‘Bulla spread sign’ is seen in which of the following condition?
**Core Concept**
The bulla spread sign is a radiological feature that helps in diagnosing a specific pulmonary condition. It is observed in conditions where air leaks through the alveolar walls and spreads within the lung parenchyma.
**Why the Correct Answer is Right**
The bulla spread sign is typically seen in conditions where there is an abnormal communication between the alveoli and the airways, such as in bullous emphysema. As the bullae expand, they can spread along the airways, leading to the characteristic bulla spread sign on imaging studies. This is due to the transmission of air from the alveoli through the thin walls of the bullae into the adjacent alveoli.
**Why Each Wrong Option is Incorrect**
**Option A:** Pneumonia is characterized by inflammation of the lung parenchyma, which does not typically result in the bulla spread sign.
**Option B:** Pulmonary edema involves fluid accumulation in the lung interstitium and alveoli, which is not associated with air leaks or bulla spread.
**Option C:** Pulmonary atelectasis refers to collapse of lung tissue, which may show up as consolidation or ground-glass opacifications on imaging, but not typically the bulla spread sign.
**Clinical Pearl / High-Yield Fact**
The bulla spread sign is a key feature of bullous emphysema, and its presence on imaging studies can help differentiate this condition from other pulmonary abnormalities.
**Correct Answer:** D. Bullous emphysema.