CT anatomical study of extreme lateral interbody fusion in thoracic spine.

Extreme Lateral Interbody Fusion (XLIF) is currently used in the clinical treatment of thoracic spine disorders and has achieved desirable results. In this study, we selected CT images of the thoracic spine from 54 patients and divided the intervertebral spaces into six regions (A, I, II, III, IV, P) using the Moro method. We observed the adjacent relationships between the thoracic spine and surrounding tissues such as the scapula, esophagus, thoracic aorta, and superior vena cava. We made four main findings: firstly, when the scapulae were symmetrical on both sides, over 80% of patients had the T1-4 II-III region obstructed by the scapulae; secondly, when the esophagus was located on the left side of the vertebral body, 3.7% to 24.1% of patients had the T4-9 region located in the II-III zone; furthermore, when the thoracic aorta was on the left side of the vertebral body, over 80% of individuals in the T4-9 segment occupied the II-III region, with the values being 55.5% and 20.4% for T9/10 and T10/11, respectively; finally, the superior vena cava was located on the right side of the T4/5 vertebra, with 3.7% of individuals having it in the II-III region, while on the left side of T5-9, 3.7% to 18.5% of individuals had it in the II-III region. Based on these findings, we suggest that XLIF should not be performed on the T1-4 vertebrae due to scapular obstruction. Selecting the left-sided approach for XLIF in the T4-11 segments may risk injuring the thoracic aorta, esophagus, and superior vena cava, while the T11/12 segment is considered safe and feasible. Choosing the right-sided approach for XLIF may pose a risk of injuring the superior vena cava in the T4/5 segment, but it is safe and feasible in the T5-12 segments.

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.

Immediate aspiration of the drug infused via central venous catheter through the distally positioned central venous dialysis catheter: An experimental study.

OBJECTIVES: The aim of this study was to construct an experimental model replicating blood flow within human superior vena cava and to determine the degree of the immediate aspiration of the drug introduced via central venous catheter through the distally positioned dialysis catheter. METHODS: A model replicating superior vena cava was built, catheters were inserted into the model, placing the orifice of the central venous catheter in positions regarding the orifice of the arterial lumen in central venous dialysis catheter (from +2 to -8 cm). Methylene blue was used as a tracer, and the concentration was determined by ultraviolet-visible spectroscopy. Four different sets of samples were generated according to infusion and aspiration speeds: continuous-slow, continuous-fast, bolus-slow, and bolus-fast. RESULTS: The concentration of the tracer was related to the distance between the catheter tips, representing a bimodal dependence. When the central venous catheter was placed distally to the central venous dialysis catheter, the aspiration of the tracer was minimal. When withdrawing the central venous catheter proximally, the aspiration of the tracer increased, reaching its peak at -4 cm with aspiration rates form 4.2% to 140.7%. Furthermore, the infusion speed of the tracer had more effect on the aspirated concentrations than the aspiration speed. CONCLUSION: Findings of our experimental model suggest that concentration of aspired drug is effected by the distance between the central venous catheter and central venous dialysis catheter, being lowest when the drug is infused distally to central venous dialysis catheter. Furthermore, the concentration of the tracer is directly proportional to the infusion speed and far less effected by the aspiration rate of the drug.

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.

Age-Related Histological Changes in Vena Caval System of Human Foetus and Adult: A Comparative Study.

BACKGROUND: It has been documented that cardiac musculature is present in both venae cavae, and they contract together with the atrium, contributing to the pumping mechanism of the heart. So, in the present study, we measured the relative thicknesses of the three histological layers at formation, termination and intermediate levels of the venae cavae along with their histological characteristics. MATERIALS AND METHODS: Ten foetal and 10 adult cadavers were used. The Superior and Inferior Venae Cavae from all three regions were excised and processed for histology. The qualitative and quantitative features of the vessels were observed and recorded. The data thus obtained was then assessed statistically. RESULTS: In superior vena cava, the tunica intima grows actively especially during late gestation. The tunica media shows active growth. The tunica adventitia growth is significant at the middle and termination levels. In inferior vena cava, the tunica intima grows actively at the level of formation. The tunica media shows the active overall growth during early gestation. The tunica adventitia shows active growth during late gestation. In qualitative analysis the plump, spindle-shaped primitive mesenchymal cells were observed. Muscle and collagen fibers show reciprocal abundance with increasing age, with the former being lesser in amount than the latter in earlier stages. Appearance of vasa vasorum was notable from 2nd trimester. The cardiac myocytes were located in the middle and outer tunics of the superior vena cava. CONCLUSION: Cardiac musculature was absent in the inferior vena; however, the vessel shows advanced rate of overall development.

