CTICasesNivolumab-Induced Organizing Pneumonia
Imaging findings
A patient with metastatic melanoma on nivolumab developed discrete, mass-like areas of consolidation in the right middle and right lower lobes with air bronchograms and subpleural sparing, initially called an infection at an outside facility. After the drug was stopped and high-dose steroids started, serial follow-up CTs over the next two months showed the consolidations evolving through a reverse-halo (atoll) appearance and clearing from the center outward as they shrank; however, after steroids were tapered, new nodules appeared in a similar, though smaller and more peripheral, airway-centered distribution, again with a reverse-halo appearance.
Key takeaways
Discrete, mass-like consolidations with air bronchograms and subpleural sparing in a patient on immune checkpoint inhibitor therapy should suggest drug-induced organizing pneumonia rather than infection or progressive metastatic disease, and the reverse-halo (atoll) sign that develops as the process heals is a helpful indicator of healing organizing pneumonia rather than worsening disease. These drug-induced organizing injuries often relapse if steroids are tapered too quickly, and, similar to chronic eosinophilic pneumonia and some cases of pericarditis, may require around six months of treatment because the underlying immune sensitization can persist even after the inciting drug is stopped.
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