Atypical chest radiological features in Covid 19: Case based review

Chest imaging plays an important role in the diagnosis and management of patients with COVID-19. Some patients may have atypical lesions on chest image. Awareness about the atypical imaging features is essential to avoid misdiagnosis/delayed diagnosis. Atypical chest imaging features in COVID-19 include central involvement, peribronchovascular involvement, isolated upper lobe involvement, nodular involvement, lobar consolidation, solitary involvement, unilateral lung involvement, interstitial emphysema, pneumomediastinum, subcutaneous emphysema, pneumothorax, hydropneumothorax, mediastinal adenopathy, cavitory lesions, bulls eye sign, necrotizing pneumonia with abscess, empyema, pleural and pericardial effusion, and subpleural sparing. In patients with atypical chest imaging features, when RT-PCR test results are positive diagnosis is certain. Diagnostic difficulty may arise when RT-PCR test results are negative. In such cases a proper epidemiologic history, typical clinical features, and exclusion of other causes for a similar chest imaging features may help in diagnosis. Causes for atypical chest imaging features include early stage of the disease when lesion can be unilateral or focal or single, late stage of the disease when lesions regress, coexisting diseases/conditions, preexisting lung parenchymal diseases, fluid overload, complications like other bacterial/ fungal infection/tuberculosis/barotrauma or involvement of other organs like kidney, heart, or liver which may lead to pleural effusion. Iatrogenic trauma, barotrauma, or drug-induced immunosuppression leading to opportunistic infections can also lead to chest imaging features. Some of the CT features like cavitory lesion, mediastinal adenopathy, and pleural and pericardial effusion may be due to complications during the course of the disease or coexistent diseases. In this pictorial essay we discuss some atypical chest images with salient learning points from each case. Awareness about the atypical chest imaging features is essential to avoid misdiagnosis/delayed diagnosis. Some of the atypical features may require further evaluation/follow up and management.