Overview
Definition:
Recurrent laryngeal nerve (RLN) injury refers to damage to the nerve responsible for motor control of the ipsilateral vocal cord, leading to dysphonia, dysphagia, and aspiration
This iatrogenic complication is most commonly associated with surgical procedures involving the neck, particularly thyroidectomy, parathyroidectomy, and anterior cervical spine surgery.
Epidemiology:
The incidence of unilateral RLN injury varies significantly depending on the type of surgery, surgeon experience, and patient factors
Post-thyroidectomy rates range from 0.3% to 3% for permanent paralysis and 2% to 8% for temporary dysfunction
Bilateral injury is less common but carries more severe consequences.
Clinical Significance:
Preventing RLN injury is paramount in neck surgery to avoid significant morbidity, impacting patient's quality of life due to voice changes, difficulty swallowing, and risk of aspiration pneumonia
Understanding its anatomy and employing meticulous surgical techniques are crucial for successful outcomes and patient safety.
Anatomy And Pathophysiology
Anatomy:
The RLN arises from the vagus nerve, loops around the subclavian artery on the right and the aortic arch on the left, before ascending in the tracheoesophageal groove to innervate the larynx
Its close proximity to the thyroid gland, recurrent laryngeal arteries, and the inferior thyroid artery makes it vulnerable during dissection.
Pathophysiology:
Injury can occur through direct trauma (ligation, transection), thermal injury from electrocautery, stretch or retraction injury, or ischemic injury due to devascularization
The functional consequences depend on whether the injury is unilateral or bilateral, and whether it affects motor or sensory fibers.
Risk Factors And Vulnerable Procedures
Risk Factors:
Factors increasing RLN injury risk include reoperation, extensive goiter or thyroiditis, retrosternal extension of goiter, malignancy, difficult dissection, and lack of intraoperative nerve monitoring
Surgeon's experience and case volume are also significant determinants.
Vulnerable Procedures:
Thyroidectomy (total, subtotal, lobectomy), parathyroidectomy (especially when ectopic or intrathyroidal), anterior cervical spine surgery, carotid endarterectomy, thoracic surgery near the aortic arch, and neck dissections are high-risk procedures for RLN injury.
Prevention Strategies Intraoperative
Identification And Dissection:
Meticulous anatomical identification of the RLN before dissection is key
Tracing the nerve from its origin in the neck or even from its vagal origin in the thorax can be beneficial
Dissection should be performed in the plane between the thyroid gland and the trachea, identifying the nerve as it enters the larynx.
Nerve Monitoring:
Intraoperative neuromonitoring (IONM) using nerve stimulators and EMG allows for real-time assessment of nerve integrity
Continuous IONM or intermittent stimulation can detect nerve compromise early, prompting changes in surgical technique
A baseline signal should be established, and significant signal loss warrants caution.
Surgical Technique:
Preserving the nerve's vascular supply is critical
Avoid aggressive ligation or division of vessels directly adjacent to the nerve
Use blunt dissection and monopolar cautery sparingly near the nerve, preferring ultrasonic dissectors or bipolar cautery at lower settings
Ligating vessels more peripherally away from the nerve is preferred.
Postoperative Assessment And Management
Immediate Assessment:
Postoperatively, patients should be assessed for voice quality and ability to cough
A detailed history of voice changes, stridor, or aspiration symptoms is crucial
Visualizing vocal cord movement via indirect or direct laryngoscopy is the gold standard for diagnosis.
Temporary Vs Permanent Injury:
Temporary dysfunction often resolves within weeks to months, while permanent injury may require long-term management
Differentiating between the two can be challenging initially
Serial laryngoscopic evaluations are important for monitoring recovery.
Management Of Injury:
For unilateral vocal cord paralysis, management ranges from voice rest and speech therapy to, in persistent cases, surgical interventions like vocal fold injection or medialization laryngoplasty
Bilateral paralysis is a surgical emergency and may require tracheostomy.
Key Points
Exam Focus:
Understand the anatomical course of the RLN and its branches, variations, and relationship to surrounding structures
Master the principles of intraoperative nerve identification and monitoring
Know the incidence, risk factors, and management strategies for RLN injury.
Clinical Pearls:
Always visualize the nerve before tying any vessel in its vicinity
Consider IONM in difficult cases or high-risk procedures
Document nerve status (visualized, monitored, or injured) in your operative notes
A low threshold for laryngoscopy if voice changes are reported postoperatively.
Common Mistakes:
Mistaking a large inferior thyroid artery for the RLN
Aggressive electrocautery near the nerve
Ligation of the nerve with its blood supply
Failing to identify the nerve during reoperation or in extensively diseased glands
Inadequate postoperative vocal cord assessment.