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AN32.1-2 | Anterior Triangle — Gate Quiz
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The anterior triangle of the neck is bounded posteriorly by:
Correct! The anterior triangle is bounded anteriorly by the midline, posteriorly by the anterior border of sternocleidomastoid, and superiorly by the inferior border of the mandible.
Anterior triangle boundaries: Medially — midline of neck. Posterolaterally — anterior border of SCM. Superiorly — lower border of mandible. SCM is the key dividing landmark between anterior and posterior triangles.
Incorrect. The posterior boundary of the anterior triangle is the anterior border of the sternocleidomastoid (SCM). SCM divides the neck into anterior and posterior triangles.
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The common carotid artery bifurcates into the internal and external carotid arteries at the level of:
Correct! The common carotid artery bifurcates at the upper border of the thyroid cartilage, which corresponds to the C4 vertebral level. This is a key surgical and radiological landmark.
Neck vertebral level landmarks: C1 = atlas (posterior to pharynx). C3 = hyoid bone. C4–C5 = thyroid cartilage (Adam's apple). C6 = cricoid cartilage (easily palpated; trachea begins here). Carotid bifurcation at C4 = upper thyroid cartilage border.
Incorrect. Carotid bifurcation = C4 = upper border of thyroid cartilage. C3 = hyoid bone. C6 = cricoid cartilage (level of the junction of larynx and trachea, and the beginning of the oesophagus).
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Which of the following structures is a content of the digastric (submandibular) triangle?
Correct! The submandibular gland is the principal content of the digastric (submandibular) triangle, along with the submandibular lymph nodes, facial artery, and the hypoglossal nerve (CN XII).
Digastric triangle = submandibular triangle. Key contents: submandibular gland (superficial part), submandibular lymph nodes, facial artery + vein, hypoglossal nerve (CN XII), mylohyoid nerve.
Incorrect. The submandibular gland lies in the digastric triangle. The carotid body and ansa cervicalis are in the carotid triangle. The superior belly of omohyoid forms a boundary of the muscular triangle.
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The ansa cervicalis innervates the infrahyoid (strap) muscles. Which muscle is NOT supplied by the ansa cervicalis but instead directly by C1 fibres travelling with CN XII?
Correct! The thyrohyoid is innervated directly by C1 fibres that hitchhike along the hypoglossal nerve (CN XII) — NOT by the ansa cervicalis. All other infrahyoid muscles are supplied by the ansa cervicalis (C1–C3).
Ansa cervicalis (C1-C3 loop) supplies: sternohyoid, sternothyroid, omohyoid. Thyrohyoid: direct C1 branch via CN XII. Geniohyoid (suprahyoid): also direct C1 via CN XII. This is frequently tested in exams.
Incorrect. The thyrohyoid is the exception — it is supplied by C1 via CN XII directly, not by the ansa cervicalis loop. Remember: "Thyrohyoid is special — like the tongue muscles, it gets a direct CN XII branch."
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An elderly patient collapses after turning his head sharply while shaving. He is found to be in sinus bradycardia. The most likely mechanism is:
Correct! The carotid sinus contains baroreceptors innervated by the sinus nerve of Hering (branch of CN IX → via glossopharyngeal). Mechanical stimulation (e.g., tight collar, head turning) triggers a reflex vagal bradycardia (and hypotension) — carotid sinus hypersensitivity.
Carotid sinus syndrome (carotid sinus hypersensitivity): Carotid sinus baroreceptors (CN IX) → nucleus tractus solitarius → dorsal vagal nucleus → CN X → SA/AV node → bradycardia + hypotension. Triggered by tight collar, head turning, shaving. Treatment: pacemaker in recurrent cases.
Incorrect. Carotid sinus hypersensitivity: mechanical pressure on the baroreceptor-rich carotid sinus → CN IX afferent → vagal (CN X) efferent bradycardia/hypotension → syncope. Common in elderly males.
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The submental triangle is the only unpaired triangle in the neck. Its lateral boundaries are formed by:
Correct! The submental triangle is bounded laterally by the anterior bellies of the digastric muscles on each side, inferiorly by the hyoid bone, and superiorly by the symphysis menti. It is the only unpaired midline triangle.
