Interpreting chest radiographs of the critically ill patients who are in intensive
care units (ICUs) poses a challenge not only for the intensive care physicians but
also for the radiologist. These challenges arise because of several factors:[1] ICU
patients are prone to several cardiopulmonary disorders which when superimposed on
the underlying pathology that prompted admission create a complex radiological appearance,
which may be difficult to interpret on the basis of imaging findings alone.[2] The
standard posteroanterior (PA) radiograph is replaced by the suboptimal anteroposterior
(AP) radiograph in the ICU patient.[3] Instrumentation, mechanical ventilation, cardiac
and other vital sign monitoring and feeding tubes, etc., detract from other findings
on the ICU chest radiograph.[4] Radiologists/Intensive care physicians are under pressure
for rapid interpretation of chest x-rays when treating critically ill patients, often
with inadequate clinical information, partly due to the fact that things can change
rapidly in the critically ill.[5] Radiological interpretation is hampered by the bewildering
array of line placements in the ICU patient, where incorrect placement is not uncommon,
which may not be obvious to the observer without clinical input.[6] Air space shadowing
in the ICU patient may have identical appearances in a variety of cardiopulmonary
pathologies. Although the imaging modality of choice in the ICU patient remains that
of chest radiography, computed tomography is often performed as computed tomographic
pulmonary angiography (CTPA) with suspected pulmonary embolism. Ultrasound is used
to confirm pleural and pericardial effusions and when pleural intervention is planned.
The aim of this paper is[1] to discuss the radiographic findings of cardiopulmonary
disorders common in the ICU patient and suggest guidelines for interpretation based
not only on the chest radiograph but also on the pathophysiology and clinical grounds.[2]
In addition, to describe the normal position of monitoring devices and other line
placements, and prompt recognition when they are misplaced or when other complications
occur.
This is a 2-part series[1]: Part I: Normal chest radiographic appearances in the ICU
patient, correct and incorrect placement of various intra-thoracic tubes and lines
and complications from instrumentation.
Part II: Radiography of lung pathologies common in the ICU patient.
The Normal Chest X-ray
The standard PA chest radiograph is rarely taken in the ICU patient and is replaced
by an anteroposterior (AP) radiograph. These radiographs are ideally obtained in the
AP projection with a patient–to–x–ray plate distance of 72 inches with the patient
in the upright position at maximum inspiration; but more often, a distance of 40 inches
is used in the supine or sitting position due to the impaired mobility of ICU patients
[Figure 1]. A radiograph obtained in this way magnifies the mediastinum and heart
due to gravitational and geometrical effects. Moreover, supine position alters the
physiology of the pulmonary vasculature, diverting the blood to lung apices — an appearance
that is regarded as normal on AP supine radiograph but considered abnormal on a PA
radiograph. Supine radiographs have further limitations, including problems of differentiating
pleural effusions from air space shadowing and detecting a pneumothorax. Exposing
a radiograph in full inspiration in an ICU patient poses further challenges as these
patients are often uncooperative or are suffering from postoperative pain [Figure
2]. A more-than-perfect inspiratory effort creates artifacts, making the diagnosis
of basilar atelectasis and pulmonary edema difficult, besides causing changes in the
apparent size of the heart and mediastinum.[1–4]
Figure 1
A normal AP chest radiograph of an ICU patient
Figure 2
Chest radiographs on the same patient a few minutes apart showing the effect of technique;
the left image shows mediastinal widening and basal clouding due to a poor inspiratory
effort; the right image has been taken in good inspiration and looks entirely normal
The sensitivity and specificity of the ICU chest radiograph are low, but its common
use stems from studies that have shown that as much as 65% of ICU chest radiographs
reveal a significant pathology that results in a change in patient management. Current
recommendations from the American College of Radiology suggest that daily chest radiographs
be obtained on patients with acute cardiopulmonary problems and those receiving mechanical
ventilation. The college further recommends that only an initial chest radiograph
is needed for the placement or change of indwelling devices.[5]
In patients that have undergone thoracotomy for whatever reason, the initial postoperative
radiographs after return from operating theatre will show the lines and tubes placed
perioperatively, such as an endotracheal tube, thoracostomy tubes, mediastinal drains
and central venous catheters. These devices need to be identified and their positions
checked for incorrect placement. Immediately following and a few days after CABG,
lower lobe atelectasis is common, usually more pronounced on the left, generally resolving
within a few days without complications. There is slight widening of the mediastinum,
but significant increase in diameter might indicate complications such as a mediastinal
bleeding. A small left pleural effusion is invariable following CABG, but a larger
pleural effusion or a subsequent increase in size may need intervention so as not
to cause respiratory compromise [Figure 3]. Therefore, comparison with previous radiographs
is essential to assess a change in size of a pleural effusion.
