Methods
Database and patient population . Institutional electronic
medical record system was queried from years 2013-2016 to identify
patients with age ≥ 50 and \(<\)85 years who received CT chest imaging
for either in inpatient, outpatient, or emergency department encounters.
We set the lower age limit of 50 years because thoracic aortic aneurysm
below this age is rare unless associated with connective tissue disease,
and the upper age limit was set as the benefit of detection leading to
intervention decreases at old age. After excluding multiple scans
obtained on the same patient during the study period, there were 21,336
scans obtained on unique patients. In patients with multiple scans, the
scan with the earliest date was used for the analysis. The Institutional
Review Board approved this study. All CT scan reports were screened for
any comments on the aortic arch and great vessels. Those reports were
further reviewed for the description and subcategorization of arch
anomalies. Also, all CT scans were screened for words and permutations
related to thoracic aortic aneurysm (TAA) (aneurysm, dilation,
dilatation, ectasia, enlargement) and reports containing such words were
further reviewed for the site and the size of the aneurysms. Aneurysms
of the abdominal aorta were excluded. The site of the thoracic aortic
aneurysm was the site of the maximum diameter of the aorta. Subjects
with missing clinical or demographic data were excluded.
Validation sample . Due to the concern that the aorta was not
accurately assessed on scans done without contrast and routine scans
done for non-thoracic pathology, a random sample of 200 scans was
generated and reviewed by two radiology trainee and a board certified
cardiothoracic radiologist with 10 years of experience in reading aorta
studies. All the 200 scans were non-contrast. The prevalence and the
type of the anomaly was documented, if found.
Patient characteristics . Indicated age, height, and weight
values were recorded at the time of the CT scan. Race was categorized
into Caucasian, African American, Asian, and other. Body surface area
was calculated using Mosteller equation.11 Smoking
history was dichotomized based on those with ≥ 5 pack-year smoking
history indicating positive smoking history. Comorbidities (aortic valve
disease, hypertension, diabetes, dyslipidemia, congestive heart failure,
cocaine use, chronic kidney disease, myocardial infarction, chronic
obstructive pulmonary disease) were chosen as commonly evaluated
cardiovascular comorbidities and were defined using ICD-10 codes. To
define aortic dilatation and aneurysm; 4 cm cut-off value was used for
the root, ascending and the aortic arch, and 3 cm was used for the
descending thoracic aorta.
Statistical analysis . Differences in the patient
characteristics were compared with two-tailed t-test for normally
distributed continuous variables and Fisher’s exact test for categorical
variables. Multivariable logistic regression model was fitted to
identify independent risk factors of TAA. Age, sex, race, BSA, history
of hypertension, diabetes, dyslipidemia, smoking history, COPD, arch
anomalies and aortic valve diseases were included in the model. P value
of <0.05 and 95% CI were used to define statistically
significant difference. Analysis was conducted using Microsoft excel
2019 and Prism 8.2 (GraphPad Software, San Diego, CA) for simple
analysis and SAS 9.4 (SAS Institute Inc, Cary, NC) for modelling.