Osteomas and Exostoses of the External Auditory Canal

Introduction

Osteomas and exostoses are benign bone growths found in the temporal bone, most commonly in the bony external auditory canal (EAC). The structure of the EAC takes a tortuous route from the external auditory meatus to the tympanic membrane (TM), through the cartilaginous lateral third to the medial bony two-thirds.

The S -shaped structure of the canal provides a protective mechanism to the TM. The function of the EAC serves not only to protect the TM, but it also conducts sound to the TM and middle ear. In conjunction with the concha, the EAC amplifies sound from 5 to 20 dB from the free field to the TM due to the resonance of both structures. Occlusion of the EAC, whether congenital or acquired, causes conductive hearing loss.

The EAC is normally self-cleansing due to the epithelial migration from the surface of the TM to the EAC. Unimpeded epithelial migration acts similar to a conveyor belt to carry cerumen and desquamated epithelial cells out to the lateral aspect of the canal, where this debris can easily be removed. Lesions that cause partial or complete occlusion of the EAC can impede epithelial migration, leading to an accumulation of cerumen and/or epithelial debris medial to the lesion. This can trigger recurrent episodes of acute otitis externa (OE) as the skin of the EAC becomes inflamed. Conductive hearing loss can also develop due to of impaction of debris if the debris is made inaccessible for cleaning by the presence of these bony growths.

Exostoses are bilateral, lamellar outgrowths of the bone of the medial EAC, typically triggered by reactive hyperemia of the EAC skin following exposure to cold water ( Fig. 127.1 ). Reactive hyperemia is seen following the initial vasoconstriction that occurs with cold exposure and is a hallmark of first-degree frostbite injury. The hyperemia reflects the attempt of the tissue to protect from further thermal injury due to recurrent exposure to cold water. The condition was originally described as “surfer’s ear” and is commonly seen in cold water surfers, kayakers, divers, and swimmers. There is a male predilection. Formation of the exostoses occurs in a time-dependent fashion, with a greater degree of EAC occlusion seen with longer durations of exposure and increasing age. Exostoses can develop along the anterior, posterior, and superior bony EAC, with anterior and posterior exostoses commonly exhibiting a sessile structure.

Fig. 127.1, View of the right external auditory canal revealing multiple broad-based exostoses located medially near the tympanic membrane.

Osteomas are relatively rare when compared with exostoses. These are solitary, unilateral bone lesions located more laterally in the bony EAC, often pedicled to the tympanosquamous or tympanomastoid suture line. Osteomas are considered true neoplasms of bone ( Fig. 127.2 ).

Fig. 127.2, Excised osteoma of the external auditory canal with its narrow pedicle located on the right side of the bony tumor.

Treatment of osteomas and exostoses is symptom dependent. Most patients with osteomas or exostoses are diagnosed incidentally on routine examination of the ear. If the degree of EAC occlusion is less than 80%, most patients require either no treatment or conservative management with periodic débridement of the EAC to prevent cerumen impaction, OE, or conductive hearing loss. Use of earplugs when exposed to cold water may slow progression of the disease in the case of exostoses.

Surgical treatment should be reserved for symptomatic patients, including patients who develop frequent OE and/or frequent cerumen impactions causing hearing loss, patients who desire a more permanent treatment to avoid the need for repeated débridement, and patients in whom the EAC has become completely occluded. The latter condition requires surgical treatment due not only to the resulting conductive hearing loss, but these patients are also at risk for cholesteatoma formation and its complications in the medial EAC due to trapped epithelial debris.

Key Operative Learning Points

1.
Reserve surgical treatment for symptomatic patients.
2.
Structures at risk for injury include the tympanic membrane, ossicular chain, temporomandibular joint (TMJ) anteriorly, and the facial nerve posteroinferiorly.
3.
Surgery is most commonly performed with a high-speed otologic drill, but the use of osteotomes can be considered as an alternative.
4.
Preservation of medially based skin flaps provides more rapid healing and a reduced risk of soft tissue stenosis postoperatively.

Preoperative Period

History

1.
History of present illness
- a.
  Question the patient regarding the presence of frequent cerumen impactions, OE, or persistent hearing loss.
- b.
  A careful history should be taken to elicit symptoms related to obstruction of the EAC, such as the need for frequent débridement of the impactions, frequent pain or otorrhea suggesting recurrent OE, and frequent or persistent hearing loss. An attempt should be made to determine the frequency and severity of symptoms and how bothersome they are to the patient.
- c.
  Question the patient regarding prior treatment and willingness to return for periodic ear cleaning.
- d.
  Determine how frequently the patient has required treatment for OE or removal of impacted cerumen, if at all. Patients in whom OE and/or cerumen impactions are occurring very often should be offered surgical treatment as an option. Also, if it is highly impractical for a patient to return for periodic ear cleaning as a form of conservative management, this is also an indication for surgical therapy.
- e.
  The patient should be questioned regarding participation in water sports.
- f.
  If the patient is an active participant in cold water sports, the patient should be counseled regarding the use of ear plugs to help slow the progression of existing exostoses and to help prevent recurrence postoperatively.
2.
Past medical history
- a.
  Need for prior treatment with débridement of cerumen and/or ototopical drops for OE
- b.
  Medical illness, including any contraindications to general anesthesia
- c.
  Prior surgical history, with attention to any prior ear surgery
- d.
  Family history, including any reactions to anesthesia
- e.
  Medications, including anticoagulants or antiplatelet drugs

