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: Radiology
Active pulmonary TB can be diagnosed on CT-scan by following finding ? 
Select and explain. 
A. Tree in bud appearance, B. Honey comb appearance, C. Ground glass appearance, D. Signet ring sign
A: Tree in bud appearance
Answer: A: Tree in bud appearance 
Explanation: Ans. is 'a' i.e., Tree in bud appearance(Ref Chapman 4n/e p.142,143; Fundamentals of radiology) Tree-in-bud sign or pattern describes the CT appearance of multiple areas of centrilobular nodules with a linear branching pattern.This is a characteristic sign of active pulmonary TB.Other impoant sign of pulmonary TB on CT is lymph nodes showing peripheral rim enhancement because of necrosis.