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Anatomy of the Pharynx

1. Overview and Definition

• Superiorly: attached to the base of the skull (basisphenoid and basal occipital bone)
• Inferiorly: continuous with the top of the esophagus at the level of vertebra C6
• Anteriorly: attached to the margins of the nasal cavities, oral cavity, and larynx
• Posteriorly: separated from the vertebral column by the retropharyngeal space (loose connective tissue)

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2. Subdivisions

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3. Nasopharynx

Basic Anatomy

• Located above the soft palate, behind the choanae (posterior nasal apertures)
• Has a roof, two lateral walls, a posterior wall, and a floor
• The roof and posterior wall are contiguous due to the sloping base of the sphenoid and occipital bones - collectively called the basisphenoid
• Always patent (walls are rigid bony/cartilaginous structures) - unlike the oropharynx and hypopharynx which open and close with swallowing

Key Features of the Lateral Wall

• Pharyngotympanic (Eustachian/Auditory) tube opening - posterior to and slightly above the level of the hard palate
• Torus tubarius - a mucosal elevation formed by the cartilaginous end of the tube projecting into the nasopharynx
• Pharyngeal recess (Fossa of Rosenmüller) - a recess posterior to the torus tubarius; clinically important as the most common site of nasopharyngeal carcinoma
• Torus levatorius - a mucosal fold overlying the levator veli palatini muscle, inferior to the torus tubarius
• Salpingopharyngeal fold - a mucosal fold that descends from the lower end of the torus tubarius

Floor

• The floor is the upper surface of the soft palate
• The pharyngeal isthmus lies posterior to the soft palate - this is the communication between the nasopharynx and oropharynx
• Closure of the isthmus during swallowing is achieved by elevation of the soft palate + contraction of the palatopharyngeal sphincter (part of the superior constrictor)

Pharyngeal Tonsil (Adenoids)

• Lymphoid tissue in the mucosa of the roof and posterior walls
• Maximal in childhood; contributes to upper respiratory tract defense
• No clear plane of cleavage (unlike palatine tonsils) - makes adenoidectomy less precise
• When enlarged = adenoids - can occlude the nasopharynx, forcing mouth breathing

Mucosa

• Ciliated pseudostratified columnar (respiratory) epithelium - unique to this part of the pharynx

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4. Oropharynx

Basic Anatomy (Clinical Boundaries from Scott-Brown's)

• Superiorly: horizontal line at the level of the hard palate (or free border of soft palate)
• Inferiorly: horizontal line through the floor of the valleculae (hyoid bone level)
• Anteriorly: vertical plane of the palatoglossal folds, including the posterior 1/3 of the tongue

Subsites (UICC/AJCC Classification)

• Base of tongue (posterior to vallate papillae / posterior 1/3)
• Vallecula (between the tongue and epiglottis)

• Palatine tonsils
• Tonsillar fossae and tonsillar (faucial) pillars
• Glossotonsillar sulci

• Inferior surface of the soft palate and uvula

Key Structures

• Suspended from the posterior border of the hard palate; a mobile flap that opens and closes on swallowing
• Contains five muscles all attached to the palatine aponeurosis
• The uvula (musculus uvulae) hangs from its free inferior border into the oropharyngeal isthmus

• Anterior pillar = palatoglossal arch (contains palatoglossus muscle) - forms the anterior boundary of the oropharyngeal isthmus
• Posterior pillar = palatopharyngeal arch (contains palatopharyngeus muscle)
• The palatine tonsil sits in the tonsillar fossa between these two arches

• Paired shallow depressions anterior to the epiglottis
• The median glossoepiglottic fold divides them in the midline
• Flanked laterally by the lateral glossoepiglottic (pharyngoepiglottic) folds
• Common site for foreign bodies (e.g., fish bones)

Mucosa

• Non-keratinized stratified squamous epithelium (same as rest of pharynx below the transitional zone)

