Ipilimumab-Induced Organizing Pneumonia on 18F-FDG PET/CT in a Patient With Malignant Melanoma.

A 60-year-old woman with history of vaginal malignant melanoma and inguinal nodal metastases underwent F-FDG PET/CT for restaging following ipilimumab (Yervoy) immunotherapy, a Food and Drug Administration-approved human monoclonal antibody targeting cytotoxic T-lymphocyte-associated antigen 4. PET/CT demonstrated mildly FDG-avid multifocal enlarging bilateral lung opacities. Within each lung lesion, there was circumferential uptake localizing to a high-attenuation rim with a photopenic ground-glass center on CT, consistent with "reversed halo sign." Patient was asymptomatic at the time of imaging. Ipilimumab was discontinued, and 3-month follow-up PET/CT revealed spontaneous complete resolution of the lung lesions, supporting the diagnosis of ipilimumab-induced organizing pneumonia.