Figure 3
An AP chest radiograph on a 55-year-old female immediately following CABG, shows hazy
opacification at the lung base and blunting of the left costophrenic angle due to
a small pleural effusion, which is a common feature following thoracotomy (black arrow)
Identifying Lines and Tubes and Other Devices
Tubes, lines and drainage catheters play a vital role in monitoring and treating critically
ill patients. Accurate placement of these devices and monitoring malfunction are crucial.
The initial portable chest radiograph plays an essential role in recognizing correct
placement and complications. All placed devices should be identified on the preliminary
radiograph as a priority in these patients before looking for cardiopulmonary disorders
[Figures 4 and 5]. Table 1 summarizes the correct positioning of various lines and
tubes.
Figure 4
On return of patient from the operating theatre or following resuscitation, all tubes
and lines should be checked and accounted for. In this patient, the position of the
tracheostomy tube is satisfactory (black arrow), but the nasogastric tube is curled
on itself and lies in the gastric fundus (white arrow); and the chest drain is also
incorrectly placed for draining the pleural effusion (thin black arrow)
Figure 5
This child has had a midline sternotomy (hollow arrowhead); a mediastinal drainage
catheter is seen in place (white hollow arrow); there is a pericardial pacing wire
(black arrow) and a nasogastric tube — all in a satisfactory position
Table 1
Identifying lines and tubes and other devices
Endotracheal tubes
Safe level 5 cm from carina (T4-T5 interspace), minimum distance 2 cm
Nasogastric tube
Ideally the distal duodenum
CVP lines
Ideally placed between proximal venous valves of the subclavian or jugular veins
and the right atrium. Jugular venous placement has lower complications.
Swan ganz catheter
The tip is wedged into the distal pulmonary artery.
The balloon is deflated once the pressure is taken, and the tip is pulled back to
the main pulmonary artery.
The tip of the catheter located within the mediastinal shadow indicates correct placement.
The thoracostomy tube
The last side-hole in a thoracostomy tube can be identified by an interruption in
the radiopaque line.
This interruption in the radiopaque line should lie within the thoracic cavity, if
not and or with evidence of subcutaneous air, a misplaced tube is suspected.
Incorrectly placed tubes for empyemas may delay drainage and result in loculation
of the purulent fluid.
Thoracostomy tubes placed within pleural fissures often cease to drain when the lung
surfaces become apposed.
Cardiac pacemakers
The tip of the cardiac pacemaker should be at the apex of the heart, and there should
be no sharp angulations along the length of the pacemaker wires.
The lateral radiograph should show the tip imbedded within the cardiac trabeculae.
For correct placement to have occurred, the tip should appear 3 to 4 mm beneath the
epicardial fat pad.
A tip that appears to be placed beyond the epicardial fat stripe may have perforated
the myocardium.
Cardiac pacers placed within the coronary sinus appear to be directed posteriorly
on the lateral chest radiographs.
The endotracheal tube
Endotracheal or tracheostomy tubes (ETs) maintain an airway access and allow mechanical
ventilation of patients with respiratory failure. These tubes are cuffed and placed
in the trachea, either via the oropharynx or introduced surgically through a tracheostomy.
If it is anticipated that the patient needs intubation for a period longer than a
week or has upper airway obstruction, a tracheostomy is usually preferred. A chest
radiograph is essential to correctly locate the tip of endotracheal tubes. Misplaced
ET may cause serious compromise of respiratory function and has been reported in 10%
of the patients. Thus, daily chest radiographs are recommended in these patients as
these devices may migrate. A correctly placed endotracheal tube lies at the level
of the mid-trachea, about 5 cm from the carina. Placing the tip at this level allows
for flexion or extension of the head. The minimal safe distance from the carina is
2 cm. Poor chest x-ray exposure may sometimes not allow recognition of the carina.
A previous radiograph, if available, may be used to estimate the position of the carina.
