A 52-year-old woman undergoes total thyroidectomy for papillary thyroid carcinoma. Intraoperatively, the surgeon notices hoarseness of voice immediately after ligation of the superior thyroid vessels on the left side. The patient is extubated without difficulty and breathing is normal, but voice changes persist. Which investigation is most appropriate to confirm the diagnosis and assess the extent of nerve injury?

Explanation

## Investigation of Choice for Intraoperative Recurrent Laryngeal Nerve (RLN) Injury ### Clinical Scenario Immediate postoperative hoarseness after thyroid surgery with normal breathing suggests unilateral RLN injury. The superior thyroid vessels are in close proximity to the external branch of the superior laryngeal nerve (SLN), but the clinical presentation (hoarseness without stridor) is more consistent with RLN injury. ### Why Laryngoscopy is the Investigation of Choice **Key Point:** Laryngoscopy with direct visualization of vocal cord position and mobility is the gold standard for diagnosing RLN injury and determining the type of injury (complete vs. incomplete paralysis). **High-Yield:** Laryngoscopy findings in RLN injury: - **Unilateral injury:** Affected vocal cord in paramedian position (cannot abduct) - **Bilateral injury:** Both cords in midline → stridor and respiratory distress - **SLN injury:** Vocal cord assumes lower position; loss of pitch control (voice fatigue) ### Diagnostic Algorithm ```mermaid flowchart TD A[Postoperative hoarseness after thyroid surgery]:::outcome --> B{Breathing normal?}:::decision B -->|Yes| C[Likely RLN or SLN injury]:::outcome B -->|No| D[Bilateral RLN injury - urgent]:::urgent C --> E[Laryngoscopy]:::action E --> F{Vocal cord position?}:::decision F -->|Paramedian, immobile| G[RLN injury confirmed]:::outcome F -->|Lower position, mobile| H[SLN injury]:::outcome D --> I[Emergency airway management]:::urgent ``` ### Why Other Investigations Are Suboptimal | Investigation | Limitation | |---|---| | **Thyroid ultrasound with Doppler** | Assesses gland vascularity, not nerve function; cannot visualize vocal cord status | | **CT neck with 3D reconstruction** | Shows anatomical detail but does not assess functional nerve injury; not real-time | | **EMG of intrinsic laryngeal muscles** | Useful for prognosis (denervation vs. neurapraxia) at 3–4 weeks, NOT acute diagnosis; requires time for denervation potentials to develop | **Clinical Pearl:** EMG becomes useful only after 10–14 days when fibrillation potentials appear. In the immediate postoperative period, laryngoscopy is diagnostic. ### Management After Laryngoscopy **Key Point:** If RLN injury is confirmed: 1. Voice rest and speech therapy initially 2. EMG at 3–4 weeks to assess prognosis 3. If no recovery by 6 months → consider vocal cord injection or medialization [cite:Sabiston Textbook of Surgery 21e Ch 38]