Anatomical variations of the aortic knob in chest radiographs

There is a paucity of data regarding the normal anatomical variations of the aortic knob (AK) on routine postero-anterior chest radiographs (PACR). The aims of the present study were to document and analyze the anatomical variations of the AK on PACRs’ in an adult Indian population. This was a crosssectional study of PACRs’ in a tertiary care hospital with attached medical college in Bangalore, India. The AKs’ in 108 (77 males and 31 females) PACRs’ of normal, healthy adults were studied using the following measurements: minimum distance of the left edge of the aortic knuckle from the midline (AKW); straight and curved length of the AK (AKS and AKC). The ratio of the AKC to the AKS was calculated and termed the AK index (AKI). The mean and standard deviation were determined for AKW, AKS and AKI. The unpaired t-test was used to check for significant sex differences in the above parameters. Spearman’s rank order correlation coefficient of the AKW, AKS and AKI with the age, BMI, CD, CA and CTR was calculated. The mean value of the AKW was significantly higher in males as compared to females. The majority of the values of AKI were between 1 and 1.2 in both sexes. The AKW showed significant positive correlations with age, the body mass index and cardiac diameter. The AKI showed a weak, although significant positive correlation with the age and the cardiothoracic ratio. The present study describes the anatomical variations of the AK, using the AKI to quantify its prominence.