Materials and Methods
Consecutive individuals who tested RTPCR positive for SARS COV2 and underwent chest
X-rays were collated during their stay in the hospital.
The initial radiograph was evaluated as negative or positive, if positive the type
of abnormality, its location, distribution, any other features of note such as cavitation,
mediastinal adenopathy, pleural effusion. Note was also made if CT was performed at
time of initial X-ray, if so whether positive or negative.
Patients who had more than one X-ray were followed up, a note was made of the progression,
regression of abnormalities, number of days to reach progression, number of days to
regression either from initial X-ray or after peak of progression. Number which had
complications such as ARDS, barotrauma, type of barotrauma, ventilator-associated
pneumonia were recorded.
Discussion
SARS COV-2 has a particular affinity for ACE-2 receptors. These are in abundance in
type 2 alveolar cells. After gaining entry into the type 2 receptor cells there is
diffuse alveolar damage resulting in exudation into the alveolar spaces.[[1], [2]]
This appears on Chest radiographs X-rays as a diffuse haziness obscuring vascular
markings, akin to the well documented ground-glass densities seen on CT scans.[[3]] With further progression in alveolar cell apoptosis the exudation may result in
denser opacities on the X-ray appearing as consolidations. These consolidations do
not incite sympathetic effusions or internal cavitation as may occur with bacterial
pneumonias. Occasionally reticular opacities may be seen on the X-ray as linear bands
due to septal/alveolar thickening due to inflammation. The distribution of abnormalities
is usually in the lung bases as well as in the periphery.[[1], [2]] [[Figures 1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12]].
Figure 1: Chest radiograph PA view of RT-PCR proven COVID positive patient showing
patchy opacities in bilateral mid and lower zones predominantly involving the peripheral
lung fields (left more than right)
Figure 2: Chest radiograph PA view of RT-PCR proven COVID positive patient shows showing
ill-defined air space consolidations with reticular opacities (black arrows) in bilateral
mid and lower zones
Figure 3: Chest radiograph of a COVID positive patient showing patchy nodular lesions
in bilateral mid and lower zones representing atypical appearance
Figure 4: Chest radiograph of COVID positive patient proven by RT-PCR showing subtle
hazy opacities (black arrow) in right lower zone
Figure 5: Chest radiograph of COVID positive patient proven by RT-PCR shows dense
airspace consolidation in subpleural region of right upper and lower zones
Figure 6: Chest radiograph of COVID positive patient proven on RT-PCR shows small
nodular consolidations involving both lung fields representing broncho-pneumonia pattern
Figure 7: Chest radiograph in a Covid positive patient proven on RT-PCR reveals diffuse
airspace consolidation in bilateral mid and lower zones (right more than left lung)
Figure 8 (A and B): (A) Chest radiograph of a RT-PCR proven COVID positive patient
shows no abnormality. (B) HRCT chest was done on same day as patient was symptomatic
revealed patchy areas of ground glass densities with interlobular septal thickening
in posterior basal segment of right lower lobe and medial basal segment of left lower
lobe
Figure 9 (A-D): Serial chest radiographs over 7 days in a patient with Covid-19 infection
depicting (A-C) progression of the disease in the first 3 days with (D) gradual resolution
of opacities over the next 4 days
Figure 10: Serial chest radiographs over 4 days in a patient with Covid-19 infection
showing progression of the disease for which patient was intubated. Follow-up radiograph
demonstrates resolution on the 4th day
Figure 11 (A and B): Serial chest radiographs at 7 days interval in a patient with
Covid-19 infection showing resolution of the diffuse consolidation involving the bilateral
mid and lower zones in Chest X-ray (A)
Figure 12 (A-D): Serial chest radiographs in RT-PCR proven COVID positive patient
showing progression of the ill-defined hazy opacities noted in right lower zone (A)
with increase in densities of opacities and involvement of bilateral mid lower zones
(B and C) and gradual regression in the densities of these opacities noted in last
chest X-ray (D)
A negative chest X-ray may be due to lack of lung involvement, early in the disease,
subtle involvement below resolution of X-rays or technical factors.[[4]] [[Figure 13]].
Figure 13: Serial chest radiographs in a patient on mechanical ventilation. Diffuse
airspace consolidation involving right lung field and left mid and lower zone. There
is resolution of the opacities visualised in right upper and bilateral mid zones
In our study 67% of patients with positive RTPCR had abnormalities on the chest X-ray.
