Anatomical variations of the azygos venous system: classification and clinical relevance / Variaciones anatómicas del sistema venoso ácigos: clasificación y relevancia clínica

The azygos venous system is highly variable in terms of its origin, course, communications, tributaries and termination of the associated veins: this study aimed to classify these anatomical variations. Thirty Thiel-embalmed cadavers aged 48­98 years (18 female, 12 male) were examined. The vertebral level of termination and diameter of the azygos, hemiazygos, accessory hemiazygos and the left superior intercostal veins were determined, as well as the termination level of the right superior intercostal vein. The azygos system was classified into 3 types; primitive (type 1), transitional (type 2) and unicolumnar (type 3). Type 2 was further divided into 5 subgroups (A to E) according to the number of retroaortic communications. Type one was observed in 3 % (n=1), type 2 in 87 % (n=26) and type 3 in 10 % (n=3) of specimens. The vertebral level of termination of the azygos, hemiazygos, accessory hemiazygos, right superior intercostal and left superior intercostal veins were between T2 and T3, T6 and T10, T5 and T9, T2 and T4, and T2 and T4 respectively. Identification and understanding these variations are important during preoperative radiological investigations and surgical procedures, especially spinal surgery between T7 and T12 using a left thoracotomy approach, to avoid injuries which may lead to postoperative hematomas.

El sistema venoso ácigos es muy variable en función de su origen, comunicaciones, afluentes y terminación de venas asociadas. Este estudio tuvo como objetivo clasificar las variaciones anatómicas relacionadas con el sistema venoso ácigos. Se examinaron treinta cadáveres embalsamados con la técnica de Thiel, con edades comprendidas entre 48-98 años (18 mujeres, 12 hombres). Se determinó el nivel vertebral de terminación y el diámetro de las venas ácigos, hemiácigos, hemiácigos accesoria e intercostales superiores izquierdas, así como el nivel de terminación del lado derecho de la vena intercostal superior. El sistema ácigos se clasificó en 3 tipos; primitivo (tipo 1), de transición (tipo 2) y unicolumnar (tipo 3). El tipo 2 se dividió en 5 subgrupos (A a E) de acuerdo con el número de comunicaciones retroaórticas. El tipo 1 se observó en 3 % (n = 1), el tipo 2 en 87 % (n = 26) y tipo 3 en 10 % (n = 3) de las muestras. El nivel vertebral de terminación de las venas ácigos, hemiácigos, hemiácigos accesoria, intercostal derecho superior e intercostales superiores izquierda se presentaron entre T2 y T3, T6 y T10, T5 y T9, T2 y T4 y T2 y T4, respectivamente. La identificación y comprensión de estas variaciones anatómicas son importantes durante las investigaciones radiológicas preoperatorias y de los procedimientos quirúrgicos, especialmente en cirugía de columna vertebral, entre los niveles T7 y T12, utilizando un abordaje de toracotomía izquierda, para evitar lesiones que pueden conducir a hematomas postoperatorios.

Anatomic variation of thorax drainage: absence of accessory hemiazygos vein

Formed by the azygos, hemiazygos and accessory hemiazygos veins, this system is responsible for the venous drainage of the thorax and partially of the abdomen. Abnormalities of this system are not uncommon, and many are referred to in literature. The complete agenesis of the accessory hemyazigos vein is associated with complete regression of the left posterior cardinal vein or atrophy of the left subcardinal vein. The reported case consists of the complete absence of the accessory hemiazygos vein, culminating in the drainage of the 4th, 5th, 6th, 7th and 8th left posterior intercostal veins directly into the azygos vein of a male cadaver. The importance of the theme is due to the necessity of recognizing patterns and frequencies of these variations when facing procedures addressing the mediastinum or the major vessels.

Formation of the azygos vein / Formación de la vena ácigos

The aim of the present study was to determine the most common origin of the azygos vein. Thirty cadavers male and female, white and non-white adult individuals of different ages fixed in 10 percent formaldehyde and dissected. All cadavers had an undisclosed clinical death and were donated to the Universidade Estadual de Ciências da Saúde de Alagoa s, Brazil. Eleven different formations were found. The right subcostal vein was was only observed in 13 cases (43.33 percent); the azygos vein was formed by the confluence of the right subcostal and right ascending lumbar vein in three cases (10 percent); by the right subcostal vein with a contribution from the inferior vena cava (IVC) in three cases (10 percent); by the right subcostal with contribution from IVC and right ascending lumbar vein in three cases (10 percent); by the right and left subcostal veins in two cases (6.66 percent); by the right and left subcostal veins and contribution from the IVC in one case (3.33 percent); by the right and left subcostal veins and left accessory renal vein in one case (3.33 percent); by the left renal vein in one case (3.33 percent); by the right subcostal and left gonadal veins with contribution from the IVC in one case (3.33 percent); by the right subcostal and left renal veins in one case (3.33 percent); and composed by the continuation of the 11th posterior intercostal vein in one case (3.33 percent). Based on the results, the right subcostal vein was the only structure with a significant presence in the formation of the azygos vein.

