CME INDIA Presentation by Dr. Hari Singh, Asst. Professor and Head, Department of Radiodiagnosis, SNMC, Agra.

  • COVID-19 (corona virus disease 2019) is a highly infectious viral disease, caused by a strain of corona virus.
  • The definitive diagnosis is made by positive RT PCR test, which is highly specific.
  • Imaging plays a very important role in diagnosis, management, monitoring of treatment and follow up.
  • Chest X ray and CT scan thorax are imaging modalities used in imaging of COVID patients.
  • Physicians these days must appraise the utility of HRCT.


Imaging approach for COVID-19 patients

Role of Chest X ray in COVID 19

  • Chest X ray plays an important role in imaging of COVID patients.
  • Chest X ray is considered primary imaging modality of choice for imaging of COVID patients because of its easy availability, portability, bed side facility, low cost and low radiation dose as compared to CT scan. 
  • One base line X ray chest should be done at time of admission to compare with subsequent examinations.
  • Chest X ray is useful in monitoring of course of disease and follow up.
  • HRCT thorax may be needed in patients having unexplained chest X ray findings.
  • Radiation dose emitted in one chest X ray – 0.02 m severt.
  • Radiation dose emitted in one CT thorax – 8.0 m severt.
  • One CT scan thorax radiation dose = 400 chest X rays.

COVID-19 HRCT Thorax

Characteristic CXR findings in COVID patient:

  • bilateral “patchy” and “confluent, ground glass and consolidative opacities in a peripheral, mid-to-lower lung zone distribution (arrows).

Nonspecific CXR findings

COVID-19 HRCT Thorax

  • Diffuse bilateral opacities including ground glass and bibasilar consolidation (arrows), in a more central distribution than in the characteristic pattern. 
  • Ill-defined, bibasilar opacities

SNMC-Agra experience

  • Till date approx. – 1800 chest X rays of COVID patients have been done in SNMC, Agra.
  • Majority of chest x rays revealed mild changes.
  • Approx. – 200 (approx. – 11%) chest X rays showed findings suggestive of severe disease.

COVID-19 HRCT Thorax

Chest X ray is useful in the follow-up of the disease.

Initial chest X ray of this patient was normal.

Chest X ray after four days – Multiple ill-defined opacities in both lungs.

Limitations of chest X ray

  • Chest X rays in most of COVID hospital are done by a portable X ray machine with technical limitations.
  • AP images from portable X ray machines produce a poorer quality image when compared with a standard chest PA radiograph done in a dedicated radiography facility .
  • Limitations of AP chest radiograph include reduced inspiratory effort because of the patient’s lying position & breathing difficulty, resulting in sub-optimal imaging. 
  • Lung changes may therefore appear either more marked or subtle lesions may be missed.

Role of HRCT thorax in COVID 19

  • HRCT thorax is an important imaging modality in evaluation of COVID patients.
  • HRCT thorax findings closely parallel the RT-PCR results.
  • HRCT has high sensitivity (95-98%) but has low specificity in detecting typical features of COVID pneumonia.
  • HRCT thorax is reserved for patients having clinic-radiological mismatch on chest X rays, assessment of disease severity, unexplained severe respiratory symptoms & patients having acute complications.
  • HRCT thorax is not advocated as screening tool for COVID patients.
  • One CT scan thorax radiation dose = 400 chest X rays.

What we see in CT

COVID-19 HRCT Thorax

CT-images of a RT PCR test positive young male, who had fever for seven days with progressive coughing and shortness of breath.

There are widespread bilateral ground-glass opacities with peripheral & posterior predominance.

Crazy Paving Pattern

COVID-19 HRCT Thorax

  • There are thickened interlobular and intra lobular lines in combination with a ground glass pattern.
    This pattern is called crazy paving pattern.
  • This crazy paving pattern is seen in a somewhat later stages of disease.

Vascular Dilatation

COVID-19 HRCT Thorax

  • A typical finding in area of ground glass attenuation is dilatation of the vessels (arrow). This is a less common finding and seen in later stages of COVID disease.


COVID-19 HRCT Thorax

  • Common finding in the areas of ground glass attenuation is tractional bronchiectasis (arrows), seen in late stages of disease due to evolving fibrosis.

Sub pleural bands and Architectural distortion

COVID-19 HRCT Thorax

  • In delayed stages of disease, there is architectural distortion with formation of sub pleural bands representing organizing pneumonia and early fibrosis.

Distribution of HRCT Patterns in COVID 19

  • Ground-glass opacification……88%.
  • Bilateral involvement…………….88%.
  • Posterior distribution…………….80%.
  • Multi lobar involvement…..……79%.
  • Peripheral distribution………….76%.
  • Consolidation ……………………….32%.

COVID-19 HRCT Thorax

CT-images of COVID-19 positive patient.

There are bilateral ground-glass opacities with a posterior predominance. Consolidation is seen in right lower lobe.

COVID-19 HRCT Thorax

Initial RT PCR testNegative

Because of clinical suspicion, HRCT chest was done which showed some areas of GGO and consolidation in the posterior parts of the lower lobes

Two days later RT PCR test was positive for COVID-19.

