Assessment of the Diameter of Thoracic Aorta by Computed Tomography of Chest

Introduction: The aim of this study was to assess the diameters of thoracic aorta of normal Nepalese people by using computed tomography scans of chest and to correlate the diameters with the patient’s age, gender, height, weight and BMI. Methods: This prospective study was performed in the Department of Radiology and Imaging, TUTH. Data were collected over the period of 4 months from June to September 2017 with the total of 99 patients who underwent contrast enhanced CT of chest in the tertiary hospital. Results: The diameter of thoracic aorta was found to be maximum at the level of aortic valve sinus (3.23+ 0.36 cms), minimum at the level of diaphragm (2.20 + 0.31 cms), and mean diameter of ascending aorta was found to be 2.73 + 0.27 cm. Conclusion: This study concluded that the diameter of thoracic aorta increased with increase in age and vice versa. The diameter of thoracic aorta decreased in the tapering fashion distally from the aortic valve sinus.


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Correspondence to: Dr. Birendra Raj Joshi Department of Radiology and Imaging TU Teaching Hospital Maharajgunj, Kathmandu, Nepal Email: bjoshi01@yahoo.com The aorta is the main artery in the human body that distributes oxygenated blood to all part of the body through the systemic circulation. It extends from the heart to about the fourth lumbar vertebra and is divided into thoracic and abdominal sections. The thoracic section is further divided into four segments: aortic bulb (root), ascending aorta, aortic arch and descending aorta.
CT angiography uses an injection of iodinerich contrast media and CT scanning to help diagnose and evaluate vascular disease or related condition such as aneurysm or Licensed under CC BY 4.0 International License which permits use, distribution and reproduction in any medium, provided the original work is properly cited blockage. Aortography is performed by x-ray with catheters, MRI, and CT which is usually the most useful technique in imagining of aorta and produce detailed image of vessels.
The specific objectives are to measure the diameter of ascending and descending thoracic aorta and to correlate with the patient's age, gender, height, weight and BMI.

METHODS
This cross sectional study was conducted in a tertiary hospital of Kathmandu on all the patients referred for contrast enhanced CT chest in Department of Radiology from June 2017 to September 2017. Axial images were obtained using Siemens Somatom Definition AS +, 128 slice CT scanner. CT scans were obtained with the patient in supine position during full inspiration. The scan range was from 2 cm above lung apices to the diaphragm. The exposure parameters were 120 kVp, 50-300 mA and a slice thickness of 5mm.
The diameters of the aorta were measured at the levels of aortic valve sinus, ascending aorta, proximal to innominate artery, transverse aortic arch, distal transverse aortic arch, aortic isthmus and descending aorta at the level of diaphragm perpendicular to the axis of the blood flow in the aorta in the operator console of the CT scanner.
Inclusion criteria were all patients referred for the contrast enhanced CT chest in the Department of Radiology and patients who were diagnosed with normal mediastinum and without history of cardiovascular diseases.
Exclusion criteria were patients having pathological changes such as pulmonary embolism, aortic aneurysm, aortic atherosclerosis, aortic regurgitation, aortic dissection, aortic stenosis and aortitis ; non-Nepalese patients and uncooperative patients.
Statistical analyses were carried out with the help of SPSS version 20 and Microsoft Excel. The mean, standard deviation, and correlation between diameters of thoracic aorta at all the levels with the age group, gender, weight group, height group, and BMI group were expressed in tables, figures and the scatter plot diagrams. Multiple planar reconstructions were generated on a view workstation (Siemens Medical Systems). The slices were manually adjusted for each aortic level to get an oblique plane strictly perpendicular to the course of the aorta. The internal diameter of the vessel was measured with an electronic caliper. All images were reconstructed and analyzed.
The data were collected in Microsoft Excel and were analyzed using SPSS program version 20. Normal distribution of the diameter was assumed. To analyze the changes of the diameters along the course of the aorta, paired samples test of neighboring diameters were used. Study was approved by institutional review board.

RESULTS
The data was collected from 99 normal subjects, 52 males and 47 females with age from 21 years old up to >70 years old.    (Table 3).
There was a significant correlation of DODA with only the age of the individual (Table 4).
There was no significant correlation of mean DOAA and DODA with the weight, height, and BMI of the individual at 0.01 level of the significance.   From the paired samples test, the sig (p value) between the pairs of adjacent diameters of aorta at different levels were less than 0.05, except in a pair of diameters at ascending aorta and proximal to innominate artery with the p value 0.715. Hence there was a statistically significant difference between the diameters of aorta at all the adjacent pairs except the pair of diameters at ascending aorta and proximal to innominate artery. (Table 6) There was a significant increase of DODA and mean DOAA with age of the participant.
The scatter plot diagrams presenting the relation of DODA and mean DOAA with age of the patient are represented in scattered plot diagrams ( Fig 3, 4). The scatter plot diagrams showed the high positive correlation between age and diameter, low positive correlation between height and diameter, high negative correlation between BMI and diameter, and low negative correlation between weight and diameter of the aorta. There was a high positive correlation between DODA and mean DOAA ( Fig 5).
Despite the adequate sample size, it was still small for generalization of the study. We measured patient's parameter manually and the value may not be consistent. In addition, the measured diameters may not be considered true as the patients were referred having certain clinical condition which warrants the need of the chest CT scan. We measured the diameter of the aorta of different patients so the level of the site of measurement might not be the same in all cases. The sample size is not adequate to generalize the result and required the measurement with large sample size.
Measurement of the aortic diameter should be taken at reproducible anatomic landmarks, perpendicular to the axis of the blood flow if measurements are taken by the CT, MRI or echocardiography. Abnormal morphology should be recognized when aortic diameter within normal limits. Further descriptive analytic studies are needed using other imaging modalities as MRI or echocardiography to confirm these results that represented in index so as to help in diagnosis of aortic problem which lead to enlargement or decreasing in its size.

CONCLUSION
The diameter of thoracic aorta was found to be maximum at the level of the aortic valve sinus (3.23+ 0.36 cms), minimum at the level of diaphragm (2.20 + 0.31 cms), and mean diameter of ascending aorta was found to be 2.73 + 0.27 cms.
The measurement of diameter of thoracic aorta at each level had significant correlation with age but not with gender, height, weight and BMI. The diameter of thoracic aorta decreased in the tapering fashion distally from the aortic valve sinus.