New findings of branching variations in subclavian arteries and supra-aortic arteries in Felis catus.

The branching of blood vessels around the heart is varied in each animal. Three branching patterns of the brachiocephalic trunk in cats have been reported. However, supra-aortic arteries in the hearts of cats have never been investigated. In this study, we hypothesized that the variations of the aortic arch, supra-aortic arteries, and vena cava were observed in domestic cats. Sixty-one hearts obtained from the cadavers of domestic cats (Felis catus) were analyzed in terms of anatomical characteristics, size, and the length of these supra-aortic vessels by using a 3D scanner. New variations of the left and right subclavian arteries were observed using the location of the internal thoracic (ITA) and vertebral artery (VA) as the criterion to group the varying patterns. We found four patterns of the left subclavian artery, which included ITA budding contralateral before VA (5%), VA budding opposite to ITA (75%), VA budding contralateral before ITA (13%) and ITA budding ipsilateral before VA (7%). In contrast, only three patterns were found in the right subclavian artery, which included VA budding opposite to ITA (20%), VA budding contralateral before ITA (19%), and ITA budding contralateral before VA (61%). Moreover, although an average vascular diameter in male cats was higher than in female subjects, the supra-aortic blood volume in both sexes was not different. The findings of this study could help fill the existing gap of knowledge on the anatomical variations of supra-aortic arteries in cats and could be used in clinical applications based on relevant anatomical data.

A Comparison of the external anatomical landmark and the radiological landmark for obtaining the optimal depth of a right internal jugular venous catheter in pediatric cardiac patients.

BACKGROUND: The external anatomical landmark and the radiological landmark have been introduced to provide estimation of the depth of right internal jugular venous catheter during insertion. AIMS: This study aimed to compare the accuracy, agreement, and reliability of the external anatomical landmark and the radiological landmark, confirmation being by transesophageal echocardiography. METHODS: This prospective observational study was conducted in children ages 1-15 years. The catheter was placed at the superior vena cava and the right atrium junction guided by transesophageal echocardiography. The catheter depth derived from the transesophageal echocardiography, the external anatomical landmark, and the radiological landmark was recorded. The optimal zone of the catheter tip was 5 mm below and 10 mm above the superior vena cava and the right atrium junction. Accuracy was assessed by the difference between the transesophageal echocardiography and the external anatomical landmark or the radiological landmark. Agreement with Bland-Altman plots and correlation were tested. RESULTS: Eighty participants, median age of 3 years, were enrolled. The median (IQR) differences between the depth of the transesophageal echocardiography and the external anatomical landmark or the radiological landmark were 0.30 (0, 0.70) and 0.10 (-0.20, 0.90) cm, respectively. Bland-Altman plots demonstrated good agreement between the depths. The catheter tips were located in the optimal zone more frequently with the external anatomical landmark than the radiological landmark (94.7% vs 64.5%). The external anatomical landmark showed a stronger correlation to transesophageal echocardiography than the radiological landmark (r = .95 vs .83). CONCLUSION: Both the external anatomical landmark and the radiological landmark enabled accurate estimation of the central venous catheter depth close to the superior vena cava and the right atrium junction. The external anatomical landmark is of more potential use than the radiological landmark in clinical practice.

Pediatric central venous catheterization: The Role of the Aortic Valve in Defining the Superior Vena Cava-Right Atrium Junction.

