A 52-year-old male tobacco chewer from rural Maharashtra presents with progressive hoarseness of voice for 3 weeks and mild dysphagia. On laryngoscopy, a unilateral vocal cord is seen in the paramedian position and does not abduct during inspiration. The patient denies any neck trauma or recent surgery. Which nerve is most likely injured, and at what anatomical level?

Explanation

## Diagnosis: Recurrent Laryngeal Nerve (RLN) Injury ### Clinical Presentation Analysis The patient presents with: - **Unilateral vocal cord in paramedian position** — characteristic of RLN injury - **Loss of abduction during inspiration** — indicates loss of posterior cricoarytenoid (PCA) function - **Hoarseness** — due to incomplete glottic closure - **Risk factors:** Tobacco use, age 52, rural Maharashtra — raises concern for thoracic/mediastinal malignancy ### Anatomical Basis of RLN Injury at the Aortic Arch **Key Point:** The **left** recurrent laryngeal nerve has a significantly longer intrathoracic course — it loops around the **aortic arch** (ligamentum arteriosum) before ascending in the tracheoesophageal groove. This makes it uniquely vulnerable to compression by mediastinal pathology, including: - Lung malignancy (Pancoast tumor, hilar lymphadenopathy) - Aortic aneurysm - Mediastinal lymphoma or metastatic nodes **High-Yield:** In a patient with **no history of neck surgery or trauma**, the most clinically important and exam-relevant site of RLN injury is the **aortic arch level** — this is the classic "Ortner's syndrome" territory and the basis of the well-known "left RLN palsy = rule out thoracic pathology" teaching point. The right RLN loops around the subclavian artery and has a shorter intrathoracic course, making it less susceptible to mediastinal disease. ### Vocal Cord Position in Nerve Injury | Nerve Injury | Vocal Cord Position | Abduction | Adduction | Voice Quality | | --- | --- | --- | --- | --- | | **RLN (complete)** | Paramedian | Lost | Intact | Hoarse, breathy | | **SLN (external branch)** | Paramedian-lateral | Intact | Weak | High-pitched, fatigable | | **Vagus nerve** | Midline/lateral | Lost | Lost | Breathy, nasal | ### Motor Innervation of Laryngeal Muscles - **RLN innervates:** All intrinsic laryngeal muscles EXCEPT cricothyroid - **Posterior cricoarytenoid (PCA)** — the ONLY abductor; its paralysis → paramedian cord position - Lateral cricoarytenoid, Interarytenoid, Thyroarytenoid (adductors) - **SLN (external branch) innervates:** Cricothyroid muscle only (pitch regulation) **Clinical Pearl:** Paramedian position + loss of abduction = RLN injury. The PCA is the ONLY muscle that abducts the vocal cords; its paralysis locks the cord in paramedian position. ### Why Aortic Arch Level (Not Thyroid Level)? 1. The stem explicitly states **no neck trauma or recent surgery** — thyroid-level injury is predominantly surgical or due to thyroid pathology (which would typically be detectable on examination) 2. The patient is a **tobacco chewer** with no mention of thyroid disease — mediastinal/thoracic malignancy is the leading non-surgical cause of unilateral RLN palsy 3. The **left RLN's loop around the aortic arch** is the anatomical landmark that makes it vulnerable to thoracic pathology — this is a classic NEET PG / AIIMS teaching point 4. Thyroid-level injury (Option B) is the most common *surgical* cause, but the aortic arch is the most important *non-surgical* anatomical vulnerability **Reference:** Gray's Anatomy 42e, Ch 32; Last's Anatomy 12e; Harrison's Principles of Internal Medicine 21e (Chapter on mediastinal disorders and vocal cord palsy)