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Study of azygos system and its variations.

INTRODUCTION: The azygos venous system develops in the basis of multiple transformations of the subcardinal veins, (1) which causes its great variability, especially on the left side. Azygos veins are important cavo-caval and porto caval junctions, thus forming collateral circulation in caval vein occlusion and in portal hypertension. (2)

The azygos venous system trnsporting deoxygenated blood from the posterior wall of the thoracic and abdomen into the superior vena cava is expected to arise from the postrior aspect of inferior vena cava at or below the level of renal veins from its development. But it is not constant. It has no symmetrically equivalent vein on the left side of the body this system varies much in the mode of orign, course, tributaries anastomosis and termination.

Azygos vein is formed by the union of the ascending lumbar veins with the right subcostal veins at the level of the 12th thoracic vertebra, ascending in the posterior mediastinum, and arching over the right main bronchus at the root of the right lung to join the superior venacave. Its tributaries, apart from its main tributary, the hemiazygos vein are the bronchial veins, pericardial veins, and posterior right intercostal veins.

The azygos system of veins is considered to be, the azygos vein, along with its left-sided counterparts, the hemiazygos vein and the accessory hemiazygos vein. Together they form an anastomosis between the superior vena cava to the inferior vena cava.

The azygos venous system is a main channel of drainage of the thoracic wall and also part of parietals of the abdomen. The large continuous channel draining the right half of the thoracic and abdominal parietals forms the agygos vein. The left complement of this venous channel which drain the upper abdominal parietals and the lower thoracic wall in named as accessory hemoazygos vein or superior hemiazygos vein. Both of them drain into the azygos vein

MATERIAL AND METHODS: The study was conducted in the department of Anatomy, Siddhartha medical College, Vijayawada. 50 cadavers used for the study were allotted for medical undergraduates in different medical colleges in Vijayawada. The cadavers available in the Department of Anatomy were injected with routine embalming fluid. In the dissection hall where the thorax remains to be dissected by the students, the exposing procedure of Azygos system was done.

The whole course of the azygos vein from the level of the subcostal vein to the point of termination into the superior vena cava has been traced and cleaned. All the right posterior intercostal veins are traced to the site of their termination into the azygos vein. Communications of the hemoazygos, accessory hemiazygos veins into the azygos vein are identified and exposed by reflecting the oesophagus and aorta upwards. Azygos vein is identified and cleaned. Right and left superior intercostal veins have been traced to their points of termination into the right and left brachiocephalic veins, correspondingly the hemiazygos and the accessory hemiazygos are traced on the left side of the bodies of the thoracic vertebrae behind the descending thoracic aorta. The terminations of the right and left ascending lumbar veins when present are traced and studied in relation to the aortic opening and the crura of the diaphragm.

RESULTS: For the study 50 cadavers have been observed for the mode of formation of Azygos vein. In the present study different aspects of azhgos venous system have been reported. Ozbek et al reported a case in which hemiazygos vein was absent. (3) A right subcostal vein joining the ascending lumbar vein formed in 70% of cases.30% of cases it is formed from back of Inferior Vena Cava. The position of Azygos vein in on right side in 53.33%, in midline in 46.66% of subjects. In the present study the level of termination of the Azygos vein is between third and fourth thoracic vertebra. Hemiazygos, the left lower complement of the Azygos vein formed by the union of left ascending lumbar and subcostal veins usually. In the present study in one case it arises from the back of Inferior venacava ascends up and receives the left ascending lumbar and subcostal veins before it joins the Azygos. Hemi azygos vein is crossing the midline at T8 towards the right side in 60% cases, at T7 in 26.66%, at T9 in 10%, at T10 in 3.33%.

DISCUSSION: The present work of the Azygos system of veins is carried out in 50 cadavers. Each part of this system of veins namely the Azygos, Hemiazygos, accessory Hemiazygos are studied. Their formation, course, relations, terminations, the tributaries and communications are explored. The Azygos system of veins show more number of variations including its origin, course, termination and its tributaries.

Abnormalities related to the azygos system are not rare. (4) These abnormalities are generally explained by the embryological development. Azygos venous system embryologically derived from subcardinal veins. The right subcardinal vein forms azygos vein and the left subcardinal vein forms hemiazygos vein. The left superior intercostal vein and accessory hemiazygos vein are derived from left posterior cardinal vein and this vein simultaneously forms upper part of azygos vein. The part that connects hemiazygos vein to azygos vein is actually reminder of the anastomosis between the left and right posterior cardinal vein. (5) The caudal part of the right supracardinal vein forms the post renal part of the IVC, while the caudal part of the left supracadinal vein and the intermediate parts of both supracadinal veins disappear

CONCLUSION: The variant azygos venous system may easily be confused with aneurysm, lymphadenopathy and tumour. (6,7) Knowledge of the variability of the azygos venous system in an important anatomical sign post in radiological diagnosis and in the surgical treatment of thoracic aorta aneurysms and tumors of the posterior mediastinum.

DOI: 10.14260/jemds/2015/827


(1.) Gesase A P, Fabian F M et al. "Double superior vena cava presenting with anomalous jugular and azygous venous systems". Indian Heart J. 2008 Jul-Aug: 60 (4): 352-8.

(2.) Elzbieta Krakowiak-Sarniwska, Marcin Wisniewski, Michai Szpinda, Helen Krakowiak. "variability of the Azygos vein system in human fetuses. Via Medica" vol. 62, No. 4: 427-430, 2003.

(3.) Jun Endo et al: "Visualization of Azygos Arch Valves using computed tomography; Comparison of Scanning Delay Times", Rokai J. Exp Clin. Med, Vol. 33 No. 2. Pp 84-89, 2008.

(4.) Hamilton W J: Hamilton Text book of Human Anatomy, London, 2nd Edition, pp. 266-7, 1976.

(5.) Mubarak M Y, (Radiology):"Azygos continuation of the inferior vena cava in carcinoma of oesophagus". Int Med J Vol. 7, 2008.

(6.) Lindsay H. C: "An abnormal vena hemiazygos" J Anat, 438-50, 1925.

(7.) Ozbek A, Dalcik, Colk T:"Multiple variations of the azygos venous system" Surg Radio Anat 21 (1): 83-5, 1999.

B. Vijaya Nirmala [1], Teresa Rani S [2]


[1.] B. Vijaya Nirmala

[2.] Teresa Rani S.


[1.] Assistant Professor, Department of Anatomy, Guntur Medical College, Guntur, affiliated to Dr. NTRUHS, Vijayawada.

[2.] Assistant Professor, Department of Anatomy Siddhartha Medical College, Vijayawada, Affiliated to Dr. NTRUHS, Vijayawada.



Dr. Teresa Rani. S. D. No. 52-1/7-7, NTR Colony, 2nd Cross Road, Vijayawada- 520008.


Date of Submission: 10/04/2015. Date of Peer Review: 11/04/2015. Date of Acceptance: 13/04/2015. Date of Publishing: 21/04/2015.
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Author:Nirmala, B. Vijaya; Teresa, Rani S.
Publication:Journal of Evolution of Medical and Dental Sciences
Article Type:Report
Date:Apr 23, 2015
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