Chapter 23

Modified mastoidectomy was considered the treatment of choice in early reports of acquired canal stenosis.1–3 Currently, canaloplasty (also called canalplasty) is considered the most optimal treatment for both bony and soft tissue canal stenoses. Canaloplasty is a surgical means to restore the natural contours and patency of the ear canal.

This chapter discusses the anatomy of external auditory canal pertinent to the understanding of surgery of the ear canal, and the pathologies that may cause canal stenosis.

ANATOMY OF THE EXTERNAL EAR CANAL

The adult external ear canal is cartilaginous in its outer third and osseous in its inner two thirds. The average ear canal length is 6.5 cm, with an average diameter of 2.5 cm. At the junction of the cartilaginous and bony canal there is a slight angulation; the cartilaginous part is inclined slightly posterosuperiorly, and the bony part is inclined anteroinferiorly. As a result, the axis of the ear canal follows a lazy S shape. The anterior canal bone is very thick above and below the head of the mandible, but thin between these two points.⁴ For this reason, the glenoid fossa is susceptible to injury during drilling in the anterior canal.

Skin over the cartilaginous canal is approximately 0.5 to 1 mm thick and consists of epidermis with papillae, a dermis, and a subcutaneous layer. The skin of the bony canal is approximately 0.2 mm thick, lacks a subcutaneous layer, and is continuous with the epithelial layer of the tympanic membrane. The thinness of the bony canal skin makes the periosteum prone to thermal irritation, which may lead to exostosis formation when a person swims in cold water.

The skin of the external canal contains hair follicles, sebaceous and ceruminous glands, which are a type of apocrine gland. The secretions of these glands combine with desquamated keratinocytes to form cerumen. Cerumen is relatively water-repellant and coats the surface of the canal skin to delay penetration of various substances through the skin. Some studies suggest cerumen has antibacterial qualities.⁵

The external auditory canal has a unique property in that is has a self-cleaning mechanism to keep the canal free of debris. In the normal ear canal, epithelial migration moves material laterally from the medial end of the canal. If such a mechanism did not exist, the lumen of the canal would gradually become occluded by keratin debris, and the transmission of sound would be impaired. Exostosis and chronic or recurrent external otitis are two of several conditions that may impair the self-cleansing mechanism of the ear canal.

Also of importance is the anatomic association of the chorda tympani and facial nerves with the bony external auditory canal. The chorda tympani passes just medial to the mid- to superior portion of the posterior fibrous annulus. The facial nerve may lie lateral to the posterior tympanic annulus in the lower part of the nerve’s vertical segment.^6,7 To prevent damage to the chorda tympani and facial nerves, care must be taken when drilling in the region of the posterior bony canal in the region of the fibrous annulus.

Acquired soft tissue stenosis of the external canal is due to some insult to the canal that results in cicatrix formation. The insult may be the result of recurrent/chronic inflammation (infection, dermato-logic disease), iatrogenic injuries (surgery, radiation), trauma (burns, chemical injury, repeated ear canal scratching, fracture), or neoplasm. In one large review, the leading cause of stenosis was chronic infection (54%) followed by prior ear surgery (20%).8 When surgery or trauma is the inciting event, many years may elapse before the acquired soft tissue stenosis requires surgical treatment.⁸

Systemic diseases of the skin (e.g., psoriasis, lupus erythematosus, scleroderma) can affect the ear canal and eventually cause external canal obstruction. One important feature of psoriasis is that mild trauma to surrounding skin induces lesions localized to the area of injury.⁹ Therefore, patients with psoriasis in or near the ear canal should be asked to avoid manipulation of the lesions, so as to prevent stenosis. Cutaneous (contact dermatitis) reactions to shampoos, medications, and foreign material in the ear canal can be severe and may require rapid medical attention to prevent scarring and stenosis of the soft tissue of the canal.

