Edited March02,2016

Medical Imaging of PneumoThorax (PNO1)

Dr WALIF CHBEIR

* We searched Medline and google for articles relating to Pneumothorax with focus on

imaging appearances and diagnostic approach.

* Key Words: - Pneumothorax/etiology. - Pneumothorax/radiography.

- Pneumothorax/ultrasonography. - Pneumothorax/diagnosis. - Acute respiratory distress

syndrome (ARDS) - Tension Pneumothorax - intensive care unit (ICU)- mechanical

ventilation. - critical care

* No financial relationships with commercial entities to disclose.

I- Definition

PNO is air in the pleural space causing partial or complete lung collapse.

II-Etiology

* Primary spontaneous pneumothorax (PSP) occurs in patients without underlying

pulmonary disease. It is thought to be due to spontaneous rupture of subpleural apical blebs or

bullae that result from smoking or that are inherited.

* Secondary spontaneous pneumothorax (SSP) It most often results from rupture of a bleb

or bulla in patients with underlying pulmonary disease. SSP is more serious than PSP because it

occurs in patients whose underlying lung disease decreases their pulmonary reserve.

--Most common: - Chronic obstructive pulmonary disease

- Asthma

- Cystic fibrosis

- Pneumonia: Pneumocystis jirovecii infection / Tuberculosis / Bacterial

pneumonia.( Cavitary or Necrotizing) .

- ARDS

-- Less common: - About 0.5% of pneumothoraces are associated with lung metastases, of

which 89% are caused by sarcomas, with osteogenic sarcoma being the most common

- Langerhans cell histiocytosis

- Lymphangioleiomyomatosis/tuberous sclerosis .

- Sarcoidosis.

- Connective tissue disorders: Ankylosing spondylitis , Ehlers-Danlos

syndrome, Marfan syndrome, Polymyositis and dermatomyositis, RA, Systemic sclerosis.

- Catamenial pneumothorax: is a rare form of SSP that occurs within 48

h of the onset of menstruation in premenopausal women and sometimes in postmenopausal

women taking estrogen . The cause is intrathoracic endometriosis, possibly due to migration of

peritoneal endometrial tissue through diaphragmatic defects or embolization through pelvic

veins.

* Traumatic pneumothorax is a common complication of penetrating or blunt chest injuries.

- In patients with penetrating wounds that traverse the mediastinum,or with severe blunt

trauma, pneumothorax may be caused by disruption of the tracheobronchial tree. Air from

the pneumothorax may enter the soft tissues of the chest and/or neck (subcutaneous

emphysema), or mediastinum (pneumomediastinum).

- Iatrogenic pneumothorax is caused by medical interventions, including transthoracic

needle aspiration and Biopsy, thoracentesis, Thoracotomy, central venous catheter placement,

mechanical ventilation and barotrauma, and cardiopulmonary resuscitation. Also: Surgical

procedures in the thorax, head, or neck. and Abdominal procedures using bowel or peritoneal

distension.

III- Symptoms and Signs ( + PhysioPatho)

* Small pneumothoraces are occasionally asymptomatic.

* Symptoms of pneumothorax typically include pleuritic chest pain and shortness of breath.

- Dyspnea may be sudden or gradual in onset depending on the rate of development and size of

the pneumothorax.

- Pain can simulate pericarditis, pneumonia, pleuritis, pulmonary embolism, musculoskeletal

injury (when referred to the shoulder), or an intra-abdominal process (when referred to the

abdomen). Pain can also simulate cardiac ischemia, although typically the pain of cardiac

ischemia is not pleuritic.

- Physical findings classically consist of absent tactile fremitus, hyperresonance to percussion,

and decreased breath sounds on the affected side. If the pneumothorax is large, the affected

side may be enlarged with the trachea visibly shifted to the opposite side. With tension

pneumothorax, hypotension can occur.

. Importantly, the volume of the pneumothorax can show limited correlation with the

intensity of the symptoms experienced by the victim, and physical signs may not be apparent if

the pneumothorax is relatively small.

