USMLE® Step 1 style questions USMLE
A 45-year-old male is brought to the emergency department after being involved in a high speed motor vehicle accident. The patient is agitated and in respiratory distress. Temperature is 37.6°C (99.7°F), pulse is 120/min, and blood pressure is 98/63 mmHg. Respirations are 25/min, and the patient has an oxygen saturation of 87% on room air. An immediate chest x-ray is obtained and demonstrates the following findings:
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Which of the following is the most likely diagnosis?
Content Reviewers:Rishi Desai, MD, MPH
Contributors:Sam Gillespie, BSc
With pneumothorax, pneumo refers to air and thorax means chest, so a pneumothorax is when there is air in the chest; more specifically air in the space between the lungs and chest wall – called the pleural space.
The pleural space lies between the parietal pleura, which is stuck to the chest wall, and the visceral pleura, which is stuck to the lungs.
The pleural space normally contains a lubricating fluid that helps reduce friction as the lungs expand and contract.
Pressure within the pleural space is established by two main opposing forces.
One is the muscle tension of the diaphragm and chest wall which contract and expand the thoracic cavity outwards, and the other is the elastic recoil of the lungs, which try to pull the lungs inward.
The two pull on each other creating a balance between the forces that creates a slight vacuum in the pleural space.
It results in the pleural space having a pressure of -5 centimeters of water relative to the pressure of 0 centimeters of water in both the thoracic cavity and the lungs.
A pneumothorax forms when the seal of the pleural space is punctured and air moves in from the outside, making the pressure in the pleural space equalize to 0 centimeters of water.
Since the negative pleural pressure is lost, the two opposing forces no longer pull on one another.
As a result, the lungs simply pull inwards and collapse, and the chest wall simply springs outward a bit.
A collapsed lung limits how well it can exchange air, and can lead to a reduction in oxygen being brought into the body, and a build-up of carbon dioxide in the body because it can’t easily get released.
There are many types of pneumothorax.
The first is a spontaneous pneumothorax which typically occurs when a bullae, which is an air pocket, forms on the surface of the lungs and breaks.
Bullae form when the alveoli, which are the terminal ends of the lung where gas exchange occurs, develop a tiny leak and air slowly seeps into the surrounding lung tissue.
Typically the alveoli heals up, otherwise it would itself lead to a pneumothorax.
But the result is a bullae.
If the bullae breaks, it creates a large hole in the visceral pleura and air can go from the airway directly into the pleural space.
A primary spontaneous pneumothorax is one that develops in the absence of an underlying condition - most typically it’s in a thin, tall, adolescent male who is hold his breath, creating a lot of internal pressure.
A secondary spontaneous pneumothorax is one that develops in someone with an underlying lung disease, like Marfan’s syndrome, cystic fibrosis, emphysema, or lung cancer.
A pneumothorax refers to an abnormal collection of air or gas in the pleural space that causes a loss of negative pressure. Like pleural effusion (liquid buildup in that space), pneumothorax may interfere with normal breathing. Pneumothorax can either be traumatic, or spontaneous. Traumatic pneumothorax occurs due to an injury to the chest, such as a broken rib or puncture wound. On the other hand, spontaneous pneumothorax can happen without an apparent cause. It is commonly seen in patients with lung diseases such as COPD, cystic fibrosis, asthma, smokers, and people with Marfan syndrome. Symptoms of pneumothorax can include chest pain, shortness of breath, and difficulty breathing. The diagnosis is typically made with a chest X-ray or CT scan. Treatment for a pneumothorax may require a chest tube to remove the air or gas and re-expand the lung.