COVID-19 pneumonia: the great radiological mimicker

Abstract

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has rapidly spread worldwide since December 2019. Although the reference diagnostic test is a real-time reverse transcription-polymerase chain reaction (RT-PCR), chest-computed tomography (CT) has been frequently used in diagnosis because of the low sensitivity rates of RT-PCR. CT findings of COVID-19 are well described in the literature and include predominantly peripheral, bilateral ground-glass opacities (GGOs), combination of GGOs with consolidations, and/or septal thickening creating a "crazy-paving" pattern. Longitudinal changes of typical CT findings and less reported findings (air bronchograms, CT halo sign, and reverse halo sign) may mimic a wide range of lung pathologies radiologically. Moreover, accompanying and underlying lung abnormalities may interfere with the CT findings of COVID-19 pneumonia. The diseases that COVID-19 pneumonia may mimic can be broadly classified as infectious or non-infectious diseases (pulmonary edema, hemorrhage, neoplasms, organizing pneumonia, pulmonary alveolar proteinosis, sarcoidosis, pulmonary infarction, interstitial lung diseases, and aspiration pneumonia). We summarize the imaging findings of COVID-19 and the aforementioned lung pathologies that COVID-19 pneumonia may mimic. We also discuss the features that may aid in the differential diagnosis, as the disease continues to spread and will be one of our main differential diagnoses some time more.

Keywords: COVID-19; Chest CT; Differential diagnoses; Mimicker; Pneumonia.

Fig. 1

CT findings of COVID-19 pneumonia. a The first CT scan obtained on illness day 4 revealed patchy GGOs in both the lungs. b On day 8, the number and size of GGOs increased. c Consolidations were the dominant CT finding on day 14

Fig. 2

Other infectious diseases that COVID-19 pneumonia may mimic. a Axial CT image shows a consolidation with rounded morphology in the right lower lobe. Hemophilus influenza was detected in the respiratory panel. b Similar round consolidation is observed in the right upper lobe. The patient was tested positive on RT-PCR for COVID-19 pneumonia. The respiratory panel was negative for other causes. c Axial CT image shows GGOs with associated consolidations in a patient with Hemophilus influenza pneumonia. d In a patient diagnosed with COVID-19 pneumonia, bilateral GGOs with consolidations are observed on axial CT image similar to (c). e Axial CT image shows GGOs in bilateral upper lobes in an immunosuppressed patient compatible with PJP infection. f Bilateral upper lobe GGOs in a patient diagnosed with COVID-19 pneumonia. GGOs superimposed on emphysematous parenchyma may interfere with PJP. Subpleural sparing is in favor of PJP. g Axial CT image shows bilateral consolidative opacities in lower lobes in a patient diagnosed with influenza A pneumonia. h In a patient diagnosed with COVID-19 pneumonia, bilateral opacities are observed in lower lobes

Fig. 3

Fungal infection and COVID-19 pneumonia. a, b Axial (a) and sagittal (b) CT images show bilateral nodular opacities in a patient diagnosed with microbiologically proven aspergillosis. c, d Axial (c) and sagittal (d) CT images show nodular opacities in a COVID-19 patient. Note that the central part of the opacities in COVID-19 pneumonia has a relatively lower density (d)

Fig. 4

Bacterial super-infection in COVID-19 pneumonia. CT scan was obtained in a patient previously diagnosed with COVID-19 pneumonia upon clinical deterioration. Axial CT image shows bilateral peribronchovascular nodular GGOs, centrilobular nodular opacities, and consolidations in the right lung. Peripherally located GGOs are observed in the right middle lobe. Respiratory tract sample was positive for Hemophilus influenza

Fig. 5

Distribution of ground-glass opacities in pulmonary edema and COVID-19 pneumonia. a, b Bilateral predominantly central GGOs are observed in a patient with pulmonary edema. Subpleural sparing is seen. There is also cardiomegaly and bilateral pleural effusion (asterisks). c, d In two different COVID-19 patients, diffuse GGOs are seen in bilateral upper lobes on axial CT images. The absence of ancillary findings such as pleural effusion and cardiomegaly may help in the differential diagnosis

