The superior laryngeal nerve leaves the vagus and divides into internal and external branches at a variable level. The external branch descends beside the inferior pharyngeal constrictor toward the cricothyroid muscle and passes close to the superior thyroid pedicle. Its small caliber and partial muscular coverage may make stimulation positive before the nerve is visible [1]. By contrast, the internal branch travels with the superior laryngeal artery through the thyrohyoid membrane and supplies much of the supraglottic sensation. It usually lies above the plane used for superior-pole vessel control. Injury to this branch becomes a consideration when sensory loss or impaired airway protection is suspected [4].

Anatomical communications between the laryngeal nerves can complicate interpretation. Galen’s anastomosis joins the internal laryngeal nerve to the recurrent laryngeal nerve; it is not the usual motor pathway of the EBSLN [5]. Separate connections between the EBSLN and recurrent laryngeal nerve have also been demonstrated [6]. These connections may carry an evoked response to muscles detected by an endotracheal electrode. Their presence and size vary, so they cannot be assumed to preserve cricothyroid function after EBSLN injury.

Cernea classification describes the crossing point of the EBSLN relative to the upper pole. A type 1 nerve crosses the superior thyroid vessels more than 1 cm above the pole. Type 2a crosses within 1 cm, whereas type 2b passes below the upper border of the gland and directly enters the usual area of pedicle division [7]. The classification is an operative relationship rather than a fixed measurement in the neck. Enlargement of the gland and the direction of traction may alter the position seen during surgery.

Friedman classification addresses muscular coverage. The nerve may remain superficial to the inferior constrictor, run partly within its lower fibers, or be covered by the muscle. This distinction is useful when deciding whether further visual exploration is likely to help [8]. The frequency of each pattern varies across published series. In a meta-analysis of 56 studies and 13,444 hemilarynges, identification rates and subtype distributions differed between cadaveric and operative studies [9]. Surgeons should therefore avoid treating a prevalence estimate from one series as an anatomical rule.

Neither classification measures nerve function. Their main value is to warn that exposure may be difficult. A prospective cohort of 136 patients found associations between some low-crossing or partly intramuscular courses, intraoperative amplitude changes, and postoperative acoustic findings [10]. These results support closer attention to such anatomy, but they do not predict injury in an individual patient. A small amplitude change also cannot establish permanent palsy without clinical follow-up.

Superior-pole dissection should begin with a view of the upper pole, cricothyroid muscle, inferior constrictor, and the vessels that will be divided. The medial plane beside the pole and the sternothyroid insertion on the thyroid cartilage help orient the search. Ng et al. identified the EBSLN in 111 of 127 attempted lobectomies and related its entry into muscle to the sternothyroid insertion [12]. This landmark is useful for orientation. The reported distance, however, should not be used as a fixed point for incision in another patient.

Extensive exposure of the EBSLN is seldom necessary. The surgeon needs enough information to protect the nerve during the next step: a short visible segment, its direction, or a repeatable stimulation response may be adequate. Friedman et al. reported high identification rates with a systematic anatomical approach [8]. A recent prospective series visualized 82 of 100 nerves [13], leaving nearly one fifth unconfirmed by sight. When the nerve is covered by constrictor muscle, cutting additional fibers simply to display a longer segment may increase risk without improving vessel control.

Branches of the superior thyroid vessels are usually safest when isolated and controlled one at a time close to the capsule. The segment placed in a ligature, clip, or sealing device should be short and visible. Capsular dissection limits unnecessary lateral work but does not create an absolute safe zone, since a type 2b nerve may also lie near the gland. An apparently avascular plane can still contain neural tissue. Visual identification or stimulation should clarify the intended vessel division rather than encourage a larger field of dissection [3][13].

Retraction is useful only while it improves the view. When the upper pole is held under excessive tension, the nerve may be stretched and the tissue planes become harder to judge. Releasing the pole or changing the angle of traction is appropriate if the next vessel cannot be seen [3]. Bleeding should first be managed with pressure and suction until the vessel stump and surrounding tissue are visible. Blind application of a broad clamp can include the EBSLN [1][3]. A normal response to stimulation before this event documents function at that moment; it does not protect the nerve during subsequent hemostasis.

