Cadaveric dissection of connection between accessory hemiazygos vein and left brachiocephalic vein.

PURPOSE: The azygos system of veins has many anatomical variations that can impact mediastinal and vascular interventions. While radiological reports on these are of great clinical value, this study is among the first to present a high-quality cadaveric dissection of a rare anatomical variant to supplement previously published radiologic studies. The azygos venous system consists of the azygos vein (AV), hemiazygos vein (HAV), and the accessory hemiazygos vein (AHAV), which develop from the last portion of the posterior cardinal veins. The normal anatomical configuration includes drainage of the posterior intercostal veins, vertebral vein, esophageal veins, HAV, and AHAV to an unpaired right-side AV at the level of the 8th/9th thoracic vertebra. The reported incidence of AHAV draining directly into the left brachiocephalic vein is 1-2%. METHODS: An adult formalin-fixed 70-year-old female cadaver was dissected as part of a medical gross anatomy elective course. RESULTS: Gross documentation of a direct connection of the HAV to the AHAV with the AHAV draining into the left brachiocephalic vein. CONCLUSION: It is important to note the variations of the azygos system to avoid confusion with a potential pathology such as mediastinal masses. Understanding of the rare variant reported here could be useful in the prevention of iatrogenic bleeding from the misplacement of venous catheters and help facilitate radiological diagnosis in the incidence of venous clot formation.

Normal variations of the superior vena cava and azygos venous system depiction by CT scan in the adult Thai population.

BACKGROUND: Identification of normal variations to the thoracic central venous system anatomy is essential in radiological intervention and cardiothoracic surgery to prevent complications. PURPOSE: To estimate the prevalence and pattern of normal variations of superior vena cava (SVC) and azygos venous system as well as factors associated with normal variations of SVC. MATERIAL AND METHODS: Venous-phase chest CT of 1336 patients were retrospectively reviewed. Age, sex, and underlying disease were recorded. SVC diameter and cross-sectional area were measured to evaluate for associations with normal variations. RESULTS: The prevalence of normal anatomical variations of SVC and azygos venous system were 0.3% and 1.5%, respectively. Duplicated SVC was the most common variations. The most common variation for the azygos venous system was the connection between the hemiazygos and accessory hemiazygos veins draining into the left brachiocephalic vein (12/1336 cases, 0.9%). The median (interquartile range [IQR]) cross-sectional area compared between normal SVC (297.2 mm2) and duplicated SVC (223.5 mm2) showed a statistically significant difference (P = 0.033). CONCLUSION: This study determined the prevalence of rare normal variations of the azygos venous system, a connection between the hemiazygos and accessory hemiazygos veins draining into the left brachiocephalic vein. The prevalence of normal variations of the SVC and azygos venous system in the adult Thai population was similar with that of previous publications. Cross-sectional area was the only factor with a significant association with SVC variations.

A reappraisal of pediatric thoracic surface anatomy.

Accurate knowledge of surface anatomy is essential for physical examination, invasive procedures, and anatomy education. Individual factors such as age make surface landmarks variable so accurate descriptions are needed. The aim of this study is to describe age-related surface landmarks for intrathoracic structures in children. A total of 156 thoracic computed tomography scans of children aged 0-18 years were categorized into six groups, and the associations between major intrathoracic structures and surface landmarks were analyzed. Sternal angle is an accurate surface landmark for the azygos vein-superior vena cava junction in all age groups. However, the aortic arch (except in the 0-1 year group), the bifurcation of the pulmonary trunk and the tracheal bifurcation in those aged 15-18 years were not within this plane. The left brachiocephalic vein was located behind the ipsilateral sternoclavicular joint except in the 1-3 years group, and the right was behind it in children older than 6 years. The apex of heart was at the 5th intercostal space level in the 0-1 and 12-18 years groups; however, it was higher in the other groups. The lower borders of the lungs were at the sixth costal cartilage level in the midclavicular line, eighth intercostal space level in the midaxillary line, and T12 adjacent to the vertebral column in the 15-18 years group; the lower borders were at higher levels in younger children. Defining the variations in surface anatomy by in vivo studies will increase its clinical and pedagogical value.

