Keratosis Obturans and External Auditory Canal Cholesteatoma

Definition and epidemiology

Keratosis obturans (KO) is a dense plug of shed skin layers (keratin) filling the bony part of the ear canal. External auditory canal cholesteatoma (EACC) arises when keratinising squamous epithelium extends into a localised area of periostitis in the canal wall and erodes the underlying bone. EACC was first described by Toynbee in 1850 but was long confused with KO; the two were separated by Piepergerdes et al. (1980) (Shin et al., 2010). The distinction matters because the treatment differs (Owen et al., 2006). This entry covers canal cholesteatoma, which is a separate entity from middle ear cholesteatoma.

EACC can be primary (spontaneous) or secondary. In a Danish series of 48 cases, the annual incidence was 0.30 per 100,000 (0.15 for primary cases); 52% were primary and the rest followed surgery (19%), radiotherapy (15%), inflammation (10%) or trauma (4%) (Owen et al., 2006). In a Korean series of 29 patients the mean age was 22.8 years, with 14 cases of spontaneous and 9 of congenital origin (Shin et al., 2010). There are no reliable figures for the frequency of KO; in Malaysia 67 ears in 64 patients were seen over 18 months, and an association with humid weather was noted (Chong and Raman, 2017).

Symptoms and signs

In the classic description KO affects younger people, is often bilateral and causes severe acute pain and conductive hearing loss, with an inflamed drum and canal skin. EACC presents later in life, is unilateral and causes chronic dull pain and discharge, while hearing is usually preserved (Heilbrun et al., 2003; Owen et al., 2006). In the Danish series, patients with primary EACC had a mean age of 57, earache was the commonest complaint at 60%, and 24% had no symptoms at all (Owen et al., 2006). In a series of 13 patients from the United States, discharge was the commonest complaint, followed by hearing loss and pain (Heilbrun et al., 2003).

Recent series show that this classic distinction does not always hold. In the Malaysian KO series most patients were young women, but involvement was mostly unilateral, and symptom severity seemed related to the presence of granulation tissue (Chong and Raman, 2017). Persaud et al. (2004) reported that no consistent symptom or examination finding reliably separates the two conditions, and that the most useful finding for EACC is localised bone necrosis or sequestrum without an epithelial covering.

Causes and risk factors

In both conditions the canal skin’s self-cleaning by outward migration fails and keratin accumulates in the bony canal. The cause of KO is not known for certain; an association with humid climate has been reported (Chong and Raman, 2017). In EACC the key event is thought to be the settling of squamous epithelium on a localised area of periostitis in the canal wall (Shin et al., 2010).

Secondary EACC can develop after ear surgery, head and neck radiotherapy, canal inflammation or trauma, or on a background of congenital canal stenosis or atresia. In primary cases a history of mechanical trauma, such as cotton buds or hearing aids, was found in 48%, and smoking in 83% of patients with records (Owen et al., 2006). These findings do not prove causation, but for audiologists they make it important to check for an earmould that rubs or presses on the canal wall.

Audiological and clinical assessment

The diagnosis is made by examination and cleaning under the microscope; once keratin is removed, the canal wall, bone surface and eardrum are assessed. In KO, how hard the plug is to remove depends on how far the canal has widened (Chong and Raman, 2017). In EACC a localised hollow in the canal wall, exposed bone or a sequestrum may be seen, and the eardrum is usually normal (Owen et al., 2006).

• Computed tomography (CT): EACC shows a soft-tissue mass in the canal with erosion of the adjacent bone; erosion was present in all 13 cases, the inferior and posterior walls were most often involved and bone fragments were seen in seven. Spread reached the middle ear (5 cases), mastoid (4), facial canal (2) and tegmen tympani (1). In KO the canal is widened smoothly all round, without focal erosion (Heilbrun et al., 2003).
• Staging: Naim et al. (2005) classified EACC into four stages on histological and clinical grounds, and Shin et al. (2010) proposed a CT-based staging that can be used before surgery (see the second table below).
• Pure-tone audiometry: keratin blocking the canal causes a mild to moderate conductive loss; in EACC hearing is usually normal unless the canal is completely occluded. A drop in bone-conduction thresholds suggests middle or inner ear involvement and should be reported to the doctor.
• Tympanometry: a blocked canal gives a flat trace with low ear canal volume; repeating the test after cleaning shows the state of the drum and middle ear. A probe should not be inserted if there is erosion or exposed bone in the canal wall.
• Biopsy: where there is granulation tissue or a mass, canal cancer and necrotising otitis externa must be excluded.

The differential diagnosis includes earwax impaction, otitis externa, middle ear cholesteatoma extending into the canal, necrotising otitis externa and cancer of the ear canal. The table below summarises the classic distinction between the two conditions; recent series show that some of these features overlap.

Treatment and audiological rehabilitation

The two conditions are treated differently, and treatment decisions rest with the doctor (Owen et al., 2006). In KO the mainstay is careful removal of the keratin plug under the microscope; painful plugs firmly stuck to the canal may need several sessions. Because the plug tends to re-form, regular review and cleaning are needed. If the canal is markedly widened and problems keep recurring, surgical canal repair may be considered.

In EACC treatment depends on the extent of disease. Limited lesions can be controlled by removing keratin and necrotic bone under the microscope with regular follow-up. Shin et al. (2010) used canaloplasty for CT stage I, canaloplasty with tympanoplasty for stage II, canaloplasty with mastoidectomy for stage III and individually planned surgery for stage IV; among 29 patients there were two recurrences and three cases of canal stenosis. In the Danish series, stage III-IV cases were operated on through the canal or from behind the ear, bone defects were repaired with fascia and, in extensive cases, cartilage, and two recurrences occurred over a mean follow-up of two years (Owen et al., 2006).

Hearing is re-measured after cleaning or surgery. For hearing aid users, ear impressions are taken only when the canal is clean and healed, and a mould that presses constantly on one spot of the canal wall is modified. After canaloplasty or mastoidectomy the shape of the canal changes and a new mould may be needed; if the canal cannot be used, bone conduction implants can be considered with the doctor.

Impact on quality of life and advice

Both conditions can usually be managed with regular review and cleaning, but because they tend to recur, follow-up may be long. Repeated blockage and pain can affect work and social life, and for hearing aid users not being able to wear the aid regularly makes communication harder. If surgery is needed, keeping the ear dry during healing and attending check-ups are important.

Practical advice: do not clean your ears with cotton buds or other objects; leave the removal of wax and keratin to your doctor. Keep to the recommended review intervals and attend even without symptoms. If you use a hearing aid, tell your audiologist about any spot where the mould presses or hurts. If you smoke, stopping benefits your ears as well as your general health. Seek help without waiting for your appointment if you develop offensive discharge, facial weakness or dizziness.