Pneumothorax radiological presentation

Typical radiographic signs

Radiographs in suspected pneumothorax are optimally obtained with the patient standing. In this position, air rises to the upper parts of the chest, accumulating at the lung apex.

The main radiographic pattern includes:

• Visceral pleural line: it detaches from the inner surface of the chest wall.
• Transradiant zone: the space between the visceral pleural line and the chest wall lacks normal pulmonary and vascular markings.
• Density changes: the partially or completely collapsed lung may appear denser.

If signs are inconclusive on a standard inspiratory radiograph, the pneumothorax becomes more pronounced (accentuated) on a radiograph obtained during breath-holding at maximal expiration.

Challenges in imaging interpretation

There are pitfalls on radiographs that can mimic a pneumothorax. Common causes of overdiagnosis include:

• Avascular zones at the lung apices in bullous disease.
• Linear shadows from external objects: artifacts from clothing, medical dressings, and tubing.
• Skin folds: this issue is particularly relevant when examining neonates and elderly patients who "slump" against the image cassette in the anteroposterior projection.

The main differential sign that allows distinguishing a skin fold or artifact from a true visceral pleural line is that false lines usually extend further and go beyond the anatomical boundaries of the chest wall.

Tension pneumothorax

Tension pneumothorax (Tension Pneumothorax) is a critical, life-threatening condition where intrapleural pressure becomes positive relative to atmospheric pressure throughout most of the respiratory cycle. This causes severe impairment of gas exchange and hemodynamics.

Crucial rule: the diagnosis is made clinically. Treatment must be initiated immediately, prior to performing radiography. If an X-ray is nevertheless performed, it demonstrates:

1. Pronounced shift of mediastinal structures to the healthy (contralateral) side.
2. Flattening (depression) of the ipsilateral diaphragmatic dome — this is the most reliable radiographic criterion.

It should be remembered that a mild mediastinal shift can also be observed in simple (non-tension) pneumothorax due to the preservation of negative pressure in the healthy hemithorax.

Etiological Classification

Pneumothorax in adults is divided into spontaneous and traumatic.

Primary Spontaneous Pneumothorax occurs in the setting of visually healthy lungs.

• Epidemiology: predominantly affects young males (20–40 years old).
• Cause: rupture of an apical pleural bleb (bleb).
• Imaging nuance: during remission, blebs are not visible on standard radiographs in 80% of patients; CT is required for their detection.
• Recurs in one-third of cases without treatment.

Secondary spontaneous pneumothorax develops in the setting of underlying diseases:

• Obstruction: asthma, COPD (COPD), cystic fibrosis.
• Infections: cavitary pneumonia, tuberculosis, fungal infections, AIDS.
• Tumors (metastatic sarcoma) and pulmonary infarction.
• Diffuse diseases: pulmonary Langerhans cell histiocytosis, lymphangioleiomyomatosis.
• Rare causes: Marfan syndrome, endometriosis (catamenial pneumothorax).

Traumatic pneumothorax can be iatrogenic (resulting from thoracotomy, biopsy, tracheostomy, central venous catheterization) or non-iatrogenic (blunt and penetrating chest trauma, tracheal and esophageal ruptures).

Complications and combined forms

A small volume of fluid in pneumothorax is ignored in the diagnosis, but with a significant accumulation, the term changes.

• Hemopneumothorax: frequently accompanies trauma. In spontaneous cases, clinically significant hemothorax occurs in only 2% of patients. Clotted blood in the pleura can mimic tumor masses on a radiograph.
• Pyopneumothorax: a rare condition usually resulting from esophageal perforation or necrotizing pneumonia.
• Adhesions: appear on radiographs as straight band-like shadows extending from the lung edge to the chest wall. They limit collapse but can maintain a continuous air leak or cause hemorrhage if ruptured.

Class and exam questions

What else to study on this topic

• CT semiotics of apical pleural blebs in primary pneumothorax.
• Differential diagnosis of hemothorax and pleural tumors on CT.
• The "comet tail" artifact on pleural ultrasound and its significance.
• Bronchopleural fistula: mechanisms of formation and imaging appearance.

Other topics in the «Chest Radiology» section

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