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5. Laryngopharynx (Hypopharynx)

Basic Anatomy (Clinical Boundaries from Scott-Brown's)

• Extends from the superior margin of the epiglottis (level of the cranial border of the hyoid bone) to the lower margin of the cricoid cartilage at C6, where the pharynx becomes the esophagus
• The laryngeal inlet (aditus) is the missing anterior segment - the communication between the larynx and pharynx, bounded superiorly by the epiglottis, laterally by the aryepiglottic folds, and inferiorly by the arytenoids and cricoid cartilage

Subsites

1. Piriform recesses (fossae/sinuses) - bilateral
2. Posterior pharyngeal wall
3. Postcricoid area (pharyngo-esophageal junction)

Piriform Recess - Clinically Most Important

• Bilateral channels lateral to the laryngeal inlet between the larynx medially and the thyroid cartilage/thyrohyoid membrane laterally
• Medial boundary: quadrangular membrane of the larynx
• Lateral boundary: thyrohyoid membrane (superiorly), thyroid cartilage lamina (inferiorly)
• Broader superiorly, narrower inferiorly - funnel-shaped
• Function: directs food and liquid around the laryngeal inlet into the esophagus
• Clinical: foreign bodies commonly lodge here; tumors can silently expand asymptomatically until neck nodes appear

Postcricoid Area

• Extends from the arytenoid cartilages to the inferior border of the cricoid cartilage
• Forms the anterior wall of the hypopharynx
• Lateral margins merge with the medial wall of the piriform recesses

Mucosa

• Predominantly stratified squamous epithelium with goblet cells

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6. Pharyngeal Wall - Layers (from Scott-Brown's)

1. Mucous membrane - respiratory in nasopharynx; squamous below
2. Submucosa (fibrous layer, also called pharyngobasilar fascia at its inner aspect)
3. Pharyngobasilar fascia - inner fascial layer, thicker, lines the deep surface
4. Muscular layer - constrictors + longitudinal muscles
5. Buccopharyngeal fascia - outer thin layer, part of the pretracheal fascia

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7. Muscles of the Pharynx

A. Constrictor Muscles (Circular - form most of the wall)

The inferior constrictor has two parts - thyropharyngeus (from thyroid) and cricopharyngeus (from cricoid, acts as upper esophageal sphincter). The triangular gap between them is Killian's dehiscence - a site of muscular weakness in the posterior pharyngeal wall. A Zenker's (pharyngeal) diverticulum occurs when mucosa herniates through this gap.

B. Longitudinal Muscles (Elevate the pharynx)

Key point: Stylopharyngeus is the only pharyngeal muscle supplied by CN IX - all others are vagus [X].

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8. Waldeyer's Tonsillar Ring

• Bounded by palatoglossal and palatopharyngeal arches
• Encapsulated - unlike all others in Waldeyer's ring - this provides the surgical dissection plane during tonsillectomy
• The floor of the tonsillar bed is the superior constrictor
• Surface has multiple crypts and an intratonsillar cleft
• Blood supply: tonsillar branch of the facial artery (main supply; enters inferior pole through superior constrictor) + ascending palatine, ascending pharyngeal, lingual, descending palatine arteries
• Venous drainage: pharyngeal venous plexus + external palatine (paratonsillar) vein - this vein is commonly injured in tonsillectomy and causes post-operative bleeding
• Lymphatics drain to: jugulodigastric (tonsillar) lymph node (level II) - the first node to enlarge in tonsillitis
• Nerve supply: tonsillar plexus (branches of glossopharyngeal [IX] + lesser palatine nerve from maxillary [V2])
  • Because CN IX also innervates the tympanic cavity via the tympanic nerve, tonsil pathology can cause referred otalgia

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9. Blood Supply

Arteries (all ultimately from external carotid artery)

• Ascending pharyngeal artery (direct branch of external carotid)
• Ascending palatine and tonsillar branches of facial artery
• Branches of maxillary and lingual arteries

