Head & neck

Drawn from this guide's own material, each ending on its exam trap. Nothing loads from YouTube until you tap one.

• The Circle of Willis in 90 SecondsWatch · 1:48

  Exam trap: CN III palsy + dilated pupil → PComm aneurysm · Pupil spared in a diabetic → usually microvascular

• Epidural vs Subdural Hematoma in 90 SecondsWatch · 1:39

  Exam trap: Lens · stops at sutures → epidural → artery · Crescent · crosses sutures → subdural → vein

• Horner Syndrome in 90 SecondsWatch · 1:39

  Exam trap: Horner: SMALL pupil · mild droop · CN III palsy: heavy droop · down and out · often a BIG pupil

• The Cavernous Sinus in 90 SecondsWatch · 1:40

  Exam trap: CN VI is often hit FIRST · It lies free in the sinus, beside the carotid

• Bell's Palsy vs a Central Facial Palsy in 90 SecondsWatch · 1:35

  Exam trap: A drooping mouth alone does not give the level · Forehead still wrinkles → central (stroke) · Forehead paralyzed too → the nerve (Bell's palsy)

• The Recurrent Laryngeal Nerve in 90 SecondsWatch · 1:42

  Exam trap: Inferior thyroid a. → recurrent laryngeal → hoarseness · Superior thyroid a. → external laryngeal → lost high pitch

• The Extraocular Muscles in 90 SecondsWatch · 1:46

  Exam trap: Superior oblique: a depressor and intorter · Test it ADDUCTED, looking down and in · CN IV palsy: worst reading or on stairs

Relationships, supply, levels, and what happens when each fails.

