dag2017@med.cornell.edu

The reverse halo sign is a lung finding on CT in which there is a consolidation with central ground glass. It was once considered to be highly specific for a diagnosis of cryptogenic organizing pneumonia. There are now many recognized causes of the reverse halo sign, or atoll sign. The purpose of this exhibit is to: review the imaging features of the reverse halo sign and what this finding corresponds to on a microscopic level review the various diseases that result in the reverse halo sign review clinical features and other imaging findings in addition to the reverse halo sign that may narrow the differential diagnosis

Examples of the reverse halo sign with pathologic correlates. Diseases that cause the reverse halo sign Organizing pneumonia Pulmonary Infarct (due to pulmonary embolus or percutaneous ablation) Post-radiation therapy Invasive fungal pneumonia (aspergillosis and mucormycosis) Necrotizing Vasculitis - granulomatosis with polyangiitis and eosinophilic granulomatosis with polyangiitis Primary lung adenocarcinoma Lymphoma Resolving bacterial pneumonia Lipoid pneumonitis