Alternatively, the position of the tip of the ET can be assessed by looking at the
upper dorsal spine. As the carina normally lies at the T4-T5 interspace, the tip of
the endotracheal tube lying at this level is regarded as correct placement [Figures
6 and 7]. The Dee method has been devised for approximating the position of the carina.
This involves identifying the aortic arch and then drawing a line inferomedially through
the middle of the arch at a 45-degree angle to the midline. The intersection of the
midline and the diagonal line is the most likely position of the carina. This is a
cumbersome method for the busy ICU physician/radiologist and is seldom used.
Figure 6
A position of the tip of the endotracheal tube is high at the level of the spinous
process of D1 (arrow)
Figure 7
An incorrectly placed ET with the tip in the right main bronchus (arrow), causing
partial atelectasis of the left lung
ETs are misplaced in approximately 10% of the patients. A comparatively common misplacement
is when the tube enters the right main stem bronchus, due to its more vertical orientation.
This position impairs the left lung ventilation, leading to collapse of the left lung;
similarly, if the endotracheal tube enters the bronchus intermedius, the right upper
lobe may collapse. ET that has been placed at a higher level may slip into the pharynx
or the esophagus, causing gastric air distension with the potential danger of reflux
of gastric contents and aspiration. More serious complications of ETs include tracheal
stenosis, tracheal rupture, cord paralysis, cervical and mediastinal emphysema, hematoma
and abscess formation.
When upper airway injury is suspected, a lateral radiograph may be useful. The soft
tissue space between the trachea and cervical spine is increased in diameter to over
the width of one vertebral body in the presence of a hematoma or infection.
Severe injury such as tracheal rupture should be suspected in patients with pneumothorax,
pneumomediastinum, subcutaneous emphysema in the neck or precipitous respiratory failure
following intubation [Figure 8]. Most tracheal ruptures are placed posteriorly.[6–9]
Figure 8
A scout film from a CT scan (left) shows narrowing of the trachea following prolonged
ET placement. An axial CT confirms tracheal stenosis (right)
The thoracostomy tube
Thoracostomy tubes are often placed into the pleural space to treat a pneumothorax
or drain pleural fluid [Figure 9]. Chest radiographs are often obtained following
placement of thoracostomy tubes to identify their position. It is important to recognize
that on a supine AP radiograph, air accumulates anteriorly and fluid gravitates posteriorly.
This fact is taken into account when placing thoracostomy tubes relevant to the pathology
in hand. Determining whether a tube is anterior or posterior is often difficult with
a single AP chest radiograph. Thoracostomy tubes placed within pleural fissures often
cease to drain when the lung surfaces become apposed. Correct placement of thoracostomy
tube fenestrations within the thoracic cavity is important to proper functioning of
these tubes. The last side-hole in a thoracostomy tube can be identified by an interruption
in the radiopaque line. This interruption in the radiopaque line should lie within
the thoracic cavity, if not and or with evidence of subcutaneous air, a misplaced
tube should be suspected. Incorrectly placed tubes for empyemas may delay drainage
and result in loculation of the purulent fluid.[10]
Figure 9
A subpulmonic effusion mimicking an elevated right hemidiaphragm. A pleural drain
has been misplaced
The feeding tube
Nasogastric tubes (NGs) are used to feed patients or for gastric aspiration in appropriate
clinical circumstances. Radiographs are seldom required for accurate placement of
NG tubes and are not used except when the patient is unconscious and there is risk
of placement of the tube into the bronchial tree. There are other exceptions where
a chest radiograph is useful and may prevent serious consequences, which include instances
where small-bore feeding tubes are inserted and in status-post esophagectomy [Figures
10–12]. The lower tip of the NG is generally placed in the upper small bowel, which
may be confirmed with an abdominal radiograph.[11–14]
Figure 10
The nasogastric tube has entered the left lower lobe bronchus, causing partial collapse
and consolidation of the left lower lobe. This serious misplacement can particularly
happen in unconscious patients and patients on ventilators
Figure 11
A small-bore feeding tube has been misplaced into the left lower lobe bronchus, causing
left lower lobe consolidation (solid white arrow)
Figure 12
A lateral radiograph of the neck showing a collection of air in the prevertebral soft
tissue space due to esophageal perforation secondary to a difficult intubation (arrow)
Monitoring central venous pressures
Central venous pressures (CVPs) are monitored by central vein catheters placed either
through the subclavian or the internal jugular vein; or occasionally via the femoral
vein, particularly in babies where access via jugular or subclavian vein is unavailable.