El objetivo del estudio fue verificar cual es la disposición más frecuente del origen de la vena ácigos. Fueron disecados 30 cadáveres de individuos adultos, de ambos sexos, de diferentes grupos étnicos, fijados en formaldehído al 10 por ciento, donados a la Universidade Estadual de Ciencias da Saúde de Alagoas. Se encontraron 11 formaciones diferentes. En 13 casos (43,33 por ciento) se observó sólo la vena subcostal derecha; en 3 casos (10 por ciento) la vena ácigos estaba formada por la confluencia de las venas subcostal derecha y lumbar ascendente derecha; en 3 casos (10 por ciento) formado por las venas subcostal derecha y una contribución de la vena cava inferior VCI; en 3 casos (10 por ciento) por las venas subcostal derecha y contribución de la VCI y lumbar ascendente derecha; 2 casos (6,66 por ciento) por las venas subcostales derecha e izquierda; en 1 caso (3,33 por ciento) por las venas subcostal derecha, izquierda y contribución de la VCI; en 1 caso (3,33 por ciento) por las venas subcostal derecha e izquierda y renal accesoria izquierda; en 1 caso (3,33 por ciento) por la vena renal izquierda; en1 caso (3,33 por ciento) por las venas subcostal derecha, gonadal izquierda y contribución de la VCI; en 1 caso (3,33 por ciento) por las venas subcostal derecha y renal izquierda y en 1 caso (3,33 por ciento) por la continuación de la 11 vena intercostal posterior. Con base en los resultados podemos concluir que la vena subcostal derecha fue la única estructura con presencia significativa en la formación de la vena ácigos.

Anatomy of the azygos vein examined by computerized tomography imaging

To examine the anatomy of the azygos vein AV using different parameters. Therefore, the diameter of the AV at its opening into the superior vena cava, the opening level of the AV into the superior vena cava, and the position of the AV, with respect to the vertebral column and carina, were examined by CT. Chest CTs of 103 cases [42 female and 61 male] were reviewed at the Department of Radiology, Faculty of Medicine, Hacettepe University, Ankara, Turkey between July 2004 and February 2005. The CT examinations were performed with a Philips AU E1 spiral CT [Rotterdam, Netherlands] with the following parameters: 120 Hv; 200 mAs; slice thickness: 7 mm; pitch: 1; reconstruction index: 7 mm. The results were statistically analyzed. The diameter of the AV at the opening into the superior vena cava ranged between 4.3 mm and 16 mm. The AV was in the midline in 41 cases. The arching and opening level of the AV was at the fifth thoracic vertebra in most cases. The opening level was most often at the same level as the carina. Hemiazygos veins were detected in 90 patients. The parameters measured in this study may be useful in surgical procedures of the mediastinum and during the interpretation of chest radiographs

A veia ázigos direita na cutia (Dasyprocta aguti, rodentia) / The right azygos vein in agouti (Dasyprocta aguti, rodentia)

O comportamento da veia ázigos, sua formação e topografia foram estudados em 10 cutias (Dasyprocta aguti, rodentia) adultas (6 machos e 4 fêmeas, capturadas no estado do Piauí, Brasil). Este trabalho tem por objetivo constituir a base de outras investigações, particularmente aquelas referentes à exploração zootécnica desta espécie. O sistema de veia ázigos foi injetado com látex - Neoprene 671, e os animais foram colocados em solução aquosa de formol a 10 por cento, e dissecados. Em todas as espécies foi observado que a veia ázigos sempre chega na veia cava cranial em nível do quarto espaço intercostal. A veia ázigos recebe em (50 por cento) dos casos as veias intercostais à direita e (50 por cento) à esquerda. As tributárias da veia ázigos são: as veias frênicas (100 por cento) e a veia bronco esofágica (30 por cento). A veia hemiázigos aparece em todos os casos à esquerda e em 60 por cento dos casos à direita. A veia ázigos comunica-se com a veia hemiázigos esquerda (90 por cento), e com a direita (100 por cento), com a veia cava caudal e veias intervertebrais, com igual freqüência (30 por cento).

A veia ázigos no coelho (Oryctolagus cuniculus, L.1758) / The azygos vein of the rabbit (Oryctolagus cuniculus, L.1758)

A veia ázigos foi estudada em 40 coelhos, cujos vasos foram injetados com latex e dissecados. Notou-se que em quase todos (97,5 por cento) os casos ela termina na veis cava cranial. A veia hemazigos foi encontrada em 90 por cento dos casos a direita, e em 100 por cento dos casos a esquerda. Foram indentificadas tribuitarias, cujas incidencias foram analisadas.