The amount of heat delivered near a nerve varies with the device, power setting, activation time, intervening tissue, and residual jaw temperature. Most experimental safety data concern the recurrent laryngeal nerve and often come from animal models. They support short activation, physical separation, and adequate cooling, but they cannot provide a universal 3 - 5 mm margin for every device and operative setting [14]. In a confined field where the EBSLN cannot be separated confidently, cold division followed by a tie or clip may give better control [1][14]. Recently activated jaws can remain hot after the device has stopped, including the surface turned away from the nerve.

Nerve protection should not compromise the planned thyroid resection. There is no established role for routinely leaving upper-pole tissue to protect the EBSLN. Similarly, a suspected tumor should not be opened to create more working space. Failure to separate the nerve warrants a fresh assessment of the exposure and the likely cause, which may be displacement, scar, or true invasion. Any decision to limit resection or sacrifice an involved structure belongs to the oncological strategy and informed consent, rather than to routine mobilization of the upper pole.

During stimulation, conduction through the EBSLN is suggested by contraction of the ipsilateral cricothyroid muscle. Stimulating the muscle directly does not test the proximal nerve. Endotracheal surface electrodes may record an evoked laryngeal waveform, while some studies use a needle electrode placed in the cricothyroid muscle. A stable response obtained before superior-pole dissection and again after the vessels have been divided documents continuity at those two time points [3].

The cricothyroid twitch and the endotracheal waveform should be documented separately. Anatomical connections may transmit the stimulus to muscles in contact with the tube electrode, but this pathway is variable [6]. Waveform quality also depends on tube position, electrode contact, neuromuscular blockade, stimulation technique, and the tissue between probe and nerve. Loss of a trace requires technical troubleshooting before nerve injury is diagnosed. Conversely, a preserved final waveform cannot rule out all causes of postoperative dysphonia. Intermittent stimulation provides selected checks during the operation; it is not continuous surveillance.

Barczyński et al. randomized 210 women to visual identification alone or visual identification combined with IONM. Final analyses included 101 patients and 202 nerves in the visual group and 100 patients and 200 nerves in the monitored group. Identification was a nerve-level outcome; voice was assessed by patient. Videostrobolaryngoscopy was performed preoperatively and on postoperative day 1, with repeat examinations at 3 and 6 months if abnormalities persisted. Phonation testing took place at 2 - 3 weeks and 3 months. Early deterioration meant a decrease of at least 10% in maximum phonation time, voice level, or fundamental frequency, or an increase of more than four GRBAS points. IONM increased identification from 34.3% to 83.8% and was associated with fewer early abnormalities. The voice differences were no longer present at 3 months [15]. Thus, the trial supports improved identification and a short-term functional benefit but does not demonstrate the same reduction in permanent disability.

In the trial by Masuoka et al., 252 patients were assigned to recording-based monitoring or conventional hand-held stimulation. Nerve identification was reported per nerve. The secondary clinical endpoint was patient-level voice impairment at 3 months, assessed by phonation testing and the EBSLN Voice Impairment Index-5. Visual identification occurred in 48.8% of monitored nerves and 17.8% of conventionally stimulated nerves; the corresponding rates for identification by stimulation were 89.2% and 17.8%. Women in the monitoring group reported less subjective impairment [16]. The control group was not unstimulated, so the study compared different approaches to mapping and recording. It did not equate an intraoperative electrical event with permanent palsy.

Uludag et al. enrolled 133 patients with 211 nerves at risk. Sixty-five patients (105 nerves) underwent superior-pole dissection without a deliberate attempt to identify the EBSLN. In the monitored arm, 68 patients (106 nerves) underwent IONM-assisted identification. Injury was defined by loss of the intraoperative cricothyroid electromyographic response after dissection. Results were reported both per patient and per nerve, and Voice Impairment Index-5 scores were obtained before surgery and at 1, 3, and 6 months. Electrophysiological injury was recorded in 9 of 105 control nerves and 1 of 106 monitored nerves; postoperative voice scores also favored monitoring [17]. These figures should always be quoted with their nerve-level denominator.

