Structure which is not part of the left cardiac silhouette on a normal X-ray chest PA view is – Correct Answer: a) Left pulmonary artery
Left pulmonary artery does not form part of the left heart border as it curves down posteriorly and is seen within the cardiac silhouette. Main pulmonary artery forms the left heart border just below the aortic knuckle.
An enlarged left atrial appendage on the left border is called the third mogul sign, the first and second moguls being aortic knuckle and main pulmonary artery. Main pulmonary artery segment is usually not prominent on a normal chest X-ray and is called the pulmonary bay. If it bulges out, it indicates dilatation.