• Cranial fossae and the foramina. Anterior fossa: the cribriform plate (olfactory fibers, CN I). Middle fossa: the optic canal (CN II and the ophthalmic artery), the superior orbital fissure (CN III, IV, V1, VI and the superior ophthalmic vein), foramen rotundum (V2), foramen ovale (V3 and the lesser petrosal nerve), and foramen spinosum (the middle meningeal artery). Posterior fossa: the internal acoustic meatus (CN VII and VIII), the jugular foramen (CN IX, X, XI and the internal jugular vein), the hypoglossal canal (CN XII), and the foramen magnum (the medulla, the vertebral arteries, and the spinal roots of XI). "Standing Room Only" orders the middle-fossa row for V1, V2, V3.
• Meninges, bleeds, and the dural venous sinuses. Dura (with its falx cerebri and tentorium cerebelli folds), arachnoid, and pia. An EPIDURAL hematoma is arterial — usually the middle meningeal artery torn under the thin pterion — lens-shaped, stopped by the sutures, often with a lucid interval. A SUBDURAL hematoma is venous — bridging veins torn in the elderly or in shaken infants — crescent-shaped and crossing sutures. A spontaneous (non-traumatic) subarachnoid hemorrhage is usually a ruptured berry aneurysm: the worst headache of life. Venous blood drains through the dural sinuses (superior sagittal → confluence → transverse → sigmoid → internal jugular vein); the cavernous sinus beside the sella carries the internal carotid artery and CN VI inside it and CN III, IV, V1, and V2 in its lateral wall.
• The cranial nerves and their parasympathetic ganglia. Four nerves carry the head's parasympathetic outflow, each through a named ganglion: CN III → ciliary ganglion → pupillary sphincter and ciliary muscle; CN VII → pterygopalatine ganglion → lacrimal, nasal, and palatal glands, and CN VII → submandibular ganglion → submandibular and sublingual glands; CN IX → otic ganglion → parotid gland (the fibers ride the auriculotemporal nerve). CN X carries the rest to the thorax and abdomen. Sympathetic fibers reach the head from the superior cervical ganglion along the arteries — which is why a lesion anywhere along that chain gives Horner syndrome (ptosis, miosis, anhidrosis).
• The sympathetic route to the head. Presynaptic neurons sit in the lateral horn of the upper thoracic cord (about T1–T2); their axons leave through the ventral root and white ramus, climb the sympathetic trunk, and synapse in the superior cervical ganglion. Postsynaptic fibers either rejoin C1–C4 through gray rami (sweat glands and vessels of the neck and scalp) or form plexuses on the internal and external carotid arteries, riding them — then branches of the trigeminal — to the dilator pupillae, the superior tarsal muscle, the sweat glands and vessels of the face, and the lacrimal and salivary glands, whose secretion they reduce. The middle cervical (about C6) and stellate (inferior cervical fused with T1) ganglia serve mainly the upper limb and the heart. Interrupt the pathway anywhere — hypothalamus, cervical cord, lung apex, carotid wall — and the face shows Horner syndrome: mild ptosis, miosis, and anhidrosis (only a patch by the brow when the lesion is on the internal carotid).
• The face — CN VII moves it, CN V feels it. The muscles of facial expression develop from the second pharyngeal arch and are all supplied by the facial nerve, whose five branches (temporal, zygomatic, buccal, marginal mandibular, cervical) fan out through the parotid gland. Sensation comes from the trigeminal divisions: V1 (forehead, upper lid, nose bridge), V2 (cheek, upper lip), V3 (lower lip, chin, and the jaw except its angle, which is C2–C3). The facial artery crosses the mandible at the anterior border of masseter; the facial vein connects through the ophthalmic veins to the cavernous sinus, so infections of the central face ('danger triangle') can spread intracranially.
• Mastication and the temporomandibular joint. The four muscles of mastication come from the first arch and are supplied by V3: masseter, temporalis, and medial pterygoid close the jaw; the LATERAL pterygoid protrudes the mandible and opens it, pulling the condyle and articular disc forward onto the articular eminence. The TMJ is a synovial joint divided by that disc into upper (gliding) and lower (hinge) compartments. Dislocation is anterior, with the condyle trapped in front of the eminence.
• The orbit and eye movements. LR6 SO4, the rest 3: the lateral rectus is CN VI, the superior oblique is CN IV, and CN III supplies the medial, superior, and inferior recti, the inferior oblique, and the levator palpebrae superioris. To test a muscle in isolation, move the eye into the position where it is the prime mover: the superior oblique depresses the ADDUCTED eye (looking down and in, as when reading or descending stairs). CN III palsy leaves the eye 'down and out' with ptosis; a compressive lesion (posterior communicating aneurysm, uncal herniation) also dilates the pupil because the parasympathetic fibers ride on the nerve's surface, while a diabetic (ischemic) palsy usually spares it. The pupil is constricted by CN III parasympathetics and dilated by sympathetics; the upper lid is raised by levator (CN III) with help from the smooth superior tarsal muscle (sympathetic).
