A 28-year-old male presents to the emergency department with acute onset right-sided pleuritic chest pain and dyspnea. Clinical examination reveals decreased breath sounds on the right side. A bedside chest X-ray (CXR) is equivocal for pneumothorax. What is the investigation of choice to confirm the diagnosis?

Explanation

## Imaging Diagnosis of Pneumothorax — Equivocal CXR ### Clinical Context When a standard inspiratory CXR is equivocal for pneumothorax, a targeted, readily available, and cost-effective next step is required before escalating to advanced imaging. The question asks for the **investigation of choice** in this stepwise clinical scenario — not the "gold standard" or "most sensitive" modality. ### Investigation of Choice: Expiratory Chest X-ray **Key Point:** An **expiratory CXR** is the classical, first-line confirmatory investigation when an inspiratory CXR is equivocal for pneumothorax. During expiration, lung volume decreases while the pneumothorax volume remains constant, making the pleural air collection relatively larger and more conspicuous against the denser lung parenchyma. **High-Yield:** In Indian NEET PG / INI-CET curricula (as taught in standard radiology and surgery textbooks including Sutton's Textbook of Radiology and Bailey & Love), the stepwise approach is: 1. Inspiratory CXR (first-line) 2. **Expiratory CXR** (if equivocal — investigation of choice) 3. CT chest (if still uncertain or for complex/occult cases) **Clinical Pearl:** The expiratory view is: - Immediately available at the bedside - No additional radiation burden beyond a standard CXR - Non-invasive and reproducible - The standard teaching answer in NEET PG for "equivocal CXR" scenarios ### Comparison of Modalities | Feature | Expiratory CXR | HRCT Chest | Ultrasound | Fluoroscopy | |---------|---------------|------------|------------|-------------| | **First-line after equivocal CXR** | ✅ Yes | ❌ Not first-line | Adjunct (POCUS) | ❌ Not indicated | | **Bedside availability** | Immediate | Delayed | Immediate | Not applicable | | **Sensitivity for PTX** | 60–90% | >95% | 86–98% | N/A | | **Standard exam answer** | ✅ Yes | ❌ (gold standard, not IOC here) | ❌ | ❌ | | **Resource requirement** | Minimal | High | Operator-dependent | N/A | ### Why Not the Other Options? - **HRCT (A):** Gold standard and most sensitive, but NOT the "investigation of choice" in a stepwise algorithm after an equivocal CXR. It is reserved for occult, complex, or bilateral pneumothoraces, or when expiratory CXR is also inconclusive. - **Ultrasound (C):** Increasingly used in POCUS/FAST protocols and has high sensitivity, but is operator-dependent and not the classical textbook answer for this scenario in NEET PG curricula. - **Fluoroscopy (D):** Not indicated for pneumothorax diagnosis. **High-Yield:** In NEET PG examination context, "investigation of choice for equivocal CXR in suspected pneumothorax" = **Expiratory CXR** (Bailey & Love, Sutton's Radiology). [cite: Bailey & Love's Short Practice of Surgery, 27th Ed.; Sutton's Textbook of Radiology and Imaging, 7th Ed.]