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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.

Purpose:To evaluate clot size and stenotic degree on conventional computed tomographic pulmonary angiography (CTPA) with perfusion defect. Material and Methods:Fifty-two pulmonary embolism (PE) patients with 144 PE locations underwent dual-energy CTPA with an iodine distribution map. Each PE location was rated as to whether there was a perfusion defect. Clot size, stenotic degree, and other associated PE findings were evaluated. These findings were then correlated with whether the perfusion defect was present.Results: There were no associations between demographics, clinical characteristics, anatomical data, and perfusion defect. The median iodine concentration ratio was 0.11. Imaging interpretation by 2 thoracic radiologists had excellent agreement. The clot size and stenotic degree in PE were significant predictors of perfusion defect on conventional CTPA. Lesions with higher degrees of stenosis had higher percentages of perfusion defect. The generalized estimating equation (GEE) logistic regression confirmed that clot size and stenotic degree could predict PE perfusion defects on conventional CTPA. Conclusions:The 2 significant predictors of perfusion defect were occluded vessels in both small and large branches together, or complete occlusion of the pulmonary artery.