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Anatomy Atlases: Illustrated Encyclopedia of Human Anatomic Variation: Opus II: Cardiovascular System: Veins: Head, Neck, and Thorax: Azygos Vein

Illustrated Encyclopedia of Human Anatomic Variation: Opus II: Cardiovascular System: Veins: Head, Neck, and Thorax

Azygos Vein

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD

Peer Review Status: Internally Peer Reviewed

The azygos vein originates in the thorax at the level of the twelfth thoracic vertebra. It arises from lateral, intermediate, and/or medial roots or from any combination of the three. The lateral azygos root is found in 85% of bodies and arises by union of the ascending vein and subcostal vein. The intermediate root occurs in 34% of individuals. This root arises from the dorsal side of the vena cava near the level of the second lumbar segmental vein and often as a common trunk with the segmental, or right renal vein. The medial root occurs in 38% of subjects. They are small plexiform veins closely associated with the ventral side of the lumbar vertebral bodies dorsal to the aorta and its lumbar segmental branches.

The azygos vein receives the hemiazygos vein, on its left margin, as a side or double branch at about the eighth and ninth vertebra. Slightly higher, at the sixth or seventh thoracic vertebra, it receives the accessory hemiazygos vein as a single trunk in 72% of individuals. The hemiazygos and accessory hemiazygos veins are incompletely formed in 15% of individuals. When this occurs the posterior intercostal veins on the left side of the thorax may drain into the azygos vein independently. In this case the azygos vein lies on the midline.

In one clinically significant variation, the azygos curves over and grooves the right lung before entering the superior vena cava, just before it enters the heart. This is called the azygos lobe of the lung.

In one study of 200 bodies, the azygos vein showed variation in 26%. The cross connections of the hemiazygos to the azygos occurred with almost equal frequency at the eight or ninth vertebra. At least two cross connections were present in 100 %; three cross connections occurred in 4%, and four or more in 6%.

Rarely, the azygos vein passes through the aortic hiatus of the diaphragm. It may open directly into the right atrium (ascribed to the embryonic disappearance of the right common cardinal vein).

The azygos occasionally opens into the right brachiocephalic or even the right subclavian (believed to be caused by an elongated embryonic right common cardinal vein).

If the hemiazygos is under developed, its branches open directly into the azygos vein.

The azygos may receive either or both supreme intercostal veins and any combination of intercostal and lumbar veins. The left superior intercostal communicates with the azygos system in 57% of individuals.

The azygos may drain into the hemiazygos, which in turn drains into the right atrium (Gruber). The pulmonary veins have been found opening into the azygos vein.

Unusual tributaries include the right internal thoracic, superior phrenic, bronchial, and gonadal veins.

The azygos vein may be absent or doubled.

The inferior vena cava has been seen continued into the azygos vein, which is then of course extremely large. The testicular vein and, on the left side, the renal and suprarenal veins have been seen terminating in the same manner.

Poynter (1922) discussed these veins as follows: The embryology of these veins has not been worked out for man, but as Evans (1912) pointed out , there is no doubt but that the posterior cardinal veins are concerned in the formation of these veins. All of the variations I (Poynter) have encountered can be explained by the familiar figures of Hochstetter. A study of 200 bodies showed 26% variation, Soloweilschik (1899) found 22%. Many of these are of a very minor nature. The cross connections of the hemiazygos to the azygos is almost as frequent at the 8th as at the 9th vertebra and in 10% both are present. In 4%, three connections are maintained. In 12 bodies, 4 or more connections are found. In 4, bodies the left spermatic and suprarenal veins joined the accessory hemiazygos, while in 12%, a branch from or all of the left renal opened into this vein, Zumstein (1895). In 4% the accessory hemiazygos does not join the hemiazygos, but enters the coronary sinus. In 14 cases, the right and left systems do not connect, but the left forms a separate system flowing into the left anonyma except in one case which enters a persistent left cava.

Gruber (1864) saw a case in which the azygos opened into the hemiazygos, and this in turn into the right atrium. "The azygos may curve from the fourth or fifth vertebra, grooving the lung to enter the superior vena cava just before it enters the heart . " (From Poynter, 1922)

Image 98, Image 205, Image 211, Image 369, Image 439


Andreassi, G. (1941-42) über die Verbindung zwischen dem oberen und unteren Hohlvenensystem in hinblick auf die laterale und mediale Wurzel der Vena Azygos und der Vena hemiazygos. Anat. Anz. 92:240-245.

Anson, B.J., Siekert, R.G., Richmond, T.E. and W.E. Bishop. (1940) The accessory pulmonary lobe of the azygos vein. Q. Bull. Northwestern University Medical School. 24: 285-290.