These catheters are also used for safe delivery of large volumes of fluids over long
periods with minimal chances of venous thrombosis. Correct placement of the tip of
the CVP line is important for accurate measurement of central venous pressure. The
ideal location of the tip of the CVP line is between the most proximal venous valves
of the subclavian or jugular veins and the right atrium. Misplacing CVP lines is not
uncommon when lines are placed within the internal jugular vein, right atrium and
right ventricle. Placing the CVP catheter distal to the superior vena cava may cause
arrhythmias or may risk cardiac a perforation [Figures 13–17]. Other complications
of CVP line placement are a pneumothorax; and intimal injury to veins, causing perforation
or thrombosis. These complications can be avoided by using ultrasound guidance for
CVP catheter placement, and jugular vein placement is preferred because of lower complication
rates.[15–17]
Figure 13
AP chest radiograph showing the tip of an intravenous line within the left atrium
(arrow)
Figure 14
Radiograph showing the tip of an intravenous line to lie at the junction of the superior
vena cava and the left atrium
Figure 15
The intravenous line has crossed over from the superior vena cava into the azygos
vein (arrows)
Figure 16
Radiograph of chest and abdomen of a neonate following cardiac surgery, showing a
misplaced intravenous line into a hepatic vein. The intravenous line has been introduced
via the right femoral vein
Figure 17
A misplaced large-bore intravenous line crossing from the left subclavian vein into
the right subclavian vein
Monitoring pulmonary capillary wedge pressure
Pulmonary capillary wedge pressure monitors are introduced via the venous system to
help accurate assessment of the patient's volume status and can help differentiate
between cardiac and noncardiac pulmonary edema. Swan-Ganz catheters are generally
used as pulmonary capillary wedge pressure monitors. These catheters are introduced
percutaneously via the right heart and into the pulmonary artery. This allows pulmonary
wedge pressure to be calculated by inflating a balloon located at the tip of the catheter.
The tip is advanced into a distal pulmonary artery and wedged there. The balloon is
deflated once the pressure is taken, and the tip is pulled back to the main pulmonary
artery. The tip of the catheter located within the mediastinal shadow indicates correct
placement. The catheter tip should ideally be placed proximal to an interlobar pulmonary
artery [Figures 18–20]. Malpositioning of Swan-Ganz catheters may occur in a quarter
of the patients, resulting in false pulmonary capillary wedge pressure readings, risk
for pulmonary infarction, pulmonary artery perforation, cardiac arrhythmias and endocarditis.[18–23]
Figure 18
Left pneumopericardium (solid white arrow). Note that the JVP line is also falling
short of the SVC (hollow white arrow). The tip of Swan-Ganz catheter lies within the
right main pulmonary artery
Figure 19
The tip of Swan-Ganz catheter has been withdrawn into the right main pulmonary artery
(hollow arrow)
Figure 20
The tip of Swan-Ganz catheter has been withdrawn further into the main pulmonary artery
(arrow)
The intra-aortic counterpulsation balloon pump
The intra-aortic counterpulsation balloon pump (IACB) is used to decrease afterload
and increase cardiac perfusion in patients with cardiogenic shock. The device is synchronized
with either the aortic pressures or the patient's EKG, to inflate during diastole
and deflate during systole [Figure 21]. The device is introduced via the right femoral
artery to be positioned above the celiac axis in the region of the aortic isthmus
or left main bronchus. During systole, the lucent air-filled balloon appears as fusiform.[24–26]
Figure 21
Magnified view of the aortic knuckle showing the tip of an intra-aortic balloon pump
(solid white arrow); the endotracheal tube is marked by the hollow arrow
Cardiac pacing devices
ICU patients with cardiac arrhythmias or a heart block may require temporary cardiac
pacemakers. The pacing wires of these devices are introduced via the cephalic or subclavian
vein into the apex of the right ventricle. AP and lateral chest radiographs are usually
required to evaluate accurate pacemaker placement. The tip of the cardiac pacemaker
should be at the apex of the heart, and there should be no sharp angulations along
the length of the pacemaker wires. The lateral radiograph should show the tip imbedded
within the cardiac trabeculae. For correct placement to have occurred, the tip should
appear 3 to 4 mm beneath the epicardial fat pad [Figures 22–24]. A tip that appears
to be placed beyond the epicardial fat stripe may have perforated the myocardium.