Cases of high lying azygos arch and its embryological consideration.

PURPOSE: This study aimed to report cases of high-lying azygos arch and discuss the embryological basis of its development by a thorough evaluation of the anatomical features assessed using computed tomography (CT) images. METHODS: This study was approved by our institutional review board. We retrospectively reviewed chest CT images between November 2011 and November 2018. To determine high-lying azygos arch, we set the upper margin of the T4 vertebral body as the reference level. Regarding the embryological development of high-lying azygos arch, we retrospectively reviewed the CT images of 105 patients with tracheal bronchus to identify the location of the azygos arch. RESULTS: We noted that on three cases CT images, the azygos arch was located higher than the upper margin of the right main bronchus, and drained into the proximal superior vena cava (SVC) at a level higher than the conventional T4 or T5 vertebral level. All 105 patients with right tracheal bronchus showed azygos arch above the tracheal bronchus. CONCLUSION: This variation in the location of the azygos arch can mimic pathological lesion on plain radiographs, and, therefore, it is important to be aware of high-lying azygos arch. Our findings show that the azygos arch may have possibly migrated downward during embryological development.

Computed tomography angiography study of the azygos vein course and termination into superior vena cava: gender and age impact.

PURPOSE: The study highlights azygos vein (AV) topography, arrangement and confluence morphometry in dyspnoea and tachycardia patients of extrapulmonary and extracardiac aetiology. METHOD: Computed-tomography angiography of 25 male and 26 female patients (mean age 66.5 years) were studied for: thoracic vertebral (T) height of AV- superior vena cava-SVC confluence, AV course and deviations from vertebral column (VC) midline, AV and SVC diameters, distance (AV arch- lower border of carina) and gender and age impact. RESULTS: Commonest heights of the AV-SVC confluence were T5 (56.9%), T4 (31.4%), T6 (9.8%) and T3 (2%). The AV terminated into SVC after crossing the left side of VC midline in 56.9%, slightly deviated right of the midline in 37.3% and coursed right of VC in 5.9%. Mean AV and SVC diameters were 0.96 ± 0.18 cm and 1.86 ± 0.27 cm. Male predominance in AV and SVC diameters and a slight AV diameter significant increase with the age were found. The (AV highest point-lower border of carina) mean distance was 2.05 ± 0.44 cm and male predominance existed. CONCLUSION: The commonest termination height of the AV was T5, while T3 was the rarest one. Aging induces the AV leftward displacement, while gender had no impact. AV and SVC diameters had higher significant values in males, while ageing had a significant impact only in AV diameter. The AV higher diameters will be used as predictors for higher values of SVC diameter and mediastinum pathology. Such findings can be useful in mediastinal surgery, mediastinoscopy and surgery of VC deformations, neurovascular surgery of retroperitoneal organs, disc herniation and T fractures.

Anatomical investigation of the segmental vessels for the right-sided anterior surgical approach to the thoracic spine: a human cadaver study.

PURPOSE: Anterior surgical approaches to the thoracic spine are common procedures for the treatment of many diseases of the thoracic spine. Purpose of this anatomic study is to investigate the course of the segmental vessels of the thoracic spine for the anterior and lateral transthoracic approach from the right side. METHODS: 26 formalin-fixed human cadavers (20 femaless/6 male) with an average age of 84.9 ± 8.3 (range 67-97) were included. The segmental arteries and veins of the right thoracic cavity coursing between the third and twelfth thoracic vertebral body have been investigated. To define the localization of the vessels in accordance with the associated vertebral bodies, the distance between the endplates and vessels was measured in the ventral, middle and dorsal parts. RESULTS: The results of the study reveal that not only one, but also two segmental arteries and veins may course over the right hemi-vertebral body, especially in the upper and middle thoracic spine. Furthermore, in the middle and lower thoracic spine (T7-T12) the vessels course over the middle and lower third of the craniocaudal extent of the vertebral body. On the contrary, in the upper thoracic spine (T3-T6), the vessels may course over the entire extent of the vertebral body. CONCLUSION: Due to these common anatomic variations and variability of the course of the segmental vessels, spinal surgeons should remain careful in the identification of the segmental vessels in order to minimize risk of vascular injury in case of right-sided anterior and lateral approach to the thoracic spine.

