Surgery of the External Ear Canal and Pinna

Chapter 60 Surgery of the External Ear Canal and Pinna

Daniel D. Smeak

External ear canal surgery is performed to provide exposure and drainage for the vertical and horizontal ear canal or to remove irreversibly infected tissue or neoplasia. Procedures for the external ear canal include lateral ear canal resection, vertical ear canal ablation, and total ear canal ablation. Drainage of auricular hematoma is the most common surgical procedure of the pinna; this is discussed later in this chapter.

Success of ear surgery relies on the following:

• An accurate diagnosis

• An appreciation of the severity and extent of the disease

• Correct choice and technical execution of the procedure

• Appropriate postoperative medical treatment of the local disease and any underlying primary skin disorder (see Chapter 59)

As a general rule, surgical intervention is considered when appropriate medical treatment for otitis externa fails, or when medical treatment is not expected to be successful.

As ear disease progresses, more extensive surgery is often required to relieve clinical signs. Risk of complications, however, also increases as the surgery becomes more extensive.

ANATOMY

A clear understanding of ear anatomy and related structures is critical to uncomplicated ear surgery. The surgeon must identify and preserve several key structures, especially during horizontal canal dissection.

External Ear Canal

• The normal external ear canal (Figs. 60-1 and 60-2) is a 5- to 10-cm–long pliable cartilaginous tube lined by glandular epithelium, extending from the base of the pinna to the tympanic membrane.

Figure 60-1 Anatomy of the external aditus of the ear.

Figure 60-2 Important anatomic structures of the external ear canal. A, Transverse section of the head showing ear canal regions and middle ear and inner ear structures. B, Location of branches of the external carotid artery in relation to the ear canal and middle ear, and important neural structures in the external ear canal region.

Vertical Ear Canal

• From the external opening (aditus), the vertical canal (auricular cartilage) runs ventrally and slightly rostrally, before bending toward the skull to form the shorter horizontal canal.

Horizontal Ear Canal

• The horizontal canal consists of a circular (annular) cartilage extending from the ligamentous attachment to the auricular cartilage medially to the short osseous ear canal (projection of the petrous temporal bone). The canal ends at the tympanic membrane.

Important Local Structures

Salivary Glands (Fig. 60-2B)

• The V-shaped parotid salivary gland overlays the ventrolateral aspect of the vertical ear canal and extends ventral to the distal aspect of the horizontal ear canal.

Blood Vessels (Fig. 60-2B)

• Blood supply to the ear is via the great auricular artery, arising from the external carotid artery located medial to the parotid gland and ventral to the osseous bulla.

• Small branches of the great auricular and maxillary arteries run dorsally, parallel to the long axis of the pinna, and medial to the pinna cartilage.

Nerves (Fig. 60-2B)

• The facial nerve arises from the stylomastoid foramen located just caudodorsal to the osseous ear canal.

• The nerve is closely associated with the caudal aspect of the horizontal ear canal shortly after it exits the foramen, and courses directly under the horizontal ear canal.

• Terminal branches of the facial and auriculotemporal branch of the mandibular portion of the trigeminal nerve are located just rostral to the ear canal.

PREOPERATIVE CONSIDERATIONS

An accurate preoperative diagnosis along with determination of the extent and severity of disease is important when choosing the surgical procedure. Attempt to identify and control any systemic skin condition before surgery. Changes in the ear canal that usually represent irreversible disease include neoplasia, thickening and calcification of cartilage, and firm hyperplastic or proliferative epithelium. Determine if middle ear disease is present concurrently since exploration and drainage of the middle ear is recommended in addition to surgical treatment of the external ear disease (see Chapter 62).

The ear canal is difficult to prepare aseptically, and contamination is inevitable during surgery; so antibiotics should be given during the procedure. Administer a broad-spectrum, bactericidal, intrave-nous (IV) antibiotic (optimally based on preoperative culture and susceptibility) before and during surgery so that adequate levels are maintained in tissues during dissection.

Ear Palpation

Carefully palpate the ear canal and surrounding structures and determine the degree of pain elicited and if there is evidence of end-stage disease.

• Sharp pain elicited on deep palpation of the external ear canal usually indicates concurrent middle ear infection.

• Palpation of severely thickened and firm ear canal tissue indicates that irreversible changes have occurred.

Dermatologic Examination

Most chronic bilateral ear conditions in dogs are manifestations of a generalized skin condition. Failure to identify and control the primary skin condition may cause failure of the surgical procedure since the disease will likely progress in any remaining ear tissue after surgery.

• Perform a complete dermatologic examination and obtain appropriate tests to determine whether primary systemic skin disease (e.g., hypothyroidism, atopy) is present.

Neurologic Examination

• Perform a neurologic examination, especially in chronic cases of otitis externa, to evaluate for facial nerve involvement (e.g., hemifacial spasm and slow or absent palpebral reflex) and involvement of inner ear structures (e.g., nystagmus and circling).

• Evaluate the patient’s ability to hear and alert the owner to any problems before contemplating bilateral ear canal ablation.

