## Investigation of Choice for Foreign Body Airway Aspiration ### Clinical Context This child presents with the classic triad of foreign body aspiration: **acute onset coughing**, **stridor**, and **unilateral decreased air entry** after playing with peanuts. The question specifically asks for the **investigation of choice** — i.e., the diagnostic test performed to confirm the diagnosis before any intervention. ### Why Chest X-ray (Inspiratory and Expiratory Views) is Correct **Key Point:** Chest X-ray with both inspiratory and expiratory views is the **investigation of choice** for confirming suspected foreign body aspiration in children. It is non-invasive, rapidly available, and provides diagnostic information that guides subsequent management. **High-Yield Radiological Findings:** - **Inspiratory view:** May appear normal or show mild hyperinflation of the affected (left) lung if the foreign body acts as a ball-valve mechanism. - **Expiratory view:** Demonstrates **air-trapping** on the affected side — the obstructed lung fails to deflate, while the contralateral lung deflates normally. This is the most diagnostically useful finding for radiolucent objects like peanuts. - **Mediastinal shift** away from the affected side on expiration is a highly specific sign. **Clinical Pearl:** Peanuts and most organic foreign bodies are **radiolucent** and will NOT be directly visible on X-ray. However, the **indirect signs** (air-trapping, hyperinflation, mediastinal shift on expiration) confirm the diagnosis with ~80–90% sensitivity. This is why both inspiratory AND expiratory views are mandatory. ### Why Rigid Bronchoscopy (Option C) is NOT the Investigation of Choice Rigid bronchoscopy under general anaesthesia is the **gold standard for treatment** (therapeutic removal) of an airway foreign body — it is NOT classified as an "investigation." The question stem explicitly asks for the investigation of choice. Performing rigid bronchoscopy without prior imaging is inappropriate unless the child is in severe/life-threatening respiratory distress. CXR must precede bronchoscopy to confirm the side of obstruction and plan the procedure safely. *(Dhingra ENT, 7th ed., Ch. 16; Scott-Brown's Otorhinolaryngology)* ### Why Other Options Are Incorrect | Investigation | Why Not First-Line | |---|---| | **Flexible fibreoptic bronchoscopy (A)** | Diagnostic only; cannot remove most foreign bodies; not first-line investigation | | **Rigid bronchoscopy (C)** | Therapeutic, not investigative; requires GA; done after imaging confirmation | | **HRCT chest with 3D (D)** | Excessive radiation, delays treatment, reserved for complex/atypical cases | ### Advantages of CXR as Investigation of Choice 1. Non-invasive — no anaesthesia or sedation required 2. Rapid and universally available in emergency settings 3. Identifies radiopaque foreign bodies directly 4. Detects indirect signs of radiolucent FBs (air-trapping, hyperinflation) 5. Identifies complications: pneumonia, atelectasis, pneumothorax 6. Guides the bronchoscopist to the correct side before intervention **High-Yield:** In a 3-year-old who cannot cooperate with breathing commands, a **lateral decubitus X-ray** (affected side down) can substitute for the expiratory view — the dependent (obstructed) lung will remain hyperinflated rather than compressing normally. **Mnemonic — CHEST for CXR findings in FB aspiration:** - **C**heck inspiratory view for hyperinflation - **H**yperinflation persists on expiratory view (air-trapping) - **E**xamine for mediastinal shift away from affected side - **S**earch for radiopaque density - **T**ake bilateral/decubitus views to compare [cite: Dhingra PL, Diseases of Ear, Nose and Throat, 7th ed., Ch. 16; Scott-Brown's Otorhinolaryngology, Head and Neck Surgery, 8th ed.] 
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