33% were negative. Chest radiograph was negative in 26% of positive HRCT indicating
CT is far more sensitive than chest X-ray in detecting COVID 19 pneumonia. The distribution
of abnormalities were predominantly in the lower zone (70%) bilateral (61%) and peripheral
and central in location (65%) The type of abnormality was predominantly consolidation
(68%). These findings were consistent with smaller cohorts reported earlier.[[5], [6], [7]]
The diffuse alveolar damage evolves over 1-3 weeks resulting in temporal changes on
imaging. There are 3 stages of diffuse alveolar damage.[[6]]
Stage 1 is the exudative phase which occurs in the first few days after infection,
usually till day4/5. There is limited leakage of fluid into the interstitium as a
result radiographs demonstrate essentially clear lung fields.
Stage II is an inflammatory stage where there is an alveolar capillary leak of protein,
fluid resulting in diffuse alveolar opacities predominantly in the peripheral portions
of the lungs. With increasing capillary leak diffuse alveolar damage may progress
with extensive lung involvement resulting in Acute Respiratory Distress Syndrome (ARDS).
This results in loss of aerated lung tissue, impaired gas exchange, hypoxia. opacities
tend to become confluent, lungs become totally opaque, air bronchograms may be present
with injury to alveolar cells, there is decreased surfactant production and decreased
lung compliance. This is reflected in the radiographic findings of relatively small
lung volumes and atelactasis. Rarely there are associated pleural effusions; these
are usually small if present. At this juncture it is important to differentiate cardiogenic,
overhydration oedema from the alveolar oedema of ARDS. The alveolar oedema of ARDS
is not accompanied by widening of the vascular pedicle, cardiomegaly, altered pulmonary
blood flow distribution, pleural effusions and septal lines. In fact if the pulmonary
vessels can be distinguished they are often constricted in size. The opacities tend
to be in the periphery as compared to central in cariogenic oedema as well as don’t
change temporally as they do on cardiogenic oedema. In our study 9% of patients progressed
to ARDS.[[4]] [[Figures 14] and [15]].
Figure 14: Serial chest radiographs over 5 days in a case with COVID pneumonia showing
progression of density and area of airspace opacities. Patient was intubated on the
5th day and unfortunately expired one day later
Figure 15: Portable chest radiograph of COVID pneumonia patient with diffuse airspace
opacities in bilateral lung fields with relative sparing of left upper zone. Patient
was intubated and put on positive ventilation because of diffuse lung involvement.
Linear lucencies in right mid zone (red arrow) representing pulmonary interstitial
emphysema
Stage III is a fibro-proliferative phase, in this phase there is proliferation of
epithelial cells and fibroblasts with collagen deposition. A transition from alveolar
to interstitial opacities in noted.
The radiographic appearances are of progressive clearing of alveolar opacities which
are replaced by reticular opacities. In the chronic phase the radiograph often returns
to normal, occasionally residual fibrosis or cystic changes may be present.
The main complication of COVID-19 pneumonia is the development of ARDS.
The mainstay of treatment of ARDS is to recruit the alveoli in the atelectic/consolidated
portions of the lung by using high positive end expiratory pressures via mechanical
ventilation. This distends the alveoli. An effort to recruit the consolidated atelectic
portions can result in over distension of these alveoli and consequently barotrauma
due to rupture of alveoli. The radiologist has an extremely important role to play
in the detection, prevention and treatment of these complications.
The adverse effects of Positive pressure ventilation can be classified into 2 groups
-
Due to physiological effects of mechanical ventilation on heart/pulmonary vasculature
-
Direct lung injury resulting in Air leak phenomena.
During the acute phase the use of positive end expiratory pressure may result in improvement
of the chest radiograph appearances, such as clearing of previously visualised opacities.
This infact is a paradox as the positive end expiratory pressure causes overdistension
of the alveoli resulting in the apparent clearing of opacities on the chest X-ray.
This overdistension of the alveoli actually results in diversion of pulmonary blood
flow to the poorly ventilated regions resulting in paradoxical worsening of the oxygenation.
Air leak phenomena
This is the most commonly recognised manifestation of barotrauma, the development
of extra alveolar air collections which may accumulate in five compartments, the pleural
space, mediastinum, interstitium, pericardial sac and subcutaneous tissues. Although
each area has distinct radiological features, overlap exists and occasionally differentiation
can be difficult. 2% of all patients developed barotrauma, in our study 40% of patients
mechanically ventilated developed barotrauma [[Figures 16], [17], [18], [19]]. As compared with reported overall rate of 24 % in a study by McGuinness et al in patients with COVID-19 on invasive mechanical ventilation[[8]] [[Figures 16], [17], [18], [19]].
