Dr KK Aggarwal
Chest x-ray (CXR) is typically the first line imaging modality for patients with suspected Covid-19, although less sensitive than chest CT. It may be normal in early or mild disease. Even with serious disease, about 31% had normal CXR at the time of admission. Findings are most extensive about 10-12 days after onset of symptoms.
Findings ofCof most frequent are airspace opacities (described as consolidation or ground glass opacities), which are often bilateral, peripheral and mainly in the lower zone. Pleural effusion is very rare (if patient has pleural effusion, chances are that it may not be Covid).
Oblique CXR is done when lesion (subpleural or close to chest cavity) is not seen on routine AP view but there may be some data on CT.
Point of care ultrasound: It is useful to monitor disease progression in patients who have hypoxemia and hemodynamic failure. It is not a sensitive and specific modality, but its advantages are inexpensive, ease of use, repeatability and no exposure to radiation. However, there is high risk of exposure to the operator, so used less.
Findings on USG: Multiple B-lines, subpleural consolidation, irregular thickened pleural line with scattered discontinuities, alveolar consolidation, reappearance of bilateral A-lines; return of normal A-lines from B-lines suggest that the patient is improving.
CT chest: A systematic meta-analysis of 49 studies of CT features of Covid-19 by CARING showed that the commonest finding at all stages of the disease was diffuse bilateral ground glass opacity. The next common findings were consolidations and mixed density lesions. Around 78% of patients with RT-PCR positive had either ground-glass opacities or consolidation or both.
There is a significant overlap of CT scan findings between Covid and non-Covid patients, who present as SARI or ILI.
Common CT findings: Ground glass opacities, consolidation, mixed lesions, crazy paving pattern, reticulations, septal thickening (can be inter- or intra-lobular; commonly seen in advanced disease)
Specific CT findings: Halo sign, reverse Halo sign (focal rounded area of GGO surrounded by a complete ring of consolidation; one of the typical findings of Covid-19 as per RSNA), spider web sign, pulmonary vessel engorgement (prominent pulmonary vessels in relation to the lesions; it is a potential early predictor of lung impairment), vacuolar sign (vacuole-like transparent shadow <5mm in length observed in the lesion)
findings: Architectural distortion, lymph node enlargement and pleural effusion
In initial stages, GGOs can be unilateral and patchy progressing to multifocal confluent lesions with advancing disease.
If crazy paving pattern and vascular engorgement, the patient needs to be treated more aggressively.
Pulmonarye is emerging as main pathogenesis in Covid-19, which can lead to pulmonary infarction. A contrast-enhanced CT pulmonary angiography is done when PE is suspected.
CTseverity score: it scores lung opacities in all 6 lung zones (3 on each side), the sum of scores from all 6 is the overall CT score (maximum score 24). The severity of lung involvement on CT correlates with disease severity
.Extra-thoracic Covid manifestations: Covid-19-associated acute hemorrhagic necrotizing encephalopathy, multisystem inflammatory syndrome (airway inflammation and rapid development of pulmonary edema on thoracic imaging, coronary artery aneurysms and extensive right iliac fossa inflammatory changes on abdominal imaging)
CT should not be used as initial screening or diagnostic tool. It can be used to identify early markers for lung impairment in symptomatic patient with RTPCR positive for Covid-19 or for patients with non-resolving symptoms to evaluate disease progression.
The role of CT in stable pediatric patients is limited.X-ray should not be used as initial screening tool for Covid-19. In suspected patients with history of fever, dry cough, do a RT PCR first instead of chest x-ray.
All patients coming to Radiology with any respiratory symptoms should be considered a potential Covid-19 patient. Accordingly, all precautions should be taken. No mixing with other patients, maintain social distancing, sanitize equipment before using it for the next patient.Portable x-rays are used for temporal progression and resolution and also for serial follow-ups. Use a dedicated machine wherever logistically possible.