Computed tomography halo sign in pulmonary nodules: Frequency and diagnostic value

On computed tomography (CT) scanning, a ground-glass opacity zone surroundi ng a pulmonary nodule has been named the computed tomography (CT) halo sign . To investigate the frequency and diagnostic value of the CT halo sign, th e authors reviewed the CT examinations of 305 patients with proven diseases producing solitary or multiple nodules. The CT halo sign was seen in 22 pa tients (7%). Eleven patients had a solitary nodule; five patients had multi ple nodules; and six patients had nodules associated with areas of pulmonar y consolidation, or ground-glass opacity, or both. Solitary nodules were th e result of bronchioloalveolar carcinoma (n = 5), tuberculoma (n = 2), squa mous cell carcinoma, non-Hodgkin lymphoma, myxovirus infection, and metasta sis (n = 1 each). Multiple nodules were the result of metastasis (n = 2), K aposi sarcoma (n = 2), and Wegener granulomatosis (n = 1). Nodules associat ed with areas of consolidation or ground glass opacity were the result of m etastasis (n = 2), bronchioloalveolar carcinoma, bronchiolitis obliterans o rganizing pneumonia, eosinophilic pneumonia, and invasive pulmonary aspergi llosis (n = 1 each). The data showed that the CT halo sign is a nonspecific finding. It is known that in immunocompromised patients the CT hdo sign sh ould suggest invasive pulmonary aspergillosis, Kaposi sarcoma, and lymphopr oliferative pulmonary disorders. However, in immunocompetent patients, the authors found that a solitary nodule with the CT halo sign and pseudocavita tions has a high likelihood of being a bronchioloalveolar carcinoma.