Cardiac pacers placed within the coronary sinus appear to be directed posteriorly
on the lateral chest radiographs.[27–30]
Figure 22
A check radiograph following placement of a cardiac pacemaker shows the position of
electrode to lie within the apex of the right ventricle
Figure 23
A dual-lead cardiac pacemaker is seen in situ; the ventricular lead falls short of
the apex of the right ventricle
Figure 24
Fractured pacemaker wires; pieces lie in the right ventricle (lower arrow) and the
left lobe pulmonary artery (upper arrow)
Pneumothorax and other intrathoracic air collections
Extra-alveolar thoracic air collections in the ICU patients are not uncommon — often
the result of intubation, other thoracic interventional procedures and barotrauma
from positive end-expiratory pressure ventilation. This extra-alveolar air can collect
as pulmonary interstitial emphysema, pneumothorax, pneumomediastinum, pneumopericardium
or subcutaneous air.
Subcutaneous emphysema is not uncommon and often follows percutaneous intrathoracic
placement of drains and other devices. Air dissects through the fascial planes, which
usually has no clinical consequences [Figure 25]. Subcutaneous emphysema may be associated
with a pneumomediastinum; however, in the presence of isolated cervical subcutaneous
emphysema, the patient needs to be examined for upper airway injury, particularly
relevant following a difficult intubation or the placement of a new nasogastric tube.
The chest x-ray findings of subcutaneous emphysema may be striking; and the air dissecting
the fascial planes, particularly between muscle bundles in the pectoralis region,
is well seen obscuring underlying lung parenchymal changes. In the presence of subcutaneous
emphysema, the detection of a pneumothorax also can become difficult.
Figure 25
A portal supine chest radiograph showing surgical emphysema (solid white arrow) following
placement of chest drain (curved arrow). Note the shallow pneumothorax (hollow white
arrow). Surgical emphysema makes diagnosis of a pneumothorax difficult
Pneumothorax
A pneumothorax represents accumulation of air in the pleural space and it may occur
spontaneously, or secondary to trauma, it may or may not be associated with lung parenchymal
disease. Air rises to the nondependent position, and the radiographic appearance depends
upon how the radiograph has been exposed. In the erect patient, air rises to apicolateral
surface of the lung and appears as a thin, white pleural line with no lung markings
beyond [Figures 26–28]; however, the presence of lung markings beyond the pleural
line does not exclude a pneumothorax. The diagnosis of a pneumothorax may be particularly
difficult in the presence of parenchymal disease, which may alter the compliance or
affect the compliance of the lung, making collapse more difficult. A skin fold may
mimic a pneumothorax. A skin fold line when followed continues outside of the chest
[Figure 29].
Figure 26
A frontal chest radiograph showing a large left side pneumothorax causing almost complete
collapse of the left lung
Figure 27
AP chest radiograph may miss a small pneumothorax. One such example is seen above;
note the small collection of air anteriorly on the axial CT, representing a small
pneumothorax
Figure 28
Bilateral pneumothorax seen in the neonate with meconium aspiration
Figure 29
Multiple skin folds mimicking a pneumothorax (arrows)
In an ICU patient, diagnosis of pneumothorax is often made on a supine radiograph.
In a supine patient air rises anteromedially. An apical air collection in a supine
patient is a sign of a large pneumothorax. Air can sometimes be trapped in a subpulmonic
location between the lung and the diaphragm. Anterolateral extension of air into the
costophrenic sulcus may increase the radiolucency at the costophrenic sulcus. This
is called the deep sulcus sign. Other features of a subpulmonic pneumothorax include
visualization of the superior surface of the diaphragm and the superior part of the
inferior vena cava.