• Pharyngeal branches of the inferior thyroid artery (from thyrocervical trunk of subclavian artery)

Veins

• Form a pharyngeal venous plexus on the outer wall
• Drains superiorly into the pterygoid plexus (infratemporal fossa)
• Drains inferiorly into the facial vein and internal jugular vein

Lymphatics

• Deep cervical nodes
• Retropharyngeal nodes (between nasopharynx and vertebral column) - important in nasopharyngeal carcinoma
• Paratracheal and infrahyoid nodes
• Palatine tonsil drains to jugulodigastric nodes (level IIA)

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10. Nerve Supply

Motor Innervation

• Stylopharyngeus → Glossopharyngeal [IX]

The Pharyngeal Plexus

1. Pharyngeal branch of the vagus [X] (major motor nerve)
2. Branches from the external laryngeal nerve (branch of superior laryngeal nerve of vagus)
3. Pharyngeal branches of glossopharyngeal [IX]

Sensory Innervation (by region)

Gag reflex: Afferent = CN IX (sensory from oropharynx); Efferent = CN X (motor to pharyngeal muscles)

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11. Radiological Anatomy (from Cummings Otolaryngology)

• Torus tubarius, Fossa of Rosenmüller, uvula are identified on CT of nasopharynx
• Piriform sinuses - asymmetry is normal; complete lack of filling is suspicious for tumor
• Postcricoid line - formed by barium pooling between the posterior larynx and posterior hypopharyngeal wall; disruption = tumor invasion
• Cricopharyngeus muscle - lies anterior to C6 vertebra; appears as an indentation on the posterior hypopharyngeal wall
• Normal CT cross-sectional diameter of cervical esophagus: AP ≤ 16 mm, lateral ≤ 24 mm

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12. Swallowing Mechanics - Clinical Anatomy

1. Soft palate elevates → closes pharyngeal isthmus → seals nasopharynx from oropharynx (prevents nasal regurgitation)
2. Oropharyngeal isthmus opens → food enters pharynx
3. Laryngeal inlet closes (epiglottis tilts, aryepiglottic folds adduct)
4. Food is directed through the piriform recesses around the larynx into the esophagus
5. You cannot breathe and swallow simultaneously - the airway is closed at two points (pharyngeal isthmus and larynx)

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13. Summary of Key Clinical Correlations

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• Gray's Anatomy for Students, pp. 1180-1191 (pharynx, muscles, vessels, nerves)
• Scott-Brown's Otorhinolaryngology Head & Neck Surgery, pp. 781-786 (nasopharynx, oropharynx, hypopharynx, pharyngeal wall, Waldeyer's ring)
• Cummings Otolaryngology Head and Neck Surgery, p. 1876 (radiological anatomy, cross-sectional CT)

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Complete Anatomy of the Nose

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1. Embryology

• Neural crest cells proliferate and form nasal placodes
• Nasal placodes sink to form the nasal pits (primitive anterior nares)
• The bucconasal membrane normally breaks down to form the choanae - failure = choanal atresia

• Turbinate precursors appear in the 8th week of gestation
• Maxilloturbinal (from maxillary process) → inferior turbinate
• Ethmoturbinals (from ethmoid, 5 arise but only 4 persist):
  • 1st ethmoturbinal: ascending portion → agger nasi; descending portion → uncinate process (regresses)
  • 2nd ethmoturbinal → middle turbinate
  • 3rd ethmoturbinal → superior turbinate
  • 4th + 5th → supreme turbinate (when present)
• Primary furrows form between ethmoturbinals giving rise to the meati

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2. External Nose

A. Landmarks (K.J. Lee)

B. Subcutaneous Layers (K.J. Lee mnemonic: "SF DeeP")

1. S - Superficial fatty layer (connected to dermis)
2. F - Fibromuscular layer (nasal SMAS - superficial musculoaponeurotic system)
3. D - Deep fatty layer (contains neurovascular system)
4. P - Periosteum/Perichondrium

The optimal surgical plane for rhinoplasty dissection is between D and P - it is avascular and heals with minimal fibrosis.

