A 38-year-old female with a history of tongue cancer (post-radiation and chemotherapy) presents for a routine dental procedure. Intraoral examination reveals severe trismus (mouth opening <1 cm) and significant scarring of the oropharynx. You suspect a difficult airway. Which investigation is most appropriate to assess the degree of airway narrowing and guide your intubation strategy?

Explanation

## Imaging Assessment of Radiation-Induced Airway Narrowing **Key Point:** In patients with post-radiation changes and severe trismus, high-resolution CT with 3D airway reconstruction is the investigation of choice to quantify the degree of airway narrowing, identify the site(s) of stenosis, and guide intubation technique selection. ### Why CT with 3D Reconstruction Is Optimal 1. **Precise Anatomical Detail**: CT provides excellent visualization of the larynx, pharynx, and trachea with cross-sectional imaging that reveals the exact location and degree of stenosis. 2. **3D Reconstruction**: Allows assessment of the narrowest point and predicts whether conventional laryngoscopy, video laryngoscopy, or fiberoptic intubation will be feasible. 3. **Radiation-Induced Changes**: Clearly shows post-radiation fibrosis, edema, and structural distortion that affect airway management decisions. 4. **Preoperative Planning**: Enables selection of appropriate tube size and technique before induction of anesthesia. 5. **Rapid Acquisition**: Modern CT is fast and does not require patient cooperation (unlike fiberoptic examination). ### Comparison of Investigation Options | Investigation | Utility | Limitations | |---|---|---| | **CT neck with 3D airway reconstruction** | Quantifies stenosis; guides tube selection; identifies narrowest point | Radiation exposure; requires IV contrast for vascular detail | | Awake flexible fiberoptic laryngoscopy | Therapeutic (allows awake intubation); direct visualization | Invasive; requires topical anesthesia; difficult in severe trismus; does not quantify stenosis | | MRI neck | Excellent soft-tissue detail; no radiation | Longer acquisition time; patient must be cooperative; less useful for acute airway assessment | | Lateral neck radiograph | Quick; non-invasive | Limited detail; does not show cross-sectional anatomy; cannot quantify degree of stenosis | **Clinical Pearl:** In post-radiation patients with trismus, fiberoptic laryngoscopy may be impossible due to inability to open the mouth. CT imaging allows you to plan the airway strategy without requiring patient cooperation or airway instrumentation. **High-Yield:** The narrowest diameter of the airway on CT predicts the largest endotracheal tube that can be passed. A narrowing to <5 mm diameter typically requires a tube ≤6.0 mm ID. **Mnemonic: RADIATION AIRWAY ASSESSMENT** — **R**apid CT imaging, **A**irway diameter quantified, **D**irect 3D visualization, **I**dentify stenosis site, **A**void blind intubation, **T**ube size predicted, **I**ntubation strategy guided, **O**ptimal outcome, **N**o patient cooperation needed. **Tip:** Always obtain CT before attempting intubation in post-radiation patients with trismus. This prevents complications from blind instrumentation and allows selection of the correct tube size.