A 52-year-old woman with a history of lung cancer presents with progressive hoarseness for 2 months. Laryngoscopy reveals bilateral vocal cord paralysis in a paramedian position. Chest imaging shows a large mediastinal mass compressing the aorta and left main bronchus. Which nerve is most likely compressed by the malignancy?

Explanation

## Diagnosis: Bilateral Recurrent Laryngeal Nerve Compression ### Anatomical Pathway of the RLN ```mermaid flowchart TD A[Vagus nerve CN X]:::outcome --> B[Descends in neck] B --> C{Left side}:::decision B --> D{Right side}:::decision C --> E[Loops under aortic arch]:::action D --> F[Loops under right subclavian artery]:::action E --> G[Ascends in tracheoesophageal groove]:::action F --> H[Ascends in tracheoesophageal groove]:::action G --> I[Enters larynx]:::outcome H --> I J[Mediastinal mass]:::urgent --> K[Compresses aortic arch region]:::urgent K --> E K --> F ``` ### Why Bilateral RLN Compression Occurs **Key Point:** The recurrent laryngeal nerves have a unique anatomical course: - **Left RLN:** Loops under the aortic arch (vulnerable to aortic and mediastinal pathology) - **Right RLN:** Loops under the right subclavian artery (also vulnerable to mediastinal masses) - Both nerves then ascend in the tracheoesophageal groove A large mediastinal mass can compress both nerves as they loop around their respective vascular structures. ### Clinical Presentation of Bilateral RLN Paralysis | Feature | Bilateral RLN Paralysis | Bilateral SLN Paralysis | |---------|------------------------|------------------------| | Cord position | **Paramedian** (both sides) | Lateral/abducted (both sides) | | Abduction | **Lost bilaterally** | Preserved bilaterally | | Voice quality | Breathy, weak, diplophonia | High-pitched, fatigable | | Airway compromise | **Severe** (stridor, dyspnea) | Minimal | | Aspiration risk | Moderate | Minimal | **Clinical Pearl:** Bilateral paramedian vocal cord paralysis is an **airway emergency**. Patients may require tracheostomy if there is significant airway obstruction. The classic teaching is: "bilateral RLN paralysis = paramedian cords = airway crisis." ### Why Malignancy Causes Bilateral RLN Compression 1. **Location:** Lung cancer with mediastinal involvement can grow into the mediastinum 2. **Left side:** Mass compresses left RLN as it loops under the aortic arch 3. **Right side:** Mass can extend to compress right RLN in the tracheoesophageal groove 4. **Synchronous compression:** Both nerves affected simultaneously **High-Yield:** In a patient with bilateral vocal cord paralysis in paramedian position + mediastinal mass, think **bilateral RLN compression from malignancy**. This is a classic NEET PG scenario. **Mnemonic: BILATERAL RLN PARALYSIS = "PARAMEDIAN PAIR"** - **P**aramedian position (both cords) - **A**bduction lost (both sides) - **I**nspiratory stridor (airway at risk) - **R**ecurrent laryngeal nerve (both sides) - **M**ediastinal pathology (common cause) - **E**mergency airway management (may need tracheostomy) - **D**yspnea (progressive) - **I**nability to cough effectively - **A**irway obstruction (bilateral = severe) - **N**eeds imaging of mediastinum ### Investigation - **CT chest with contrast:** Defines mass extent and relationship to great vessels - **Laryngoscopy:** Confirms bilateral paramedian cord paralysis - **PET-CT:** Staging of malignancy