Ear anatomy
Ear Anatomy: External, Middle and Inner Ear for FCPS
Ear anatomy for FCPS Part 1: development, nerve and blood supply of the external ear, tympanic membrane, middle ear walls and mastoid, inner ear and hearing tests. Explains referred earache, spread of otitis media, mastoid surgery landmarks and deafness patterns.
Development
| Structure | Origin |
|---|---|
| External acoustic meatus | First pharyngeal cleft (ectoderm) |
| Auricle | Six auricular hillocks around the first cleft (three from each of arches 1 and 2) |
| Tympanic membrane | Ectoderm outside, mesoderm middle, endoderm inside |
| Middle ear and auditory tube | First pharyngeal pouch (tubotympanic recess) |
| Malleus and incus | First arch |
| Stapes | Second arch |
| Inner ear | Otic placode (surface ectoderm) forming the otic vesicle |
- Preauricular pit or sinus: a small pit just in front of the helix from incomplete fusion of the auricular hillocks; may discharge or become infected. Branchial sinuses lie along sternocleidomastoid instead.
External ear
- Auricle of elastic cartilage; external acoustic meatus about 2.5 cm (outer third cartilage, inner two-thirds bone), lined by skin with ceruminous glands.
- Blood supply: posterior auricular, superficial temporal and occipital branches of the external carotid.
| Area | Nerve |
|---|---|
| Upper lateral auricle, front of meatus, outer drum | Auriculotemporal (V3) |
| Ear lobule, lower auricle, back of auricle | Great auricular (C2–C3) |
| Upper back of auricle | Lesser occipital (C2) |
| Posterior meatus and drum | Auricular branch of vagus (Arnold's nerve): cough or vomiting when the meatus is cleaned |
| Small area of concha and meatus | Facial nerve fibres (Ramsay Hunt vesicles) |
- Pinna haematoma separates perichondrium from cartilage; drain it to prevent cauliflower ear.
Tympanic membrane
- Pars tensa (most of the drum) and pars flaccida above the lateral process of the malleus, where attic retraction pockets and cholesteatoma begin.
- The handle of the malleus runs down to the umbo; the cone of light reflects in the anteroinferior quadrant (at 5 o'clock in a right ear, 7 o'clock in a left).
- Outer surface: V3 (auriculotemporal) and X; inner surface: IX (tympanic plexus).
- In acute otitis media the drum bulges; the pain comes from the inflamed middle ear mucosa and inner drum, supplied by IX.
Middle ear (tympanic cavity)
| Wall | Relation |
|---|---|
| Roof (tegmen tympani) | Middle cranial fossa and temporal lobe |
| Floor | Jugular bulb of the internal jugular vein |
| Anterior | Internal carotid artery, auditory tube, tensor tympani |
| Posterior | Aditus to the mastoid antrum, pyramid with stapedius, facial canal descending |
| Medial | Promontory (basal turn of cochlea), oval and round windows, facial nerve prominence, lateral semicircular canal |
| Lateral | Tympanic membrane, attic wall |
- Ossicles: malleus, incus, stapes (footplate in the oval window); they amplify pressure about 20 times (mainly the drum-to-footplate area ratio).
- Muscles damp loud sounds: tensor tympani (V3) and stapedius (VII); stapedius palsy causes hyperacusis.
- Chorda tympani crosses the inner surface of the drum between malleus and incus.
- Mucosa and medial wall: tympanic plexus from IX (Jacobson's nerve), which also carries parotid secretomotor fibres onward as the lesser petrosal nerve.
- Auditory tube: lined by respiratory (pseudostratified ciliated columnar) epithelium; equalises pressure. In children it is shorter, wider and more horizontal, so otitis media is common. Blockage gives glue ear: retracted drum, fluctuating conductive deafness.
Mastoid
- The mastoid process is absent at birth and develops as the SCM pulls on it during infancy; in a child the antrum is relatively superficial.
- Suprameatal (Macewen's) triangle on the lateral temporal bone, behind and above the meatus, overlies the mastoid antrum (about 1.5 cm deep in adults): the landmark for cortical mastoidectomy.
- The sigmoid sinus lies behind the antrum: profuse bleeding from the posterior wall at mastoid surgery is sigmoid sinus bleeding. The facial nerve descends in front of it.
Spread of middle ear infection
| Direction | Complication |
|---|---|
| Up through the tegmen tympani | Extradural abscess, meningitis, temporal lobe abscess |
| Back into the mastoid | Mastoiditis, subperiosteal abscess |
| Behind the mastoid | Sigmoid (lateral) sinus thrombosis, cerebellar abscess |
| Medially | Labyrinthitis, facial palsy |
- Cholesteatoma: keratinising squamous epithelium in the middle ear, eroding bone; chronic foul discharge.
- Middle fossa fracture: haemotympanum, CSF otorrhoea, Battle's sign.
Referred earache
- Ear sensation shares V3, VII, IX, X and C2–C3 with the mouth, throat and neck.