Radiographic Examination

Perform any imaging tests before otoscopic examination because irrigation fluid entering the bulla through a damaged tympanic membrane could be misinterpreted as middle ear disease.

• Ventrodorsal skull radiograph is the view of choice to evaluate horizontal canal diameter and to help determine whether the walls of the canal have undergone irreversible calcification.

Evaluate for middle ear involvement (Chapter 61) before deciding on the surgical procedure.

• Open-mouth radiography of the bulla is the view of choice to evaluate for middle ear involvement (see Chapter 4).

Lack of osseous changes on bulla radiographs does not rule out otitis media.

• Bulla osteitis takes months to form after deep-seated infection. Changes are often very subtle, and evaluation of fluid density within the bulla on plain radiographs also is not an accurate method of diagnosis.

• Computed tomography (CAT scan) is a more sensitive imaging modality to detect subtle changes in the tympanic bulla and cavity.

Staging of Neoplastic Disease

• Perform regional lymph node aspiration, cytology, biopsy, and thoracic radiography if neoplasia is suspected in the underlying ear disease.

LATERAL EAR CANAL RESECTION—ZEPPS MODIFICATION (LECR)

Surgical Procedure

Objectives

• To expose the medial portion of the vertical canal and horizontal ear canal. Exposure enhances medical treatment of otitis externa and changes local ear conditions favoring drainage. Ventilation of the area improves the local environment by decreasing moisture, humidity, and temperature in the ear canal.

• To resect the lateral portion of the vertical ear canal to remove tumors or to relieve congenital or acquired non-proliferative vertical canal stenosis that is restricting ear drainage and interfering with medical treatment.

Do not perform LECR if the horizontal or vertical ear canal is hyperplastic and lined with proliferative tissue. In one study, LECR failed in 85% of Cocker spaniels, most likely due to their propensity to develop early hyperplastic disease. Likewise, LECR is contraindicated if medically uncontrolled primary skin disease (e.g., seborrhea) is present because progressive ear disease would be expected in the remaining section of the ear canal.

Assess whether there is evidence of concurrent otitis media in the patient; if so, surgical drainage of the middle ear is recommended along with LECR. Left untreated, clinical signs of otitis externa will persist due to persistent otic discharge originating from the middle ear.

Equipment

• Standard general surgical pack and suture

• Heavy serrated straight Mayo scissors

Technique (Fig. 60-3)

1. Place the animal in lateral recumbency with the head positioned, aseptically prepared, and draped so that the ear region, including the pinna, is exposed and all anatomic relationships are identifiable.

2. Use forceps to determine vertical canal depth and position of the horizontal canal.

3. Incise the lateral portion of the vertical ear canal and reflect ventrally.

4. Preserve the proximal portion of the lateral canal flap for a “drain board.”

5. Begin closure at the base of the flap; then appose the distal flap to the skin. Appose the remaining ear epithelium and skin so that no cartilage is exposed.

Figure 60-3 Lateral ear canal resection technique. A, Two skin incisions are extended parallel to each other from the intertragic notch and tragohelicine notch, tapering down to a distance of 1.5 to 2 cm between the incisions, about 1.5 to 2.5 cm (depending on the size of the animal) ventral to the horizontal ear canal. A transverse incision joins the two vertical incisions. Undermine the skin flap dorsally up to the margin of the aditus. B, Incise through the subcutaneous tissue to the level of the vertical ear cartilage. Expose the entire lateral aspect of the vertical ear canal by blunt and sharp dissection of the subcutaneous tissue in a rostral and caudal direction and parotid gland ventrally. C, Place an Allis tissue forceps on the tragus, and apply dorsal traction so that the vertical ear canal can be seen from the dorsal aspect of the head. With serrated scissors, make two incisions through the vertical ear canal on the rostrolateral and caudolateral margins while maintaining dorsal traction. Extend the rostral and caudal incisions ventrally in an alternating fashion until the floor of the horizontal canal is reached. The vertical canal essentially is divided into lateral and medial halves. D, Extend incisions medially toward the head until the horizontal canal is fully exposed after the lateral wall is reflected ventrally. The base of the lateral wall flap should approximate the width of the horizontal canal. More cartilage can be removed from the remaining ear canal as necessary to fully expose the remaining vertical canal. Manipulate the flap rostrally and caudally until the horizontal canal is held open as wide as possible. E, Remove the skin flap and all but the proximal portion of the lateral wall. The 1.5- to 2-cm cartilage (drain board) flap remaining is modified to lie flat and fit the skin defect ventral to the horizontal ear canal. F, Begin closure by placing simple interrupted 3-0 to 4-0 monofilament nonabsorbable sutures from the caudal and rostral margins of the most proximal aspect of the drain board to the skin. Throughout closure, place sutures through ear canal epithelium and cartilage first and then to skin to aid in skin coverage of cartilage. G, Appose the remaining portion of the flap to the skin with simple interrupted sutures so that the flap is flat against the head. Place additional sutures so that the skin and ear canal epithelium edges are apposed but not crushed.

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Tags: Saunders Manual of Small Animal Practice

Aug 27, 2016 | Posted by admin in SMALL ANIMAL | Comments Off

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