Bastien, -. (1859) Anomalie de la veine azygos droite. Soc. Biol., Comptes Rendus des Séances et Mémoires. 11:204.

Bastien, -. (1860) Anomalie de la veine azygos droite. Gazette Medicale de Paris 1860:90.

Bergman, R.A., Thompson, S.A., Afifi, A.K. and F. A. Saadeh. (1988) Compendium of Human Anatomic Variation: Catalog, Atlas and World Literature. Urban & Schwarzenberg, Baltimore and Munich.

Brooks, H.St.J. (1885) Vena azygos major ascending on the left side, and the bearing of this anomaly on the development of the azygos blood-vessels. Transactions/ Academy of Medicine in Ireland 1885:450-452.

Bouchand, -. (1862) Anomalie dans la direction de la grande veine azygos à sa termination. Bull. et Mém. de la Soc. Anatomique de Paris 1862:166-167.

Butler, H. and K. Balankura. (1952) Preaortic thoracic duct and azygos vein. Anat. Rec. 113:409-419.

Carpentier, Ch. et A. Bertaux. (1888) Anomalie des systèmes de la veine cave inférieure et des veines azygos. Archives de Physiologie Normale et Pathologique 20:79-89.

Carpentier, -. et -. Bertaux. (1888) Anomalie des systèms de la veine cave inferieure et des veines azygos, observée chez un homme adulte. Soc. Biol., Comptes Rendus Hebdomadaires de Séances et Mémoires. 40:339-340.

Cheselden, W. (1713) Some anatomical observations. Philosophical Transactions, Royal Society of London 28:282.

Collins, E.W. (1874) Accessory pulmonary lobe of the vena azygos. The Dublin J. of Med. Sci. 58 (no. 31, S.3):252-254.

Cooper, C.M. (1900) A pericardial sac in which the large azygos vein pierced the sac before opening into the superior vena cava. J. Anat. Physiol. 34:426.

Cordier, P., Devos, L. and A. Delcroix. (1938) Essai de classification des variations du systèm azygos intrathoracique (interprétation embryologique). Assoc. Anatomistes, Comptes Rendus 33:100-118.

Dévé, M.F. (1899) Le lobule de la veine azygos ou "lobule de Wrisberg." Bull. et Mém. de la Soc. Anatomique de Paris 74:489-514.

Dionis du Séjour, -. Lobe surnuméraire du poumon droit. Lobe de la veine azygos. Bull. et Mém. de la Soc. Anatomique de Paris 6:132-135.

Fisher, E. (1899) Seltener Verlauf der Vena azygos (Abspaltung eines Lungenlappens). Anat. Anz. 15:476-481.

Graf, G. (1938) Infarto emorragico di un lobo azigos polmonare in un neonato di tre settimane, portatore di una complessa cardioppatia congenita (transposizione corretta die grossi; vasi, pervietà die setti interventricolare ed interatriale). Pediatria 46:740-751.

Gruber, W. (1880) Duplicität der Vena cava superior, mit Vorkommen zweier Venae azygae und einer sufficienten Valvula an der Mündung der Vena azygos sinistra. Arch. Pathol. Anat. Physiol. Klin. Med. 81:462-465.

Gruber, W. (1881) Duplicität der Vena cava superior mit Vorkommen zweier transversaler Communicationäste und zweier Venae azygae. Arch. Pathol. Anat. Physiol. Klin. Med. 86:38-41.

Heitzman, E.R., Scrivani, J.V., Martino, J. and J. Moro. (1971) The azygos vein and its pleural reflections. Radiology 101:249-266.

Heller, A. (1900) Anomalien der Vena azygos. Verhandlungen-Deutsche Pathologische Gesellschaft. 12:248.

Holtby, J.R.D. (1915) A pleural fold containing the vena azygos. J. Anat. Physiol. 69:236-239.

Horner, W. E. (1818) A case of unusual arrangement in the ascending cava and in the external jugular veins of the human subject. Journal of the Academy of Natural Sciences of Philadelphia 1(2):401-405.

Klob, J. (1859) Einige Venen-Anomalien. Zeitschr. der Gesellschaft der Aerzte in Wien. 1859:737-738.

Klob, J. (1859) Einige Venen - Anomalien. Zeitschrift der Kaiserl. Königl. Gesellschaft der Aerzte zu Wien 15(47):733-734.

Latarjet, A. (1948) Testut's Traite d'Anatomie Humaine, 9th ed., G. Doin & Cie., Paris.

