Croup

AP view - loss of normal shoulders (lateral convexities) of  the subglottic  trachea secondary to subglottic  edema : steeple sign, pencil tip or inverted V sign
-Symmetric ,subglottic narrowing with narrow portion of the airway extending more inferiorly than the level of pyriform sinuses

Lateral radiograph-
Narrowing of subglottic  trachea
Loss of definition of subglottic  trachea
Hypo pharyngeal  overdistension
Normal epiglottis and aryepiglottic fold
Hypopharynx may be collapsed with distension of the lower cervical trachea - if expiratory image

The AP radiograph demonstrates bilateral narrowing of the subglottic airway, the "steeple sign" in the absence of epiglottic thickening 

Lateral radiograph shows distension of the hypopharynx (the patient's attempt at decreasing airway resistance)