• Nasal cavity and paranasal sinuses. Three conchae overhang three meatuses. The frontal, maxillary, and anterior ethmoidal sinuses drain into the middle meatus (via the semilunar hiatus); the posterior ethmoidal cells into the superior meatus; the sphenoid sinus into the sphenoethmoidal recess; and the nasolacrimal duct into the inferior meatus. The maxillary sinus drains through an ostium high on its medial wall, which is why it clears poorly and is the sinus most often infected. Anterior nosebleeds come from Kiesselbach's area on the septum, where branches of the ophthalmic, maxillary, and facial arteries anastomose.
• Oral cavity, tongue, and salivary glands. All tongue muscles are CN XII except palatoglossus (CN X). A hypoglossal lesion makes the tongue deviate TOWARD the weak side, because the intact genioglossus pushes it over. Anterior two-thirds: general sensation by the lingual nerve (V3) and taste by the chorda tympani (VII) riding with it. Posterior third: both by CN IX. The parotid duct pierces buccinator opposite the upper second molar; the submandibular duct opens beside the lingual frenulum and is crossed by the lingual nerve.
• Pharynx and swallowing. Three pharyngeal constrictors (superior, middle, inferior) squeeze the bolus down; stylopharyngeus (CN IX) elevates the pharynx; all other pharyngeal and palatal muscles are CN X except tensor veli palatini (V3). The gag reflex runs IX in and X out. Killian's triangle, a weak spot in the inferior constrictor, is where a Zenker diverticulum herniates. The palatine tonsil sits between the palatoglossal and palatopharyngeal arches, with the glossopharyngeal nerve deep to its bed.
• The larynx. Cartilages: thyroid (the laryngeal prominence), cricoid (the only complete ring, at C6), paired arytenoids, and the epiglottis. Every intrinsic laryngeal muscle is supplied by the recurrent laryngeal nerve EXCEPT cricothyroid, which tenses the folds and is supplied by the external branch of the superior laryngeal nerve. The posterior cricoarytenoid is the ONLY abductor — bilateral recurrent nerve injury can close the airway. Sensation above the vocal folds is the internal laryngeal nerve (the afferent limb of the cough reflex); below them, the recurrent laryngeal. The cricothyroid membrane, between the thyroid and cricoid cartilages, is the emergency surgical airway.
• The triangles and fascial compartments of the neck. Sternocleidomastoid (CN XI) divides the neck into anterior and posterior triangles. The anterior triangle holds the carotid sheath — common and internal carotid arteries medially, internal jugular vein laterally, vagus nerve posterior between them — plus the thyroid, larynx, and hyoid muscles. The posterior triangle is crossed superficially by the spinal accessory nerve on its way to trapezius (easily cut in lymph-node biopsy) and contains the cervical plexus and the trunks of the brachial plexus emerging between anterior and middle scalene. The phrenic nerve (C3–C5) runs down the anterior surface of anterior scalene; the subclavian VEIN passes in front of that muscle, the subclavian ARTERY behind it.
• The carotid system and vertebral arteries. The common carotid bifurcates at the upper border of the thyroid cartilage (about C4). The internal carotid gives NO branches in the neck; its origin dilates into the carotid sinus (baroreceptor, CN IX) with the carotid body (chemoreceptor) beside it. The external carotid branches in the neck — superior thyroid, ascending pharyngeal, lingual, facial, occipital, posterior auricular, then the maxillary and superficial temporal terminal branches — and the maxillary artery gives the middle meningeal. The vertebral arteries, first branches of the subclavians, climb through the transverse foramina of C6–C1 and enter the skull through the foramen magnum to form the basilar artery.
• The circle of Willis. The two internal carotids and the basilar (from the joined vertebrals) meet in an arterial ring around the optic chiasm and pituitary stalk: the anterior cerebrals are joined by the anterior communicating artery, and each internal carotid is joined to its posterior cerebral by a posterior communicating artery. The anterior cerebral supplies the medial hemisphere (leg and foot), the middle cerebral — the internal carotid's continuation — the lateral hemisphere (face and arm, and speech on the dominant side), and the posterior cerebral the occipital lobe (vision). Berry aneurysms sit at the ring's branch points, most often the anterior communicating artery; a posterior communicating aneurysm presses on CN III and dilates the pupil. The ring can reroute blood around a slowly narrowing vessel, but in most people it is incomplete.
• Thyroid and parathyroid glands. The thyroid's isthmus crosses tracheal rings 2–4. The superior thyroid artery (first branch of the external carotid) runs with the external laryngeal nerve; the inferior thyroid artery (from the thyrocervical trunk) is intimately related to the recurrent laryngeal nerve in the tracheoesophageal groove — the two nerve injuries of thyroid surgery. The gland descends from the foramen cecum of the tongue, so a thyroglossal duct cyst is a midline mass that moves up when the tongue protrudes. Four parathyroid glands sit on the posterior surface; the inferior pair (from the third pharyngeal pouch, with the thymus) wander most.