- After tonsillectomy the earache is carried by the glossopharyngeal nerve (tonsil bed).
- Dental pain and TMJ pain are referred via V3; laryngeal and pharyngeal pain via X.
- Persistent one-sided earache with a normal ear in a smoker: exclude a hidden upper aerodigestive tract cancer (tongue base, tonsil, piriform fossa, larynx).
Inner ear
- Bony labyrinth with perilymph (like extracellular fluid); membranous labyrinth with endolymph (high K⁺, low Na⁺).
- Cochlea: 2.75 turns; organ of Corti on the basilar membrane; hair cells are the mechanoreceptors for hearing and balance. High frequencies at the base, low at the apex.
- Utricle and saccule: linear acceleration and head tilt. Semicircular canals: angular acceleration (cristae in ampullae).
- Caloric test: cold water in the ear sets up convection currents in the endolymph of the lateral semicircular canal, causing vertigo, nausea and nystagmus.
- VIII runs with VII and the labyrinthine artery through the internal acoustic meatus. Pathway: cochlear nuclei, superior olive, lateral lemniscus, inferior colliculus, medial geniculate body, auditory cortex (areas 41, 42).
Hearing loss
| Type | Causes | Rinne | Weber |
|---|---|---|---|
| Conductive | Wax, otitis media, glue ear, perforation, otosclerosis | Negative (bone louder than air) | To the affected ear |
| Sensorineural | Presbycusis, noise, ototoxic drugs, Ménière's, acoustic neuroma | Positive | To the normal ear |
- A severe unilateral sensorineural loss can give a false-negative Rinne (bone conduction heard by the other cochlea), but Weber goes to the good ear: Rinne negative on the right with Weber to the left means a dead right ear.
- Otosclerosis: stapes footplate fixed; young women, worse in pregnancy.
- Acoustic neuroma: unilateral sensorineural deafness and tinnitus; early loss of the corneal reflex; bilateral in NF2.
- Ménière's: endolymphatic hydrops; episodic vertigo, fluctuating hearing loss, tinnitus, fullness. BPPV: brief positional vertigo; Dix–Hallpike and Epley manoeuvre.
Remember Roof to the temporal lobe, floor to the jugular bulb, front to the carotid, back to the mastoid.
Exam trap Earache after tonsillectomy is referred through IX; a persistent one in a smoker needs a throat examination for cancer.
Exam trap In conductive deafness Weber lateralises to the deaf ear.
How FCPS asks about this
- Origin of the external acoustic meatus: first pharyngeal cleft; preauricular pit from auricular hillocks.
- Cone of light: anteroinferior quadrant.
- Nerve to the ear lobule: great auricular (C2–C3).
- Landmark for the mastoid antrum: suprameatal (Macewen's) triangle.
- Bleeding from the posterior wall of the antrum: sigmoid sinus.
- Temporal lobe abscess from otitis media: spread through the tegmen tympani.
- Rinne negative, Weber to the same side: conductive deafness (e.g. glue ear, otosclerosis).
Test yourself on this topic
5 of the 27 questions in our bank on this topic. Choose an answer to see why every option is right or wrong.
A child with chronic suppurative otitis media develops fever, headache and confusion. CT shows a temporal lobe abscess. Through which part of the middle ear did infection most likely spread?
Answer: Tegmen tympani (roof)
Walls of the middle ear: roof—tegmen tympani, a thin bony plate separating it from the middle cranial fossa and temporal lobe (spread causes extradural abscess, meningitis or temporal lobe abscess); floor—jugular bulb (lateral sinus thrombosis); anterior wall—carotid canal and Eustachian tube opening; posterior wall—aditus to the mastoid antrum (mastoiditis, then cerebellar abscess via the sigmoid sinus plate); medial wall—promontory (basal turn of cochlea), oval and round windows, and the facial nerve canal (facial palsy); lateral wall—tympanic membrane.
Middle ear walls
- Roof (tegmen): temporal lobe, meningitis
- Posterior: mastoid → cerebellar abscess
- Medial: promontory, facial nerve canal
- Floor: jugular bulb
Remember Thin roof, brain above.
Why the other options are wrong
- Floor over the jugular bulb Leads to jugular bulb or sinus thrombosis.
- Anterior wall, carotid canal Carotid canal; rarely involved.
- Lateral wall (drum) The drum; spread outward.
- Eustachian tube Connects to nasopharynx.
A child with acute mastoiditis is taken for cortical mastoidectomy. On the lateral surface of the temporal bone, which of the following landmarks is used to locate the mastoid antrum?
Answer: Suprameatal (Macewen's) triangle
The suprameatal (Macewen's) triangle lies above and behind the external acoustic meatus, bounded by the supramastoid crest above, the posterosuperior margin of the meatus and a vertical line from the posterior margin of the meatus. The mastoid antrum lies deep to it, about 12–15 mm deep in adults and closer to the surface in children. Drilling here opens the antrum safely, away from the sigmoid sinus behind and the facial nerve below.