What is the history of the term "azygos vein" in the anatomical terminology?

The term "azygos vein" is in common use in modern anatomical and cardiovascular textbooks to describe the vein which ascends to the right side of the vertebral column in the region of the posterior mediastinum draining into the superior vena cava. "Azygos" in Greek means "without a pair", explaining the lack of a similar vein on the left side of the vertebral column in the region of the thorax. The term "azygos" vein was utilized firstly by Galen and then was regenerated during Sylvius' dissections and Vesalius' anatomical research, where it received its final concept as an official anatomical term. The purpose of this study is to highlight the origin of the term "azygos vein" to the best of our knowledge for the first time and its evolution from the era of Hippocrates to Realdo Colombo.

The Azygos Vein From A to Z.

Congenital and acquired abnormalities of the azygos vein can affect its size and position. Alteration of contrast material flow dynamics of the azygos vein on computed tomography can be an indication of superior vena cava obstruction. Recognition and accurate characterization of abnormalities of the azygos vein on imaging studies is critical to facilitate prompt diagnosis and direct workup when necessary. The main purpose of this article is to illustrate and describe the radiologic features of various congenital and acquired abnormalities affecting the azygos venous system.

Apprasial of the surface anatomy of the Thorax in an adolescent population.

Surface anatomy is considered a fundamental part of anatomy curricula and clinical practice. Recent studies have reappraised surface anatomy using CT, but the adolescent age group has yet to be appraised. Sixty adolescent thoracoabdominal CT scans (aged 12-18 years) were examined. The surface anatomy of the central veins, cardiac apex, diaphragmatic openings, and structures in relation to the sternal angle plane were analyzed. The results showed that the brachiocephalic vein (left and right) formed mostly posterior to the sternoclavicular joint. The superior vena cava formed close to the second costal cartilage, ±16.3 mm to the right of the midline. The apex of the heart was located in relation to the fifth intercostal space; ±78.6 mm to the left of the midline. The caval hiatus was in relation to T9 and T10; the esophageal hiatus was at T10; whereas the aortic hiatus was at T11. The sternal angle plane was in relation to the upper half of T5, which was also where the bifurcations of the trachea and pulmonary trunk were observed. The SVC/azygos vein junction and the concavity of the aortic arch were observed to be more than 10 mm superior to this plane. The results of this study further highlight the substantial variability of the surface anatomy between age groups. It also emphasizes the notion that surface anatomy is a dynamic variable and cannot be treated as a static observation. Clin. Anat. 32:762-769, 2019. © 2019 Wiley Periodicals, Inc.

A rare variation of the hemiazygos vein draining into the persistent left superior vena cava.

During an educational dissection of a 72-year-old Chinese male cadaver, the hemiazygos vein (HAV) coursing the left side that drains into the persistent left superior vena cava was observed. The HAV was formed at the junction of the 9th to 11th right posterior intercostal veins, right subcostal vein, 5th to 11th left posterior intercostal veins, and left subcostal vein; it then ascended posteriorly to the thoracic aorta. After collecting the accessory hemiazygos vein, it crossed over the aorta and the pedicle of the left lung via the hemiazygos arch, then converged with a communicative branch (vein of Marshall) that emerged from the left brachiocephalic vein to form the persistent left superior vena cava and entered the pericardium at the level of the sixth thoracic vertebra. Upon opening the pericardium of our cadaver, the persistent left superior vena cava was found to drain directly into the significantly dilated coronary sinus at the level of the eighth thoracic vertebra. The azygos vein was formed by the union of the first to eighth right posterior intercostal veins and appeared to be finer and shorter than the HAV. The persistent left superior vena cava might be the result of incomplete degeneration of the left posterior cardinal vein. Knowledge of such variations could be of great value to surgeons placing peripherally inserted central catheters because incorrect placement of the azygos venous system can be detrimental to the patient. In addition, during heart surgery, awareness of such variations may prevent major complications, such as hemorrhage or damage to vascular structures, and possibly also provide new insights and perspectives to cardiovascular surgeries.

