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.

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.

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.

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.

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.

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.

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.

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.

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.

[Vascular relationships of the right great splanchnic nerve in the thorax]. / Rapports vasculaires thoraciques du nerf grand splanchnique droit.

AIM: The surgical assumption of responsibility of the pancreatic pain requires either a truncular coelioscopic or radicular neurectomy of greater splanchnic nerves (gsn). The goal of our work is to describe the way and relations of the right gsn which are variable and rarely described. This constitutes an undeniable peroperational hemorrhagic risk during splanchnicectomy. MATERIAL AND METHODS: After a double side thoracotomy and a bilateral sterno-clavicular desarticulation on 15 adult cadaveric subjects preserved by method of Winckler we removed the sterno-costal drill plate as well as the ventral rib arch and proceeded to a mediastinal evisceration of the thorax. Then we respected only the thoracic aorta and the oesophagus, the azygos venous system, the thoracic duct and the thoracic sympathetic chain. In some of the subjects, the azygos vein was injected (after catheterization of its stick) using gelatine coloured with blue paint. We studied the way and vascular relations of the right gsn. We measured the transverse distances between the origin of the gsn on one hand and the longitudinal axes of the azygos vein and the thoracic duct on the other hand. RESULTS: The relations of the right gsn trunk during its way related to the azygos vein in particular its constitutive origin and its affluents: ascending lumbar vein and twelfth intercostal vein. Sometimes the thoracic duct even a lymphatic node was near the gsn in the posterior infra-mediastinal space. A classification of the way and vascular relations of the right gsn in the thorax identified 3 anatomical types. The average distances separating the right gsn on one hand from the azygos vein and the thoracic duct on the other hand were respectively 5.7 mm and 11.2 mm. CONCLUSION: The vascular relations of the right gsn are very variable from one subject to another but primarily venous, sometimes lymphatic. They concerned the great thoracic vessels whose respect is essential in particular at the time of mini-invasive access procedure for a cœlioscopic splanchnicectomy.

A semi-quantitative approach to variation of the azygos vein course.

The azygos vein (AV) is typically described (illustrated) as ascending vertically on the right of thoracic vertebrae. Most thoracic vein studies have focused on tributary patterns, but some have noted more leftward AV courses. This study statistically documents variation in AV course independent of tributary patterns. A more statistical approach to the probable position of AV at different vertical levels may aid clinicians in locating and assessing it in clinical contexts. The AV course was exposed in 84 cadavers by removing overlying viscera between the aortic hiatus and tracheal bifurcation. Subjectively, non-pathological specimens were digitally photographed in anterior view. For each photo, a scaled grid was used to mark the horizontal position of the AV center at each of five vertical levels. The summated numerical distributions showed the following: ∼5% of the AVs ascended on the right side (classical) position, ∼30% did not cross the midline, ∼70% included part or all of their course left of the midline, and ∼14% reached the extreme left side. Based on this data, the modal AV course (1) begins at, or to the right of, the midline, (2) deviates leftward, (3) crosses the midline below mid-level, (4) reaches a leftward maximum at about 3/5 of its course, (5) then deviates rightward (often only reaching the midline at the uppermost level). In several noticeable cases, the leftward maximum was associated with large connections to left-side veins, suggesting a possible tension mechanism exerting traction on the AV over time.

Bovine thoracoscopy: surgical technique and normal anatomy.

OBJECTIVE: To describe a surgical technique for thoracoscopy and report visible anatomy within the thoracic cavity of standing cattle. STUDY DESIGN: Prospective study. ANIMALS: Adult clinically healthy Holstein-Friesian cows (n = 15). METHODS: Each cow had four thoracoscopic examinations. Initially, the left hemithorax was examined after passive lung collapse, then again 24 hours later after CO2 insufflation. The right hemithorax was examined 24 hours later after passive lung collapse and again 24 hours later after CO2 insufflation. RESULTS: CO2 insufflation did not significantly improve visibility within the pleural space. Collapsed lung, aorta, esophagus, diaphragm, and azygos vein were readily viewed; however, the pericardial region was not consistently visible. Minor laceration of the lung occurred in 1 cow with adhesions, otherwise there were no intra- or postoperative complications. All cows recovered without signs of discomfort. No local swelling or emphysema occurred at the portals. CONCLUSIONS: Thoracoscopy can be safely performed on healthy standing cattle.

The posterior intercostal vein: a thermoregulatory gateway to the internal vertebral venous plexus.

The internal vertebral venous plexus (IVVP) plays a putative role in thermoregulation of the spinal cord. Cold cutaneous venous blood may cool, while warm venous blood from muscles and brown fat areas may warm the spinal cord. The regulating mechanisms for both cooling and warming are still unknown. Warm venous blood mainly enters the IVVP via the intervertebral veins. In the thoracic area these veins are connected to the posterior intercostal veins. In this study, anatomical structures were investigated that might support the mechanisms by which warmed venous blood from the intercostal muscles and the recently described paravertebral patches of brown adipose tissue are able to drain into the vertebral venous plexus. Therefore, tissue samples from human cadavers (n = 21) containing the posterior intercostal vein and its connections to the IVVP and the azygos veins were removed and processed for histology. Serial sections revealed that the proximal parts of the posterior intercostal veins contained abundant smooth muscle fibers at their opening into the azygos vein. Furthermore, the walls of the proximal parts of the posterior intercostal veins contain plicae that allow the vessel to dilate, thereby allowing it to serve as a pressure chamber. It is suggested that a cold induced closure of the intercostal/azygos opening can result in retrograde blood flow from the proximal posterior intercostal vein towards the IVVP. This blood flow would be composed of warm blood from the paravertebral brown adipose tissue and blood containing metabolic heat from the muscles draining into the intercostal veins.

Azygos lobe in a South African cadaveric population.

Knowledge of the prevalence, morphology, and location of the azygos lobe is essential for diagnostic and surgical procedures of the lungs related to mediastinal pathologies, especially to minimize intraoperative vascular injuries, shock, possible thoracotomy, and even the possibility of pulmonary torsion. Reports on the prevalence of the azygos lobe vary between 0.11% and 1.06%. The aim of this study was to record the prevalence and morphological description of the azygos lobe in the South African cadaveric population. A total of 704 adult cadavers dissected over a 10-year period by students in the Department of Human Anatomy at the Medunsa Campus, University of Limpopo, were studied. The prevalence and dimensions of the azygos lobe were determined with a 95% confidence interval (CI). Results indicate that an azygos lobe was present in the right lung in only four cases (prevalence 0.57%, 95% CI: 0.2%-1.6%). The mean height and width were 6.7 cm (95% CI: 4.4-9.2) and 4.5 cm (95% CI: 3.7-5.2), respectively. Observations on the morphology of the azygos lobe showed that it was rectangular (n = 3) and triangular (n = 1) in shape with smooth margins. In conclusion, the azygos lobe is a rare anomaly in the South African cadaveric population. The present results are comparable with those reported in the literature for other populations. Future radiological studies on the azygos lobe on living subjects in South Africa will be useful for further understanding of this rare but significant anomaly.

Anatomy of the thoracic aorta and of its branches.

For a surgeon performing chest operation, thorough knowledge of the anatomy of the thoracic aorta and of its branches are essential not only to ensure the preservation of adequate organ vascular supply during reconstructive surgery of the esophagus or trachea but also to avoid injury to important thoracic vascular structures. This knowledge is of paramount importance especially for surgeons performing operations for mediastinal disorders or tumors to avoid catastrophic complications. This article discusses the anatomy and the most common congenital abnormalities of the thoracic aorta and its branches.