C. Nasal Osteology

• Two nasal bones fuse in midline forming a pyramidal shape
• Nasal bones are thicker superiorly than inferiorly
• Attachments: Superior = nasal process of frontal bone; Lateral = frontal process of maxilla
• Pyriform aperture (bony opening to nasal cavity):
  • Superior = caudal margin of nasal bones
  • Inferior = alveolar process of maxilla
  • Lateral = frontal process of maxilla
  • Medial = nasal septum

D. Nasal Cartilages

E. Nasal Tip Support

• Medial and lateral crura of LLC
• Attachment of medial crura to caudal edge of quadrangular cartilage
• Attachment of ULC to LLC at the scroll area

• Skin-soft tissue envelope
• Sesamoid complex
• Interdomal ligament
• Anterior nasal spine
• Cartilaginous septal dorsum
• Membranous nasal septum

F. Nasal Muscles

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3. Nasal Cavity

• A floor, roof, medial wall (septum), and lateral wall

A. Floor

• Anterior 3/4: palatine process of maxilla
• Posterior 1/4: horizontal process of palatine bone
• ~12 mm behind the anterior nasal floor lies the incisive canal containing the nasopalatine nerve and greater palatine artery

B. Roof

• Formed by the skull base; slopes downward from anterior to posterior
• This slope is surgically important - during endoscopic sinus surgery, the skull base descends as you proceed posteriorly toward the sphenoid sinus

C. Nasal Vestibule

• The entrance of the nasal cavity
• Lined by hair-bearing keratinized squamous epithelium with sebaceous and sweat glands (vibrissae)
• Boundaries:
  • Medial = nasal septum
  • Superior and lateral = LLC
  • Inferior = alveolar process of maxilla
  • Posterior = Limen nasi (formed by the caudal margin of the ULC) - this is where skin transitions to respiratory mucosa

D. Epithelium of the Nasal Cavity (3 types)

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4. Nasal Septum

A. Bony Septum

B. Cartilaginous Septum

• The quadrilateral (quadrangular) cartilage - the most important component
• Bound to nasal bones, perpendicular plate of ethmoid, and vomer by collagenous fibers
• Continuous with the ULC superiorly at the nasal dorsum
• The septal tail (sphenoidal process) extends posteriorly between vomer and perpendicular plate - a harvest site for cartilage in revision rhinoplasty
• Inferior attachment sits in the maxillary nasal crest bound by looser tissue (pseudoarthrosis) - allows mobility, reducing fracture risk with trauma

C. Membranous Septum

• Connective tissue between the caudal portion of the septal cartilage and the columella
• Site of the hemitransfixion/transfixion incision in septoplasty

Vomeronasal Organ (Jacobsen's organ)

• Auxiliary olfactory organ for pheromone perception in animals
• In humans: largely regresses in utero; identified as a groove in the anterior-inferior nasal septum

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5. Lateral Nasal Wall

A. Bones of the Lateral Wall (anterior to posterior)

1. Frontal process of maxilla
2. Lacrimal bone
3. Medial maxillary wall (inferior) / Lamina papyracea (LP) of ethmoid (superior)
4. Perpendicular plate of palatine bone
5. Medial pterygoid plate of sphenoid (latter two form the sphenopalatine foramen)

B. Turbinates (Conchae)

• Middle and superior turbinates = ethmoid bone extensions
• Inferior turbinate = independent osseous structure (embryologically distinct)

Turbinates continuously dilate and constrict alternately every 0.5-3 hours under sympathetic control - a normal physiological phenomenon. Total nasal resistance remains constant as one side congests and the other decongests.

