External Auditory Canal Osteoma

External auditory canal osteoma is a benign, solitary, pedunculated, slow growing tumour of lamellar bone. It arises from the bony part of the external auditory canal, typically at the tympanosquamous or tympanomastoid suture line. This is the junction of the bony and cartilaginous canal (the lateral third of the bony canal).

It is rare (about 0.05 percent of the population, 0.1 to 1 percent of otology patients). It is more common in men (about 2 to 4:1), at ages 20 to 50 years.

The aetiology is unknown. Chronic irritation by cold water exposure, trauma, infection and sunburn have been suggested. It is not clearly related to water exposure as exostoses are.

Histology shows mature lamellar bone with fibrovascular channels (Haversian canals) and a periosteal and skin covering, with a fibrous stalk connection to the suture.

It is differentiated from exostoses by:

• Being solitary, unilateral and pedunculated (narrow neck).
• Originating at a suture line.
• Having a lamellar structure with vascular marrow spaces.
• Being covered with a layer of thicker periosteum and skin.

Complications: canal obstruction, cerumen retention, conductive hearing loss, recurrent otitis externa, and, rarely, canal cholesteatoma or tympanic membrane perforation.

• Usually asymptomatic and found incidentally at routine otoscopy; a slow growing mass.
• Symptoms with obstruction (when the canal is more than 80 to 90 percent narrowed): conductive hearing loss, aural fullness, tinnitus, and impacted cerumen.
• Recurrent external otitis, otalgia, otorrhoea and itching because of debris and water retained medial to the lesion.
• Otoscopy: a solitary, smooth, hard, pale or skin coloured, pedunculated, rounded mass (often 2 to 15 mm). It is attached by a narrow stalk to the canal wall near the tympanosquamous or tympanomastoid suture (the osseocartilaginous junction).
• The mass is non-tender, covered by normal skin, and firm to palpation with a probe.
• Usually unilateral.
• Rarely, vertigo and facial paralysis when it extends deeply or erodes the facial canal (should raise suspicion of other diagnoses).

• Otoscopy and otomicroscopy, with palpation using a blunt probe (hard and immobile).
• Audiometry for conductive loss when it narrows the canal; tympanometry.
• High resolution CT of the temporal bone: a well defined, rounded, pedunculated, dense bony mass with a cortical rim and a stalk arising from the canal wall, and a lamellar structure (with a central lucent medulla in some).
• CT defines its attachment, extent, and relation to the tympanic annulus, facial nerve and temporomandibular joint.
• CT excludes other lesions: exostoses (multiple, bilateral, sessile), osteochondroma, fibrous dysplasia, ossifying fibroma, cholesteatoma, keratosis obturans, squamous cell carcinoma, ceruminoma, bone metastases, or tumour like lesion.
• Biopsy is rarely needed; histology after excision confirms.

• Asymptomatic small osteomas that do not obstruct the canal or cause infection: no treatment, with periodic surveillance by otoscopy, and a patient education.
• Surgical excision is indicated for symptomatic osteomas (hearing loss, recurrent otitis externa, blockage of cleaning, tinnitus), those causing pain, canal cholesteatoma, large tumours, a diagnostic uncertainty, and cosmetic reasons:
  • Approach: transcanal (for small, lateral osteomas with accessible stalk), endaural or postauricular (for larger, deeper tumours), under general or local anaesthesia.
  • Raise a canal skin flap around the base (preserving the skin, then replaced) and expose the pedicle.
  • Remove the osteoma by drilling the stalk with a diamond or cutting burr (continuous irrigation), or by osteotome and gouge (which is quicker, but more risk of sensorineural hearing loss from noise induced trauma). Leave a rim of the underlying bone to prevent recurrence.
  • The lesion is typically removed in one piece. The skin flap is replaced, and a gelatin sponge and an antibiotic impregnated canal pack are inserted for 1 to 2 weeks.
  • Endoscopic and navigation guided techniques allow a minimally invasive approach.
  • Take care to preserve the tympanic membrane, annulus, facial nerve, chorda tympani, and the temporomandibular joint (anterior canal wall).
• Perioperative antibiotics: single dose of cefazolin 1 to 2 g intravenously, with topical antibiotic drops (ciprofloxacin 0.3 percent, 4 drops twice daily for 5 to 7 days) after surgery.
• Follow up: otoscopy at 2 weeks, 6 weeks and 3 months; the canal heals in 4 to 8 weeks; audiometry at 3 months; avoid water entry for 4 to 6 weeks.
• Complications: tympanic membrane perforation, canal skin loss and stenosis, facial nerve paresis, sensorineural hearing loss, infection, and recurrence (rare, below 5 percent if the base is removed).
• Prognosis is excellent, with recurrence being uncommon after complete removal.