External Auditory Canal Exostosis

External auditory canal exostoses are broad based, smooth, benign, bony protuberances of the tympanic part of the temporal bone in the ear canal. They are often multiple and bilateral. They arise from periosteal new bone formation in response to repeated exposure to cold water or cold wind ("surfer's ear" or "swimmer's ear").

Cold stimulates periosteal reactive bone growth, so the canal narrows with time. Number and size correlate with the duration and frequency of exposure, water temperature (below 19 degrees C), and wind chill.

They are seen in surfers, divers, kayakers, swimmers, windsurfers and sailors. Prevalence is up to 80 percent in surfers who have surfed for more than 10 years, and about 0.5 percent in the general population.

Histology: dense lamellar bone with a thin periosteum. The exostoses are sessile and covered by thin canal skin.

They are differentiated from osteoma (a solitary pedunculated lesion from the tympanosquamous or tympanomastoid suture) by their broad base, multiplicity, bilaterality and lamellar histology.

Complications:

• cerumen and debris trapping
• recurrent otitis externa
• conductive hearing loss (from canal occlusion above 80 to 90 percent)
• tympanic membrane obscuration
• rarely, cholesteatoma formed medial to the exostoses (canal cholesteatoma)

• Often asymptomatic initially; progressive ear canal narrowing over years.
• Recurrent otitis externa, with ear pain, itching and discharge, because of water and debris trapped behind the exostoses.
• Conductive hearing loss, fullness, and tinnitus, when the lumen is below 1 to 2 mm.
• Cerumen impaction and difficulty cleaning the ear.
• Otoscopy: multiple smooth, pale, hard, sessile bony bulges that arise from the canal walls (most commonly the posterior and anterior walls, close to the tympanic membrane, near the annulus), covered by thin skin, narrowing the lumen to a slit, and obscuring the tympanic membrane.
• Tender when instrumented, with easy bleeding of the thin overlying skin.
• Rare cholesteatoma (white keratin debris) medial to the exostosis.

• Diagnosis is clinical, by otoscopy and otomicroscopy, with a history of cold water exposure (years of surfing or diving).
• Grading of canal occlusion (Grade I: below 33 percent; Grade II: 33 to 66 percent; Grade III: above 66 percent) at examination.
• Audiometry (conductive loss if severe) and tympanometry (when the drum is visible).
• CT of the temporal bone for planning surgery: shows the broad based bony nodules, extent, relation to the tympanic annulus, facial nerve, temporomandibular joint, and the remaining canal calibre; excludes cholesteatoma, and differentiates from osteoma.
• Rule out other causes of canal stenosis: osteoma, keratosis obturans, malignant tumours, chronic infection and congenital stenosis.

• Prevention (for surfers, divers and swimmers): protect the ears from cold water and wind with custom moulded earplugs (vented plugs), neoprene hoods or surf caps, and ear bands. Aim to avoid direct cold water entry. Early use of protection reduces progression and recurrence.
• Dry the ears after exposure (a hair dryer on a low cool setting, tilt of the head, or drying drops of 50/50 isopropyl alcohol and acetic acid). Avoid cotton buds.
• Asymptomatic exostoses: observation and education.
• Medical therapy for otitis externa: aural toilet with microsuction, topical antibiotic steroid drops (ciprofloxacin 0.3 percent with dexamethasone 0.1 percent, 3 to 4 drops twice daily for 7 days, or gentamicin hydrocortisone drops) with a wick if the canal is oedematous, and analgesia (paracetamol 1 g every 6 hours, ibuprofen 400 mg every 8 hours).
• Regular microsuction cleaning for those with wax and debris trapping (every 3 to 6 months).
• Surgical canalplasty is indicated for recurrent or chronic otitis externa, hearing loss, canal obstruction above 80 to 90 percent, difficulty with cleaning, canal cholesteatoma, or for surfers wishing to continue their sport with significant occlusion.
  • Procedure: an endaural or postauricular approach (under general anaesthesia), with elevation of a canal skin flap (sparing the tympanic annulus and drum).
  • Remove the bone using a drill with a diamond burr (continuous irrigation) or osteotomes, sometimes with the endoscopic approach. Take care to protect the tympanic membrane, annulus, chorda tympani, facial nerve (posterior wall, near the mastoid segment) and temporomandibular joint (anterior wall).
  • The skin is replaced as a split thickness skin graft if denuded, and the canal packed with antibiotic soaked dressing for 2 to 3 weeks.
  • Results: resolution of symptoms in over 90 percent, and hearing improvement in 50 to 100 percent in those with preoperative conductive loss.
  • Complications: tympanic membrane perforation, canal stenosis (2 to 5 percent), sensorineural hearing loss (about 1 to 2 percent), facial nerve injury (rare), temporomandibular joint injury, taste disturbance, and recurrence of exostoses if exposure is resumed (about 10 percent over 10 years).
• Postoperative care: keep the ear dry for 4 to 6 weeks, avoid water sports for 6 to 8 weeks, then return with protection; regular follow up.
• Prognosis: excellent after surgery, with recurrence minimised by ear protection.