HRCT thorax changes in COVID over time

Early stage0-4 daysGGO, partial crazy paving, lower number of involved lobes.
Progressive stage5-8 daysProgressive extension of GGO, increased crazy paving pattern.
Peak stage10-13 daysConsolidation with above findings.
Late stage≥ 14 daysTractional bronchiectasis, sub pleural bands and architectural distortion.

COVID-19 HRCT Thorax

  • Early phase COVID-19

There are widespread GGO’s without consolidation. No architectural distortion is seen.

COVID-19 HRCT Thorax

COVID-19 infection – late phase

Bilateral areas of GGO.

The ground glass densities are more pronounced with:

  • Fibrotic bands (arrows).
  • Dilated vessels are seen in in affected area (circle).

Based on the CT-findings COVID-19 infection was assumed to be in late phase.

COVID-19 HRCT Thorax

COVID 19 – Late phase

The HRCT images show:

  • Bilateral sub pleural GGOs with fibrous bands (yellow arrow).
  • Mild tractional bronchiectasis in right lower lobe (green arrow).

CT Severity score (CT SS) in COVID

According to CT Severity score (CT SS), affected lung parenchyma is divided into 5 parts:

  • Right upper lobe
  • Right middle lobe
  • Right lower lobe
  • Left upper lobe
  • Left lower lobe

CT Severity score (CT SS) in COVID

Each lobe is graded based on percentage of involvement:

  • 0%             = 0 points
  • <5%            = 1 point
  • 5-25%        = 2 points
  • 25-50%      = 3 points
  • 50-75%      = 4 points
  • 75-100%    = 5 points

Total score is obtained by adding the  grades of individual lobes.

Total CT SS:

  • 0-8             = mild disease
  • 9-14           = moderate disease
  • 15-25         = severe disease

COVID-19 HRCT Thorax

COVID-19 RT PCR positive case with CT SS score of 4, showing small peripheral ground glass opacities in right lower lobe and left upper lobe.

COVID-19 HRCT Thorax

COVID-19 RT PCR positive case with moderate CTSS of 14 showing typical peripheral patchy ground glass opacities involving all the lobes.

CME INDIA Take Home Message:

  • Imaging plays a very important role in diagnosis & monitoring of treatment of COVID patients.
  • Chest X ray & HRCT thorax are imaging modalities used in imaging of COVID patients.
  • Base line chest X ray should be done at the time of admission of patient, so that it may be compared with subsequent chest X rays during treatment & follow up.
  • Chest X ray should be used as primary imaging tool in COVID patients during treatment and follow up as & when required.
  • HRCT thorax should be reserved for patients having unexplained & indeterminate chest X ray findings and moderate to severe category cases.
  • HRCT thorax is not advocated as screening tool for COVID patients.
  • Radiation hazard must be considered while advising CT thorax (one CT thorax = 400 chest x rays).
  • ALARA (as low as reasonably achievable) principle of radiation protection should be applied.

CME INDIA Learning Points:

  • HRCT Thorax: All go in favor of Corona:
    1. Peripheral lesions
    2. Ground Glass Haziness
    3. Consolidation patches
    4. Reverse Halo sign
    5. Vaculation sign
    6. Air Bronchograms
    7. Prominent Pulmonary Vessels
    8. Crazy Pavement Patterns on CT-SCAN
  • What is Reverse Halo Sign:

COVID-19 HRCT Thorax

This sign is defined as a focal rounded area of ground-glass opacity surrounded by a complete or near-complete ring of consolidation observed on chest computed tomography. It has been found in COVID-less commonly

  • Chest radiographs may be unremarkable. It can show nonspecific multi-lobar consolidations that can rapidly progress by day 10–12 following symptom onset, to severe pneumonia with bilateral ground-glass opacities, usually in peripheral distribution.
  • CT scan findings, though not specific for COVID-19-associated pneumonia, may be more sensitive for diagnosis than chest radiograph. CT is useful especially where viral testing may be constrained or during a false-negative nasopharyngeal real-time RT-PCR test in mild or severe suspected cases.
  • CT findings, including ground-glass opacities are most prominent from day 0 to day 4 after symptom onset (usually bilateral and peripheral distribution), which can become very extensive with disease progression and present as multifocal solid consolidative opacities.
  • The American College of Radiology (ACR) in the USA currently recommends against using CT scanning for screening or diagnosis of COVID-19, except when needed for assessment of disease severity and management.
  • The accuracy of chest CT in symptomatic emergency department patients is high. But used as a single diagnostic test, CT cannot safely diagnose or exclude COVID-19. CT can be used as a quick tool to categorize patients into “probably positive” and “probably negative” cohorts.
  • CT has the advantage that the results can be available almost directly. Chest CT can show characteristic findings including areas of ground-glass, with or without signs of reticulation (so called “crazy paving pattern”), consolidative pulmonary opacities in advanced stages and the “reverse halo” sign.
  • Peripheral areas of ground glass are a hallmark of early COVID-19. It can easily be missed at chest X-rays; CT scanning has an advantage over chest X-rays in the early stages of COVID-19.
  • The sensitivity of RT PCR may be suboptimal, which makes it difficult to compare with HRCT. But chest CT scan can help to differentiate those with high risk (suspicious CT) and those with low risk of COVID-19 (non-suspicious CT). So, CT can be used as a quick tool to categorize patients into “probably positive” and “probably negative” cohorts.

CME INDIA Tail Piece:

COVID-19 HRCT Thorax

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