A tension pneumothorax is accumulation of air within the pleural space due to free
ingress of air with limited egress of air. The intrapleural pressure exceeds atmospheric
pressure in the lung during expiration (ball-valve mechanism). The diagnosis of tension
pneumothorax is a clinical one based on respiratory and cardiac compromise. Diagnosis
of a tension pneumothorax in a critically ill patient can be extremely challenging,
partly due to the fact that lung pathology such as ARDS may reduce lung compliance,
preventing total lung collapse as occurs in a tension pneumothorax. Similarly, a mediastinal
shift, a hallmark of tension pneumothorax, may not occur with the use of PEEP. Signs
of a tension pneumothorax include depression of a hemidiaphragm, a shift of the heart
border, the superior vena cava and the inferior vena cava.[31–32]
Pneumomediastinum
A pneumomediastinum represents air in the mediastinum and may be related to pulmonary
interstitial air dissecting centripetally in the intubated patient [Figures 30 and
31]. Mediastinal air may also represent a leak from a major airway injury or air dissecting
through fascial planes from the retroperitoneum. Unlike a pneumopericardium, air from
a pneumomediastinum often dissects up into the neck. Moreover, a pneumopericardium
can extend inferior to the heart. A pneumomediastinum usually remains asymptomatic.
However, occasionally a retrosternal crunch may be heard on auscultation. Radiographic
features of a pneumomediastinum include air around the great vessels, the medial border
of the superior vena cava, and the azygos vein seen as surrounding lucencies. Air
may also be seen outlining the aortic knuckle, descending aorta and the pulmonary
arteries. A posteromedial pneumomediastinum is usually the result of esophageal rupture,
where air dissects into the paraspinal costophrenic angle and beneath the parietal
pleura of the left diaphragm. The result is a V-shaped lucency called the V-sign of
Naclerio.[33]
Figure 30
AP and cross-table chest radiograph on a 1-year-old child showing extensive pneumomediastinum;
note that the air is extending to the root of the neck, differentiating it from a
pneumopericardium)
Figure 31
A scout film and axial CT scans showing the distribution of air following a retropneumoperitoneum.
Note the pneumomediastinum (arrow)
Pneumopericardium
A pneumopericardium refers to an accumulation of gas/air between the myocardium and
pericardium [Figures 32–34]. Pneumopericardium can be an occasional complication of
pneumothorax but is more often found in the postoperative cardiac patient. The chest
x-ray findings are those of a lucent line around the heart, extending up to the main
pulmonary arteries. Air may accumulate inferior to the cardiac shadow, which crosses
the midline above the diaphragm, which is said to be diagnostic for pneumopericardium,
the so-called continuous diaphragm sign.[34]
Figure 32
Chest x-ray findings of a pneumopericardium shown as a lucent line around the heart
extending up to the main pulmonary arteries (solid white arrows). Air may accumulate
inferior to the cardiac shadow, which crosses the midline above the diaphragm, which
is said to be diagnostic for pneumopericardium, the so-called continuous diaphragm
sign (hollow arrow)
Figure 33
Frontal and lateral radiographs depicting a pneumopericardium
Figure 34
A frontal radiograph and axial CT depicting a pneumopericardium. Note the surgical
emphysema at the root of the neck
Pleural effusions
Pleural effusions are accumulations of fluid within the pleural space [Figures 35–41].
Pleural effusions occur frequently in the ICU patients, which may be secondary to
heart failure, fluid overload, hypoproteinemia, infection, pulmonary embolism, thoracic
and upper abdominal surgery, neoplastic disease, subphrenic inflammatory processes,
trauma and ascites. The fluid could be blood, chyme, pus, transudates or exudates.
The radiographic appearance of a pleural effusion is dependent on the position of
the patient. Pleural fluid accumulates in the dependent areas of the chest. A pleural
effusion is easier to identify in the erect patient as fluid collects at the base
of the lung, causing costophrenic angle blunting and decreased visibility of the lower
lobe vessels. In the supine position, identification of a pleural effusion is more
challenging. In the supine position, pleural fluid accumulates in the posterior basilar
space, which appears as homogenous density that increases in intensity towards the
lung base. The normal bronchovascular markings are retained in this veil-like density.
With increasing amount of pleural fluid, the diaphragm loses its contour and costophrenic
angle may be obliterated. However, it should be remembered that the pleural space
may accommodate up to a liter of fluid above the diaphragm without blunting of the
costophrenic angle. With larger pleural effusions, the fluid may appear as pleural
cap at the lung apex, making it easier to identify on a supine radiograph. The fluid
may sometimes accumulate on the medial side of the lung, appearing as a widened mediastinum.
Often, smaller pleural effusions are missed on supine chest radiographs despite meticulous
technique. When effusions are not readily apparent on a supine chest radiograph but
clinically suspected, a lateral decubitus film is indicated. The film should be taken
with the side of the patient suspected to have an effusion in the dependent position.
