This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: ENT
Which among the following causes 'thumb sign' on an X-ray lateral view of the neck? 
Select and explain. 
A. Acute epiglottitis, B. Acute laryngo trachea bronchitis, C. Acute tonsillitis, D. Acute laryngitis
A: Acute epiglottitis
Answer: A: Acute epiglottitis 
Explanation: Thumb sign is typically seen in acute epiglottitis due to swollen epiglottis. It is better appreciated in lateral view of neck. Normally, the epiglottis is quite thin in the anteroposterior (AP) dimension, resembling a little finger, whereas the abnormal, inflamed epiglottis appears shoer and has an increased AP dimension, resembling a thumb. Acute epiglottitis is usually caused by infection with H influenzae type B.