notizen.(Elfte Auflage). München: Verlag von J.F. Bergmann.
  10. ^ Triepel, H. (1910). Die anatomischen Namen. Ihre Ableitung und Aussprache. Mit einem Anhang: Biographische Notizen.(Dritte Auflage). Wiesbaden: Verlag J.F. Bergmann.
  11. ^ a b c Hyrtl, J. (1880). Onomatologia Anatomica. Geschichte und Kritik der anatomischen Sprache der Gegenwart. Wien: Wilhelm Braumüller. K.K. Hof- und Unversitätsbuchhändler.
  12. ^ Kraus, L.A. (1844). Kritisch-etymologisches medicinisches Lexikon (Dritte Aufgabe). Göttingen: Verlag der Deuerlich- und Dieterichschen Buchhandlung.
  13. ^ a b Dorland, W.A.N. & Miller, E.C.L. (1948). The American illustrated medical dictionary. (21st edition). Philadelphia/London: W.B. Saunders Company.
  14. ^ Sliosberg, A. (1975). Elsevier’s medical dictionary in five languages. English/American / French / Italian / Spanish and German. (2nd edition). Amsterdam/Oxford/New York: Elsevier’s Scientific Publishing Company.
  15. ^ a b Dirckx, J.H. (Ed.) (1997).Stedman’s concise medical dictionary for the health professions. (3rd edition). Baltimore: Williams & Wilkins.
  16. ^ Foster, F.D. (1891-1893). An illustrated medical dictionary. Being a dictionary of the technical terms used by writers on medicine and the collateral sciences, in the Latin, English, French, and German languages. New York: D. Appleton and Company.
  17. ^ Barker, L.W. (1907). Anatomical terminology with special reference to the [BNA]. With vocabularies in Latin and English and illustrations. Philadelphia: P. Blakiston’s Son & Co.
  18. ^ Federative Committee on Anatomical Terminology (FCAT) (1998). Terminologia Anatomica. Stuttgart: Thieme
  19. ^ a b Donáth, T. & Crawford, G.C.N. (1969). Anatomical dictionary with nomenclature and explanatory notes. Oxford/London/Edinburgh/New York/Toronto/Syney/Paris/Braunschweig: Pergamon Press.
  20. ^ International Anatomical Nomenclature Committee (1966). Nomina Anatomica. Amsterdam: Excerpta Medica Foundation.
  21. ^ a b International Anatomical Nomenclature Committee (1977). Nomina Anatomica, together with Nomina Histologica and Nomina Embryologica. Amsterdam-Oxford: Excerpta Medica.
  22. ^ International Anatomical Nomenclature Committee (1983). Nomina Anatomica, together with Nomina Histologica and Nomina Embryologica. Baltimore/London: Williams & Wilkins
  23. ^ International Anatomical Nomenclature Committee (1989). Nomina Anatomica, together with Nomina Histologica and Nomina Embryologica. Edinburgh: Churchill Livingstone.
  24. ^ a b Kachlik, D., Baca V., Bozdechova, I., Cech, P. & Musil, V. (2008). Anatomical terminology and nomenclature: past, present and highlights. Surg Radiol Anat, 30 459-466.
  25. ^ Drukker, J, & Walvoort, H.C. (2000). Terminologia anatomica: een nieuw anatomisch referentiewerk. Nederlands Tijdschrift voor Geneeskunde, 144, 890–891.
  26. ^ Warwick, R. (1978). The future of Nomina Anatomica -a personal view. J. Anat., 126(1), 221-223.
  27. ^ His, W. (1895). Die anatomische Nomenclatur. Nomina Anatomica. Der von der Anatomischen Gesellschaft auf ihrer IX. Versammlung in Basel angenommenen Namen. Leipzig: Verlag Veit & Comp.
  28. ^ Kopsch, F. (1941). Die Nomina anatomica des Jahres 1895 (B.N.A.) nach der Buchstabenreihe geordnet und gegenübergestellt den Nomina anatomica des Jahres 1935 (I.N.A.) (3. Auflage). Leipzig: Georg Thieme Verlag.
  29. ^ Stieve, H. (1949). Nomina Anatomica. Zusammengestellt von der im Jahre 1923 gewählten Nomenklatur-Kommission, unter Berücksichtigung der Vorschläge der Mitglieder der Anatomischen Gesellschaft, der Anatomical Society of Great Britain and Ireland, sowie der American Association of Anatomists, überprüft und durch Beschluß der Anatomischen Gesellschaft auf der Tagung in Jena 1935 endgültig angenommen. (4th edition). Jena: Verlag Gustav Fischer.
  30. ^ Triepel, H. (1908). Memorial on the anatomical nomenclature of the anatomical society. In A. Rose (Ed.), Medical Greek. Collection of papers on medical onomatology and a grammatical guide to learn modern Greek (pp. 176–193). New York: Peri Hellados publication office.
  31. ^ a b c Kossmann, R. (1903). Allgemeine Gynaecologie. Berlin: Verlag von August Hirschwald.
  • Brodbelt, A; Stoodley, M (Oct 2007). "CSF pathways: a review.". British journal of neurosurgery 21 (5): 510–20. PMID 17922324. doi:10.1080/02688690701447420. 
  • Strazielle, N; Ghersi-Egea, JF (Jul 2000). "Choroid plexus in the central nervous system: biology and physiopathology.". Journal of neuropathology and experimental neurology 59 (7): 561–74. PMID 10901227. 

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