Analysis of multiple variations in azygos venous system anatomy with its classification: A cadaveric study

The azygos venous system varies greatly in mode of its origin, course, number of vertical channels, number of horizontal anastomoses and nature of termination. Anatomical knowledge of such variations is of immense importance in radiological investigations and surgical intervention of posterior mediastinum pathologies. The present study was undertaken on 30 adult embalmed cadavers aging between 40-65 years, to determine the anatomical variations of the azygos system and to classify accordingly. The vertebral level and diameter of the azygos, hemiazygos, accessory hemiazygos veins at their origin and terminations were also observed. The azygos system was classified into 3 types as per the Anson & McVay system: primitive (type I), transient (type II) and unicolumnar (type III). Type II was further subdivided into 5 subgroups (A to E) according to the number of retroaortic communications. Type I was observed in 1 case (3.33%), type II in 27 (90%) and type III in remaining 2 cases (6.67%). The vertebral level of termination of the azygos, hemiazygos, accessory hemiazygos veins were between T2 and T3, T6 and T10, T6 and T9 respectively. Variations in the formation of azygos system is not an uncommon phenomenon and these variations may easily mislead the radiologists while performing CT/MRI of posterior mediastinum or cardiothoracic surgeons while performing vascular surgeries in this region

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The anatomy of the thoracic duct at the level of the diaphragm: A cadaver study.

BACKGROUND: Injury and subsequent leakage of unrecognized thoracic duct tributaries during transthoracic esophagectomy may lead to chylothorax. Therefore, we hypothesized that thoracic duct anatomy at the diaphragm is more complex than currently recognized and aimed to provide a detailed description of the anatomy of the thoracic duct at the diaphragm. BASIC PROCEDURES: The thoracic duct and its tributaries were dissected in 7 (2 male and 5 female) embalmed human cadavers. The level of origin of the thoracic duct and the points where tributaries entered the thoracic duct were measured using landmarks easily identified during surgery: the aortic and esophageal hiatus and the arch of the azygos vein. MAIN FINDINGS: The thoracic duct was formed in the thoracic cavity by the union of multiple abdominal tributaries in 6 cadavers. In 3 cadavers partially duplicated systems were present that communicated with interductal branches. The thoracic duct was formed by a median of 3 (IQR: 3-5) abdominal tributaries merging 8.3cm (IQR: 7.3-9.3cm) above the aortic hiatus, 1.8cm (IQR: -0.4 to 2.4cm) above the esophageal hiatus, and 12.3cm (IQR: 14.0 to -11.0cm) below the arch of the azygos vein. CONCLUSION: This study challenges the paradigm that abdominal lymphatics join in the abdomen to pass the diaphragm as a single thoracic duct. In this study, this occurred in 1/7 cadavers. Although small, the results of this series suggest that the formation of the thoracic duct above the diaphragm is more common than previously thought. This knowledge may be vital to prevent and treat post-operative chyle leakage.

The collateral venous system in late pregnancy: A systematic review of the literature.

Recent literature has reported an association between maternal supine sleep position and stillbirth during late pregnancy. In this position the gravid uterus almost completely obstructs the inferior vena cava. A small number of women experience supine hypotension, thought to be due in part to inadequate collateral venous circulation. The aim of this paper is to review the literature describing the anatomy of the collateral venous system and in particular the azygos system, the abdominal portion of which has not been well studied. A systematic review was conducted using the electronic databases: Medline, Embase, Scopus, and Google Scholar. Relevant anatomical and radiological literature concerning the azygos system in particular was reviewed. The search was limited to adult human studies only. The collateral venous system can be divided into superficial, intermediate and deep systems. The azygos system in particular provides immediate collateral venous circulation in the event of acute inferior vena caval obstruction. The abdominal portion of this pathway, including the ascending lumbar vein, has not been well studied and there are certain variations that can render it ineffective. In conclusion, the collateral venous system provides an alternative route for blood to flow back to the systemic circulation when acute occlusion of the inferior vena cava occurs in the supine position during late pregnancy. However, certain anatomical variations can render this pathway ineffective, and this could have implications for the development of supine hypotension and stillbirth in late pregnancy. Clin. Anat. 30:1087-1095, 2017. © 2017 Wiley Periodicals, Inc.

