Reversed Halo Sign on Computed Tomography: State-of-the-Art Review

Abstract

The reversed halo sign (RHS) is a chest computed tomography (CT) pattern defined as a focal round area of ground-glass attenuation surrounded by a crescent or ring of consolidation. The RHS was first described as being relatively specific for cryptogenic organizing pneumonia but was later observed in several other infectious and noninfectious diseases. Although the presence of the RHS on CT may help narrow the range of diseases considered in differential diagnoses, final diagnoses should be based on correlation with the clinical scenario and the presence of additional disease-specific CT findings. However, frequently a biopsy may be needed to establish the diagnosis. Organizing pneumonia is the most frequent cause of the RHS. This is a distinct clinical and pathologic entity that can be cryptogenic or secondary to other known causes. Morphologic aspects of the halo, particularly the presence of small nodules in the wall or inside the lesion, usually indicate an active granulomatous disease (tuberculosis or sarcoidosis) rather than organizing pneumonia. Immunocompromised patients presenting with the RHS on CT examination should be considered to have an infection until further analyses prove otherwise. Pulmonary zygomycosis and invasive pulmonary aspergillosis are typically seen in patients with severe immunosuppression, most commonly secondary to hematological malignancies. Other causes of the RHS include noninvasive fungal infections such as paracoccidioidomycosis, histoplasmosis, and Pneumocystis jiroveci pneumonia. Furthermore, Wegener's granulomatosis, radiofrequency ablation, and lymphomatoid granulomatosis may also lead to this finding. Based on a search of the PubMed and Scopus databases, we review the different diseases that can manifest with the RHS on CT.

CT morphological features of the reversed halo sign in pulmonary paracoccidioidomycosis

“…This smooth appearance has been described in a variety of diseases, 9,12,14,19 especially in OP, which is the most common cause of this sign. 18 Hence, this feature alone cannot be used to distinguish PCM from OP.…”

“…Several authors have attempted to document the presence of multiple RHSs in a wide spectrum of diseases, such as cryptogenic OP (COP), tuberculosis, sarcoidosis, invasive fungal infections and granulomatosis with polyangiitis. 10,12,[17][18][19][20] Nevertheless, in a study comparing RHS characteristics in tuberculosis and COP, 18 solitary and multiple lesions were observed in both diseases. Indeed, although multiple RHSs were found in all patients with PCM in our study, this finding is not specific.…”

“…10,11,18,21 Histopathological analysis has revealed the presence of granulomas within the ring portion of and/or inside the RHS. 12,18 Hence, this RHS characteristic is attributed to the presence of multiple granulomas and may be useful in differential diagnosis. 18 Neither pattern (nodular walls or internal nodularity) has been described in any patient with OP.…”

“…18 Neither pattern (nodular walls or internal nodularity) has been described in any patient with OP. 12,18 Although active tuberculosis is highly suspected in patients presenting the RHS with nodular walls, especially in association with centrilobular nodules and endobronchial spread, 10,11,14 PCM should be Reticulation 0 (0%) Figure 5. 69-year-old male with pulmonary paracoccidioidomycosis.…”

“…The presence of small nodules in the wall or inside the RHS lesion indicates active granulomatous disease, 6,10,11 and reticulation in the centre of the halo suggests diseases or conditions that cause pulmonary infarction, such as invasive pulmonary aspergillosis and pulmonary embolism (PE). 12,13 The recognition of specific characteristics of the RHS associated with pulmonary PCM has important clinical implications that may enable the early institution of treatment.…”