Subcutaneous emphysema (SE) is a medical sign signifying the presence of free air or gas trapped underneath the skin’s subcutaneous layer. This condition is not a disease but indicates an underlying problem causing an air leak within the body. The most distinctive physical symptom is a palpable crackling sensation, known as crepitus, which feels similar to touching bubble wrap when the affected skin is pressed. SE most commonly affects the chest, neck, and face due to the anatomical pathways air follows.
How Air Enters the Subcutaneous Tissue
The appearance of air in the subcutaneous tissue is governed by mechanical principles, specifically the creation of a pressure gradient between an internal air-filled cavity and the soft tissues. A breach in the wall of a structure like the lung, airway, or esophagus allows air to escape into adjacent body spaces, such as the mediastinum or pleural space. The air then follows the path of least resistance, dictated by the body’s connective tissue layers.
These connective tissue layers, known as fascial planes, function like interconnected hallways running throughout the body. Air tracks along these planes from the chest cavity upwards into the neck, face, arms, or abdomen, causing characteristic swelling. The persistence of the air leak, rather than the amount of air, determines the extent of the emphysema.
Causes Related to Thoracic Trauma and Pulmonary Conditions
The most frequent source of the air leak is an injury or condition affecting the chest cavity, particularly the lungs and airways. A collapsed lung (pneumothorax) is a primary cause, occurring when air leaks from the lung into the surrounding space, and then breaches the chest wall to reach the subcutaneous tissue. This often results from blunt trauma, such as a severe blow to the chest, or penetrating injuries like stab or gunshot wounds.
Severe physical force can cause rib fractures, and the sharp ends of these broken bones may tear the lung tissue, facilitating the air leak. High-pressure events within the respiratory system can also cause air leaks. This phenomenon, known as barotrauma, commonly occurs in patients on mechanical ventilation whose lungs are over-inflated, causing small air sacs (alveoli) to rupture.
Procedures involving the chest can also introduce or facilitate air leaks, often termed “surgical emphysema.” Examples include accidental puncture of the lung during central venous line placement or complications arising from cardiothoracic surgery. An improperly functioning chest tube, designed to remove air from the chest cavity, can also push air back into the soft tissues, exacerbating the condition.
Causes Related to Upper Airway and Digestive Tract Damage
Air leaks originating from the throat, neck, and upper digestive tract are significant causes of subcutaneous emphysema from non-pulmonary sources. The trachea and larynx, which form the upper airway, can be damaged during medical procedures like intubation or as a result of direct neck trauma. A tear in the wall of the trachea allows air to escape immediately into the deep tissues of the neck.
The esophagus, the tube connecting the throat to the stomach, is another potential source. This often involves a spontaneous rupture called Boerhaave syndrome, typically caused by forceful vomiting. This tear releases air and potentially digestive contents into the mediastinum, from where it rapidly tracks up into the neck and face. Complications from endoscopic procedures can also cause a perforation.
Certain non-thoracic procedures can introduce air into the tissue planes, particularly those that use pressurized air. Complex dental procedures utilizing high-speed, air-driven instruments, or injuries to the sinuses and facial bones, can force air into the soft tissues of the face and neck. Rare but serious causes include infections with gas-producing bacteria, such as necrotizing fasciitis, which generate gas within the tissues.
Identification and Resolution
The diagnosis of subcutaneous emphysema is often made during a physical examination when the characteristic crepitus is felt by the healthcare provider. While the physical sign is telling, imaging studies are necessary to confirm the diagnosis and locate the underlying source of the air leak. A chest X-ray may show air in the soft tissues, sometimes displaying a distinct pattern known as the “ginkgo leaf sign” when air outlines the chest muscles.
A computed tomography (CT) scan is the most sensitive imaging tool, capable of precisely mapping the extent of the trapped air and pinpointing the exact location of the internal breach. Treatment is focused entirely on resolving the underlying cause, such as repairing a torn lung or stabilizing a ruptured airway. Once the source of the air leak is sealed, the air pressure gradient reverses.
Subcutaneous emphysema is typically a self-limiting condition; the trapped air is gradually reabsorbed into the bloodstream and eliminated by the body over days to a couple of weeks. In severe cases, where air accumulation is extensive and causes complications like airway compression, procedures may be performed to decompress the tissue. This involves placing small catheters or making tiny incisions to allow excess air to escape, reducing pressure on surrounding structures.