Pneumothorax: A High-Yield USMLE Review
Pneumothorax is air in the pleural space that collapses the lung, presenting with instantaneous-onset dyspnea and pleuritic chest pain. It ranges from small and asymptomatic to life-threatening tension pneumothorax. Tension pneumothorax is a can't-miss, clinically diagnosed emergency that must be decompressed before imaging, making pneumothorax a recurring theme across respiratory, emergency, and physical-exam questions.
Pathophysiology
Air enters the pleural space and eliminates the negative pressure that keeps the lung expanded, so the lung on that side collapses. With less aerated lung and interposed air between the lung and chest wall, breath sounds diminish, percussion becomes hyperresonant, and tactile fremitus falls. In tension pneumothorax, a one-way valve mechanism traps progressively accumulating air under pressure, which pushes the mediastinum and trachea toward the opposite side and compresses the great veins—reducing venous return to cause hypotension and distended neck veins.
Presentation
- Sudden (instantaneous) onset of dyspnea and pleuritic (sharp, worse with breathing) chest pain
- Tachycardia and tachypnea
- Decreased or absent breath sounds and hyperresonance to percussion on the affected side
- Decreased tactile fremitus and asymmetric chest expansion on the affected side
- May be asymptomatic if the pneumothorax is small
- Tension pneumothorax: severe dyspnea and respiratory distress, hypotension, distended neck veins, and tracheal deviation away from the affected side
Diagnosis
- Physical exam localizes the lesion: hyperresonance with absent breath sounds points to pneumothorax (versus dullness with absent breath sounds, which suggests effusion); tracheal deviation away from the affected side and asymmetric expansion support the diagnosis
- Tension pneumothorax is a CLINICAL diagnosis—unilateral chest pain, respiratory distress, decreased breath sounds, tracheal deviation, and hypotension—and must not wait for imaging
Management
- Observation for a small, stable primary spontaneous pneumothorax (<2 cm) with close follow-up; supplemental oxygen accelerates resorption
- Needle aspiration for small-to-moderate primary pneumothorax, which may avoid a chest tube
- Chest tube (tube thoracostomy) for large (>2 cm), secondary spontaneous, symptomatic, traumatic pneumothorax, or failure of aspiration
- Tension pneumothorax: immediate needle decompression at the 2nd intercostal space, midclavicular line, BEFORE imaging, followed by chest tube
- Recurrence prevention: after a second episode, consider pleurodesis or VATS with bleb resection
High-yield
- Hyperresonance + absent breath sounds = pneumothorax; dullness + absent breath sounds = effusion (clean discriminator)
- Tracheal deviation AWAY from the affected side signals tension pneumothorax (lung/mediastinum pushed away); deviation toward suggests volume loss like atelectasis
- Tension pneumothorax is one of the lethal 'can't-miss' causes of chest pain—diagnose clinically and decompress immediately, never wait for a chest X-ray
- Primary pneumothorax has a high recurrence rate (~30%)
- Instantaneous-onset dyspnea places pneumothorax alongside PE, flash pulmonary edema, and arrhythmia at the top of the differential
Pitfalls
- Waiting for imaging to confirm tension pneumothorax—this delays lifesaving needle decompression
- Confusing pneumothorax with pleural effusion; both cause absent breath sounds and decreased fremitus, but percussion (hyperresonant vs. dull) discriminates them cleanly
- Missing an asymptomatic small pneumothorax because the presentation can be silent
- Anchoring on ACS in a chest-pain patient and overlooking tension pneumothorax as a lethal alternative
Don't just memorize Pneumothorax — practice reasoning through it on branching cases where your decisions shape the patient.