In the order a dissection meets them — each with the one relationship that identifies it. Your lab's study list is the authority; use this to check yours against.

1. 1Pterion — H-shaped junction of frontal, parietal, temporal, and sphenoid bones over the middle meningeal artery
2. 2Coronal suture — between the frontal bone and the two parietal bones
3. 3Sagittal suture — the midline seam between the two parietal bones
4. 4Lambdoid suture — between the parietal bones and the occipital bone
5. 5Squamous suture — the arched seam between the temporal and parietal bones
6. 6Bregma — where the coronal and sagittal sutures meet; the anterior fontanelle in an infant
7. 7Lambda — where the sagittal and lambdoid sutures meet; the posterior fontanelle in an infant
8. 8Anterior fontanelle — the diamond-shaped soft spot at bregma; the largest and last to close, at about 13–24 months
9. 9Posterior fontanelle — the triangular soft spot at lambda; closes by about 6–8 weeks after birth
10. 10Crista galli — the ethmoid's midline crest that anchors the front of the falx cerebri
11. 11Sella turcica — the sphenoid's saddle; the pituitary sits in its hypophyseal fossa
12. 12Cribriform plate — the perforated ethmoid carrying olfactory nerve fibers
13. 13Optic canal — carries CN II and the ophthalmic artery
14. 14Superior orbital fissure — CN III, IV, V1, VI and the superior ophthalmic vein
15. 15Foramen rotundum — the maxillary nerve (V2)
16. 16Foramen ovale — the mandibular nerve (V3)
17. 17Foramen spinosum — the middle meningeal artery
18. 18Internal acoustic meatus — the facial and vestibulocochlear nerves
19. 19Jugular foramen — CN IX, X, XI and the internal jugular vein
20. 20Hypoglossal canal — CN XII, just above the occipital condyle
21. 21Foramen magnum — the medulla, the vertebral arteries, and the spinal roots of XI
22. 22Olfactory nerve — CN I; fibers through the cribriform plate to the bulb above it (smell)
23. 23Optic nerve — CN II; through its canal to the chiasm (vision)
24. 24Oculomotor nerve — CN III; superior orbital fissure to four eye muscles, levator, the pupil's sphincter and the ciliary muscle
25. 25Trochlear nerve — CN IV; the thinnest, leaving the back of the brainstem for superior oblique
26. 26Trigeminal nerve — CN V; the head's main sensory nerve, its ganglion in the middle cranial fossa
27. 27Ophthalmic nerve — V1; superior orbital fissure; forehead and cornea sensation
28. 28Maxillary nerve — V2; foramen rotundum; cheek, upper teeth, and palate
29. 29Mandibular nerve — V3; foramen ovale; lower-face sensation and the muscles of mastication
30. 30Abducens nerve — CN VI; a long course over the clivus and through the cavernous sinus to lateral rectus
31. 31Facial nerve — CN VII; in at the internal acoustic meatus, out at the stylomastoid foramen, then through the parotid
32. 32Vestibulocochlear nerve — CN VIII; internal acoustic meatus to the cochlea and vestibule (hearing, balance)
33. 33Glossopharyngeal nerve — CN IX; jugular foramen; stylopharyngeus, parotid, posterior-third taste, carotid sinus
34. 34Falx cerebri — the midline dural fold between the hemispheres
35. 35Tentorium cerebelli — the dural shelf roofing the posterior fossa
36. 36Falx cerebelli — the small midline dural fold between the cerebellar hemispheres
37. 37Diaphragma sellae — the dural roof over the sella, pierced by the pituitary stalk
38. 38Superior sagittal sinus — along the falx's attached edge; arachnoid granulations drain into it
39. 39Arachnoid granulations — tufts that push through the dura and return CSF to the venous sinuses, mainly the superior sagittal
40. 40Inferior sagittal sinus — in the free lower edge of the falx cerebri
41. 41Great cerebral vein — of Galen; joins the inferior sagittal sinus to form the straight sinus
42. 42Straight sinus — along the falx–tentorium junction to the confluence
43. 43Confluence of sinuses — at the internal occipital protuberance, where the superior sagittal, straight, and occipital sinuses meet
44. 44Occipital sinus — in the attached edge of the falx cerebelli, draining up to the confluence
45. 45Transverse sinus — in the tentorium's attached edge, from the confluence to the sigmoid
46. 46Sigmoid sinus — S-shaped, in a groove on the temporal bone; becomes the internal jugular vein at the jugular foramen
47. 47Cavernous sinus — beside the sella; ICA and CN VI inside, III, IV, V1, V2 in its wall
48. 48Emissary veins — valveless veins through the skull linking scalp veins to the dural sinuses
49. 49Middle meningeal artery — grooves the inner skull beneath the pterion
50. 50Circle of Willis — the arterial ring under the brain joining the carotid and vertebrobasilar systems
51. 51Basilar artery — the two vertebral arteries joined on the front of the pons
52. 52Anterior cerebral artery — the medial frontal and parietal lobes (the leg area)
53. 53Middle cerebral artery — the internal carotid's continuation; the lateral hemisphere (face and arm)
54. 54Posterior cerebral artery — the basilar's terminal branch; the occipital lobe (vision)
55. 55Anterior communicating artery — joins the two anterior cerebrals; the commonest berry-aneurysm site
56. 56Posterior communicating artery — joins the internal carotid to the posterior cerebral; its aneurysm compresses CN III
57. 57Orbicularis oculi — closes the eyelids (CN VII)
58. 58Orbicularis oris — purses and closes the lips (CN VII)
59. 59Buccinator — the cheek muscle the parotid duct pierces