Le Cat de Roüen. (1738) Histoire de l'Acad. des Sc. de Paris pour 1738, page 45.

Little, P.E. (1880) Abnormality of the great cardiac vessels; Absence of the superior vena cava. Dublin Journal of Medical Science 60:443-445.

Mori, M. (1929) Ein Fall von verdoppelterVena cava inferior. Igaku - Kenkiu 3(9):1343-1345. In Japanese.

Morison, B.G. (1879) The arrangement of the azygos and superior intercostal veins in the thorax. J. Anat. Physiol. 13:346-349.

Motti, E. (1893) Anomalie degli organi interni nei malati di menti. Rara anomalia polmonale. Giornale Internazionale della Scienze Mediche 15:881-892.

Nakano, K. (1931) Uber die persistierenden Vv. supracardinales als Verdopplung der V. cava inferior. Hokkaidô - Igaku - Zasshi 9:10891096. In Japanese.

Nandy, K. and C.B. Blair, Jr. (1965) Double superior venae cavae with completely paired azygos veins. Anat. Rec. 15:1-9.

Nathan, H. (1960) Anatomical observations on the course of the azygos vein. Thorax 15:229-232.

Poynter, C.W.M. (1922) Congenital anomalies of the arteries and veins of the human body with bibliography. The University Studies of the University of Nebraska 22:1-106.

Pozzi, S. (1872) Note sur les lobes surnuméraires du poumon droit de l'homme et en particulier sur une anomalie réversive (existence d'un lobus impar). Revue d'Anthropologie 1:413-451.

Regen, F.P. (1927) The supposed homology of the vena azygos and vena cava inferior considered in light of new facts concerning their development. Anat. Rec. 35:129-148.

Sandifort, Ed. (1777) Azyga vena duplex, p. 120. Observationes Anatomico-Pathologicae, Apud. P.v.d. Eyk et D. Vygh, Leiden.

Sandifort, Ed. (1777) Azyga vena cum ductu thoricico communicans, p. 138. Observationes Anatomico-Patholigicae, Apud P.v.d. Eyk et D. Vygh, Leiden.

Schaefer, E.A., Symington, J, and T.H. Bryce, Eds. (1915) Quain's Anatomy, 11th ed., Longmans, Green, and Co., London.

Sieb, G.A. (1934) The azygos system of veins in American White and American Negroes, including observations on the inferior caval venous system. Am. J. Physiol. Anthrop. 19:39-163.

Sperino, G. (1887) Polmone destro bilobato con lingula sopraannumeraria in corrispondenza dell'apice - Decorso anormale della grande vena azigos. Giornale della Accademia di Medicina di Torino 35:265-263.

Sylwanowicz, W. (1931) Sur les valvules du systéme des azygos. Assoc. Anatomistes, Comptes Rendus 26:503-506.

Tadokoro, H. (1930) Ein Fall von linksseitiger Vena cava inferior, welcher beginnt mit den Zusammenfluss der V. hypogastrica communis (V.iliaca int. comm.) und der beiden Vv. iliacae externae. Kaibôgaku - Zasschi 2:1029 -1036. In Japanese.

Taguchi, K. (1901) Über die Varietäten der Vena cava inferior beim Menschen. Juntendô - Iji - Kenkiukwai - Zasshi 343:1-17. In Japanese.

Taruffi, C. (1880) Sulle anomalie delle vene azigos ed emiazigos. Mem. Accad. Sci. Istituto di Bologna S. 4, 2:675-681.

Tichomiroff, M. (1895) Ein Fall von congenitalem Mangel der linken Lunge mit Persistenz der linken oberen Hohlvene bei einem erwachsenen. Internationale Monatsschrift für Anatomie und Physiologie 12:37-45.

Vaket, L., Poppelier, G. and P. Vermeire. (1958) Sur un case d'anomalie combinée de la veine cave supérieure et du systèm azygos. Acta Anat. 32:235-239.

Valentin, -. (1791) Double viene azigos. J. de Médecine, Chirurgie, Pharmacie, &c. 86:238-239.

Wilde, I.C. (1740) Obserfationes Anatomicae Rariores. Obseruatio III. De vena azygos trunco duplici. Comentarii Academiae Scientiarvm Imperialis Petropolitanae 12:318-320.

Wrisberg, Enr. (1777) De vena azyga duplici. Novi commentari Soc. R. Scientiarium Gottingensis Obs III.

Wutzer, C.W. (1834) Einmündung des Ductus thoracicus in die Vena azygos. Arch. Anat. Physiol. Wissen. Med.1834:311-318.

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