A 49-year-old man with acute myeloid leukemia developed fever and hypoxemia while undergoing induction chemotherapy. He had been severely neutropenic (absolute neutrophil count < 500 cells/μL) for 16 days and was not on antifungal prophylaxis. Contrast-enhanced computed tomography of the chest showed a focus of ground-glass opacity surrounded by a 1.5 cm rim of consolidation, known as the reverse halo sign (RHS) (Fig. 1). Polymerase chain reaction testing of bronchial washings detected Rhizopus microsporus DNA, consistent with invasive pulmonary mucormycosis (IPM).

Figure 1
figure 1

The reverse halo sign. Contrast-enhanced computed tomography of the chest showing a focal lung lesion with central ground-glass opacity (black arrow) surrounded by dense consolidation (yellow arrow), known as the reverse halo sign.

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The RHS has been identified in numerous noninfectious diseases.1,2 However, in an immunocompromised host, it is presumed to indicate an invasive fungal pneumonia, particularly when the rim of consolidation is thicker than 1.0 cm.3,4,5,6 The RHS occurs more often in IPM than invasive pulmonary aspergillosis (IPA) and strongly predicts IPM in immunocompromised hosts.3,4,7,8,9 Therefore, the presence of the RHS in an immunocompromised host should prompt clinicians to consider initiating liposomal amphotericin B (the preferred initial treatment of IPM) instead of voriconazole (the preferred treatment for IPA, but without activity against IPM).10,11 Recognizing the clinical significance of the RHS may improve patient outcomes by allowing for early initiation of appropriate antifungals and timely surgical consultation to consider resection.11,12