## Clinical Presentation Analysis **Key Point:** Vocal cord paralysis in a smoker with lung cancer and mediastinal involvement is a classic presentation of recurrent laryngeal nerve (RLN) compression by a left hilar/mediastinal mass. ## Anatomical Basis The left recurrent laryngeal nerve has a unique course: - Arises from the left vagus nerve in the thorax - Loops under the aortic arch (left side) or pulmonary artery (right side) - Ascends in the tracheoesophageal groove - Vulnerable to compression by mediastinal masses, especially left hilar tumors ## Vocal Cord Position in RLN Paralysis **High-Yield:** In RLN paralysis, the affected vocal cord typically rests in a **paramedian position** (slightly abducted from midline) due to: - Loss of all intrinsic laryngeal muscles except cricothyroid (innervated by superior laryngeal nerve) - Cricothyroid muscle (innervated by SLN) pulls the cord slightly laterally - Results in incomplete glottic closure → hoarseness + weak cry ## Why Left Hilar Mass Causes Left RLN Paralysis | Finding | Explanation | | --- | --- | | Left hilar mass | Directly compresses left RLN as it loops under aortic arch | | Mediastinal lymphadenopathy | Extends compression along RLN course | | Paramedian cord position | Pathognomonic for RLN paralysis | | Hoarseness + dysphagia | RLN innervates all intrinsic muscles + pharyngeal sensation | **Clinical Pearl:** Lung cancer is the most common malignant cause of RLN paralysis in adults; esophageal cancer is second. Always suspect malignancy in unilateral vocal cord paralysis until proven otherwise. ## Differential Consideration **Mnemonic: SLAP for RLN Paralysis Causes** — **S**urgery (thyroid, cardiac), **L**ung cancer, **A**ortic pathology, **P**ancreatic cancer. In this case, lung cancer with mediastinal involvement is the clear culprit. 
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