What is pulmonary interstitial emphysema?

• A. Air dissecting upward into the soft tissues of the neck
• B. Trapped collections of air in the acinus portion of the lung
• C. Air released into the tissues surrounding the bronchi
• D. An airless section of the lung

Answer: (C)

Pulmonary interstitial emphysema occurs when air escapes from alveoli into the lung’s interstitial spaces, typically tracking along the peribronchovascular interstitium around the bronchi and vessels. This makes air reside in the tissues surrounding the bronchi, which is exactly what the option describes. In neonates on positive-pressure ventilation, this interstitial air can extend and even spread toward the mediastinum or chest wall, but the defining feature is air within the interstitial tissue itself rather than in the airway lumen or outside the lung.

Other ideas described in the distractors aren’t the same: air dissection into the neck tissues would be subcutaneous emphysema extending from the chest; trapped air in the acinus points to alveolar-level air spaces rather than the interstitial space; an airless region would be atelectasis, not interstitial emphysema.