The reversed halo sign with a reticulonodular pattern as unusual findings of pulmonary infarct in acute pulmonary embolism: case report and literature review

Abstract

The reversed halo, also known as the atoll sign, is a distinct sign with ring-shaped consolidation and central lucency. The reversed halo sign, initially emerging in cryptogenic organizing pneumonia, has been observed in various pulmonary diseases, including pulmonary embolism. The presence of this sign in the subpleural, posterior basal parts of the lower lobes, predominantly when solitary, should raise the possibility of other causes, such as pulmonary infarction. We present a case of acute pulmonary embolism with pulmonary infarction discovered on a CT pulmonary angiogram in our emergency department, where the pulmonary infarction appears as a reverse halo sign with a reticulonodular pattern. The reticular nodular pattern in the halo sign is not typical of a pulmonary infarct presenting with a reverse halo sign. To our knowledge, this is the first case of pulmonary infarction in acute pulmonary embolism with the appearance of a reverse halo sign with a reticulonodular pattern.