Macewen's triangle
- Above and behind the external meatus
- Overlies the mastoid antrum
- Antrum 12–15 mm deep in adults
- Avoids sigmoid sinus and facial nerve
Remember Drill in Macewen's triangle to find the antrum.
Exam trap In a child the mastoid process is small, so the antrum is relatively superficial.
Why the other options are wrong
- Tip of the mastoid process Contains air cells but the antrum lies higher and deeper.
- Stylomastoid foramen region The facial nerve exit; drilling here endangers it.
- Asterion on the lateral skull Marks the transverse–sigmoid sinus junction.
- Root of the zygomatic arch Lies in front of the meatus, away from the antrum.
A 30-year-old woman has progressive bilateral hearing loss over five years that worsened noticeably during her last pregnancy; her mother wore hearing aids from the age of 40. Rinne test is negative on both sides, Weber is central, and both tympanic membranes look normal and mobile. Tympanometry is type As. At surgery, where is the abnormal bone most likely to be found?
Answer: Stapes footplate at oval window
Otosclerosis is an inherited disorder in which abnormal spongy bone forms in the otic capsule, most often just in front of the oval window. It fixes the stapes footplate in the oval window, so sound vibrations are not transmitted to the inner ear, causing conductive hearing loss with a normal drum and a negative Rinne test. Oestrogen and pregnancy may speed progression. Stapedotomy with a prosthesis restores transmission.
Otosclerosis
- Spongy bone in otic capsule
- Fixes stapes footplate
- Conductive loss, normal drum
- Worse in pregnancy
Remember Normal drum, conductive loss, young woman: otosclerosis.
Exam trap A flamingo-pink blush behind the drum (Schwartze sign) is seen in active disease but is uncommon.
Why the other options are wrong
- Handle of malleus on the drum Malleus fixation is rare and drum movement would be affected.
- Incudostapedial joint capsule Joint erosion occurs in chronic otitis media, not otosclerosis.
- Round window membrane niche Round window involvement is uncommon.
- Apical turn of the cochlea Cochlear otosclerosis causes sensorineural loss, less common than footplate fixation.
A 30-year-old man with a long-standing foul ear discharge from an attic cholesteatoma has brief vertigo whenever he presses on his tragus. At surgery the bony prominence on the medial wall of the attic and aditus is eroded. Which part of the inner ear has been exposed?
Answer: Lateral semicircular canal
The lateral (horizontal) semicircular canal forms a bony bulge on the medial wall of the aditus and attic, right where a cholesteatoma expands. It is therefore the commonest site of a labyrinthine fistula. When the bone is eroded, pressure changes in the ear canal move the perilymph and stimulate the canal, causing vertigo and nystagmus: the fistula sign. The cochlea lies further forward and medial, behind the promontory.
Labyrinthine fistula
- Lateral canal bulges into the aditus
- Eroded by attic cholesteatoma
- Pressure causes vertigo, nystagmus
- Positive fistula sign
Remember Tragal pressure vertigo in cholesteatoma: lateral canal fistula.
Exam trap Removing cholesteatoma matrix from a fistula can cause total deafness; the surgeon must know beforehand.
Why the other options are wrong
- Basal turn of the cochlea Lies behind the promontory, deeper and further forward.
- Posterior semicircular canal Lies posteriorly, deep in the petrous bone, away from the attic.
- Superior semicircular canal Lies on the roof of the petrous bone; its dehiscence is usually not from cholesteatoma.
- Endolymphatic sac Lies on the posterior surface of the petrous bone, near the dura.
A 32-year-old woman who grinds her teeth has earache on the right. The ear canal and drum are normal, but the right temporomandibular joint is tender and clicks. Which of the following nerves best explains why the joint pain is felt in the ear?
Answer: Auriculotemporal nerve
The auriculotemporal nerve, a branch of the mandibular nerve, supplies the temporomandibular joint and also the skin of the external acoustic meatus, the outer tympanic membrane and the front of the auricle. Pain from the joint is therefore readily felt as earache. A normal ear examination with a tender, clicking joint is a typical picture of TMJ dysfunction.
TMJ earache
- Auriculotemporal (V3) supplies TMJ
- Also supplies ear canal and drum
- Normal ear: look at the joint
Remember Earache with a normal ear: check TMJ, teeth and throat.
Exam trap Always examine the throat and larynx in an adult with otalgia and a normal ear.
Why the other options are wrong
- Great auricular nerve Supplies the lower auricle and parotid skin, not the joint.
- Lesser occipital nerve Supplies the scalp behind the ear.
- Chorda tympani Carries taste and secretomotor fibres; not pain from the joint.
- Greater petrosal nerve Carries secretomotor fibres to the lacrimal gland.
Where this sits in the CPSP syllabus
- Paper 1: Head, neck and back, Ear: external, middle and inner
- Surgery & Allied, Paper 2: Head and neck, Ear: external, middle and inner