* Primary Spontaneous Pneumothorax (PSP) :

- Classically in tall, thin, asthenic men. Most patients are between 20 and 40 years of age, and

the male-to-female ratio is approximately 5 to 1. It is thought to be due to spontaneous rupture

of subpleural apical blebs or bullae that result from smoking or that are inherited. It generally

occurs at rest, although some cases occur during activities involving reaching or stretching. PSP

also occurs during diving and high-altitude flying .

- It usually causes limited symptoms. Chest pain and sometimes mild breathlessness are the

usual predominant presenting features. People who are affected by PSPs are often unaware of

potential danger and may wait several days before seeking medical attention. PSPs more

commonly occur during changes in atmospheric pressure, explaining to some extent why

episodes of pneumothorax may happen in clusters. It is rare for PSPs to cause tension

pneumothoraces.

* Secondary Spontaneous Pneumothorax: Symptoms in SSPs tend to be more severe than

in PSPs, as the unaffected lungs are generally unable to replace the loss of function in the

affected lungs. Hypoxemia is usually present and may be observed as cyanosis. Hypercapnia

is sometimes encountered; this may cause confusion and if very severe may result in comas.

The sudden onset of breathlessness in someone with COP), cystic fibrosis, or other serious lung

diseases should therefore prompt investigations to identify the possibility of a pneumothorax.

* Traumatic pneumothorax (TP) Traumatic pneumothoraces have been found to occur in up

to half of all cases of chest trauma, with only rib fractures being more common in this group.

The pneumothorax can be occult (not readily apparent) in half of these cases, but may enlarge

particularly if mechanical ventilation is required. They are also encountered in patients already

receiving mechanical ventilation for some other reason.

- Many patients also have a hemothorax (hemopneumothorax).

- In patients with penetrating wounds that traverse the mediastinum or with severe blunt trauma,

pneumothorax may be caused by disruption of the tracheobronchial tree.

- Air from the pneumothorax may enter the soft tissues of the chest and/or neck (subcutaneous

emphysema), or mediastinum (pneumomediastinum).

- Patients commonly have pleuritic chest pain, dyspnea, tachypnea, and tachycardia.

- Breath sounds may be diminished and the affected hemithorax hyperresonant to

percussion—mainly with larger pneumothoraces. However, these findings are not always

present and may be hard to detect in a noisy resuscitation setting.

- Subcutaneous emphysema causes a crackle or crunch when palpated; findings may be

localized to a small area or involve a large portion of the chest wall and/or extend to the neck;

extensive involvement suggests disruption of the tracheobronchial tree.

- Air in the mediastinum may produce a characteristic crunching sound synchronous with the

heartbeat (Hamman sign or Hamman crunch), but this finding is not always present and also is

occasionally caused by injury to the esophagus.

* Open pneumothorax

- Some patients with traumatic pneumothorax have an unsealed opening in the chest wall.

when the opening is sufficiently large, the ventillation on the affected side is eliminated

respiratory mechanics are impaired and the inability to ventilate the lungs causes respiratory

distress and respiratory failure.

* Tension pneumothorax ( TP) is accumulation of air in the pleural space under pressure,

compressing the lungs and decreasing venous return to the heart. Although multiple definitions

exist, a tension pneumothorax is generally considered to be present when a pneumothorax leads

to significant impairment of respiration and/or blood circulation.

- Tension pneumothorax develops when a lung or chest wall injury is such that it allows air

into the pleural space but not out of it (a one-way valve). As a result, air accumulates and

compresses the lung, eventually shifting the mediastinum, compressing the contralateral

lung, and increasing intrathoracic pressure enough to decrease venous return to the heart,

causing shock. These effects can develop rapidly, particularly in patients undergoing

positive pressure ventilation.

- Causes include patients receiving positive-pressure ventilation (most commonly) with

mechanical ventilation or particularly during resuscitation, failed central venous cannulation,

simple (uncomplicated) pneumothorax with lung injury that fails to seal following penetrating

or blunt chest trauma and in patients with lung disease.

- Symptoms and signs initially are those of simple pneumothorax, tachypnea and increased

heart rate . As intrathoracic pressure increases, patients develop hypotension, tracheal

deviation, neck vein distention and respiratory distress. The affected hemithorax is

hyperresonant to percussion with reduced expansion and often feels somewhat distended,

tense, and poorly compressible to palpation. Rarely, there may be cyanosis, altered level of

consciousness.

