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AN29.1-AN30.5 | Posterior triangle of neck — Gate Quiz
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The floor of the posterior triangle of the neck is covered by which layer of fascia?
Correct! The floor of the posterior triangle is covered by the prevertebral fascia, overlying the prevertebral muscles (splenius capitis, levator scapulae, scalenus medius, scalenus posterior). The roof is the investing layer of deep cervical fascia.
Posterior triangle: Roof = investing layer of deep cervical fascia + platysma. Floor = prevertebral fascia covering splenius capitis, levator scapulae, scalenus medius, scalenus posterior. Contents lie between these fascial layers.
Incorrect. Floor = prevertebral fascia (over prevertebral muscles). Roof = investing layer of deep cervical fascia (with platysma). The distinction of roof vs floor is frequently tested.
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The sternocleidomastoid muscle receives its motor innervation from:
Correct! The sternocleidomastoid is innervated by the accessory nerve (CN XI) for motor function, with proprioceptive and pain fibres from C2-C3 (ventral rami). The same nerve also supplies trapezius.
CN XI (accessory nerve): motor to SCM and trapezius. In the posterior triangle it is superficial (at risk in biopsy). Spinal accessory nerve palsy: inability to shrug (trapezius), weakness turning head to opposite side (SCM). The nerve is tested in clinical examinations.
Incorrect. SCM motor supply = CN XI (accessory nerve) + proprioception from C2-3 ventral rami. The cervical plexus (C3-4) mainly provides sensory branches to the neck; C2-3 provide proprioceptive input to SCM.
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Erb's palsy results from injury to which nerve roots and which mechanism?
Correct! Erb's palsy affects C5-C6 roots. It results from violent widening of the angle between the neck and shoulder — stretching the upper brachial plexus beyond its limit. This occurs in neonates during shoulder dystocia and in adults during high-speed RTAs.
Memory tip: Erb = upper roots (C5-C6) = neck-shoulder angle widened. Klumpke = lower roots (C8-T1) = arm pulled upward. Erb's → waiter's tip deformity. Klumpke's → claw hand ± Horner's. Both common in obstetric injury (birth palsy).
Incorrect. Erb's = C5, C6. Mechanism = violent stretching of neck away from shoulder (angle widening). Klumpke's = C8, T1. Mechanism = forcible upward traction on abducted arm.
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A patient with Klumpke's palsy (C8-T1 injury) also presents with ptosis, miosis, and anhidrosis on the ipsilateral side. The additional finding of Horner's syndrome indicates:
Correct! Horner's syndrome (ptosis, miosis, anhidrosis) in Klumpke's palsy indicates a preganglionic injury of T1 roots close to the sympathetic chain. The T1 root carries preganglionic sympathetic fibres to the superior cervical ganglion for the eye and face. Preganglionic injury = worse prognosis.
Horner's syndrome in brachial plexus injury = root avulsion (preganglionic) = poor prognosis (cannot repair an avulsed root). Postganglionic lesions distal to the stellate ganglion do NOT cause Horner's. In Klumpke's with Horner's, the preganglionic T1 sympathetic fibres are torn along with the T1 nerve root.
Incorrect. Horner's syndrome in Klumpke's = preganglionic T1 root avulsion. The sympathetic fibres leave the spinal cord via T1 ventral ramus and travel to the superior cervical ganglion. Avulsion proximal to this level → Horner's. This indicates the injury is very proximal (root avulsion) — poor prognosis for recovery.
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In a 3-year-old with congenital right sternocleidomastoid contracture (torticollis), the head is positioned with:
Correct! The SCM on one side: tilts the head to the SAME side AND rotates the chin to the OPPOSITE side. A contracted right SCM → tilts head to the right + rotates chin to the left.
SCM actions (one side): lateral flexion ipsilateral + chin rotation contralateral. Torticollis: head tilt = ipsilateral to contracted SCM; chin = contralateral. This is a classic anatomy-to-clinical bridge question. Compare bilateral SCM contraction: neck flexion (draws chin down).
Incorrect. SCM action: lateral tilt to SAME side + chin rotation to OPPOSITE side. Right SCM shortening → head tilts right + chin points left.
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Which dural fold separates the cerebral hemispheres from the cerebellum?
Correct! The tentorium cerebelli is a horizontal dural fold that separates the posterior cranial fossa (cerebellum and brainstem) from the middle cranial fossa (cerebral hemispheres). The notch in the tentorium (tentorial notch/incisura) allows the midbrain to pass through.
Four dural folds: Falx cerebri (vertical, between cerebral hemispheres), Tentorium cerebelli (horizontal, between cerebrum and cerebellum), Falx cerebelli (vertical, between cerebellar hemispheres), Diaphragma sellae (roof of pituitary fossa). The tentorial notch is clinically important: uncal herniation through it compresses CN III → dilated (blown) pupil in head injury.
