Exostoses and Osteoma

Definition and epidemiology

Exostoses and osteomas are two distinct benign bony lesions arising from the bony part of the external ear canal. Exostoses are broad-based bony swellings in the inner (medial) bony canal, close to the eardrum and circumferential in distribution; they are usually multiple, bilateral and symmetrical. An osteoma is usually a single, pedunculated, smooth, round mass lying more laterally along the tympanomastoid or tympanosquamous suture (Raymond, 2023).

Because exostoses are associated with repeated exposure to cold water and cold air, they are known as ‘surfer’s ear’. In a study of 202 surfers, 38% had exostoses; the odds were 5.8 times higher in those who surfed mainly in cold water and 3.8 times higher in professionals, and each additional year of surfing increased the risk of developing exostoses by 12% (Kroon et al., 2002). Reported prevalence in surfers ranges from 38% to 73.5% (McParland et al., 2019). The condition is not new: at Körtik Tepe, an early sedentary settlement in Diyarbakır, Türkiye, exostoses were found in 35.2% of 128 individuals and were attributed to intensive contact with freshwater sources (Koruyucu et al., 2018). Osteomas, by contrast, are often symptom-free and found incidentally (Raymond, 2023).

Symptoms and signs

Most lesions cause no symptoms and are seen incidentally on examination. As the canal narrows, water and wax collect behind the lesions; the commonest complaints are a sensation of trapped water after swimming or showering, blockage, intermittent reduced hearing and recurrent otitis externa (McParland et al., 2019). In a surgical series of 67 patients the main complaints were wax retention, otitis externa and hearing loss (Costa et al., 2021).

A persistent conductive hearing loss develops only when the canal is severely narrowed or the space behind the lesions is completely filled with wax and debris. On otoscopy, exostoses appear as multiple hard, rounded swellings in the medial canal covered by thin, pale skin, and only part of the eardrum can be seen. An osteoma is a single pedunculated mass lying further out. Kroon et al. (2002) graded lesions by canal patency as normal, mild or moderate-severe, and found 69% of exostoses to be mild and 31% moderate-severe.

Causes and risk factors

Exostoses are reactive new bone formed when cold water repeatedly stimulates the thin skin and periosteum of the bony canal, and are thought to represent a cold-induced periostitis (Raymond, 2023). Water below 19 °C or cold air is the main environmental factor, and water sports such as surfing, swimming and diving carry a risk (McParland et al., 2019). Longer exposure increases both the likelihood and the severity of exostoses (Kroon et al., 2002). The lesions grow slowly over years and can recur after surgery if cold-water exposure continues (McParland et al., 2019). The cause of osteoma is unknown.

Histologically, exostoses consist of dense bone rich in osteocytes, laid down in parallel concentric layers beneath the periosteum, without marrow. An osteoma consists of lamellar bone with an outer cortex and inner marrow spaces, and contains fibrovascular channels (Raymond, 2023; Carbone and Nelson, 2012). Fibrovascular channels were once proposed as the distinguishing feature, but a larger series found them in some exostoses too, showing that histology alone does not always separate the two. Site, number and appearance are therefore considered together (Carbone and Nelson, 2012).

Audiological and clinical assessment

The diagnosis rests on the history (cold-water exposure, water sports) and otoscopy, and the two lesions are usually told apart by site, number and the appearance of their base. CT is not routinely needed; it is requested when surgery is planned, to show the depth and medial extent of the lesion (Raymond, 2023; McParland et al., 2019).

• Otoscopy: record approximate canal patency as a percentage and how much of the eardrum is visible; photographs help comparison over time.
• Pure-tone audiometry: hearing is normal while the canal remains patent. When wax or water closes the canal, a mild conductive loss with an air-bone gap is seen and bone conduction is normal. Preoperative bone-conduction thresholds are the baseline for detecting any sensorineural change after surgery.
• Tympanometry: probe placement and an airtight seal are difficult in a narrow, irregular canal, and results are unreliable without a seal. An occluded canal gives a flat trace with low ear canal volume.
• Speech audiometry: thresholds agree with the pure-tone average, and word recognition scores are usually preserved.
• Hearing aid users: narrowing makes impressions, device insertion and real-ear measurement (REM) harder; when taking an impression, the otoblock must not be pushed beyond the medial lesions and impression material must not be left behind them.

The differential diagnosis includes keratosis obturans and external auditory canal cholesteatoma, other canal tumours and earwax impaction behind the lesions. Recurrent infection is discussed in detail in the entry on otitis externa.

Treatment and audiological rehabilitation

No treatment is needed for people without symptoms; monitoring and protecting the ear from cold water are sufficient (Raymond, 2023). Microscopic cleaning is used when wax or debris blocks the canal, and drops when otitis externa develops. Surgery is considered for severely obstructive lesions, frequent otitis externa and conductive hearing loss; the decision rests with the surgeon (McParland et al., 2019; Raymond, 2023).

The operation (removal of the exostoses with canalplasty) is performed through the canal or from behind the ear, using a drill or an osteotome, and preserving the canal skin reduces the risk of stenosis. A symptomatic osteoma is removed surgically through the canal or from behind the ear, and complete removal of its base lowers the chance of recurrence (Raymond, 2023). In a series of 401 ears in 327 patients treated by postauricular drill canalplasty, delayed healing occurred in 4.5% of ears and eardrum perforation in 0.2%. Bone-conduction thresholds at 4 kHz worsened by a mean of 3.7 dB, by more than 15 dB in 4.8% of ears, and exostoses recurred in 8 of 91 ears followed long term, up to 15 years after surgery (House and Wilkinson, 2008). In another series of 67 patients, 14.9% had surgical complications, but these did not significantly reduce satisfaction with the operation (Costa et al., 2021).

Once the canal is opened, the conductive component usually closes. Postoperative audiometry shows both the closure of the air-bone gap and any high-frequency sensorineural change, so comparing bone-conduction thresholds before and after surgery is important. Hearing aid users need a new impression once the canal has fully healed. People who continue to be exposed to cold water are advised to wear earplugs, a hood or a swimming cap, as recurrence is more common with continued exposure (McParland et al., 2019).

Impact on quality of life and advice

Exostoses often remain silent for years, but trapped water, recurrent infection and fluctuating hearing can affect both the performance and the enjoyment of people who do water sports. After surgery the ear must be kept dry for the period set by the surgeon, which is a real restriction for athletes in regular training and may be considered when timing the operation.

Practical advice: if you regularly swim, surf or dive in cold water, protect your ears with suitable earplugs and a hood; dry the outer ear after water sports and do not put objects into the canal. If water is often trapped in your ear, or you have blockage or discharge, see an ENT doctor and keep up with regular reviews. If you use a hearing aid, tell your audiologist when the fit of your mould changes or it starts to hurt more often.