The trachea

The normal trachea is usually well seen on conventional frontal radiographs, lying just to the right of the midline and extending from the larynx at the level of the cricoid cartilage at about C-4 to the carina at about T-5. On the lateral radiograph, the trachea inclines gently posteriorly in a relatively straight line, normally maintaining an even caliber throughout. The trachea diminsishes in caliber at its bifurcation into right and left main-stem bronchi. On an expiratory chest film in infants and young children, the trachea buckles anteriorly and to the right, sometimes so markedly as to be alarming to the inexperienced observer. Preliminary observations on the size of the normal trachea from infancy to 18 months of age were reported. More recently, others studied the trachea by computed tomography. The latter investigators have shown that both the length and cross-sectional areas increase with age and correlate well with body height. If tracheal pathology is suspected, the air column can be optimally visualized using xeroradiography or filtered, high-kilovoltage magnification techniques. The latter method is usually preferred because of lower radiation exposure. Fluoroscopy of the normal trachea shows little, if any, change in caliber during quiet breathing unless peripheral airway obstruction is present; then the trachea can collapse by up to 50% on expiration. The trachea is also well visualized by computed tomography (CT). Narrowing of the tracheal lumen is perhaps better appreciated by this modality than any other