<prompt> What is the normal cardiothoracic ratio in children?30-3540-4550-5560-65  <response>: The cardiac silhouette occupies 50-55 of the chest width. Cardiomegaly is present when the cardiothoracic CT ratio is more than 55.The CTR is measured on a PA chest x-ray and is the ratio of maximal horizontal cardiac diameter to maximal horizontal thoracic diameter inner edge of ribsedge of pleura. A normal measurement should be 0.550.Refer: Nelsons Textbook of Pediatrics, SAE, 1st edition, pg no. 2170 