A thyroidectomy is a common surgical procedure involving the removal of all or part of the thyroid gland, a butterfly-shaped organ located at the base of the neck. This operation carries a specific risk because of the close anatomical relationship between the thyroid and the nerves that control voice function. To protect these delicate structures, surgeons increasingly rely on technological assistance, primarily the Nerve Integrity Monitoring System (NIMS). The NIMS device is an advanced tool that provides real-time feedback on nerve function, allowing the surgical team to navigate the complex surgical field with greater precision.
The Recurrent Laryngeal Nerve: Why Monitoring is Essential
The Recurrent Laryngeal Nerve (RLN) is a pair of nerves responsible for the movement of the vocal cords. These nerves originate in the chest, loop up into the neck, and travel directly behind the thyroid gland before entering the larynx. Because of this close path, the nerves are highly susceptible to injury during thyroid tissue removal.
The RLN controls the opening and closing of the vocal cords. Damage to one nerve can lead to vocal cord paralysis on that side, resulting in a hoarse voice and changes in vocal quality. If both nerves are injured, a rare but significant complication, the vocal cords can become paralyzed in a closed position. This causes severe difficulty breathing and may necessitate an emergency tracheostomy to secure the airway.
How Nerve Monitoring Technology Works
The Nerve Integrity Monitoring System (NIMS) operates using electromyography (EMG), which measures the electrical activity of muscles. The system consists of three main components: a specialized endotracheal tube, a stimulating probe, and a monitor unit. The endotracheal tube, inserted for anesthesia, is equipped with embedded surface electrodes that rest against the vocal cords’ surface. These electrodes detect the electrical signals of the laryngeal muscles.
When the surgeon touches a nerve with the stimulating probe, the probe emits a low-level electrical current. If the nerve is intact, this current travels down the nerve pathway, causing the laryngeal muscles to contract. The electrodes detect this muscle contraction as an EMG signal. The monitor unit translates this signal into a visible waveform and an audible tone, confirming the nerve’s functional status and guiding the surgeon’s dissection.
NIMS Application During the Operation
The practical application of NIMS ensures continuous nerve protection throughout the thyroidectomy. The procedure begins by obtaining a baseline signal, achieved by stimulating the vagus nerve (the parent nerve of the RLN) early in the operation. This confirms the monitoring system is functioning and establishes a reference point for all subsequent measurements.
Nerve Mapping and Dissection
As the surgeon begins the dissection, the stimulating probe is used for nerve mapping. This involves sweeping the area near the thyroid to locate the recurrent laryngeal nerve before it is visually identified. Once the nerve is found and dissected, monitoring provides real-time feedback during critical steps, such as separating the thyroid from the nerve near the ligament of Berry.
Warning and Final Check
A sudden decrease in the EMG signal amplitude serves as an immediate warning of mechanical or thermal stress. This allows the surgeon to pause and adjust their technique before irreversible damage occurs. A final check signal is performed by stimulating the nerve just before the surgical wound is closed to confirm the nerve’s functional integrity has been preserved.
Patient Expectations and Post-Surgical Results
Nerve Integrity Monitoring significantly improves the ability of the surgical team to identify and preserve the recurrent laryngeal nerve, but its use does not entirely eliminate the risk of nerve injury. Patients should understand that the monitoring system is a safeguard and a guide, not an absolute guarantee against temporary or permanent voice changes.
Post-operative vocal issues can still occur, often due to temporary nerve bruising or stretching, a condition known as neuropraxia. This condition causes hoarseness that typically resolves within weeks or months.
Permanent nerve damage, though less common with monitoring, can result from severe injury mechanisms like thermal trauma or crushing. If the NIMS records a loss of signal during the procedure, that data provides an early indication of potential temporary nerve dysfunction, informing post-operative care.
In cases of unilateral signal loss during a planned total thyroidectomy, the monitoring data may prompt the surgeon to stage the surgery, removing only one side of the thyroid to avoid the severe complication of bilateral vocal cord paralysis.