Abstract Background It has been accepted that reversed halo sign (RHS) appeared on a computed tomography (CT) image in immunocompromised patients indicates an invasive fungal infection, but its pathophysiology remains obscure as to what this image implies. Therefore, the present report describes detailed radiological and histopathological findings of a case of invasive pulmonary mucormycosis (IPM) presenting RHS with comparison to those from a lesion of discrete nodule caused by invasive pulmonary aspergillosis (IPA), and discusses the pathophysiological implications of this characteristic image. Case presentation RHS had been clinically noted at the time of recovering of bone marrow function of a 64-year-old Japanese man who had chemotherapy for his acute lymphoblastic leukemia. Histological examination of the surgically removed lung revealed a lesion of IPM. This was composed of coagulation necrosis of septa at the center of lesion with preservation of air content which was encompassed outer rim comprising triplet structure; liquefaction, consolidation, and organization from the inner to the outer layer. In addition, Micro-CT examination confirmed reticular structure and monotonous high density at the central coagulation necrosis preserving air content and surrounding consolidation, and organization lesion of the IPM lesion. Conclusion Our investigations suggest that RHS might be understood as a kind of immune reconstitution syndrome and be the initial and prior status of air crescent sign. Virtual Slides The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/3480054198968132