C. Meati and Sinus Drainage

D. Middle Turbinate - Detailed (ENT High-Yield)

• Concha bullosa - pneumatized middle turbinate; present in ~1/3 of the population; can narrow ethmoid infundibulum
• Paradoxical MT - lateral surface of MT is convex (reversed curve)

E. Key Endoscopic Landmarks

1. First lamella = Uncinate process (UP)
2. Second lamella = Ethmoid bulla (EB)
3. Third lamella = Basal lamella of middle turbinate (key division between ant. and post. ethmoid)
4. Fourth lamella = Basal lamella of superior turbinate
5. Fifth lamella = Basal lamella of supreme turbinate (when present)

• Crescent-shaped bone of ethmoid origin; shields the natural maxillary ostium
• Vertical portion attaches to the lacrimal line (frontal process of maxilla / lacrimal bone junction)
• Horizontal portion attaches to inferior turbinate
• The superior attachment of the UP determines frontal sinus drainage:
  • Attaches to LP → frontal sinus drains medial to UP, directly into middle meatus (80% - most common)
  • Attaches to fovea ethmoidalis or MT → frontal sinus drains into ethmoid infundibulum

F. Osteomeatal Complex (OMC)

• Posterior boundary: Basal lamella of MT
• Medial: MT
• Lateral: Lamina papyracea
• Superior: Fovea ethmoidalis

G. Key Structures

• 2D crescentic opening into the ethmoid infundibulum
• Bounded anteriorly by UP, posteriorly by the ethmoid bulla

• 3D trough: UP (medial) + LP (lateral) + ethmoid bulla (posterosuperior)
• Opens inferiorly at the maxillary sinus natural ostium

Upper/lower punctum → Canaliculi → Common canaliculus → Valve of Rosenmüller → Lacrimal sac → Nasolacrimal duct → Valve of Hasner → Inferior meatus

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6. Nasal Valves

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7. Blood Supply

Nasal Septum

• Sphenopalatine artery → posterior septal artery → posteroinferior septum
  • The posterior septal artery is the basis of the nasoseptal mucosal flap (workhorse flap for endoscopic skull base reconstruction)
• Greater palatine artery → enters via incisive canal → anteroinferior septum
• Septal branch of superior labial artery (from facial artery) → caudal septum and columella

• Anterior ethmoid artery → anterosuperior septum
• Posterior ethmoid artery → posterosuperior septum

The anterior nasal septum is where the anterior ethmoid artery, posterior septal artery (from sphenopalatine), and the septal branch of the superior labial artery anastomose into a rich vascular bed of long capillary loops. This is:

• The most common site of epistaxis (90% of nosebleeds)
• Vulnerable to turbulent airflow, dry air, and digital trauma

Lateral Nasal Wall

• Sphenopalatine artery (dominant supply) - enters through sphenopalatine foramen, just inferior to horizontal attachment of MT; the crista ethmoidalis is the endoscopic landmark to find this vessel
• Anterior and posterior ethmoid arteries (from ophthalmic / ICA) - supply superior lateral wall
• Greater palatine artery - inferior lateral wall near palate
• Facial artery branch - small contribution to anterior lateral wall

1. Orbit (within the orbital fat)
2. Anterior cranial fossa (above cribriform plate)
3. Nasal cavity (where it may be dehiscent and visible during ESS)

Veins

• Drain via sphenopalatine vessels into the pterygoid plexus posteriorly
• Drain into facial veins anteriorly
• Superiorly, ethmoidal veins communicate with the superior ophthalmic system
• May have direct connections through the foramen cecum into the superior sagittal sinus (route of intracranial spread of infection)

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8. Nerve Supply

Sensory Innervation

Autonomic Innervation (the Vidian nerve pathway)

• Greater superficial petrosal nerve (parasympathetic, from CN VII) - presynaptic fibers
• Deep petrosal nerve (sympathetic, from the superior cervical ganglion on the ICA)

Vidian neurectomy can be performed for intractable vasomotor rhinitis to reduce hypersecretion.

