Labyrinthine Fistula

Labyrinthine fistula is an abnormal opening in the bony otic capsule, most often the lateral semicircular canal, which exposes the membranous labyrinth to middle ear pressure changes. Pressure changes or sound then provoke vertigo.

It is found in 5% to 10% of cholesteatoma, and in about 10% of those with larger disease. Other causes are chronic otitis media, previous ear surgery, trauma, barotrauma and, rarely, superior canal dehiscence.

Pathophysiology.

Bone erosion by cholesteatoma matrix and enzymes uncovers the endosteum. Pressure from the external ear canal then moves endolymph, stimulating the vestibular receptors and causing vertigo and nystagmus.

Vertigo on pressing the tragus, coughing, straining or loud sounds (Tullio phenomenon), unsteadiness, hearing loss, and a history of chronic ear discharge. The vertigo lasts as long as the pressure stimulus.

Red flags.

• Sensorineural hearing loss.
• Facial weakness.
• Headache, fever or neck stiffness (labyrinthitis, meningitis).
• Persistent severe vertigo.

The fistula test (pneumatic otoscopy or tragal pressure) produces nystagmus and vertigo (Hennebert sign), though it is negative in about a third of patients with fistula. Audiometry shows conductive or mixed loss. High resolution CT of the temporal bone shows erosion of the otic capsule (usually the lateral semicircular canal). Magnetic resonance imaging is done when intracranial complications are suspected.

Differential diagnosis.

• Superior semicircular canal dehiscence.
• Perilymph fistula from the oval or round window.
• Benign paroxysmal positional vertigo.
• Ménière disease.
• Vestibular neuritis.
• Labyrinthitis.

The treatment is surgical removal of cholesteatoma, with the matrix over the fistula left in place or removed with sealing of the defect with bone dust, fascia or cartilage. Avoid pressure on the ear, nose blowing with force and heavy lifting before surgery.

• Prednisolone (perioperative, for sensorineural loss or labyrinthitis): 1 mg/kg orally once daily (maximum 60 mg) for 5 to 7 days then taper over 7 days; monitor glucose, blood pressure and mood; reduce in older adults and give gastric protection.
• Prochlorperazine (short term vertigo control): 5 mg orally three times daily for up to 3 days; maximum 20 mg daily; monitor for dystonia and sedation; avoid in older adults with dementia and reduce the dose in hepatic impairment.
• Ciprofloxacin 0.3% ear drops: 4 drops into the ear twice daily for 7 days for active otorrhoea; avoid the neomycin and gentamicin drops, which are toxic to the inner ear.

Do not irrigate the ear. Give intravenous antibiotics for intracranial complications.

Monitoring. Audiometry before and after surgery, and postoperative vertigo and nystagmus at 1 week.

Referral and escalation. ENT urgently; neurosurgery for intracranial extension.

Special groups. Older adults need falls prevention and care with vestibular sedatives.