COVID-19 began in Wuhan in December, 2019 with the emergence of new pneumonia cases that presented with features similar to those caused by SARS and MERS virus. Coronavirus belonged to the family of coronaviridae, and therefore caused features similar to the SARS and MERS virus which also belong to the same family. In about 30 percent of COVID-19 cases, there is lung injury that results in acute respiratory distress; this lung injury is most evident on high resolution chest CT (HRCT), which has both diagnostic and prognostic value. HRCT facilities are available in the same labs that also perform mri in islamabad.
What are the HRCT changes in COVID-19?
In COVID-19 positive patients, high-resolution CT changes, as per evaluation by the expert radiologists showed lung consolidations as well as broncho-vascular thickenings.
Ground glass opacities (GGO) on the HRCT are the most common finding in the COVID-19 patients. These bilateral (present in both lungs), multifocal opacities are mostly present on the periphery that may appear unifocal in the early phase of disease.
The most common site of these ground glass opacities is in the right lung—inferior lobe; the middle lobe is less frequently involved Another typical finding in the region of ground glass opacities is the widened vasculature and traction bronchiectasis.
Crazy paving pattern is also observed in the later stage of disease. Crazy paving appears when there are thickened interlobular (inside the lobes) and interlobular (between the lobes) lines in addition to the ground glass opacities.
Subpleural bands along with distortion of the lung architecture is also found in some cases.
What is the CT involvement score?
Based on the finding on the HRCT, lung involvement is given a score. Higher score corresponds to a more serious illness. There are two methods for the severity assessment, based on the visual appearance and by scoring the percentage of the lobes involved. The total score can range from 0 to 25, with 0 showing no involvement and 25 showing maximal involvement.
What are the changes on the HRCT over time
In the early stages of disease, from the first to fourth day, there is a lower number of involved lobes with ground glass opacities and partial crazy paving.
In the progressive stage of disease from fifth to eighth day, there is extension of ground glass opacities with increase in crazy paving pattern.
In the peak stage from day ten to thirteen, there is consolidation in the lungs with gradual resolution in the absorption stage two weeks after onset.
What are the changes on HRCT in the advanced stage?
In the advanced-phase of disease there is an increase in the frequency of ground glass opacity. Moreover, there is an overlaying reticular pattern of crazy paving, fibrotic streaks, pleural effusion, distortion of the bronchi, vacuolar sign and appearance of the subpleural line.
Comparing the HRCT and the chest x-ray
In the early phase of disease, the chest x-ray alone is insufficient for diagnosis. Even when there are ground glass opacities in the HRCT, the chest x-ray done at the same time would not show any changes. However, for the follow-up of the disease, chest x-ray is a useful investigation. It can show consolidation and ground-glass opacification. Labs that perform chest x ray in Islamabad are readily available. HRCT, on the other hand, can play a role in triage of the COVID-19 patient, help in making the diagnosis with more accurate scoring of disease severity, predict if the patient is going to take a turn for the worse, or improve with therapy.