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9. Key Clinical Correlations

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• Scott-Brown's Otorhinolaryngology Head & Neck Surgery Vol. 1, pp. 1009-1016 (external nose embryology, nasal cavity, nasal septum, blood supply)
• K.J. Lee's Essential Otolaryngology, pp. 509-513 (embryology, external anatomy, nasal cartilages, turbinates, OMC, osteomeatal complex)
• Scott-Brown's Otorhinolaryngology, pp. 1014-1016 (nasal septum, Kiesselbach's plexus, turbinate cycle)
• Cummings Otolaryngology Head and Neck Surgery, p. 189 (imaging of nasal cavity, anatomic variants)

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Complete Anatomy of the Ear

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Part 1: The External Ear

A. The Auricle (Pinna)

• Auriculotemporal nerve (branch of V3 / mandibular) - anterior auricle and EAC
• Greater auricular nerve (C3 - cervical plexus) - lower lateral face, lobule, lower auricle
• Lesser occipital nerve (C2, C3) - posterior scalp and upper auricle
• Arnold's nerve (auricular branch of vagus, CN X) - posterior EAC and floor of EAC
  • Stimulation → cough reflex (Arnold's reflex / ear-cough reflex)
• Facial nerve (CN VII) twigs - small contribution

Because the EAC has vagal innervation via Arnold's nerve, inserting a cotton bud or syringing the ear can trigger coughing, or rarely fainting (vasovagal). This is also why referred otalgia can arise from the larynx, pharynx, and esophagus.

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B. External Auditory Canal (EAC)

• Fissures of Santorini - two or three vertical perforations in the anterior cartilaginous canal wall; allow passage of infection / tumor to the parotid gland
• Incisura terminalis - superior gap in the cartilaginous canal; used for the endaural incision in ear surgery
• Isthmus - narrowest point, ~5 mm from the TM; the anterior recess (wedge between TM and anterior canal wall) is deep to the isthmus and difficult to access surgically
• Tympanic sulcus - bony groove at the medial end where the TM annulus sits; absent superiorly (notch of Rivinus)
• Suture lines in the bony canal:
  • Tympanosquamous suture - anterior wall
  • Tympanomastoid suture - posterior wall
  • These form the "vascular strip" landmarks in surgery

• Adults: Pull pinna upward and backward
• Neonates/infants: Pull pinna downward and backward (the bony EAC is undeveloped; TM is more horizontal)

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Part 2: The Middle Ear

A. Tympanic Membrane (TM)

1. Squamous epithelium (skin, continuous with EAC)
2. Radiate fibrous layer (outer fibrous layer - inserts onto manubrium of malleus)
3. Circular fibrous layer (inner; arranged circumferentially at periphery)
4. Mucosal layer (continuous with middle ear mucosa)

• Average total area: 70-80 mm²
• Average vibrating surface: 55 mm² (effective area for sound transduction)
• Lies at a 45° angle to the long axis of the petrous pyramid in adults

• Umbo - most medial/depressed point; where the tip of the malleus manubrium attaches
• Mallear stria (light stripe) - line of manubrium visible through TM
• Lateral process of malleus - anterosuperior knuckle-like projection
• Cone of light - anteroinferior light reflex (right ear: 5 o'clock; left ear: 7 o'clock)
• Annulus - fibrocartilaginous ring anchoring TM to tympanic sulcus

Through the translucent pars tensa you can see: long process of incus, incudostapedial joint, round window niche, chorda tympani, promontory.