Aygun et al. published a randomized study in 2026 using a cohort enrolled during 2015-2016. Both groups underwent recurrent laryngeal nerve monitoring during superior-pole dissection, but only the intervention group had specific mapping of the EBSLN. The study defined injury as absent or lost cricothyroid electromyographic activity after completion of thyroidectomy and analyzed the result per nerve at risk. The endpoint occurred in 15.4% of control nerves and 2.1% of monitored nerves [18]. Since the measurement was made at the end of surgery, these values represent intraoperative electrophysiological events rather than permanent clinical palsy rates.

The same pattern appears in the pooled evidence. A 2019 meta-analysis of seven studies found a higher EBSLN identification rate with IONM [19]. Evidence for a lasting improvement in voice remains less secure. Control procedures, denominators, definitions of injury, and voice tests varied between studies, as did the timing of assessment. An event recorded immediately after dissection cannot be combined uncritically with a deficit that persists months later.

Deliberate protection of the EBSLN is part of every superior-pole dissection, but device use may reasonably differ between institutions. Routine IONM is practical where equipment, trained staff, and a consistent protocol are available. In other settings, selective use is most defensible for large goiters, upper-pole tumors, reoperations, or anatomy that remains uncertain after exposure. This position follows current guidance: monitoring adds functional information but does not replace direct, controlled dissection [2][3].

Postoperative assessment should ask about the activity that exposes the problem: high notes, sustained speech, projection, or a familiar singing task. Flexible laryngoscopy documents vocal-fold movement and may reveal edema or another structural cause. If mobility is preserved, stroboscopy and selected acoustic measures may clarify persistent symptoms. In three patients with electromyographically confirmed superior laryngeal weakness, phonatory findings included ipsilateral bowing and shortening, unequal vocal-process height, and false-fold hyperadduction; there was no shared abnormality at rest [21]. A three-case report cannot define a diagnostic pattern. Cricothyroid needle electromyography is useful when confirmation of denervation would alter diagnosis or counseling, but the value of the study depends on timing and operator experience [22]. Permanent injury should not be assigned on the basis of a single early visit.

Voice guidelines recommend documenting postoperative change between 2 weeks and 2 months and arranging laryngeal examination when a change is present [2]. Earlier assessment is warranted for severe dysphonia, airway concern, or suspected aspiration. Dysphagia and choking deserve a separate evaluation because they are not specific for internal-branch injury. When aspiration is suspected, instrumental swallowing assessment can define the impairment and guide diet or rehabilitation [23].

A stepwise evaluation is useful when voice symptoms persist despite normal vocal-fold mobility. The first step is to document the complaint with a patient-reported measure and a task that reproduces it. Flexible laryngoscopy follows, with stroboscopy when the initial examination is unrevealing. Cricothyroid laryngeal electromyography is reserved for cases in which the result would change the diagnosis, prognosis, or discussion with the patient. Referral to a laryngologist and speech-language pathologist then allows treatment to be matched to the identified disorder [2][22][23]. This sequence also reduces the chance of labeling structural, inflammatory, or compensatory dysphonia as EBSLN palsy.

An unexpected loss of intraoperative response requires a pause. The team should first check the equipment, tube or electrode position, neuromuscular blockade, and stimulation method, then review the last operative step. Traction can be released immediately. A recently placed ligature should be reassessed if signal loss followed its application [3][22]. Confirmed transection requires specialist judgment about repair, as no single reconstructive method has been shown to restore normal dynamic cricothyroid function reliably. Voice during the first postoperative days is too early to judge neural recovery or the result of repair.

Treatment of persistent dysfunction is guided by the cause and by how much the deficit affects the patient. Voice therapy may lessen excessive effort and maladaptive compensation. Structural or neuromuscular procedures require laryngological assessment [23]. Nasseri and Maragos reported improvement in most of nine patients treated with combined type IV and type I thyroplasty for unilateral superior laryngeal weakness [24]. This small uncontrolled series does not provide routine indications for patients after thyroidectomy. Vitamins and so-called neurotrophic medication also lack evidence for restoration of EBSLN function. Decisions about further treatment should follow serial symptoms and objective findings rather than a promised recovery interval or an automatic operation at 6 months.