Thumb sign in lateral X- ray of neck seen in -: (A) Epiglottitis, (B) Internal haemorrhage, (C) Saccular cyst, (D) Ca epiglottis
Answer is A. 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).