Figure 16 (A-F): Serial chest radiographs (A-F) in a COVID positive patient who presented
with acute breathlessness. (A) Normal initial OPD Chest radiograph. (B-F) Subsequent
Chest radiographs show progression of the patchy ground glass opacities to diffuse
consolidation for which patient required ventilatory support. (F) Mediastinal emphysema
(black arrow) is noted as a result of barotrauma
Figure 17: Portable chest X-ray of a COVID pneumonia patient with bilateral diffuse
involvement of lungs developed right-sided pneumothorax with collapse of underlying
right lung and mediastinal shift towards left due to barotrauma. Incidentally noted
is a well-defined oval radiolucency representing a pneumatocele in right lower zone
(black arrow)
Figure 18: Portable Chest radiograph after chest tube insertion in Covid positive
patient with bilateral diffuse air space consolidation requiring positive pressure
ventilation developed left sided pneumothorax likely due to barotrauma resulting in
collapse of the underlying left lung and mediastinal shift towards right. A well-defined
oval radioluceny in periphery of left mid zone representing a pneumatocele (black
arrow) with linear radiolucencies in left mid and lower zones around heart representing
pulmonary interstitial emphysema
Figure 19: Portable chest X-ray in a Covid pneumonia patient on mechanical ventilation
developed mediastinal emphysema (black arrow) and diffuse subcutaneous emphysema as
a result of barotrauma. Linear radiolucencies noted in right mid zone representing
pulmonary interstitial emphysema. Incidentally noted is central line coiled back in
left IJV (red arrow)
Pulmonary interstitial emphysema
This occurs due to rupture of alveoli with resultant leak of air into the interstitium,
interstitial emphysema. This air then dissects along the vascular sheaths and interlobular
septae, paths of least resistance, centrally to the hilum. resulting in a pneumomediastinum.
and peripherally to the pleura resulting in a pnuemothorax. Pulmonary interstitial
emphysema is difficult to observe on radiographs as the air in the interstitium is
difficult to detect against the background of dark alveolar air. Pulmonary interstitial
emphysema becomes much easier to detect in a consolidated lung as the consolidation
contrasts the air in the interstitium.
The earliest radiographic signs are a mottled increase in the radio-lucency of the
lung anteriorly and medially around the heart, as well as the diaphragmatic surface.
There may be streaky linear radiolucencies radiating from the hila to the periphery
of the lung. These may resemble air bronchograms, they however differ from air bronchograms
by the fact that they do not branch nor do they taper to the periphery.[[9]]
They may form pnuematoceles which may coalesce to form large subpleural cysts.
Pneumomediastinum
The mediastinum is anatomically defined as the space between the two lungs, it is
enveloped all round by parietal pleura. It contains two air filled structures, the
trachea and the oesophagus. Any air outside these structures is pathological. As the
air collects around the mediastinal structures, the great vessels, the cardiac contour
is demarcated extremely well. Streaky vertically oriented opacities may be visualised
extending superiorly into the neck. Normally the infracardiac surface of the diaphragm
is not visualised, this is as the density of the cardiac structures and diaphragm
are similar. In a pneumomediastinum air dissects inferiorly into the infracardiac
region, separating the cardiac and diaphragmatic densities producing a continuous
diaphragm sign. The diaphragm is seen in its entire extent. The mediastinal pleura
may be visualised as a thin line surrounding the mediastinal air.[[10], [11]]
Pneumothorax
This is the most common life threatening emergency in patients supported by mechanical
ventilation. Pneumothorax usually follows the development of pneumomediastinum. The
relatively thin mediastinal pleura ruptures when overdistended with air. Once a pneumothorax
develops in a patient on the ventilator it may rapidly increases in size to become
a tension pneumothorax.[[11], [12]]
The most important radiographic feature of a pnuemothorax is the presence of a thin
white line representing the visceral pleura with air on both sides of this white line,
air in the pleural space and air in the lung parenchyma. Other signs are absence of
lung markings beyond the visceral pleural line and hypertranslucency of the pleural
space. Unfortunately, in most patients with suspected barotrauma only supine X-rays
are possible. In these situations detection of a pneumothorax may be difficult and
the signs are different. The principles are the same, air collects in a nondependent
location such as the anterio-medial or subpulmonary location, when the air leak is
large, air may collect in the apicolateral location. The displaced visceral pleural
line is difficult to demonstrate on a supine radiograph X-ray. In the absence of this
specific sign secondary signs to demonstrate the collection of extrapleural air is
important. As air collects in the anterior costophrenic sulcus there is transradiancy
in the hypochondrial region overlying the diaphragm. There is increased sharpness
of adjacent mediastinal margin and diaphragm. The costophrenic sulcus becomes deep
with a well-defined margin. The inferior edge of collapsed lung becomes visible. Ipsilateral
hemidiaphragm is depressed. Cardiac margins become sharp and pericardial fat pads
become well outlined. A pneumothorax suspected on a supine film can be confirmed on
a cross table lateral view or lateral decubitus with suspect side uppermost. If there
is any doubt, CT chest is very useful, as it would be confirmatory.