Fig. 6

COVID-19 pneumonia-mimicking vasculitic diseases. a Axial CT image of a patient diagnosed with granulomatosis with polyangiitis shows bilateral upper lobe GGOs with superimposed septal thickenings due to hemorrhage. Bilateral minimal pleural effusion is seen (asterisks). b Similar bilateral upper lobe GGOs with superimposed septal thickenings are observed in COVID-19 pneumonia. c Bilateral mostly peripheral subtle GGOs in a patient diagnosed with eosinophilic granulomatosis with polyangiitis (Churg-Strauss)(arrows). d Peripheral subtle GGOs are seen in a COVID-19 patient as an early finding (arrows)

Fig. 7

COVID-19 pneumonia-mimicking adenocarcinoma of the lung. a Axial chest CT image shows a rounded focal opacity histopathologically proven to be adenocarcinoma in the right upper lobe (arrow). b–d CT images of three different COVID-19 patients demonstrating unifocal round opacities mimicking adenocarcinoma (arrows)

Fig. 8

COVID-19 pneumonia-mimicking multifocal adenocarcinoma of the lung. a, b Multiple randomly distributed GGOs with superimposed septal thickening in both lungs, histopathologically proven to be adenocarcinoma. c, d Multiple GGOs in a COVID-19 patient with rounded morphology and superimposed septal thickenings mimicking multifocal adenocarcinoma

Fig. 9

COVID-19 pneumonia mimicking hemorrhagic metastases. a Multiple bilateral GGOs with superimposed intralobular septal thickenings in a patient with hemorrhagic epithelioid angiosarcoma metastases. b In a patient diagnosed with COVID-19 pneumonia, bilateral multiple GGOs with superimposed intralobular septal thickenings are observed in the upper lobes

Fig. 10

The reverse halo sign in cryptogenic organizing pneumonia and COVID-19 pneumonia. a Axial CT image showing organizing pneumonia presenting with reverse halo sign (arrows). b A rounded opacity with reverse halo sign and surrounding GGOs in the right lower lobe in COVID-19 pneumonia (arrow). GGOs are seen in the right middle lobe and medial right lower lobe (white arrows)

Fig. 11

Drug toxicity and COVID-19 pneumonia. a Bilateral peripheral GGOs are observed in the axial CT image of a patient receiving bleomycin chemotherapy for testicular malignancy. Following the discontinuation of the drug, opacities were completely resolved. b In a patient diagnosed with COVID-19 pneumonia, bilateral multiple GGOs resembling (a) are seen

Fig. 12

Crazy-paving pattern. a, b Crazy-paving pattern in pulmonary alveolar proteinosis (PAP). c, d Axial CT images of a patient with COVID-19 show widespread GGOs with crazy-paving pattern in both lungs

Fig. 13

The reverse halo sign in sarcoidosis and COVID-19 pneumonia. a Sarcoidosis presenting with organizing pneumonia pattern, peripheral GGOs, and reverse halo signs (arrows). b Opacities in COVID-19 pneumonia with reverse halo sign in right lower lobe (arrow). Concomitant multifocal opacities are observed

Fig. 14

Pulmonary infarction and COVID-19 pneumonia. a Axial CTA image in the mediastinal window shows thrombi in pulmonary artery branches (white arrows). b In the same patient, pulmonary infarction is seen as a subpleural wedge-shaped opacity in the right lung (arrow). c Pulmonary CT angiography was obtained in a patient presented with shortness of breath to the emergency department. CT angiography showed subpleural opacities, but there was no thrombus in the related pulmonary artery branch (arrow). The patient’s COVID-19 RT-PCR result turned out to be positive

Fig. 15

COVID-19 pneumonia-mimicking interstitial lung disease. a, b In desquamative interstitial pneumonia (DIP), bilateral peripheral GGOs are observed. c, d Axial CT image showing bilateral subpleural GGOs and opacities in a patient diagnosed with COVID-19

Fig. 16

Eosinophilic pneumonia and COVID-19 pneumonia. a Nodular GGOs are seen in the right upper lobe in a patient diagnosed with eosinophilic pneumonia (arrows). b, c Axial CT images of a patient with COVID-19 show nodular GGOs in the right lower lobe (arrows)

Fig. 17

Aspiration pneumonia and COVID-19 pneumonia. a The patient had a stroke and was intubated. Axial CT image shows bilateral lower lobe consolidations and centrilobular nodular opacities (arrows) suggestive of aspiration pneumonia. b Contrast-enhanced CTA was obtained for suspected pulmonary embolism in a patient diagnosed with COVID-19 pneumonia. CT image shows bilateral consolidations in lower lobes and scattered foci of GGOs (arrows)