This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory System, Subject name: Pediatrics
Lateral X-ray of the upper airway in a 2-year-old boy reveals a "thumb sign". The most likely diagnosis is: 
Select and explain. 
A. Laryngeal polyps, B. Epiglottitis, C. Subglottic hemangioma, D. Laryngeal edema
B: Epiglottitis
Answer: B: Epiglottitis 
Explanation: Ans. B. EpiglottitisEpiglottitis is characterized by inflammatory edema of the epiglottis along with upper airway obstruction. It is usually a cause of severe respiratory distress in young children and is associated with sudden onset high fever, drooling of saliva and the child in a typical "tripod position". Cause is usually S. pneumonia, or less frequently, H. influenza.