Subcutaneous Emphysema

Subcutaneous emphysema is a finding on imaging tests that indicates air trapped within the soft tissues, typically beneath the skin. It can occur due to trauma, infections, or iatrogenic causes such as surgical procedures. While the presence of subcutaneous emphysema may not always signal a medical emergency, identifying its source and extent is important for appropriate patient management.

How Subcutaneous Emphysema Appears on X-ray

X-ray are often the first imaging study to reveal subcutaneous emphysema. The trapped air appears as radiolucent (dark) streaks within the soft tissues. These streaks may outline muscle planes or spread diffusely depending on the severity of the condition.

Key features of subcutaneous emphysema on X-ray include:

Black, streaky, or bubble-like air pockets in the soft tissues

Association with pneumothorax or pneumomediastinum in the chest which may require urgent intervention

Limitations of X-ray for Subcutaneous Emphysema

While X-rays are useful for detecting subcutaneous emphysema, they have limitations:

Low sensitivity for small amounts of air, especially in obese patients

Difficult differentiation from normal soft tissues, especially in cases of minimal air infiltration

CT Imaging of Subcutaneous Emphysema

Computed tomography (CT) is the best imaging modality for detecting subcutaneous emphysema. It provides detailed visualization of the air distribution, underlying injuries, and any associated conditions such as pneumothorax or tracheal rupture.

On CT, subcutaneous emphysema appears as:

Lobulated or streaky collections of air within the soft tissues

Air dissecting along muscle planes and fascial layers

Better visualization of the extent of air spread, which may involve deep tissue layers

Associated pathology, such as rib fractures, lung lacerations, or mediastinal air leakage

Why CT is Preferred for Subcutaneous Emphysema

CT imaging is superior to X-ray because:

It can detect even small amounts of air that X-rays might miss

It allows for precise localization of air pockets

It helps differentiate between subcutaneous emphysema and other conditions like necrotizing fasciitis, which can have overlapping clinical symptoms

In my practice, CT scans have been particularly valuable in trauma cases. For example, in patients with blunt chest trauma, subcutaneous emphysema extending along the neck and mediastinum often suggests a tracheobronchial injury, pneumothorax or lung injury.

Common Causes of Subcutaneous Emphysema on Imaging

Identifying the cause of subcutaneous emphysema is essential for proper management. The most common causes include:

Trauma-Related Subcutaneous Emphysema

Rib fractures: Air leaks from lung injury which tracks into the soft tissues

Penetrating injuries: Air enters through open wounds in the chest or neck

Blunt trauma: Sudden increases in airway pressure may cause air leakage into tissue planes

Surgical and Procedural Causes

Endotracheal intubation: Air may escape due to tracheal injury or barotrauma

Chest tube placement: Can introduce air into soft tissues

Laparoscopic surgery: Carbon dioxide insufflation can track into subcutaneous tissues

Infections and Gas-Producing Bacteria

Necrotizing fasciitis: Subcutaneous emphysema in the setting of soft tissue infection is a red flag for gas-forming bacteria

Gas gangrene: A surgical emergency where bacterial gas formation mimics air infiltration on imaging

Spontaneous Subcutaneous Emphysema

Pneumomediastinum: Air from alveolar rupture can dissect into subcutaneous tissues without clear external trauma

Severe coughing or vomiting (Macklin effect): High intrathoracic pressures cause alveolar rupture, allowing air to migrate into soft tissues

When Subcutaneous Emphysema Requires Urgent Attention

While mild cases resolve on their own, radiologists must identify signs that indicate a serious underlying problem, including:

Extensive air tracking into the mediastinum, suggesting pneumomediastinum

Tracheal or esophageal injury, seen as air escaping from deep structures

Tension pneumothorax, which may require immediate decompression

Signs of infection, such as soft tissue thickening, fluid collections, or inflammatory changes.

Conclusion

Subcutaneous emphysema is a finding on imaging studies that is often benign.  It can sometimes however indicate serious underlying pathology that needs urgent treatment.  X-ray is useful for initial detection, but CT is the best test for assessing the extent and cause of subcutaneous emphysema.

Trauma, surgery, and infections are common causes, and distinguishing between them is important for management.  Extensive air tracking in the tissues, mediastinal involvement, or associated pneumothorax should prompt urgent evaluation. Radiologists play an important role in alerting doctors to potential complications, guiding further imaging and treatment.

 

References

1.https://www.ncbi.nlm.nih.gov/books/NBK542192/

2.https://www.medicalnewstoday.com/articles/subcutaneous-emphysema

3.https://jetem.org/chest_trauma/