A review of the internal branch of the superior laryngeal nerve (IbSLN) that frames it as the key sensory gatekeeper of the supraglottic larynx. The article follows the nerve from vagal origin to thyrohyoid membrane entry, then into its variable branching and procedural relevance.
Vrapciu AD · Brezean I · Tudose RC · Rusu MC · Triantafyllou G · Piagkou M · doi: 10.3390/diagnostics15131711
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The IbSLN is the larger branch of the superior laryngeal nerve and follows an oblique anterior-inferior-medial course toward the thyrohyoid membrane, usually alongside the superior laryngeal artery.
Direct separation of internal and external branches from the vagus has been reported in about 5–6% of cases.
The nerve courses near the greater horn of the hyoid, which helps localisation in surgery and regional block.
Its distance from the cervical spine increases as it descends, but its membrane entry still overlaps cervical operative levels.
Traditional teaching emphasises post-membrane trifurcation, but the review shows that branching before membrane penetration is common and sometimes extremely frequent depending on the series.
Extralaryngeal branching can be common and in some reports reaches very high prevalence.
The nerve may divide into two to five branches, not just a fixed trifurcation.
Branches supply the supraglottic mucosa and contribute to protective reflex arcs.
Loss of IbSLN integrity may lead to impaired laryngeal sensation, absent cough reflex, silent aspiration and phonatory dysfunction. Conversely, selective block of the nerve is useful in airway and cough-related procedures.
The nerve is at risk during thyroidectomy, carotid surgery and anterior cervical approaches.
IbSLN block facilitates awake intubation and other upper-airway procedures.
Ultrasound-guided block or steroid injection is being used in chronic neurogenic cough.