AN38.1-3 | Larynx — Gate Quiz

Correct. The posterior cricoarytenoid (PCA) is the ONLY abductor of the vocal cords. It pulls the muscular process of the arytenoid posteriorly → the arytenoid rotates → the vocal process (and attached vocal cord) moves laterally (abducts) → opens the rima glottidis. All other intrinsic laryngeal muscles adduct or tense the cords.

Posterior cricoarytenoid (PCA) = the only abductor of the vocal cords. Memory: 'PCA Opens.' Bilateral PCA paralysis (bilateral RLN injury) → both cords adducted → rima glottidis critically narrowed → respiratory failure.

Correct. The cricothyroid muscle is the only intrinsic laryngeal muscle supplied by the external branch of the superior laryngeal nerve (not the RLN). It lengthens and tenses the vocal cord, increasing pitch. This is why external SLN injury causes inability to reach high pitch, but the cord still moves (RLN intact).

All intrinsic laryngeal muscles are supplied by the recurrent laryngeal nerve EXCEPT the cricothyroid, which is supplied by the external laryngeal nerve (external branch of the superior laryngeal nerve, from CN X). This is a perennial exam question.

Correct. The subglottis is encircled by the cricoid — the only complete ring in the respiratory tract (made of inelastic hyaline cartilage). Any oedema of the subglottic mucosa cannot expand outward (the rigid cricoid prevents it) — it can only expand inward, critically narrowing the airway. This explains why even mild subglottic oedema in croup causes significant stridor and respiratory distress.

The cricoid cartilage forms a complete inelastic ring around the subglottis. In a child (where the subglottis is already narrow), even small amounts of mucosal oedema cause critical circumferential narrowing — the oedematous mucosa has nowhere to expand but inward (the rigid cricoid prevents outward expansion). This is the anatomical basis of croup's danger.

Correct. Ortner syndrome (cardiovocal syndrome): the enlarged left atrium in mitral stenosis can compress the left recurrent laryngeal nerve as it loops under the aortic arch, causing left vocal cord paralysis and hoarseness. This is the classic presentation in a patient with known rheumatic mitral stenosis — particularly relevant in India where rheumatic heart disease remains prevalent.

Ortner syndrome = left RLN compression by an enlarged cardiovascular structure — classically a massively dilated left atrium in rheumatic mitral stenosis (or aortic aneurysm). The left RLN's long loop under the aortic arch makes it particularly vulnerable to mediastinal pathology. This is a well-known association in Indian medicine because of the high prevalence of rheumatic heart disease.

Correct. The left RLN loops under the arch of the aorta at the ligamentum arteriosum (the remnant of the ductus arteriosus). This gives it a much longer intrathoracic course compared to the right RLN (which loops under the right subclavian artery at the root of the neck). The left RLN's longer course makes it vulnerable to more mediastinal pathologies.

Left RLN = loops under the aortic arch (at the ligamentum arteriosum). Right RLN = loops under the right subclavian artery (at the root of the neck). The asymmetry reflects embryological development: both nerves originally hooked under the 6th pharyngeal arch artery — on the right, the 6th arch involutes (leaving only the ductus arteriosus remnant on the left).

Correct. This is acute epiglottitis (high fever, drooling, tripod positioning, inspiratory stridor, toxic-looking child). The cardinal rule: DO NOT examine the throat or disturb the child — any stimulation can trigger complete laryngospasm and death. Immediate management: keep the child calm with parent, urgent anaesthetic review, controlled airway in theatre, IV antibiotics (ceftriaxone). Croup protocol (nebulised adrenaline + dexamethasone) is for croup (barking cough, steeple sign, subglottic), not epiglottitis.

Acute epiglottitis (NOT croup): high fever, drooling, toxic child, tripod sitting position. NEVER examine the throat in a conscious child with suspected epiglottitis. The swollen epiglottis can completely obstruct the airway if disturbed. Croup (parainfluenza, barking cough, steeple sign on X-ray) is treated with dexamethasone — completely different condition.

Correct. The true vocal cords (glottis) have a paucity of lymphatics. Lymphatic vessels are almost absent from the vocal cord epithelium and the vocal ligament. This means even a T1 glottic tumour very rarely spreads to lymph nodes at diagnosis (N0 in >95%). Radiotherapy can therefore cure the primary disease without having to address nodal disease. In contrast, supraglottic tumours have rich bilateral lymphatics → T1 supraglottic tumours are frequently N+ at diagnosis → worse prognosis despite same local stage.

The paucity of lymphatics in the glottis is the key anatomical reason for the excellent prognosis of T1 glottic carcinoma. The tumour is typically N0 at presentation — radiotherapy cures the primary site. This anatomical fact is one of the most important in head and neck oncology.

Correct. The relationship between the RLN and the inferior thyroid artery is highly variable. The RLN may pass anterior to the artery (~50%), posterior to the artery (~30%), or between its branches (~20%). This means the RLN cannot be reliably identified by its position relative to the inferior thyroid artery — it must be visually identified and traced directly. Ligating the artery without identifying the RLN first risks inadvertent RLN injury.

The RLN-inferior thyroid artery relationship is notoriously variable: anterior (50%), posterior (30%), or between branches (20%). This is why surgeons must visually identify and trace the RLN before ligating the artery — relying on the 'usual' position is not safe. The standard of care in thyroid surgery is to identify and display the RLN throughout its course in the neck.

Correct. If the RLN is not found in the tracheo-oesophageal groove, the most important diagnosis to consider is a non-recurrent RLN — a variant present in 0.5–1% of patients, in which the right RLN arises directly from the vagus and courses transversely to the larynx. It is always associated with an aberrant right subclavian artery. The surgeon must trace the vagus nerve carefully to find a direct transverse branch and avoid ligating it as the inferior thyroid artery.

A non-recurrent RLN is the most dangerous anatomical variant in thyroid surgery. It takes a transverse course directly from the vagus nerve to the larynx and can be mistaken for the inferior thyroid artery. It is always associated with an aberrant right subclavian artery (arteria lusoria). Tracing the vagus nerve carefully before applying any ligature is the safe approach.

Correct. Cricothyrotomy is performed through the cricothyroid membrane — the easily palpable midline structure between the inferior border of the thyroid cartilage and the superior border of the cricoid cartilage. It is the fastest, most accessible emergency airway access site, located below the vocal cords. The cricothyroid arteries run along its superior border — make the incision in the lower 1/3 to avoid them.

Cricothyrotomy = incision through the cricothyroid membrane (between thyroid and cricoid cartilages). It is the go-to emergency airway access when intubation fails. The thyrohyoid membrane is above the laryngeal inlet (would not bypass the obstruction). The cricotracheal membrane and lower trachea are the sites for elective tracheostomy.