Adoption of azygos, hemiazygos, and dartos.

Exceptions to the anatomical nomenclature rule that names must be in proper Latin include a few terms that contain borrowed Greek adjectives that are not declined like Latin words. Adoption of these adjectives into Latin would change about a half-dozen terms, e.g., vena azyga, vena hemiazyga, and fascia darta. The anatomical nomenclature rules apply only to the Latin terms, so there is no requirement to alter the way azygos, hemiazygos, and dartos are used in equivalent terms in other languages. Clin. Anat. 30:450-451, 2017. © 2017 Wiley Periodicals, Inc.

A rare variant between the left superior vena cava and the azygos vein.

During the educational dissection of a 68-year-old Chinese male cadaver, an azygos vein (AV) coursing on the left side with double superior vena cava was observed. The left superior vena cava (LSVC) began from the confluence of the left internal jugular and left subclavian veins, and extended downwards medially into the left edge of the dilated coronary sinus. The right superior vena cava was formed by the union of the right internal jugular and right subclavian veins, and drained into the right atrium from the above. The AV was formed by the union of the right and left ascending lumbar veins at the level of the tenth thoracic vertebra. It ascended along the left margin of the thoracic vertebra, receiving almost the bilateral posterior intercostal veins and then extended into the LSVC on the left wall via the azygos arch. Better understanding of these variations will reduce unnecessary and potential harmful testing, and unneeded patient anxiety.

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.

Situs inversus with levocardia, infrahepatic interruption of the inferior vena cava, and azygos continuation: a case report.

Situs inversus incompletus is a rare congenital condition in which the major abdominal organs are reversed or mirrored from their normal positions. It is often associated with multiple congenital anomalies. We present the case of a 38-year-old woman with dyspnea and a clinical history of chronic kidney disease and kidney transplantation. Echocardiography showed a right atrial mass, and analysis of multidetector computed tomography angiography revealed the interruption of the inferior vena cava with an increase of the azygos vein and azygos continuation. These congenital malformations are often associated with deep vein thrombosis and/or pulmonary thromboembolism and explained the occurrence of dyspnea. Cardiac magnetic resonance with contrast medium confirmed the presence of the right atrial mass, the characteristics of which were attributed to interatrial thrombus, which was further confirmed by the success of thrombolytic therapy and the remission of symptoms. In conclusion, we described a case of situs inversus with levocardia in association with infrahepatic interruption of the inferior vena cava, and azygos continuation with cardiac thrombus and chronic renal failure.

Comprehensive Imaging Review of the Superior Vena Cava.

The superior vena cava (SVC) is the largest central systemic vein in the mediastinum. Imaging (ie, radiography, computed tomography [CT], magnetic resonance [MR] venography, and conventional venography) plays an important role in identifying congenital variants and pathologic conditions that affect the SVC. Knowledge of the basic embryology and anatomy of the SVC and techniques for CT, MR imaging, and conventional venography are pivotal to accurate diagnosis and clinical decision making. Congenital anomalies such as persistent left SVC, partial anomalous pulmonary venous return, and aneurysm are asymptomatic and may be discovered incidentally in patients undergoing imaging evaluation for associated cardiac abnormalities or other indications. Familiarity with congenital abnormalities is important to avoid image misinterpretation. Acquired abnormalities such as intrinsic and extrinsic strictures, fibrin sheath, thrombus, primary neoplasms, and trauma can produce mild narrowing to complete occlusion, the latter leading to SVC syndrome. Each imaging modality plays a role in evaluation of the SVC, helping to determine the site, extent, and cause of pathologic conditions and guide appropriate management. Commonly performed interventional procedures for fibrin sheath and benign and malignant strictures include low-dose thrombolytic infusion, fibrin sheath disruption, venous angioplasty, and stent placement.