## Etiology of Unilateral Vocal Cord Paralysis **Key Point:** Unilateral vocal cord paralysis results from injury to the recurrent laryngeal nerve (RLN) or vagus nerve along their anatomical course. ### Common Causes of Unilateral VCP | Cause | Mechanism | Frequency | |-------|-----------|----------| | Thyroid surgery | RLN injury during dissection | Most common iatrogenic | | Lung malignancy (apex) | Pancoast tumor invading RLN | Common malignancy-related | | Skull base tumors | Vagal nerve involvement at skull base | Vagal involvement | | Cardiac surgery | RLN injury during aortic procedures | Iatrogenic | | Aortic aneurysm | Compression of RLN | Cardiovascular cause | | Mediastinal pathology | RLN compression/invasion | Mediastinal involvement | ### Why Bilateral Carotid Artery Stenosis is NOT a Cause **High-Yield:** Bilateral carotid artery stenosis affects cerebral perfusion and is a risk factor for stroke, but it does NOT directly cause vocal cord paralysis. The carotid arteries do not course with the recurrent laryngeal nerve in a manner that would result in nerve injury from stenosis alone. The RLN descends in the neck medial to the carotid sheath but is not compressed by carotid pathology. **Clinical Pearl:** While carotid dissection or carotid surgery can injure the vagus or RLN, simple stenosis of the carotid artery does not cause vocal cord paralysis. ### Anatomical Basis The recurrent laryngeal nerve: - Branches from the vagus nerve (CN X) - On the left: loops under the aortic arch - On the right: loops under the subclavian artery - Ascends in the tracheoesophageal groove - Vulnerable to injury from thyroid, lung, cardiac, and mediastinal pathology **Warning:** Do not confuse carotid stenosis with carotid dissection or carotid surgery — the latter two can cause vagal injury, but stenosis alone cannot.
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