The reversed halo sign: update and differential diagnosis

Abstract

ABSTRACT. The reversed halo sign is characterised by a central ground-glass opacity surrounded by denser air-space consolidation in the shape of a crescent or a ring. It was first described on high-resolution CT as being specific for cryptogenic organising pneumonia. Since then, the reversed halo sign has been reported in association with a wide range of pulmonary diseases, including invasive pulmonary fungal infections, paracoccidioidomycosis, pneumocystis pneumonia, tuberculosis, community-acquired pneumonia, lymphomatoid granulomatosis, Wegener granulomatosis, lipoid pneumonia and sarcoidosis. It is also seen in pulmonary neoplasms and infarction, and following radiation therapy and radiofrequency ablation of pulmonary malignancies. In this article, we present the spectrum of neoplastic and non-neoplastic diseases that may show the reversed halo sign and offer helpful clues for assisting in the differential diagnosis. By integrating the patient's clinical history with the presence of the reversed halo sign and other accompanying radiological findings, the radiologist should be able to narrow the differential diagnosis substantially, and may be able to provide a presumptive final diagnosis, which may obviate the need for biopsy in selected cases, especially in the immunosuppressed population.

Reversed Halo Sign in Invasive Fungal Infections

“…The RHS has been reported in a wide spectrum of diseases, including noninfectious diseases and infectious diseases such as invasive fungal infections (IFIs). (4,5) Because of this broad differential diagnosis, the RHS is considered a nonspecific sign. However, certain morphological characteristics of the RHS can aid in establishing a diagnosis.…”

“…In immunocompromised patients, a reticular pattern within the halo and a thick rim of consolidation are highly suggestive of IFI. (4,5) With regard to the reticular RHS, information regarding the immunological status of the patient is fundamental for the differential diagnosis. In immunocompetent patients, the reticular RHS corresponds, as a rule, to pulmonary infarction, usually secondary to thromboembolic disease.…”

“…Although the final diagnosis should be based on the clinical manifestations, a lung biopsy is required in some cases. (4,5) IFIs are associated with high morbidity and mortality. Therefore, patients with IFI should be treated immediately, given that early administration of high-dose antifungal therapy has been associated with improved outcomes.…”

“…Therefore, patients with IFI should be treated immediately, given that early administration of high-dose antifungal therapy has been associated with improved outcomes. (4,5) Diagnosis can be challenging, especially for general radiologists encountering patients outside the context of transplantation centers, and any delay in treatment can significantly increase mortality. In conclusion, a reticular pattern within the RHS and a thick rim of consolidation in an immunocompromised patient are highly suggestive of IFI.…”

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.…”