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B. Tympanic Cavity (Middle Ear)

• Promontory - formed by the basal turn of cochlea; covered by the tympanic plexus (formed by Jacobson's nerve = tympanic branch of CN IX, + branches from carotid plexus)
  • Jacobson's nerve "points" toward the cochleariform process - a surgical landmark for locating the facial nerve
• Oval window (fenestra vestibuli) - superior to promontory; occupied by the footplate of the stapes (average 1.41 mm × 2.99 mm); sealed by the annular ligament
• Round window (fenestra cochleae) - inferior to promontory; sealed by the round window membrane (secondary tympanic membrane); leads to scala tympani; separated from oval window by the subiculum
• Facial nerve (horizontal segment) - runs in a bony canal (fallopian canal) just superior to the oval window; makes first genu (sharp bend) anteriorly above the cochleariform process, then runs posteriorly
• Lateral semicircular canal - prominent bulge on medial wall of epitympanum; most commonly injured/violated landmark in mastoid surgery
• Cochleariform process - spoon-shaped bony prominence where tensor tympani tendon bends to insert on malleus; key surgical landmark for the first genu of the facial nerve
• Ponticulus - bony ridge from oval window to sinus tympani (defines superior extent of sinus tympani)
• Subiculum - bony ridge from round window to sinus tympani (defines inferior extent of sinus tympani)

• Contains: head of malleus + body and short process of incus (in the fossa incudis)
• Fossa incudis (houses short process of incus) = key surgical landmark for the facial nerve
• Cog - bony projection from tegmen above the cochleariform process; separates anterior epitympanic space (supratubal recess) from rest of attic
• Leads via the aditus ad antrum to the mastoid antrum (first area pneumatized in the mastoid)

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C. Ossicles

• Head - in the epitympanum; articulates with body of incus
• Neck - where chorda tympani passes medially
• Manubrium (handle) - embedded in the TM; the umbo is at its tip
• Lateral process - short projection visible through TM
• Anterior process - attached to petrotympanic fissure by anterior malleal ligament

• Body - in epitympanum; articulates with malleus head
• Short process (crus breve) - points posteriorly into fossa incudis
• Long process (crus longum) - descends parallel to manubrium; ends in the lenticular process which articulates with the head of the stapes

• Head - articulates with lenticular process of incus (incudostapedial joint)
• Anterior crus and posterior crus - the two arching limbs
• Footplate - oval plate that seals the oval window; average size 1.41 mm × 2.99 mm

• Superior malleal ligament (head to roof of epitympanum)
• Lateral malleal ligament
• Anterior malleal ligament (to petrotympanic fissure)

• Posterior incudal ligament (short process to fossa incudis)

Stapedius is the smallest muscle in the human body. Paralysis of CN VII → hyperacusis (abnormal sensitivity to sound) due to loss of stapedius dampening.

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D. Chorda Tympani

• Branch of the facial nerve (CN VII) that enters the middle ear through the posterior canaliculus
• Passes medial to the neck of the malleus, lateral to the long process of the incus, and anterior to the TM
• Exits via the anterior iter (canal of Huguier) and the petrotympanic fissure
• Carries: taste from the anterior 2/3 of the tongue + parasympathetic fibers to submandibular and sublingual glands
• Visible through the TM on careful otoscopy

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E. Eustachian (Pharyngotympanic/Auditory) Tube

• Total length: ~35-38 mm
• Adult: Upper 1/3 bony (from middle ear) + lower 2/3 cartilaginous (to nasopharynx); follows an inferiorly angled course (at ~45° to horizontal)
• Child: Greater proportion is cartilaginous; more horizontal course; shorter and wider - explains much higher incidence of otitis media in children
• Opens during swallowing / yawning (via tensor veli palatini muscle)
• Normally closed at rest (preventing reflux of nasopharyngeal bacteria)
• Isthmus = narrowest point at bony-cartilaginous junction

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Part 3: The Inner Ear

1. Osseous (bony) labyrinth - perilymph-filled bony cavity
2. Membranous labyrinth - endolymph-filled membranous sacs and ducts within the osseous labyrinth

