Common findings in the lung parenchyma

The findings found in the CXR are described according to the glossary of terms of the Fleischner Society¹⁵.

Interstitial opacity: Small and innumerable linear opacities, focal or diffuse, are caused by the partial occupation of the airspace. Regarding interstitial thickening, it is due to fluid, cells or fibrosis, partial collapse of the alveoli, increased volume of capillary blood or a combination of them¹⁶(Figure 1A). They are seen as faint opacities on CXR, but with greater attenuation than pulmonary airspace. In SARS-COV-2 involvement, these images are present during the course of the disease, predominate in the periphery but can extend to the hilar region. The distribution is focal and unilateral in early stages, then it is bilateral and diffuse^12,17(Figures 2A,3,4).

Alveolar opacity: It is caused by the total occupation of exudate in the pulmonary alveoli¹⁵. In the X-ray it is seen as homogeneous opacities with greater attenuation than the interstitial ones, poorly defined and blurred margins, and they may present an air bronchogram¹⁸(Fig.1B). In SARS-COV-2 infections and in other viral pneumonias, alveolar involvement is multifocal, which differentiates them from bacterial pneumonias that generally involve a single segment or lobe^14,17,18(Figure 5B).

Interstitial alveolar opacities: It is a mixed image of interstitial infiltrate to which alveolar opacities are added in the same places¹⁵(Figure 1C). They have been described in the course of the evolution of the SARS-COV-2 viral pneumonia and they are correlated with moderate to severe disease¹²(Figures 5A, 5C).

Uncommon findings in the lung parenchyma

Pleural effusion: Its appearance depends on the amount of fluid, the position of the patient and the presence of adhesions. In the standing position, the pleural effusion has a characteristic appearance, such as a homogeneous inferior opacity in the lateral costophrenic sinuses with a concave interface towards the lung¹⁴. Pleural effusion is difficult to identify with the patient in the decubitus position, in poor general condition, and on mechanical ventilation, so a standing or semi-sitting chest X-ray is suggested whenever possible. In the context of SAR-COV-2 infection, initial reports suggested the absence of this finding; however, current studies with CT in larger populations have demonstrated the presence of pleural effusion in the 2nd week of evolution and in patients who became complicated, the pleural effusion was visualized at the end of the 3rd week¹².

Hilar prominence: The causes of hilar prominence are due to lymphatic or vascular pathology such as pulmonary thromboembolism¹⁴. Viral and bacterial pneumonic infections can cause lymph node hypertrophy; In patients with SARS-COV2 infection, these findings have been described on CT, but they are rare and generally present in late stages of infection in patients with unfavorable evolution¹². Pulmonary thromboembolism is another complication recently described in these patients. In CXR, prominence of the hila is observed due to dilation of the pulmonary arteries and vascular redistribution towards the upper lobes at the expense of vascular dilation¹⁴; the examination of choice is CT angiography.

Single focal consolidation: It is the alveolar pattern that occupies a segment or lung lobe, and it is caused by bacteria such as pneumococcus¹⁴.

Nodules/masses: The presence of these findings is unlikely to be of infectious; however, they can cause differential diagnosis problems with consolidations and atelectasis¹⁴.

In the evaluation of CXR, a diagnostic classification of high, intermediate, low/inconclusive suspicion is proposed, based on the presence of common findings. The presence of unusual findings should lead us to think about differential diagnoses. Some authors consider that these findings are more reliable in young patients under 50 years of age because they are less likely to be confused with images of pre-existing lung disease⁷(Table 1).

Scenario 1(Figure 6)

Patient with moderate to severe pulmonary clinical picture and confirmed laboratory test for infection by SARS-COV-2.

Radiographic diagnosis - scenario 1:

Lung involvement compatible with SARS-VOC-2 viral pneumonia

Initial RALE Score (if it is the first X-ray): ___ / 8

RALE Score (evolution): ___ / 8 (from the second radiograph)

Scenario 2 (Figure 6)

Patient with suspected SARS COV-2 infection, moderate to severe clinical picture, laboratory result is not available or a false negative is suspected or there is no availability of laboratory tests and there is no availability of tomography, then radiography could be useful with a probability diagnosis (sensitivity of the radiograph: 69%), and taking into account the time of evolution from the onset of symptoms.

Radiographic diagnosis - scenario 2: In this scenario, the radiographic diagnosis must be made based on probabilities of suspicion, this classification was proposed for the CT reports, which we have adapted for the radiographic diagnosis, adding the respective recommendations. SeeTable 1.

Radiographic findings of high suspicion for atypical pneumonia due to SARS-COV-2: request confirmation with laboratory / CT test

Radiographic findings of intermediate suspicion for atypical pneumonia due to SARS-COV-2: request confirmation with laboratory test / CT

Radiographic findings of low suspicion / inconclusive for atypical pneumonia due to SARS COV-2: consider alternative diagnosis according to clinical picture and history, clinical follow-up is suggested

Normal radiography, infection by SARS-COV-2 is not ruled out: request tests of laboratory / CT

Scale of evolution

The most widely accepted scale to evaluate the evolution of radiographic images is the RALE Score proposed by Warren et al, to quantify pulmonary edema and adapted by Wong et al.⁹to evaluate quantitative progression of SARS-COV-2 infection. The scale consists of dividing the lung fields into 4 equal parts in such a way that 25% is assigned to each division and in each lung separately, with this procedure 8 equal parts are achieved (4 in the right and 4 in the left pulmonary field), to which 1 point is assigned to each area and a total score of 8 is achieved if all the segments were affected. The score is determined by adding the areas with suspicious images (Figure 7).Other authors prefer to assess lung involvement by assigning a score dividing the lung fields into thirds⁷as used in the 2003 coronavirus pandemic; we prefer to use the RALE Score proposed by Wong.

From a qualitative point of view, the appearance of alveolar opacities during the course of the disease^9,12,20and pleural effusion after the 3rd week are considered unfavorable¹².

In the report: Radiographic evolution:

RALE Score (1st. CXR)

Favorable radiographic evolution due to decrease in the number of compromised lung area, RALE Score (../8)

Stationary radiographic evolution since…. (date), RALE Score (../8)

Unfavorable radiographic evolution due to greater involvement of the pulmonary areas and / or areas with alveolar infiltrate / pleural effusion are added or increased, tomography is suggested, RALE Score (../8)

Figure 1.  Common findings in CXR in the SARS-COV-2 context. A: Soft diffuse opacity. B: Alveolar opacity (∆). C: Alveolo-interstitial opacities (o). 

Figure 2.  Common findings and lesions suggestive of SARS COV-2. A: Faint, multifocal peripheral opacities in bilateral middle third. B: Peripheral multifocal alveolo-interstitial opacities. C: Faint diffuse peripheral opacity in both pulmonary fields predominantly on the left. 

Figure 3.  Location and distribution of the CXR findings in the SARS-COV-2 context. A: Location by segments in the RxT B: Focal distribution (★). C: Diffuse distribution (in the circle). 

Figure 4.  Location of the different types of lesions that conditions SARS COV-2, predominantly peripheral and bilateral. 

Figure 5.  Cases of high suspicion of SARS COVID-2. A: Diffuse bilateral alveolo-interstitial opacities of peripheral and basal distribution. B: Focal opacities in the right lung field with areas of peripheral parenchymal consolidation and left perihilar linear opacities. C: Faint bilateral peripheral opacities predominantly on the left, associating areas of alveolo-interstitial involvement. 

Figure 6.  SARS-COV-2clinical picture (moderate-severe). 

Figure 7.  Actual score. Determination by score assigned 1 point for every 25% of each lung.