Edited March02,2016

Updated on Septembre 30, 2016

Medical Imaging of PneumoThorax (PNO4)

Dr WALIF CHBEIR

V- Diagnosis

* The diagnosis of PNO is suspected in stable patients with dyspnea or pleuritic chest pain and

is confirmed with upright inspiratory chest x-ray. Radiolucent air and the absence of lung

markings juxtaposed between a shrunken lobe or lung and the parietal pleura are diagnostic of

pneumothorax.

- Tracheal deviation and mediastinal shift occur with large pneumothoraces.

* Small pneumothoraces (eg, < 10%) are sometimes overlooked on chest x-ray. In patients

with possible pneumothorax, lung markings should be traced to the edge of the pleura on chest

x-ray. Conditions that mimic pneumothorax radiographically include emphysematous bullae,

skinfolds, folded bed sheets, and overlap of stomach or bowel markings on lung fields. -

Ultrasonography (done at the bedside during initial resuscitation) and CT are more sensitive for

small pneumothoraces than chest x-ray.

* Traumatic PNO: Diagnosis is usually made by chest x-ray. Ultrasonography (done at the

bedside during initial resuscitation) and CT are more sensitive for small pneumothoraces than

chest x-ray.

* The size of the pneumothorax, stated as percent of the hemithorax that is vacant, can be

estimated by x-ray findings. The numerical size is valuable mainly for quantifying progression

and resolution rather than for determining prognosis.

* Open PNO: The diagnosis is made clinically and requires inspecting the entire chest wall

surface.

* In critical care and in patients with severe ARDS (ARDS & PNO) , Patients with

pneumothorax did not have the traditional clinical and radiologic signs and the most repeatable

finding may be a subtle drop in oxygenation measurements without another obvious cause

(Loculated Pneumothorax: A Special Challenge In Critical Care) .

The diagnosis of pneumothorax in critical illness is made from the history and examination of

the patient and confirmed, where possible, by radiological investigation. The factors that are

important in the history relate to the underlying disease process and any potential for iatrogenic

pneumothorax .

The early and accurate diagnosis of pneumothorax in ARDS patients is mandatory since this

complication carries an increased mortality. Furthermore, small pneumothoraces in these

patients can cause severe hemodynamic or pulmonary compromise. This is the reason why

pneumothorax must always be suspected in any patient with ARDS who experiences an acute

worsening in respiratory function, accompanied with dyspnea and hypoxemia, which is usually

unresponded to oxygen therapy.

- Portable chest X-ray is the first diagnostic evaluation imaging being used and the procedure

of choice for the documentation of lung underlying pathology or the presents of lines, tubes or

devices. Nevertheless, often exhibits diagnostic disadvantages, taking into account that

pneumothoraces in ARDS patients may have unusual, as well as subtle features and small sized

pneumothoraces or loculated pneumothoraces, can be missed on chest X-ray. Furthermore,

other types of air leaks, such as pneumomediastinum and interstitial pulmonary emphysema,

may be more difficulty observed by chest radiographs .

- Cases have been described in medical literature, referring to patients presenting clinical

deterioration but unchanged chest X-ray and functioning chest drains (Acute respiratory

distress syndrome and pneumothorax; ref 14). This is the reason why, especially in patients under

mechanical ventilation, serial and daily chest radiographs are necessary in the evaluation of

underlying lung pathology.

- There for, if a pneumothorax is suspected and is unrevealed on chest X-ray, a more

specific diagnostic imaging like chest-computed tomography (CT) is necessary. CT scan in

patients with ARDS, as explained above , can reveal a variety of abnormalities , is helpful in

understanding the extent of the underlying lung parenchyma distraction and is quite more

sensitive in identifying pneumomediastinum andpneumothorax, which are frequently observed

in patients with ARDS.

- Nevertheless, chest-CT evaluation is seldom employed in patients with ARDS, especially

patients with severe respiratory failure under mechanical ventilation, mostly due to problems

concerning the transfer and monitoring of these critically ill patients.

- Due to these technical difficulties of chest-CT, an essential diagnostic method in critically ill

patient gaining respect is lung-ultrasonography, a relatively easy to perform, portable and

inexpensive diagnostic imaging. Lung-ultrasonography can prove an alternative diagnostic

procedure in the difficult diagnosis of pneumothorax in critically ill patients with severe

ARDS, which not only permits bedside assessment of lung pathology but also assists in the

evaluation of mechanical ventilation parameters, as well as the evaluation of lung

overdistension and PEEP-induced lung recruitment .

- In the same setting, Loculated pneumothorax provides only subtle clinical clues. The only

clinical evidence may be deteriorating oxygenation without another obvious cause. US findings

may be equivocal . The abscence of lung sliding may be caused by pno but it has others causes

as well . The presence of Lung Sliding indicates that there is no PNO but alone doen't exclude

the diagnostic, while the abscence of lung sliding only indicates that there may be one ( because

it has others causes as well). Scan the entire chest for B lines. (Clinical chest US: from the ICU to the bronchoscopic

suite).

