Thumb sign in lateral X-ray of neck seen in:

In epiglottis: A plain lateral soft tissue radiograph of neck shows the following specific features Thickening of the epiglottis--the thumb sign Absence of a deep well-defined vallecula--the vallecula sign Steeple sign i.e. Narrowing of subglottic region is seen in chest X-ray of patients of laryngotracheobronchitis (i.e. croup).