Incorrect. Tentorium cerebelli = horizontal fold separating cerebrum (above) from cerebellum (below). Falx cerebri = vertical fold between cerebral hemispheres. Falx cerebelli = between cerebellar hemispheres. Diaphragma sellae = roof of pituitary fossa.
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A 12-year-old develops severe headache, fever, and signs of raised intracranial pressure 2 weeks after a poorly treated middle ear infection. CT venography shows thrombosis of the sigmoid sinus. The spread from the middle ear occurred through which route?
Correct! Otitis media → mastoiditis → mastoid air cells become infected → infection spreads via the mastoid emissary vein (connecting the mastoid region to the sigmoid sinus) → sigmoid sinus thrombosis (lateral sinus thrombosis). This is a classical complication of otitis media.
Complications of otitis media: (1) Mastoiditis → (2) mastoid emissary vein thrombophlebitis → (3) sigmoid sinus (lateral sinus) thrombosis → (4) raised ICP (Queckenstedt's test positive on that side) → (5) IJV thrombosis. Also: intracranial abscess via Trautmann's triangle. Management: IV antibiotics ± mastoidectomy ± anticoagulation.
Incorrect. The mastoid emissary vein runs through the mastoid foramen, connecting the posterior scalp/mastoid region to the sigmoid sinus. Mastoiditis infects this vein → retrograde thrombophlebitis → sigmoid sinus thrombosis.
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A 45-year-old man presents with gradually worsening vision "like wearing blinkers." Examination shows loss of both temporal visual fields with intact central and nasal fields. The most likely cause is:
Correct! Bitemporal hemianopia (loss of both temporal visual fields = "blinker" or "tunnel" vision) is the classic visual field defect of optic chiasm compression. A pituitary macroadenoma expanding superiorly compresses the crossing nasal fibres of both eyes at the chiasm → both temporal fields lost.
Visual field defects by lesion site: Optic nerve (before chiasm) → monocular blindness. Optic chiasm (crossing nasal fibres) → bitemporal hemianopia (pituitary adenoma, craniopharyngioma). Optic tract (after chiasm) → contralateral homonymous hemianopia. Temporal lobe (Meyer's loop) → superior quadrantanopia (pie in the sky). Occipital lobe → homonymous hemianopia with macular sparing.
Incorrect. Bitemporal hemianopia = optic chiasm lesion. Pituitary macroadenoma is the most common cause. The chiasm is immediately above the pituitary gland. Chiasm compression → crossing nasal fibres cut → bitemporal field loss.
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Scalenus anterior is a key landmark in neck surgery and is related to a major vessel syndrome. Which important clinical relationship does this muscle have with the subclavian vessels?
Correct! Scalenus anterior lies between the subclavian artery (which passes posterior to it) and the subclavian vein (which passes anterior to it). The phrenic nerve descends on the anterior surface of scalenus anterior. Thoracic outlet compression of the subclavian artery occurs in the space behind scalenus anterior.
Scalenus anterior is a landmark for: (1) Phrenic nerve (C3,4,5) — descends on its anterior surface; (2) Subclavian vein — anterior to it; (3) Subclavian artery — posterior to it; (4) Brachial plexus — between scalenus anterior and medius. In scalenectomy for TOS, the nerve to phrenic must be protected.
Incorrect. Scalenus anterior key relationships: subclavian VEIN = anterior (in front of scalenus anterior). Subclavian ARTERY = posterior (behind scalenus anterior). Phrenic nerve = on anterior surface of scalenus anterior. Brachial plexus roots = between scalenus anterior and medius.
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Following a cervical lymph node biopsy in the posterior triangle, a patient complains of drooping of the right shoulder and difficulty raising the right arm above horizontal. Examination shows wasting of the right trapezius. This is most consistent with injury to which structure?
Correct! The accessory nerve (CN XI) runs superficially across the posterior triangle and is at risk during lymph node biopsy. Division of CN XI → trapezius denervation → shoulder drop, inability to shrug, difficulty abducting arm above 90° (trapezius stabilises the scapula to allow full arm elevation). Wasting of trapezius confirms the diagnosis.
CN XI in the posterior triangle: emerges from posterior border of SCM (midpoint) → crosses posterior triangle obliquely → enters trapezius (deep surface). At risk in: cervical lymph node biopsy, radical neck dissection. Result: trapezius paralysis → shoulder drop, scapular winging (lower angle), difficulty arm abduction above shoulder level (rotator cuff needs stable scapular base).
Incorrect. Trapezius wasting + shoulder drop after posterior triangle biopsy = accessory nerve (CN XI) injury. The trapezius is innervated by CN XI; its loss prevents stable scapular positioning required for arm elevation above 90°.
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