Skin folds may mimic the white line of displaced pleura. Skin folds are often in pairs
as well as often cross the midline, diaphragm or chest wall. Lines or tubes projecting
over the lung may also simulate the white visceral pleural line. In these cases, the
other signs of a pneumothorax are absent and the appliances can be seen exiting the
confines of the thoracic cage.[[13]]
A pneumothorax is considered under tension when the pressure in the pleural space
exceeds atmospheric pressure. The ipsilateral lung collapses with mediastinal shift,
especially displacement of the azygo oesophageal recess. There may also be evidence
of inversion of the diaphragm and flattening of the heart especially the IVC and SVC
impairing normal venous return to the right heart.[[14]]
Pneumothorax is treated by placing a thoracic tube. If there is only air in the pleural
space, the thoracic tube is placed anteriorly in the second intercostal space, if
there is a mixture of air and fluid then the tube is placed in the sixth or seventh
interspace in the mid axillary line.
Subcutaneous emphysema
Air can dissect along the fascial planes of the neck, chest and abdominal walls from
the mediastinum or pleura. Often the presence of air in the chest wall in a patient
on mechanical ventilation is the first sign of barotrauma. Due to the presence of
subcutaneous emphysema, pneumothorax or underlying parenchymal abnormalities may not
be detected on the chest radiograph. Rarely subcutaneous emphysema may be due to a
necrotising soft tissue infection. Radiographically multiple lucencies of varying
configurations may be seen within the soft tissues of the neck and thorax. Subcutaneous
emphysema present is of little clinical significance.
Ventilator-associated pneumonia
Due to the immunosupressed state of critically ill patients bacteria colonise in the
endotracheal/tracheostomy tube. The endotracheal or tracheostomy tube allows free
passage of bacteria into the lower segments of the lung, thus these maybe imbibed
into the lungs with each breath, also they may be propelled down by suctioning and
bronchoscopy.[[15], [16]] This results in an infectious pneumonia. The key to the diagnosis is the presence
of new opacities, especially cavitation, pleural effusions. Clinical and laboratory
parameters support the diagnosis. On chest X-ray these may be difficult to demonstrate
on the background of white out lung. [[Figures 20] and [21]]. In our study 2/29 (7%) patients on invasive/mechanical ventilation developed-associated
pneumonia.
Figure 20 (A-D): Serial portable chest radiographs in a Covid positive patient requiring
mechanical ventilation, showing (A) dense consolidation in right upper and mid zone
(this was a new finding as compared to old X-rays). (B-D) shows cavitation in dense
consolidation. Endotracheal tube swab (ETS) grew Acinetobacter Baumanii on culture.
Pneumonia resolved on appropriate antibiotic therapy as shown in follow up chest X-rays
Figure 21 (A-D): Serial portable chest radiographs in a Covid positive patient. (A)
showing airspace consolidation in right lung and left mid and lower zone (B) resolution
in the density and extent of airspace consolidation in right lung field and left mid
zone (C) ill-defined consolidation in right mid and lower zone (new finding-red arrow).
Microbiological investigations revealed Acinetobacter Baumanii on culture (D) shows
resolution of extent and density of opacities noted in right mid and lower zones after
appropriate antibiotic treatment
Conclusion
The chest X-ray is an important diagnostic tool in the detection and management of
Covid-19 pnuemonia. Chest X-ray is useful tool to detect changes to suggest the diagnosis,
CT chest however has a higher sensitivity. The common CT findings of bilateral involvement,
peripheral distribution, and predominantly in lower zones were also appreciated on
CXR which was commensurate with other studies.[[1], [5], [17]] Portable CXR being a bedside modality can be used to monitor the progression, regression
of lung changes, complications in the form of ARDS, barotrauma, ventilator-associated
pneumonia and misplaced tubes and lines helping reduce the morbidity and mortality.
This has been included in WHO guidelines for the use of chest imaging in Covid-19
of 11 Jun 2020 which gives conditional recommendation (R2.2) to use CXR for the diagnosis
in symptomatic cases as it can be performed with portable equipment at the point of
care which reduces the risk of cross-infection.[[18]]
