A 38-year-old female with a history of laryngeal papillomatosis presents for repeat laser-assisted endoscopic resection. The anaesthetist is concerned about airway obstruction during induction. Which investigation is most appropriate to quantify the degree of laryngeal narrowing and guide tube size selection?

Explanation

## Rationale for Investigation Choice **Key Point:** Flexible nasopharyngoscopy with measurement of the subglottic diameter is the most practical and clinically useful investigation to assess the degree of laryngeal narrowing and guide endotracheal tube (ETT) selection in laryngeal papillomatosis. ### Why Flexible Nasopharyngoscopy? Flexible nasopharyngoscopy offers: 1. **Direct visualization** of the larynx and subglottic region in the awake patient 2. **Functional assessment** — allows assessment during breathing and phonation 3. **Measurement capability** — permits estimation of subglottic diameter to guide ETT size 4. **Safety** — non-invasive, does not trigger airway reflexes, can be performed in the clinic 5. **Repeatability** — can be performed serially to monitor disease progression ### Clinical Pearl: **Clinical Pearl:** In laryngeal papillomatosis, recurrent lesions cause progressive narrowing of the subglottic airway. Flexible nasopharyngoscopy allows you to visualize the narrowest point (usually at the level of the cricoid ring) and estimate the diameter, which directly informs ETT size selection. A tube that is too large risks further trauma and stenosis; one that is too small may not provide adequate ventilation. ### High-Yield: **High-Yield:** The **subglottic diameter** measured on nasopharyngoscopy is the single best predictor of ETT size tolerance in laryngeal pathology. Normal subglottic diameter is 4.5–5.5 mm in adults; tubes must be selected accordingly. ### Comparison Table: Investigations for Laryngeal Narrowing | Investigation | Visualization | Functional Assessment | Measurement Accuracy | Awake/Safe | Clinical Utility | | --- | --- | --- | --- | --- | --- | | **Flexible Nasopharyngoscopy** | **Excellent** | **Yes** | **Good** | **Yes** | **First-line** | | High-res CT Larynx | Excellent | No | Excellent | Yes | Anatomical detail, stenosis grading | | Rigid Direct Laryngoscopy | Excellent | Limited | Good | No (requires GA) | Therapeutic, but invasive | | Acoustic Rhinometry | None | No | N/A | Yes | Measures nasal airway only | ### Mnemonic: SCOPE for Flexible Endoscopy **Mnemonic:** **SCOPE** — **S**afe, **C**linically useful, **O**bservation of function, **P**racticable, **E**ffective for measurement. ### Difficult Airway Assessment Pathway ```mermaid flowchart TD A[Laryngeal Papillomatosis]:::outcome --> B[Anticipated Difficult Airway?]:::decision B -->|Yes| C[Flexible Nasopharyngoscopy]:::action C --> D[Measure Subglottic Diameter]:::action D --> E{Diameter < 4 mm?}:::decision E -->|Yes| F[Plan smaller ETT + awake fiberoptic intubation]:::action E -->|No| G[Standard ETT size acceptable]:::action F --> H[Secure airway safely]:::outcome G --> H ```