## **Core Concept**
The question tests the understanding of diagnostic imaging features of active pulmonary tuberculosis (TB) using computed tomography (CT) scans. Active pulmonary TB is characterized by specific radiological findings that help differentiate it from latent or inactive TB. The key is to identify features that indicate active disease.

## **Why the Correct Answer is Right**
The correct answer, **Cavitary lesions**, is a feature of active pulmonary TB. Cavitary lesions are air-filled cavities within the lung parenchyma, often seen in active TB due to caseous necrosis and subsequent expulsion of necrotic material into the airspaces. These lesions are typically thick-walled and can be single or multiple. They are a hallmark of post-primary or active TB.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Ground-glass opacification can be seen in various lung conditions, including infections, but it is not specific for active TB. While it can be a feature, it is not as specific or diagnostic as cavitary lesions for active pulmonary TB.
- **Option B:** Fibrotic changes are more indicative of healed or latent TB rather than active disease. These changes include scarring and volume loss, which are sequelae of previous TB infection rather than signs of active inflammation or disease progression.
- **Option D:** Tree-in-bud pattern, while indicative of endobronchial spread of TB, is indeed a feature of active TB but the question seems to be pointing towards a more specific and overt sign like cavitary lesions.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that while cavitary lesions are highly suggestive of active pulmonary TB, they are not present in all cases. The presence of these lesions, along with symptoms such as cough, fever, night sweats, and weight loss, significantly supports the diagnosis of active TB. CT scans provide more detailed images than chest X-rays and are particularly useful in identifying these features.

## **Correct Answer:** . Cavitary lesions