Figure 2. In A, axial CT scan of the chest of an asymptomatic, immunocompetent 54-year-old male patient, showing a right lower lobe pulmonary nodule surrounded by areas of ground-glass opacity (the CT halo sign); the final diagnosis was primary adenocarcinoma. In B, axial CT scan of the chest of an immunosuppressed 19-year-old male patient, showing multiple, randomly distributed pulmonary nodules surrounded by ground-glass opacities (the CT halo sign); the final diagnosis was aspergillosis.