Submental triangle: Lateral — anterior belly of digastric (bilateral). Inferior — hyoid bone. This is the only midline (unpaired) sub-triangle. Contents: submental lymph nodes (drain chin, lower lip, floor of mouth, tongue tip).
Incorrect. The submental triangle (unpaired, midline) is bounded by the anterior bellies of both digastric muscles laterally and the hyoid bone inferiorly. The posterior bellies of digastric form the upper boundary of the digastric triangle.
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During radical neck dissection for oral cancer, the surgeon inadvertently injures the hypoglossal nerve (CN XII) unilaterally. On asking the patient to protrude the tongue post-operatively, the tongue will deviate towards:
Correct! CN XII supplies all ipsilateral tongue muscles. On the injured side, the genioglossus (which protrudes the tongue) is paralysed. The intact contralateral genioglossus pushes the tongue toward the paralysed (affected) side — deviation toward the lesion.
CN XII (hypoglossal) palsy: LMN — tongue deviates to the SAME side (toward the lesion) on protrusion. UMN — tongue deviates to the OPPOSITE side (contralateral). Genioglossus is the protruder; when one side is weak, the other pushes the tip toward the weak side.
Incorrect. Lower motor neuron CN XII lesion: tongue deviates TOWARD the affected (weak) side on protrusion. The healthy genioglossus on the opposite side pushes the tongue across. Remember: tongue goes TO the lesion in LMN CN XII palsy.
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The facial artery crosses the inferior border of the mandible (where its pulse is palpable) at which landmark?
Correct! The facial artery crosses the inferior border of the mandible at the anterior border of masseter. This is the site where the facial artery pulse is classically palpated in clinical examination.
Facial artery pulse: palpated at the inferior border of the mandible, at the anterior margin of masseter. After crossing, the artery continues onto the face as it travels toward the medial canthus. It gives labial branches to upper and lower lips.
Incorrect. The facial artery winds around the submandibular gland, hooks under the posterior belly of digastric, then crosses the inferior border of the mandible at the anterior border of masseter — the pulse palpation point.
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A thyroglossal cyst recurs after simple excision. The reason for recurrence is failure to remove:
Correct! The thyroglossal duct passes through (or around) the body of the hyoid bone. Sistrunk's operation excises the cyst + central hyoid body + the tract up to the foramen cecum. Omitting the hyoid body leaves duct epithelium behind, causing recurrence.
Sistrunk's operation for thyroglossal cyst: (1) excise cyst, (2) excise central portion of hyoid body (thyroglossal duct passes through it), (3) trace and excise duct to foramen cecum at tongue base. Cure rate >95%. Failing to remove the hyoid = high recurrence.
Incorrect. Recurrence after simple excision is due to residual duct epithelium in the tract through the hyoid body. Sistrunk's operation must include excision of the central hyoid body + suprahyoid tract to prevent recurrence.
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A 45-year-old patient presents with a firm, pulsatile, slowly enlarging swelling at the angle of the jaw. It is mobile side to side but not up-and-down. Carotid angiography shows the internal and external carotid arteries splayed apart at their origin — the "lyre sign". The most likely diagnosis is:
Correct! The "lyre sign" (splaying of the internal and external carotid arteries) on angiography is pathognomonic of a carotid body tumour (chemodectoma/paraganglioma). It arises from the chemoreceptor cells at the carotid bifurcation in the carotid triangle.
Carotid body tumour (paraganglioma): At carotid bifurcation in carotid triangle. Pulsatile + transmitted pulsation. Mobile horizontally, not vertically. Lyre sign/split sign on angiography. Highly vascular — pre-operative embolisation before surgical excision. 10% bilateral, 10% malignant.
Incorrect. The "lyre sign" (splayed carotid arteries at their bifurcation) on angiography is the hallmark of a carotid body tumour. It arises within the adventitia of the carotid bifurcation and is hence mobile side-to-side (with the carotid) but not vertically.
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