COVID-19 CT scan

Non-contrast Chest CT scan is an effective method for the rapid diagnosis of COVID-19 and monitoring the disease progression. Chest CT scan findings in patients infected with coronavirus can include unilateral or bilateral pneumonia, mottling and ground glass opacity, focal or multifocal opacities, consolidation, and septal thickening with subpleural and lower lobe involvement.

• Non-contrast Chest CT scan is an effective method not only for the rapid diagnosis of COVID-19 but also for monitoring the disease progression. ^[1]
• Given the high sensitivity of chest CT, it can be used in suspected patients with negative RT-PCR. ^[2]
• Various chest CT features have been found diagnostic for COVID-19 that are associated with:
  • Duration of illness
  • Severity of illness

• Bilateral ground glass opacities ± consolidation in posterior and peripheral lung regions are considered as the hallmark for COVID-19. ^[3]
• However, there are a large number of typical and atypical chest CT findings for COVID-19 that are summarized in the figure below. ^{[4] [5]}

• Findings on chest CT scan suggestive of COVID-19 are summarized in the table below.^[4][6][7]

CT manifestations of COVID-19
CT findings	Definition	CT picture
Ground glass opacity	Hazy opacity in the lungs with well defined bronchial and vascular margins the most common imaging finding due to infection, chronic interstitial lung disease, and acute lung injury
Consolidation	a parenchymal density with ill-defined bronchial and vascular margins filling with infectious material [fluid, cells, tissue] due to cellular exudates in alveoli The presence of consolidation is a sign of disease progression
Crazy paving pattern	Septal thickening of inter and intra-lobar regions with the background of the Ground glass opacity Similar to paving stones Due to alveolar edema and acute inflammation of the lung Sign of progression
Reticuldar pattern	Linear opacities in the lungs Due to Interstitial thickening of inter and intralobular septa
Air bronchogram	Air-filled bronchi Low attenuated areas in the lung
Bronchiectasis	Irreversible dilatation of the lung airways Bronchus diameter more than 1.5 cm due to inflammation, obstruction and impaired clearance
Pleural effusion	Accumulation of fluids in the pleural space The presence of pleural effusion in COVID-19 is associated with poor prognosis.

• Chest CT scan findings in patients infected with COVID-19 are usually:
  • Bilateral peripheral lung opacities^[8]
  • without subpleural sparing

• Right and left lower lung lobes were the most common involved lobes (65% and 63%) in COVID-19. ^[6]

• Time interval between onset of symptoms and chest CT manifestations is classified into 3 stages^[6]:
  • Early: between 0-2 days
  • Intermediate: between 3-5 days
  • Late: between 6-12 days
• Ground-glass opacities and consolidation are more likely to develop in the intermediate and late stages. ^[6]
• Linear opacities, crazy-paving pattern, and reverse halo sign usually develop during the late stages. ^[6]

• The presence of lymphadenopathy and pericardial effusion are associated with severe COVID-19 pneumonia. ^[4]
• chest CT manifestations are usually resolved within 14 days of symptoms onset. ^[9]

The Radiological Society of North America (RSNA) classified CT findings of COVID-19 infection into four categories which were endorsed by the Society of Thoracic Radiology and the American College of Radiology (ACR):