Physical Examination

1.
Binocular microscopic examination of the ears

Binocular microscopy should be performed to determine the location and extent of any exostoses or osteoma present. Attention should be paid to the percentage of obstruction of a cross section of the EAC caused by the lesions. Additionally, binocular microscopy enables the surgeon to determine whether the ear may be adequately cleaned in its present state or whether there are locations medially, anteriorly, or posteriorly that are inaccessible and therefore at risk for cholesteatoma formation or persistent trapped debris.
2.
Otologic endoscopy

This can be performed as an adjunct to binocular microscopy to assess the medial EAC for trapped debris and to determine the medial extent of exostoses or osteoma, if not visible due to severe stenosis.
3.
Audiometry and tuning fork testing

Tuning fork testing should be performed on all patients to screen for a conductive hearing loss. A full audiogram with tympanometry and acoustic reflex testing should be performed preoperatively on all surgical candidates to assess the type and degree of any pre-existing hearing loss and to counsel the patient on expected improvement following surgery. Audiometry may also document a pre-existing high frequency sensorineural hearing loss (SNHL). As high frequency SNHL can be a surgical complication due to noise exposure from the high-speed drill and/or contact with the ossicular chain, any pre-existing SNHL must be documented for patient counseling and medicolegal purposes.
4.
Head and neck examination

A full otolaryngologic examination should be performed to ensure there are no other factors that could potentially impact the decision for surgery, including the presence of a difficult airway or craniofacial anomalies that could portend an aberrant anterior course of the facial nerve.

Imaging

Computed Tomography

A high-resolution temporal bone computed tomography (CT) should be obtained preoperatively in cases of osteoma extensive enough to prevent visualization of the medial EAC ( Fig. 127.3 ). The CT confirms the diagnosis, evaluates for possible medial cholesteatoma, and determines the location and width of the pedicle. Osteomas have the appearance of a well-circumscribed bony lesion pedicled at the tympanosquamous or tympanomastoid suture line, slightly hypodense compared to cortical bone of the mastoid. The location of the pedicle is usually readily identified to allow for surgical planning ( Fig. 127.4 ).

Fig. 127.3, Right external auditory canal with a posteriorly based osteoma (O) obstructing complete examination of the medial canal and tympanic membrane. P, Posterior.

Fig. 127.4, Axial, A, and coronal, B, bone-windowed computed tomography images demonstrating a pedunculated attachment to the lateral posterior canal wall (arrows). The remaining external auditory canal and middle and inner ear are normal.

In cases of severe exostoses with near complete or complete closure of the EAC, temporal bone CT should also be performed to evaluate for the presence of a cholesteatoma medially that would need to be addressed surgically. The preoperative CT can also indicate the medial extent of the exostoses, as the growths can abut the TM, requiring special care during removal to avoid trauma to the TM.

Indications

1.
Complete or near complete occlusion of the EAC, causing accumulation of epithelium that cannot be débrided in the office
2.
Persistent conductive hearing loss caused by occlusion of the EAC or by persistent entrapment of cerumen or epithelial debris
3.
Recurrent acute OE poorly controlled with medical management, particularly if reactive soft tissue stenosis is noted
4.
Frequent cerumen impactions requiring an unacceptably high number of office visits for treatment

Contraindications

1.
Medical comorbidities that put the patient at an unacceptably high risk of general anesthesia

Surgery for exostoses frequently requires a postauricular approach and is typically performed under general anesthesia, which may be contraindicated in the case of severe cardiopulmonary disease. Surgical removal of a single osteoma, particularly if on a narrow pedicle, is often possible under local anesthesia.
2.
Active OE

Attempts should be undertaken prior to surgery to eradicate or maximize control of any OE present in the operated ear. Active OE at the time of surgery can increase the risk for cellulitis and exuberant granulation tissue during the healing process, which can lead to soft tissue stenosis of the EAC.

Preoperative Preparation

1.
Discontinue any anticoagulants/antiplatelet medications for at least 7 days preoperatively if possible or as directed by the prescribing physician.
2.
Treat any active or ongoing OE with ototopical antibiotics until the time of surgery.
3.
Evaluate preoperative imaging, if obtained, to help determine the surgical approach and type of anesthesia to be used.

You're Reading a Preview

Become a Clinical Tree membership for Full access and enjoy Unlimited articles

Become membership

If you are a member. Log in here