60. 60Parotid gland — largest salivary gland; the facial nerve branches inside it
61. 61Parotid duct — crosses masseter and opens opposite the upper second molar
62. 62Facial nerve branches — temporal, zygomatic, buccal, marginal mandibular, cervical
63. 63Masseter — elevates the mandible; bulges when the teeth clench
64. 64Temporalis — fan-shaped elevator inserting on the coronoid process
65. 65Lateral pterygoid — the only muscle of mastication that opens the jaw
66. 66Medial pterygoid — elevator forming a sling with masseter around the ramus
67. 67Facial artery — crosses the mandible at masseter's anterior border
68. 68Superficial temporal artery — pulse in front of the ear; terminal branch of the external carotid
69. 69Maxillary artery — deep terminal branch of the external carotid; gives the middle meningeal
70. 70Levator palpebrae superioris — raises the upper lid (CN III)
71. 71Superior oblique — CN IV; its tendon turns through the trochlea
72. 72Lateral rectus — CN VI; abducts the eye
73. 73Medial rectus — CN III; adducts the eye
74. 74Ciliary ganglion — parasympathetic relay behind the eye for CN III
75. 75Pterygopalatine ganglion — in its fossa on V2; relays CN VII fibers to the lacrimal, nasal, and palatal glands
76. 76Submandibular ganglion — hangs from the lingual nerve; relays chorda tympani fibers to two salivary glands
77. 77Otic ganglion — just below foramen ovale, medial to V3; relays CN IX fibers to the parotid
78. 78Nasal conchae — superior, middle, and inferior scrolls, each over its meatus
79. 79Middle meatus — frontal, maxillary, and anterior ethmoidal sinuses open here
80. 80Inferior meatus — the nasolacrimal duct opens here
81. 81Maxillary sinus — the largest paranasal sinus, draining through a high ostium
82. 82Sphenoid sinus — below the sella; the transsphenoidal route to the pituitary
83. 83Kiesselbach area — the anterior septal plexus where most nosebleeds start
84. 84Genioglossus — protrudes the tongue (CN XII)
85. 85Lingual nerve — V3 sensation to the anterior tongue, carrying chorda tympani fibers
86. 86Submandibular duct — opens beside the frenulum; crossed by the lingual nerve
87. 87Submandibular gland — wraps around the posterior border of mylohyoid
88. 88Palatine tonsil — between the palatoglossal and palatopharyngeal arches
89. 89Hyoid bone — at C3; anchor for the suprahyoid and infrahyoid muscles
90. 90Thyroid cartilage — the laryngeal prominence; the carotids bifurcate at its upper border
91. 91Cricoid cartilage — the only complete laryngeal ring, at C6
92. 92Cricothyroid membrane — the emergency airway site between the thyroid and cricoid cartilages
93. 93Cricothyroid muscle — tenses the vocal folds; supplied by the external laryngeal nerve
94. 94Posterior cricoarytenoid — the only abductor of the vocal folds
95. 95Epiglottis — elastic flap that tips over the laryngeal inlet in swallowing
96. 96Vocal folds — the true cords, below the vestibular folds, bounding the rima glottidis
97. 97Sternocleidomastoid — divides the anterior from the posterior triangle (CN XI)
98. 98Spinal accessory nerve — crosses the posterior triangle superficially to reach trapezius
99. 99Carotid sheath — carotid artery, internal jugular vein, and vagus nerve together
100. 100Carotid sinus — dilation at the internal carotid origin; baroreceptor on CN IX
101. 101External carotid artery — the carotid that branches in the neck, superior thyroid first
102. 102Internal carotid artery — no branches in the neck; climbs the carotid canal into the cavernous sinus
103. 103Internal jugular vein — lateral in the carotid sheath; a central-line target
104. 104Vagus nerve — posterior in the sheath, between the artery and the vein
105. 105Hypoglossal nerve — loops forward across both carotids above the hyoid
106. 106Ansa cervicalis — C1–C3 loop on the sheath supplying the infrahyoid muscles
107. 107Lesser occipital nerve — C2 (sometimes C3); scalp behind the ear, along the back edge of sternocleidomastoid
108. 108Great auricular nerve — C2–C3; skin over the parotid and the ear, crossing sternocleidomastoid
109. 109Transverse cervical nerve — C2–C3; skin of the front of the neck
110. 110Supraclavicular nerves — C3–C4; skin over the clavicle and shoulder
111. 111Suboccipital nerve — C1 dorsal ramus; motor only, to the four suboccipital muscles
112. 112Greater occipital nerve — C2 dorsal ramus; pierces semispinalis to the back of the scalp
113. 113Third occipital nerve — C3 dorsal ramus; skin of the lower back of the scalp
114. 114Anterior scalene — phrenic nerve on its face; subclavian vein in front, artery behind
115. 115Phrenic nerve — C3–C5, descending on anterior scalene
116. 116Vertebral artery — first subclavian branch, climbing through the transverse foramina
117. 117Thyrocervical trunk — subclavian branch giving the inferior thyroid artery
118. 118Superior cervical ganglion — the top of the sympathetic trunk (about C1–C3); the relay for the head's sympathetics
119. 119Middle cervical ganglion — small, at about C6, near the inferior thyroid artery
120. 120Stellate ganglion — the inferior cervical ganglion fused with T1, in front of the neck of the first rib
121. 121Thyroid gland — isthmus over tracheal rings 2–4
122. 122Superior thyroid artery — first external carotid branch, beside the external laryngeal nerve
123. 123Parathyroid glands — four small glands on the posterior thyroid
124. 124Recurrent laryngeal nerve — in the tracheoesophageal groove beside the inferior thyroid artery