Acquired soft tissue stenosis of the external canal is uncommon. For postinflammatory acquired atresia, Becker and Tos¹⁰ reported an annual incidence of 0.6 per 100,000. Many other large series of acquired soft tissue stenosis report, on average, treating one case of soft tissue stenosis per year.^4,11–13

Many terms have been used to describe acquired soft tissue stenosis of the external canal including medial meatal fibrosis,^12–14 chronic stenosing external otitis,⁴ and postinflammatory acquired atresia.¹⁰ The pathophysiology of acquired soft tissue canal stenosis is unknown because there are currently no experimental animal models. It is believed that the canal passes through several stages before developing the soft tissue stenosis. In the first stage of development, some type of insult (e.g., infectious, traumatic) produces granulation tissue of the ear canal, tympanic membrane, or combination of the two sites. The granulation tissue becomes infected and the tissue proliferates. This stage is considered the active or immature phase. Eventually, a mature stage ensues whereby the granulation tissue forms a well-developed fibrous plug lined by squamous epithelium. The disease process ceases to continue when the atresia reaches the lateral end of the bony canal.¹⁵

PATIENT PRESENTATION

Exostoses usually do not produce clinical symptoms. If the exostoses are large enough, patients may develop recurrent external otitis because the lesions may prevent the natural elimination of cerumen/desquamated epithelium from the external canal. Conductive hearing loss is possible when the exostoses tamponades cerumen against the tympanic membrane or when the external canal is occluded by the exostoses. For similar reasons, osteomas and fibrous dysplasia of the external canal can also present with recurrent external otitis or conductive hearing loss.

The ear canal must be narrowed considerably to develop clinically significant conductive hearing loss. Hearing loss does not become significant until there is an aperture of 3 mm or less. High-frequency conductive hearing loss is seen initially followed by lower-frequency loss as the aperture narrows below 3 mm.

The clinical presentation of patients with acquired soft tissue stenosis depends on the phase of the disease process at the time of presentation. When the disease is in the active phase, patients complain of chronic or recurrent discharge. During the mature phase, conductive hearing loss is the main complaint. Audiometric testing usually shows a 20- to 40-dB conductive hearing loss in the mature phase.^4,8,10–14 Volume measurements of the external auditory canal are also below normal.

As mentioned previously, there are many possible causes for acquired soft tissue stenosis of the ear canal. The clinical presentation may be the same whether the cause is benign or malignant. For this reason, the diagnosis of lesions of the external canal is made based on a careful history and cultures or biopsy.

A high-resolution computed tomography (CT) of the temporal bones is recommended for select cases of bony stenosis and for all cases of soft tissue stenosis (Fig. 23–1). CT is recommended for bony stenosis when the tympanic membrane cannot be visualized. For both bony and soft tissue stenosis, CT can help define disease medial to the stenosis. Becker and Tos¹⁰ have reported a 9% incidence of cholesteatoma medial to soft tissue stenosis.

INDICATIONS FOR TREATMENT

Medical management may be employed initially in select cases of soft tissue stenosis. Surgery is an option for cases that fail medical management.

For both bony and soft tissue stenosis, surgical treatment is recommended when the patient develops chronic/recurrent external otitis or conductive hearing loss. Another indication for surgery is difficulty fitting a hearing aid.

Oncologic procedures are necessary when benign or malignant tumors cause canal obstruction. A description of these types of procedures is beyond the scope of this chapter.

MEDICAL MANAGEMENT

If identified early, soft tissue stenosis may be treated medically. Cases that may respond to medical therapy may include, but are not limited to, the early stages after surgery or radiation. Many options are available for medical management and would be based on each individual case. One option would include periodic dilatation of the external canal by placement of expandable ear wicks. Antibiotic-steroid otic drops are used and the ear is repacked every 4 to 10 days for 6 to 8 weeks. Local injections of Kenalog or Decadron should be used if there is little to no response to the dilatation technique within the first 4 weeks. For less severe cases, another option for treatment would include the use of steroid cream or drops on a daily basis for several weeks. If the ear canal opens with either of these techniques, periodic cleaning and frequent irrigations with acetic acid alcohol solutions help to maintain patency. Patients who do not respond to these treatments are candidates for surgery.

SURGICAL MANAGEMENT

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