An infant presents with unilaterally decreased breath sounds. Which condition must be considered?

• A. Pulmonary hypoplasia
• B. Bronchopulmonary dysplasia (BPD)
• C. Respiratory distress syndrome (RDS)
• D. Pneumonia

Answer: (A)

Unilateral decreased breath sounds point to a localized lung issue rather than a diffuse process affecting the entire lungs. Pulmonary hypoplasia fits this pattern because it is a developmental underdevelopment of one lung, leading to reduced airways, smaller lung volume, and diminished breath sounds on the affected side. It can be present at birth and may be associated with conditions like oligohydramnios, renal anomalies, chest wall abnormalities, or diaphragmatic compression, all of which create a lasting, localized deficit in ventilation that shows up as decreased breath sounds on the affected side.

Bronchopulmonary dysplasia and respiratory distress syndrome are typically diffuse processes that involve both lungs and present with widespread findings, crackles, and respiratory compromise rather than a localized decrease in sounds. Pneumonia can be unilateral, but the question’s focus on a persistent, localized reduction in breath sounds in an infant makes a developmental, hypoplastic lung the more fitting consideration. Imaging like a chest X‑ray would help confirm reduced lung volume on the side and may reveal mediastinal shift or other signs supporting hypoplasia.