The distinctions that lose points on the practical, year after year.

• Superior orbital fissure vs optic canal. The optic canal carries only CN II and the ophthalmic artery; everything else entering the orbit (III, IV, V1, VI and the superior ophthalmic vein) uses the superior orbital fissure beside it. On a skull the canal is the round hole in the lesser wing; the fissure is the slit between the wings.
• The tongue deviates TOWARD the lesion. With a right CN XII lesion, the left genioglossus is unopposed and pushes the protruded tongue to the RIGHT — toward the weak side. The uvula does the opposite: with a right CN X lesion, the intact left palatal muscles pull the uvula to the LEFT, away from the lesion. Students mix the two directions.
• Cricothyroid is the one exception. Every intrinsic laryngeal muscle is on the recurrent laryngeal nerve except cricothyroid (external laryngeal branch of the superior laryngeal). A thyroidectomy injury to the external branch causes a weak, easily fatigued voice that can't reach high pitches; a recurrent injury causes hoarseness from a paralyzed fold.
• Epidural is arterial, subdural is venous. Lens-shaped, suture-limited, with a lucid interval → epidural, middle meningeal artery. Crescent-shaped, crossing sutures, in an elderly or alcohol-using patient → subdural, bridging veins. The shape on CT and the vessel are paired; learn them together.
• Testing the superior oblique. The superior oblique is an intorter and depressor, but it is tested with the eye ADDUCTED and looking down, because that is where it is the prime depressor. A CN IV palsy shows vertical diplopia worst when reading or walking downstairs, and patients tilt the head AWAY from the affected side to compensate.
• The internal carotid has no neck branches. If a vessel in the carotid triangle gives off branches, it is the external carotid — no matter where it lies. The internal carotid, though usually posterolateral at its origin, is identified by NOT branching until it enters the skull.
• Spinal accessory nerve in the posterior triangle. It runs superficially, just under the investing fascia, from the posterior border of sternocleidomastoid to trapezius — the one important structure in a triangle students treat as empty. Cutting it during a node biopsy produces a drooping shoulder and difficulty abducting above the horizontal.
• Pupil-sparing vs pupil-involving CN III palsy. The pupillomotor fibers run on the outside of the nerve, where compression reaches them first and the ischemia of diabetes reaches them last. A 'down and out' eye with a dilated pupil is an aneurysm until proven otherwise; with a normal pupil in a diabetic, it is usually microvascular.