The aortic valve (AV) has been used as a surrogate marker for the superior vena cava-right atrium (SVC-RA) junction during the placement of central venous catheters. There is a paucity of evidence to determine whether this is a consistent finding in children. Eighty-seven computed tomography scans of the thorax acquired at local children's hospitals from April 2010 to September 2011 were retrospectively collected. The distance between the SVC-RA junction and the AV was measured by dual consensus. The cranio-caudal level of the junction and the AV were referenced to the costal cartilages (CCs) and anterior intercostal spaces (ICSs). The results confirmed that the SVC-RA junction has a variable relationship to the AV. The junction was on average 3.1 mm superior to the AV. This distance increased with age. In the <1-year-old age group, the junction was on average 1.3 mm superior to the AV (range: -6 to 11 mm). In the 1-2 years old age group: 3.5 mm (range: -8 to 15 mm). In the 3-6 years old: 3.8 mm (range: -9 to 13 mm). In the >7 years old age group: 4 mm (range: -11 to 16 mm). The surface anatomy of the SVC-RA junction was variable, ranging from the second ICS to sixth CC. The SVC-RA junction has a predictable relationship to the AV, and this can be used as an adjunct marker for accurate placement of central venous catheters except in the smallest neonates. Clin. Anat. 32:778-782, 2019. © 2019 Wiley Periodicals, Inc.

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.

CT of the paraumbilical and ensiform veins in patients with superior vena cava or left brachiocephalic vein obstruction.

The purpose of this study was to elaborate on the anastomoses between the paraumbilical and systemic veins, particularly the ensiform veins. The connections with the ensiform veins have received little attention in the anatomical and radiological literature, and remain incompletely described. Too small to be reliably traced in normal CT scans, the paraumbilical veins can dilate in response to increased blood flow from systemic veins in superior vena cava obstruction (SVCO), allowing a study of their arrangement and connections. Collateral paraumbilical veins were therefore analyzed retrospectively in 28 patients with SVCO using CT. We observed inferior and superior groups of collateral vessels in 23/28 (82%) and 17/28 (61%) patients, respectively. Inferior veins ascended towards the liver and drained into portal veins (19/28, 68%) or the umbilical vein (8/28, 29%); superior veins descended and drained into portal veins. The inferior veins (N = 27) could be traced to ensiform veins in almost all of the cases (26/27, 96%), and a little over half (14/27, 52%) were also traceable to subcutaneous and deep epigastric veins. They were opacified by ensiform (25/27, 93%), deep epigastric (4/27, 15%) and subcutaneous (4/27, 15%) veins. The superior veins (N = 17) were supplied by diaphragmatic (13/17, 76%) and ensiform veins (4/17, 24%); the diaphragmatic veins were branches of collateral internal thoracic, left pericardiacophrenic and anterior mediastinal veins. Collateral ensiform veins were observed in 22 patients and anastomosed with internal thoracic (19/22, 86%), superior epigastric (9/22, 41%), diaphragmatic (4/22, 18%), subcutaneous (3/22, 14%) and anterior mediastinal veins (1/22, 5%). These observations show that the paraumbilical veins communicate with ensiform, deep epigastric, subcutaneous and diaphragmatic veins, joining the liver to the properitoneal fat pad, anterior trunk, diaphragm and mediastinum. In SVCO, the most common sources of collateral flow to the paraumbilical veins are the ensiform and diaphragmatic branches of the internal thoracic veins.

A reappraisal of pediatric thoracic surface anatomy.

Accurate knowledge of surface anatomy is fundamental to safe clinical practice. A paucity of evidence in the literature regarding thoracic surface anatomy in children was identified. The associations between surface landmarks and internal structures were meticulously analyzed by reviewing high quality computed tomography (CT) images of 77 children aged from four days to 12 years. The results confirmed that the sternal angle is an accurate surface landmark for the azygos-superior vena cava junction in a plane through to the level of upper T4 from birth to age four, and to lower T4 in older children. The concavity of the aortic arch was slightly below this plane and the tracheal and pulmonary artery bifurcations were even lower. The cardiac apex was typically at the 5th intercostal space (ICS) from birth to age four, at the 4th ICS and 5th rib in 4-12 year olds, and close to the midclavicular line at all ages. The lower border of the diaphragm was at the level of the 6th or 7th rib at the midclavicular line, the 7th ICS and 8th rib at the midaxillary line, and the 11th thoracic vertebra posteriorly. The domes of the diaphragm were generally flatter and lower in children, typically only one rib level higher than its anterior level at the midclavicular line. Diaphragm apertures were most commonly around the level of T9, T10, and T11 for the IVC, esophagus and aorta, respectively. This is the first study to provide an evidence-base for thoracic surface anatomy in children. Clin. Anat. 30:788-794, 2017. © 2017Wiley 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.