- Recent studies have shown that the development of tension features may not always be as

rapid as previously thought. Deviation of the trachea to one side and the presence of raised

jugular venous pressure (distended neck veins) are not reliable as clinical signs.

- In case of Tension pneumothorax occuring in someone who is receiving mechanical

ventilation, it may be difficult to spot as the person is typically receiving sedation; it is often

noted because of a sudden deterioration in condition.

- This is a medical emergency and may require immediate treatment without further

investigations. Without appropriate treatment, the impaired venous return can cause systemic

hypotension and respiratory and cardiac arrest (pulseless electrical activity) within minutes.

* Acute respiratory distress syndrome, critically ill adults and pneumothorax:

- pneumothorax is common in ventilated critically ill patients . Approximately 50% of patients

with ARDS who require mechanical ventilation will develop a pneumothorax during their

treatment. The ARDS damages the lung parenchyma, and the high intrathoracic pressures

resulting from mechanical ventilation of stiff lungs contributes to rupture of the diseased lung

tissue.

- In patients with minimal pulmonary reserve, even a small pneumothorax can have adverse

hemodynamic effects or cause tension that rapidly induces cardiovascular collapse and death.

- Many factors may precipitate the occurrence of pneumothorax in ARDS, such as the

mechanical ventilation settings, the clinical severity of ARDS and the underlying pulmonary

pathology (like preexisting emphysema).

- Up to 96% of patients who develop pneumothorax while receiving ventilation will progress

to tension pneumothorax because the machine blows air out of the hole in the lung into the

pleural space with positive pressure.

- Tension pneumothorax occurs when intrapleural pressure exceeds atmospheric pressure.

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. 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.

++++

. Also, In patients with severe ARDS and pleural adhesions, most if not all of cardinal

clinical signs of Tension PNO (sudden increase in ventilation pressures, severely reduced

breath sounds on the affected side, jugular venous distention, and the dreaded mediastinal shift)

that results in cardiovascular collapse will be absent. The lung may be so diseased, stiff and

noncompliant that it does not fully collapse when air trapped in the pleural space presses on it.

If only a small portion of the lung is externally compressed, the mediastinum will not be

affected Therefore, radiographic evidence of extrapulmonary air collections becomes even

more important in this group of critically ill patients.

. Adherence of inflamed pleura to the chest wall ( parietal pl) may confine a

pneumothorax to a loculated portion of the pleural space around the site of the air leak.

Even daily chest radiographs can miss small loculated pneumothoraces. Two studies reported

by Chon and colleagues (cf num ref) reported that in critically ill, mechanically ventilated

adults, 33% to 50% of "missed" pneumothoraces (that is, pneumothoraces too small or subtle to

be seen on the radiograph until retrospective review) progressed to tension. Even small areas of

compression on the lung can have a significant impact on pulmonary function when the lungs

are so dysfunctional to begin with.

- The most repeatable finding of PNO in patients with severe ARDS was a subtle drop in

oxygenation measurements. Patients showed an improvement in PaO2 within 24 hours of

chest tube insertion and pneumothorax resolution.

. Loculated pneumothorax provides only subtle clinical clues. The only clinical evidence

may be deteriorating oxygenation without another obvious cause.

. 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.

. 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.

* Complications of PNO

- In most reported series, the rate of recurrence of spontaneous pneumothorax on the same side

is as much as 30%.

- On the contralateral side, the rate of recurrence is approximately 10%.

- Other complications include the following: Reexpansion pulmonary edema . Bronchopleural

fistula Occurs in 35% of patients, Pneumomediastinum and pneumopericardium and Tension

pneumothorax. Tension PNO may occur after spontaneous pneumothorax, although it is more

common after traumatic pneumothorax or with mechanical ventilation.

* In summary: A simple unilateral pneumothorax, even when large, is well tolerated by most

patients unless they have significant underlying pulmonary disease. However, tension

pneumothorax can cause severe hypotension, and open pneumothorax can compromise

ventilation.