PNO that is not in immediate contact with the chest wall will not be identified on US ( e.g.

Loculated PNO against medistinum).

Be prepared for chest CT scans if ever Lung US is inconclusive for this hard-to-catch

complication of mechanical ventilation in patients with ARDS.

* Tension pneumothorax is a clinical diagnosis, not a radiographic diagnosis, because the

respiratory and hemodynamic consequences of tension pneumothorax do not have radiographic

equivalents in many circumstances. Radiographic signs of tension (mediastinal shift, inversion

of diaphragm, enlargement of affected hemithorax) can occur in the absence of adverse

physiologic effects, and the physiologic effects of pleural tension may be present without

radiographic signs of tension ( critically ill p.) .

- In ARDS, the diseased noncompliant lung may not collapse in the presence of a

pneumothorax, and the controralateral lung may be too stiff to allow mediastinal shift. Thus,

tension pneumothorax in ARDS can present as a loculated paracardiac or subpulmonic air

collection with little or no mediastinal shift and only slight changes of the cardiac contour.

- Treatment should not be delayed pending radiographic confirmation. Although cardiac

tamponade also can cause hypotension, neck vein distention, and sometimes respiratory

distress, tension pneumothorax can be differentiated clinically by its unilateral absence of breath

sounds and hyperresonance to percussion.

- Although non-specific, the association of respiratory and haemodynamic signs found with a

tension pneumothorax are a medical emergency. Severe haemodynamic compromise will

require urgent needle decompression of the pneumothorax before its diagnosis being confirmed

radiologically. Fortunately this situation is uncommon and there is frequently time for

radiological investigations to help establish the diagnosis of a simple pneumothorax.

VI- Significant Points

* A large pneumothorax is radiographically defined as one with > 2 cm from pleural surface to

lung edge; this is an objective indication for drainage

* Don’t wait for a radiograph if there are clinical signs of a tension pneumothorax.

Tension pneumothorax is a medical emergency and may require immediate needle

decompression before radiological investigation.

- Treat the patient not the radiograph. Don’t act on a radiographic appearance if it does not fit

the clinical picture. Get an expert opinion on the radiograph first.

* Skin folds, companion shadows, the scapula, and previous lung surgery or chest drain

placement may all mimic pneumothoraxes on XRay Chest.

* In the supine patient, pneumothoraxes are best seen at the lung bases and adjacent to the

heart.

The “deep sulcus sign” describes a costophrenic angle that extends more inferiorly than

usual as a result of air lying in the costophrenic angle. The liver appears more radiolucent than

usual due to air lying anteriorly in the costophrenic angle, and on the left side, air will

outline the medial aspect of the hemidiaphragm under the heart.

* What other radiological investigations may be used to confirm the diagnosis of PNO in acute

traumatic setting and in critically ill patients?

- A radiograph with the patient in a lateral decubitus position, with the affected side uppermost,

can be helpful in demonstrating a lung edge.

- In patients well enough to be transported, thoracic computed tomography can be helpful in

locating the position of a pneumothorax and accurately siting a chest drain.

- US and CT are more sensitive than Chest X-Ray Radiography in detection PNO. CT is the

gold standard. US is done at the bedside during initial resuscitation of trauma patient and in

critically ill patient in ICU.

- The early and accurate diagnosis of pneumothorax in ARDS patients is mandatory since this

complication carries an increased mortality. Portable chest X-ray is the first diagnostic

evaluation imaging. If a pneumothorax is suspected and is unrevealed on chest X-ray, Lung

USG is now an alternative method to Chest CT mostly due to the cumbersome nature of this

technique in critically ill patients.

* The negative predictive value of Chest US for lung sliding is reported as 99.2–100%,

indicating that the presence of sliding effectively rules out a pneumothorax. For some authors,

lung sliding ALONE does not exclude PNO and scanning of the entire anterior chest for B-

Lines is mandatory (Ultrasonography in the ICU: Practical Applications).

- However, the absence of lung sliding does not necessarily indicate that a pneumothorax is

present. In fact, Lung sliding is abolished in a variety of conditions other than pneumothorax.

- Lung Sliding and B lines are not present on a patient with PNO. M Mode can help

differenciate between a seashore sign or Stratosphere or bar code signs ( SeaShore = no PNO).

* Blind chest drain placement into a loculated pneumothorax may lead to an iatrogenic air leak

from direct trauma to the pleura and worsening the patient’s clinical condition.

* An immediate post-treatment radiograph is essential to detect complications and ensure a

satisfactory drain position

* A chest drain apparently well positioned on frontal radiograph may be lying in the soft

tissues, in a lung fissure, or within the substance of the lung.

VII- References

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