Objective: The reversed halo sign (RHS) is a rare finding of chest computed tomography (CT) for coronavirus disease-2019 (COVID-19) pneumonia. This study aimed to examine the frequency and characteristics of RHS in chest CT examinations of patients with reverse transcription-polymerase chain reaction (RT-PCR)-confirmed COVID-19, to evaluate the relationship between this finding and the clinical course, and to contribute to the differential diagnosis.

Methods: Chest CT data of 1500 patients who had positive RT-PCR tests for suspected COVID-19 pneumonia between March 16, 2020, and April 26, 2020, were evaluated retrospectively. This study included 49 patients with RHS. Patients were classified into two groups as the hometreated group and hospitalized group. The number of RHS; their craniocaudal, lobar, and peripheral-central distribution; morphological features of the wall structure; change over time; and additional findings were evaluated.

Results: Of the patients with RHS, 27 (55%) were treated at home, while 22 (45%) were treated in the hospital. The number of RHS lesions was higher in the hospitalized group. Lower zone involvement and predominance were common in both groups. The home-treated group mostly had oval-shaped lesions (44%), while oval- and round-shaped lesions were common in the hospitalized group (55%). The wall thickness of the reversed halo ring was greater in the hospitalized group. Incomplete ring morphology was common in both groups. Laboratory examinations showed a significant difference between the groups in terms of the monocyte counts and C-reactive protein and D-dimer levels (p=0.04, p=0.002, and p=0.023, respectively).

Conclusion: RHS plays an important role in the differential diagnosis of COVID-19 pneumonia from other diseases based on its characteristic distribution pattern and morphological features.