In Mycobacterium avium complex pulmonary disease, which imaging finding is most typical?

• A. Cavitary lesions in the upper lobes
• B. Diffuse interstitial markings without nodules
• C. Pleural effusions with lymphadenopathy
• D. Scattered small nodules in the middle and lower lobes

Answer: (D)

In MAC pulmonary disease, the most typical imaging pattern is a nodular/bronchiectatic form. This shows bronchiectasis with scattered small nodules, reflecting infection and inflammation of the small airways. The distribution commonly centers in the middle lobe and lingula, with nodules along bronchovascular bundles and around the bronchi. That combination—bronchiectasis plus small nodules in the middle to lower lung regions—is classic for MAC and helps distinguish it from other mycobacterial infections.

Cavitary lesions in the upper lobes are more characteristic of the fibrocavitary form of MAC or reactivation TB, not the nodular/bronchiectatic pattern. Diffuse interstitial markings without nodules don’t fit the typical MAC appearance, and pleural effusions with lymphadenopathy are not the hallmark of MAC PDis. So scattered small nodules in the middle and lower lobes best reflect the common MAC imaging presentation.