Where this region shows up again — in clinical medicine, on rotations, and on the boards.

• Epidural hematoma. A blow to the side of the head fractures the thin pterion and tears the middle meningeal artery; the patient may be lucid before rapidly deteriorating as the arterial bleed expands. CT shows a biconvex collection that does not cross sutures. It is a neurosurgical emergency — evacuation before uncal herniation compresses CN III (a blown pupil on the same side).
• Bell's palsy vs a central facial palsy. A lower motor neuron facial nerve lesion (most often Bell's palsy, now diagnosed clinically) paralyzes the WHOLE half of the face, forehead included, and may add loss of taste, hyperacusis, and a dry eye depending on the level. An upper motor neuron lesion (stroke) spares the forehead because the forehead's motor neurons receive input from both hemispheres. Forehead involvement is the discriminator.
• Horner syndrome. Ptosis (loss of the superior tarsal muscle), miosis, and facial anhidrosis from interruption of the three-neuron oculosympathetic pathway anywhere from the hypothalamus to the orbit — a lateral medullary stroke, a Pancoast tumor at the lung apex, or a carotid dissection (which spares most facial sweating). The ptosis is mild because the levator (CN III) still works.
• Cavernous sinus thrombosis. A central-face or sinus infection spreads backward through the facial and ophthalmic veins, whose blood can flow toward the sinus: fever, proptosis, chemosis, and ophthalmoplegia — CN VI often first, because it lies free in the sinus beside the internal carotid — with V1/V2 sensory loss.
• Epistaxis. About 90% of nosebleeds arise anteriorly at Kiesselbach's area and stop with firm pressure on the soft nose while leaning forward. Posterior bleeds (from sphenopalatine branches) are heavier, occur in older and hypertensive patients, and often need posterior packing.
• Thyroidectomy nerve injuries and hypocalcemia. Ligating the inferior thyroid artery risks the recurrent laryngeal nerve (hoarseness; bilateral injury can cause stridor and airway obstruction); ligating the superior thyroid artery risks the external laryngeal nerve (lost high pitch). Removing or devascularizing the parathyroids causes hypocalcemia with perioral tingling, Chvostek and Trousseau signs in the following days.
• Cricothyrotomy. When the airway can't be secured from above, the cricothyroid membrane is found by sliding a finger down from the laryngeal prominence into the soft notch above the cricoid ring. It is superficial, relatively avascular, and above the thyroid isthmus — the reason it is the emergency site rather than a tracheostomy.
• Carotid sinus massage and hypersensitivity. Pressure over the carotid bifurcation stimulates the sinus baroreceptors (CN IX afferent, CN X efferent), slowing the heart — used to break some supraventricular tachycardias. In carotid sinus hypersensitivity, a tight collar or a head turn can cause syncope.
• Thyroglossal duct cyst vs branchial cleft cyst. A MIDLINE neck mass that rises when the tongue protrudes is a thyroglossal duct cyst (the thyroid's path of descent). A LATERAL mass along the anterior border of sternocleidomastoid in a young patient is a branchial (second cleft) cyst. Location is the diagnosis.
• Trigeminal neuralgia and dental anesthesia. Paroxysmal, electric pain in a V2 or V3 distribution triggered by chewing or touch is trigeminal neuralgia, treated first with carbamazepine. The same nerve anatomy underlies the inferior alveolar block, which also numbs the lower lip and, through the nearby lingual nerve, the tongue.