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. ALSO KNOW Steeple sign i.e. narrowing of subglottic region is seen in chest X-ray of patients of laryngotracheobronchitis (i.e. croup).