A 32-year-old man presents to the emergency department with a stab wound to the left chest wall following an altercation. The wound is 2 cm long with clean, sharp margins and minimal surrounding tissue damage. The examining physician suspects penetration into the pleural cavity. Which investigation is most appropriate to determine the depth of penetration and assess for pneumothorax or hemothorax?

Explanation

## Investigation of Choice for Stab Wound to the Chest ### Clinical Context A hemodynamically **stable** patient with a penetrating chest wound and suspected pleural cavity involvement requires rapid, non-invasive imaging to assess for: - Pneumothorax or hemothorax - Mediastinal injury - Foreign body retention ### Why Chest X-ray (PA + Lateral) is the First-Line Investigation **Key Point:** In a **stable** patient with penetrating chest trauma, Chest X-ray (CXR) — posteroanterior and lateral views — is the **investigation of choice** as the initial imaging modality. This is consistent with ATLS (Advanced Trauma Life Support) guidelines and standard forensic/clinical teaching (Reddy & Rao, Forensic Medicine; Harrison's Principles of Internal Medicine). **High-Yield:** CXR can detect: - **Pneumothorax** — visceral pleural line, collapsed lung (sensitivity 85–90%) - **Hemothorax** — blunting of costophrenic angle, opacification of hemidiaphragm (sensitivity 80–85%) - **Mediastinal widening** — suggesting great vessel injury - **Foreign body** — if retained in the wound tract **Clinical Pearl — PA vs. Lateral views:** - **PA view**: Detects pneumothorax ≥2 mm, assesses cardiac silhouette and mediastinum - **Lateral view**: Localizes wound depth relative to mediastinal structures and diaphragm; detects posterior collections missed on PA alone ### Why CT Chest is NOT the First-Line Choice Here **Clinical Pearl:** Although CT chest with contrast offers superior anatomical detail and higher sensitivity for occult injuries, it is **not** the first-line investigation in a stable patient because: 1. **Time delay** — CT requires transport to the scanner, which is inappropriate if the patient deteriorates 2. **Radiation and contrast risk** — unnecessary if CXR is diagnostic 3. **ATLS protocol** — CXR is the mandated initial imaging; CT is reserved for equivocal CXR findings or when surgical planning is needed CT is escalated to **only if**: CXR is equivocal, clinical suspicion remains high despite normal CXR, or multi-organ injury is suspected. ### Why Other Options Are Incorrect - **Ultrasound (FAST/chest)**: Useful for detecting hemothorax/pericardial effusion at bedside but operator-dependent and cannot assess depth of penetration reliably - **Diagnostic laparoscopy**: Invasive surgical procedure; inappropriate for a chest wound (anatomically misplaced distractor); reserved for suspected diaphragmatic or abdominal injury ### Diagnostic Accuracy Summary | Finding | CXR Sensitivity | CXR Specificity | |---------|----------------|----------------| | Pneumothorax | 85–90% | >95% | | Hemothorax | 80–85% | >95% | **High-Yield Mnemonic — STAB-CXR:** **S**table patient, **T**horacic penetration, **A**ssess with **B**asic imaging → **C**hest **X**-ray **R**outine first. [cite: Reddy & Rao Forensic Medicine 34e Ch 12; ATLS 10th Edition, American College of Surgeons]