An extremely rare case report of surgery of lung cancer with the absence of azygos vein.

In thoracic surgery, we occasionally encounter vessel anomalies. We herein report an extremely rare surgical case with the absence of the azygos vein. Mediastinal vascular abnormalities are said to be rare. The etiology of vascular abnormalities of the whole body, including the chest is known gene mutations, hormone abnormalities, infection, and trauma. But, many causes have been unknown. In thoracic surgery field, there is some reports and literature about pulmonary arteriovenous malformation, pulmonary sequestration, and partial anomalous pulmonary venous return. But reports about absence of azygos vein are not much. It is considered that it is less likely to become a problem in clinical. As we discussed in the paper, it will be more interesting if the association with PLSVC reveals from more cases. A 58-year-old man was admitted to our hospital in order to undergo operation for the treatment of lung cancer. We detected absence of the azygos vein by preoperative computed tomography (CT). Furthermore, three-dimensional angiography (3D-angiography) showed that the right superior intercostal vein and hemiazygos vein in the left thoracic cavity were more developed than usual. Then, we discuss the key points during surgery and suggest the potential association between the absence of the azygos vein and a persistent left superior vena cava (PLSVC).

Defining the surface anatomy of the central venous system in children.

Pediatric emergency physicians, pediatric critical care specialists, and pediatric surgeons perform central venous catheterization in many clinical settings. Complications of the procedure are not uncommon and can be fatal. Despite the frequency of application, the evidence-base describing the surface landmarks involved is missing. The aim of the current study was to critically investigate the surface markings of the central venous system in children. The superior vena cava/right atrial (SVC/RA) junction, superior vena cava (SVC) formation, and brachiocephalic vein (BCV) formation were examined independently by two investigators. Three hundred computed tomography (CT) scans collected across multiple centers were categorized by age group into: 0-3 years, 4-7 years, and 8-11 years. Scans with pathology that distorted or obscured the regional anatomy were excluded. The BCV formation was commonly found behind the ipsilateral medial clavicular head throughout childhood. This contrasts with the variable levels of SVC formation, SVC length, and SVC/RA junction. In the youngest group, SVC formation was most commonly at the second costal cartilage (CC), but moved to the first CC/first intercostal space (ICS) as the child grew. The SVC/RA junction was at the fourth CC in the youngest group and moved to the third CC/third ICS as the child grew. This study demonstrates the variable anatomy of SVC formation and the SVC/RA junction with respect to rib level. This variability underscores the unreliability of surface anatomical landmarks of the SVC/RA junction as a guide to catheter tip position.

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.

Use of vertebral body units to locate the cavoatrial junction for optimum central venous catheter tip positioning.

BACKGROUND: Central venous catheter (CVC) placement plays an important role in clinical practice; however, optimal positioning of the CVC tip remains a controversial issue. The objective of this study was to evaluate the use of vertebral body unit (VBUs), to locate the cavoatrial junction (CAJ), for optimal CVC tip placement based on chest radiography (CXR) using the carina as a landmark. METHODS: 524 patients who underwent coronary computed tomographic angiography (CTA) and CXR were included. The position of the CAJ was identified using VBUs, and the efficacy of VBUs for locating the CAJ with the carina as a landmark was analysed using multiple regression analysis. A VBU was defined as the distance between two adjacent vertebral bodies, including the inter-vertebral disk space. RESULTS: The mean (sd) distance from the carina to the superior CAJ was 54.3 (9.7) mm on CTA; the mean distance in VBUs at the level of the carina was 21.4 (1.7) mm on CTA and 22.6 (2.1) mm on CXR. The mean CAJ position was 2.5 VBUs below the carina on CTA and 2.4 VBUs below on CXR with 95% limits of agreement between -0.6 and +0.3. CONCLUSIONS: The position of the CVC tip in relation to the carina can be described using the thoracic spine as an internal ruler, and the position of the CAJ in adults was reliably estimated to be 2.4 VBUs below the carina. CLINICAL TRIAL REGISTRATION: KCT0001319.