**Question:** A 4-year-old child presents with a history of chronic left lower lobe pneumonitis. On contrast bronchography, the area involved with the pneumonitis does not fill, whereas the area around it does fill. The most likely diagnosis -

A. Bronchial atresia
B. Bronchial stenosis
C. Bronchial obstruction
D. Bronchogenic cyst

**Correct Answer:** D. Bronchogenic cyst

**Core Concept:**

Bronchography is a diagnostic procedure that uses contrast material to visualize the bronchial tree and its relation to the lungs. It is particularly useful in cases of suspected congenital abnormalities like bronchial tree anomalies, which can lead to chronic pneumonitis.

**Why the Correct Answer is Right:**

In the given scenario, the area of pneumonitis does not fill with contrast material on bronchography, whereas the surrounding area does fill. This suggests a congenital anomaly affecting the bronchial tree. A bronchogenic cyst is a rare congenital cystic lesion that arises from the abnormal development of the embryonic foregut. These cysts can obstruct the bronchial tree, leading to chronic pneumonitis and focal atelectasis (pneumonitis) as seen in the question.

**Why Each Wrong Option is Incorrect:**

A. Bronchial atresia is the complete absence of a bronchus, leading to a fixed airless area on imaging. In contrast, the correct answer shows a dynamic obstruction causing pneumonitis.

B. Bronchial stenosis refers to a narrowing of the bronchus, which would cause fixed areas of pneumonitis, not the focal atelectasis seen in this case.

C. Bronchial obstruction refers to a general narrowing or blockage of the bronchial tree, which does not explain the focal nature of the pneumonitis and atelectasis observed in the case.

**Clinical Pearl:**

Bronchogenic cysts are a rare cause of focal pneumonitis and should be considered in children presenting with chronic pneumonitis, even if the clinical presentation is not typical. This diagnostic clue from the imaging study of choice helps in reaching the correct diagnosis.