A. Cochlea (Hearing)

• Scala vestibuli and scala tympani connect at the helicotrema at the apex of the cochlea
• Perilymph is similar to extracellular fluid; maintained in the scala vestibuli and tympani
• Endolymph is unique (intracellular fluid composition); maintained by the stria vascularis (lateral wall of scala media)

• Base of cochlea → high frequency sounds (20,000 Hz)
• Apex (helicotrema) → low frequency sounds (20 Hz)
• Width increases from base to apex; stiffness decreases from base to apex

• Inner hair cells (IHC) - single row; ~3,500; primary afferent transducers (~95% of cochlear nerve fibers synapse here)
• Outer hair cells (OHC) - three rows; ~12,000; amplify basilar membrane movement (electromotility); first affected in noise-induced hearing loss and ototoxicity
• Covered by the tectorial membrane (stereocilia contact)
• Spiral ganglion cells (in Rosenthal's canal in the modiolus) send axons forming the cochlear nerve (CN VIII)

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B. Vestibular Labyrinth (Balance)

• Utricle - horizontal orientation; responds to horizontal linear acceleration and gravity
• Saccule - vertical orientation; responds to vertical linear acceleration and gravity
• Both contain maculae (sensory epithelium with otoliths/otoconia on a gelatinous membrane)

• The membranous labyrinth drains via the endolymphatic duct (through the vestibular aqueduct in the petrous bone) to the endolymphatic sac (a blind-ended sac between dural layers on the posterior petrous surface)
• The endolymphatic sac is the only part of the labyrinth that contains immunocompetent cells
• Dysfunction → endolymphatic hydrops (excess endolymph) → Ménière's disease

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C. Cochlear and Vestibular Nerves (CN VIII)

• Cochlear nerve - cell bodies in spiral ganglion (Rosenthal's canal); transmits hearing
• Vestibular nerve - cell bodies in Scarpa's ganglion; transmits balance; has superior and inferior divisions

• Facial nerve (CN VII) - in the anterosuperior quadrant of the IAC
• Nervus intermedius (sensory/parasympathetic branch of VII)

• Anterosuperior = Facial nerve (CN VII)
• Anteroinferior = Cochlear nerve
• Posterosuperior = Superior vestibular nerve
• Posteroinferior = Inferior vestibular nerve

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D. Labyrinthine Fluids Summary

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E. Blood Supply of the Inner Ear

• It is an end artery with no collateral circulation → any interruption → sudden sensorineural hearing loss or vestibular failure
• It divides into the cochlear artery and vestibular artery

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Summary: Six Walls of the Tympanic Cavity (High-Yield)

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Key Clinical Correlations

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• Shambaugh Surgery of the Ear, pp. 54, 801-802 (EAC, tympanic cavity, mesotympanum, epitympanum, hypotympanum)
• K.J. Lee's Essential Otolaryngology, pp. 270-271 (TM layers, ossicle anatomy, ligaments)
• Cummings Otolaryngology Head and Neck Surgery, pp. 2447, 2455 (TM structure, membranous labyrinth, cochlear fluids, organ of Corti)
• Scott-Brown's Otorhinolaryngology Head & Neck Surgery Vol. 2, pp. 781-784 (EAC detailed structure, epithelial migration, Santorini fissures)

1. Pharynx - three divisions, muscles, Waldeyer's ring, blood/nerve supply, clinical correlations
2. Nose - external nose, nasal cavity, septum, lateral wall, OMC, blood supply (Kiesselbach's plexus), nerve supply
3. Ear - external ear (auricle, EAC), middle ear (TM, tympanic cavity walls, ossicles, Eustachian tube), inner ear (cochlea, vestibular labyrinth, IAC contents)

• Larynx anatomy
• Paranasal sinuses in depth
• Temporal bone / mastoid anatomy
• Salivary glands
• Neck spaces and fascial layers
• Or any clinical topic (e.g., otitis media, epistaxis management, cholesteatoma, vertigo)