Middle Ear Surgery

Anatomy

• The tympanic cavity is found in the petrous temporal bone
• Lateral wall is mostly the tympanic membrane
• It contains the ossicles - malleus, incus and stapes
• The medial wall houses the oval window and the round window to the cochlea
• The attic is the area of the middle ear cavity superior to the ossicles
• The Eustachian tube connects the middle ear to the nasopharynx, and helps with equalisation of air pressure
• The aditus connects the middle ear posteriorly to the mastoid air cells

Function

• Sound waves vibrate the tympanic membrane
• This movement is transmitted via the ossicles to the oval window on the medial wall of the tympanic cavity
• Stapes movement generates a pressure wave in perilymph with displacement at the round window
• This stimulates the hair cells in the cochlea to produce electrical signals to the brain

The middle ear is primarily an amplifier. Every time sound travels from air to fluid, the changes in impedance cause a loss of signal.

By taking the vibrations of a larger membrane (tympanic membrane) and conducting them to a much smaller one (oval window) the mechanical signal is amplified to offset this loss.

Give me numbers damnit!

Well since you ask...

• The tympanic membrane is around 17x the area of the oval window
• The ossicular system gives a leverage ratio of 1.3:1
• The overall amplification is around 25 dB

This is highly unlikely to be examinable, but it's such a massive flex to whip out on an ENT list.

• From the brainstem the facial nerve travels through the temporal bone
• Enters via internal acoustic meatus and travels in the bony facial canal
• Passes through labyrinthine segment to the geniculate ganglion
• Tympanic segment runs horizontally along medial wall above oval window
• Mastoid segment runs vertically down to the stylomastoid foramen
• Chorda tympani supplies taste anterior 2/3 tongue and runs across middle ear between malleus and incus, so you can get disturbance of taste if this gets damaged

The facial canal can be incomplete in various places, exposing the nerve in the middle ear cavity and putting it at higher risk of injury.

As a result, the surgeons may monitor the facial nerve, which will affect how you conduct your anaesthetic.

• Frequencies from 20 to 20 000 Hz can be detected
• The human auditory system is most sensitive between 500 and 4000 Hz
• Between 85 and 250 Hz you can hear the surgeon asking you to make the bleeding stop

• Auriculotemporal nerve - from V3 - sensation of external acoustic meatus and tympanic membrane
• Greater auricular nerve - from cervical plexus - sensation to EAM
• Auricular branch of vagus - sensation to EAM
• Glossopharyngeal nerve - sensation to middle ear cavity

If you're interested, Jacobson’s nerve (tympanic branch of IX) forms the tympanic plexus and supplies mucosa, and is responsible for referred otalgia when you have a sore throat.

• Anterior tympanic artery
• Superior tympanic branch of middle meningeal artery

Both from the maxillary artery

• Posterior tympanic branch of stylomastoid artery
• Inferior tympanic branch of ascending pharyngeal artery
• Caroticotympanic branches of internal carotid artery

If you can't remember these just say 'multiple small branches of the external carotid, with small contributions from the internal carotid as well'.

Venous drainage is via the pterygoid plexus and superior petrosal sinus.

• Chronic otitis media - tympanoplasty
• Cholesteatoma - mastoidectomy
• Hearing loss - cochlear implant insertion
• Otosclerosis - stapedotomy/stapedectomy
• Tympanosclerosis - tympanoplasty with or without ossiculoplasty
• Perforated tympanic membrane - myringoplasty

• I would start with a comprehensive anaesthetic pre-assessment including history, examination and review of relevant investigations
• Patients may have hearing loss, making communication and consenting more difficult - may require sign language interpreter, or at least be able to lip-read
• Paediatric patients may have congenital syndromes that will affect their airway management - Stickler syndrome, Klippel-Feil syndrome
• In adults I would particularly want to assess for any comorbidities that would contraindicate hypotensive anaesthesia - cardiovascular disease, sickle cell, pregnancy, infancy <1 year, carotid stenosis etc
• Congenital sensorineural hearing loss can be associated with long QT syndrome in Jervell and Lange-Nielsen syndrome, so I would review an ECG prior to anaesthesia.

• Tympanoplasty
• Mastoidectomy*
• Stapes surgery

*Technically. Very rare in UK.

• Patient preference
• Surgeon preference
• Avoiding pain of local anaesthetic injection
• To guarantee a motionless patient

• Optimise surgical field
• Avoid excessive arterial hypotension
• Facilitate facial nerve monitoring where required
• Avoid coughing on emergence
• Avoid post operative pain and nausea and vomiting

• Reduced access to patient's head
• Long procedure
• Need to control ventilation to avoid hypercapnoea
• Difficult airway (if syndromic)

In many patients, a supraglottic device is often fine, and can help avoid coughing on emergence.

• Less coughing
• Avoidance of neuromuscular blockade for facial nerve monitoring
• Faster list turnover

• Long surgery so patient needs to empty bladder immediately before surgery
• Caution with pressure points, ensure lines well padded
• Consider catheter if more than two or three hours
• Avoid excessive fluid therapy
• Minimal surgical exposure so temperature can be easily maintained with forced air warming device
• NIBP is usually sufficient, but consider arterial line for longer procedures or if planning to use hypotensive anaesthesia
• Mechanical thromboprophylaxis
• If the surgeon's need to use nerve monitoring, then a single small dose of rocuronium for intubation has usually worn off by the time they need the facial nerve to work again (plus you always have sugammadex)

• Remifentanil TIVA
• Increased depth of anaesthesia
• Alpha 2 agonists - clonidine, dexmedetomidine
• Magnesium
• Beta blockers

• Lasers are sometimes used for cholesteatoma surgery (KTP or potassium-titanyl-phosphate lasers since you ask)
• CO2 lasers are also used for stapedotomy

Standard laser questions for the exam are covered in our post here.

Usually performed before two and a half years of age to aid speech development, so invariably this is a paediatric case.

• A cortical mastoidectomy is performed to open up the facial recess
• A flexible electrode is passed into the scala tympani of the cochlea
• The electrode is connected to a receiver-stimulator unit which is fixed under the skin to the skull
• The external unit sits over this, held in place by a magnet, and converts sound into code that is transmitted to the receiver-stimulator unit
• Can also have telemetry functionality to allow measurement of how well the implant is functioning

The key is to avoid coughing and bucking on the tube as this can damage the surgical repair

Options include:

• Deep extubation
• Exchange for supraglottic airway while deep
• Remifentanil infusion to facilitate smooth emergence
• Lidocaine IV 2 minutes before extubation

• Local anaesthetic with adrenaline by the surgeon
• Paracetamol
• NSAIDs where relevant
• Oral opioids (ideally avoid as will worsen PONV)
• Topical local anaesthetic (ear pack soaked in levobupivacaine 0.5%)

There are nerve blocks you can do, such as auriculotemporal nerve block or great auricular nerve block, but this will depend on who you're working with.

• Taste change
• Transient facial palsy
• CSF leak
• Meningitis
• Persistent facial nerve palsy
• Vertigo
• Sensorineural hearing loss

Kids often get delirium after middle ear surgery, which can be offset with alpha-2 agonists like clonidine.

• Young patients
• Longer procedure times
• Direct stimulation of vestibular apparatus
• Suction-irrigation (temperature changes stimulate vestibular apparatus)

There is a 60-80% risk of PONV with middle ear surgery, compared to a baseline of 10% for other procedures, so use lots of antiemetics!

In patients with vestibular symptoms, consider betahistine.