The lateral decubitus film would not only confirm smaller pleural effusions but can
also differentiate between loculated and free effusions. The latter information is
important when pleural drainage is planned, as loculated effusions may need more than
one drain. A pleural effusion at the lung base is termed a subpulmonic effusion and
is a common occurrence in the ICU patient. On the chest radiograph, a subpulmonic
pleural effusion appears as a raised hemidiaphragm with flattening and lateral displacement
of the dome. A lateral decubitus film can usually resolve this.
Figure 35
Hazy opacification of the whole of the left hemithorax, suggestive of pleural effusion
following thoracic surgery
Figure 36
Bilateral pleural effusions following fluid overload. Note the bilateral basal and
mid-zone opacification and obscuration of the hemidiaphragms. The lack of an air bronchogram
excludes air space consolidation
Figure 37
Radiographs showing the value of lateral radiography in the detection of smaller pleural
effusions. There is blunting of the right costophrenic angle on the erect radiograph
(left), but the appearances are not diagnostic of a pleural effusion. However, the
lateral decubitus film (right) shows layering of the pleural fluid (arrow)
Figure 38
A CT scout film shows a subpulmonic effusion with a misplaced pleural drain. The axial
scan confirms the presence of a subpulmonic effusion and depicts the misplaced pleural
drain
Figure 39
Encysted pleural effusion seen en face as an oval opacity; its margin is partially
well defined and partially ill defined (AP radiograph). On the lateral radiograph,
the effusion appears as a homogenous density with biconvex edges
Figure 40
Loculated pleural effusion along the left lateral chest wall, which mimics an extra-pleural
mass (L), but hazy opacification at the right lung base and blunting of the right
costophrenic angle suggest pleural disease/thickening
Figure 41
Frontal radiograph showing vague opacification at the left lung base, suggestive of
a pleural effusion that followed a difficult intravenous line placement. The ultrasound
image (right) shows solid component within the posterior costophrenic angle, suggestive
of a hemothorax. An ultrasound scan can easily differentiate a clear pleural effusion
from a hemorrhagic pleural effusion
Loculated pleural effusions may pose a diagnostic challenge, especially when fluid
is retained within the fissures; and in particular, when the fissures are incomplete.
A loculated effusion in the minor fissure and right middle lobe atelectasis may be
difficult to differentiate on a supine chest radiograph. Interlobar effusion appears
as a homogenous density with biconvex edges and preservation of the minor fissure,
while atelectasis appears as an inhomogeneous density with concave margins and obliteration
of both the right heart border and minor fissure. CT or an erect lateral radiograph,
if possible, may resolve the issue.[35–39]
Pericardial effusions
Pericardial effusions are accumulations of fluid between the visceral and parietal
pericardium [Figures 42–44]. They usually cannot be seen on plain chest radiographs,
and smaller effusions are difficult to differentiate from cardiomegaly. A variety
of pathologies may cause pericardial effusions, including lymphatic or venous obstruction
by tumors, changes in osmotic pressures, or inflammation of the pericardium causing
increased permeability. Generally, pericardial effusions only become symptomatic when
the intrapericardial pressure rises by 3 or 4 mm Hg. A hemopericardium may follow
cardiac surgery or trauma. The rapidity at which the pericardial effusion accumulates
dictates hemodynamic consequences. Radiographically, a pericardial effusion appears
as cardiomegaly with a change in cardiac silhouette, resulting in a featureless, globular
or “water bottle” shape. The best and quickest way to determine the presence of a
pericardial effusion is by echocardiography.[40–43]
Figure 42
The chest radiograph and CT scan were taken on the same day, 7 hours apart. There
is nothing suspicious on the chest radiograph to suggest a pericardial effusion. There
is blunting of the left costophrenic angle, suggestive of a small pleural effusion.
However, the axial CT scan shows a small pericardial effusion and moderate bilateral
pleural effusions
Figure 43
The radiograph on the left was taken on admission of the patient, showing an enlarged
globular heart secondary to pericardial effusion due to severe hypothyroidism. The
image on the right was taken 3 weeks later, showing resolution of the pericardial
effusion
Figure 44
Pericardial effusions may not be that obvious on a chest radiograph. A CT scout film
(left) shows nonspecific cardiomegaly in a patient with a clinical diagnosis of viral
myocarditis. An axial CT section through the mediastinum shows a moderate-sized pericardial
effusion