ABSTRACT: The middle and inner ear are complex organs. Inflammation and thickening of the skin within the ear canal can lead to pain and bacterial infection. The ear canal is often affected by generalised skin irritation because of its warm, moist environment. Surgery of the middle or inner ear is indicated when medical management is ineffective or is unlikely to be so. Ear disease and surgery are both irritating and painful for the patient. Good nursing skills and observation are needed to ensure these patients are comfortable the disease or surgery.
This article discusses conditions of the middle and inner ear. Therefore, correction of aural haematomas and procedures on the external ear to repair defects after trauma, are not considered.
The middle ear
The primary function of the middle ear is conduction of sound waves. It consists of:
* the opening of the auditory tube the three aural ossicles (malleus, incus and stapes)
* muscles and ligaments associated with the ossicles
* the space within the tympanic bulla.
The tympanic bulla, or cavity, is situated behind the tympanic membrane, through which sound is transmitted. It is lined with mucous membrane and contains the tympanic nerve, cochlea, auditory tube and vestibular window. The ossicles are small bones – the stapes being the smallest bone in the body – which concentrate the sound waves.
The information from the middle ear passes into the inner ear. Debris and mucous secretions are continuously directed into the pharynx by a combination of muscular pumping action and mucociliary clearance.
The inner ear
The functions of the inner ear are to pick up sound and maintain balance. It is a maze of bony ducts and sacs filled with perilymphatic fluid. Three semi-circular canals, containing nerves, lead to the vestibule; whilst a shell-like bony structure, called the cochlea, winds around the hollow core, which contains the cochlear nerve.
A canine cochlea has 3.25 turns, a human 2.5 and a bird 0.75. The canine cochlea contains about 10,000 hair cells. The inner ear also contains endolymph that cushions and protects the structures within it.
Aural disease
Both acquired and congenital problems can be associated with ear disease. Inflammation and thickening of the skin within the ear canal may be part of a generalised skin condition, but can it lead to secondary bacterial infection – and is usually very painful.
Because of its warm, moist environment, the ear canal can be significantly affected by generalised skin irritation, such as that caused by atopy. Mild inflammation may cause an overgrowth in the innate cutaneous bacteria and yeast organisms leading to further inflammation and consequent damage to the skin of the ear canal giving rise to a cycle of deterioration (Figure 1).
Figure 1: Inflammation
Acquired conditions associated with ear disease include:
• otitis externa
• otitis media
trauma through a penetrative injury
• neoplasm of the ear canal.
Otitis media is the most common ear problem in canine patients and is usually caused by bacterial invasion via the external ear canal. Although the infection will normally access the middle ear through a damaged and perforated tympanic membrane, it has been recognised that bacteria may pass through an intact or thickened membrane.
It is also possible for the membrane to heal after perforation, thus trapping the bacterial infection. Further research is needed to determine how the transmission occurs. The yeast Malassezia and the bacteria Staphylococcus intermedia and Pseudomonas spp. are most commonly associated with septic otitis media.
Predisposing factors
Predisposing factors for ear disease can include:
• breed
• stenosis of the canal
• the presence of excessive hair in the ear canal
• the presence of contaminated water resulting from activities such as swimming epithelial damage, leading to the build-up of debris
• production of excessive cerumen in the ear canal.
The ear may become diseased following over-use of antimicrobials and intrusive cleaning techniques, such as the excessive use of cotton buds, as well as sensitivity to some products, such as neomycin.
Surgical intervention
Surgery of the middle or inner ear is indicated when medical management is ineffective or is unlikely to be effective (Figures 2 – 6). It is also necessary when the tympanic membrane requires decompression.
Figure 2: Bulla osteotomy
Figure 3: Preparation for lateral ear resection
Figure 4: Lateral wall resection
Figure 5: Lateral wall removed after lateral wall resection
Figure 6: Healing after surgery
Surgery requires the removal of the primary cause and its effects, such as removal of debris and diseased tissue.
Ear canal ablation
The favoured surgical approach for treatment of septic otitis media is via lateral access to the tympanic bulla. A lateral wall ablation may be indicated during the early stages of the disease to open it up and thereby change the environment of the ear canal.
A total ear canal ablation may be necessary, however, especially with end- stage ear disease, because it is effective in both removing the diseased tissue from the external meatus and in allowing drainage of the tympanic chamber.
Much of the debris can be removed through irrigating and aspirating the tympanic chamber using gentle pressure. More resistant material can be gently scraped away from the site.
All diseased tissue and debris should be removed to prevent c
omplications from abscess or fistula formation occurring postoperatively. Hearing may be preserved, to a degree, by avoiding damage to the ossicles; but surgical restructuring of the anatomy of the canal will lead to alternation in sound perception.
Myringotomy
A grommet, or tympanostomy tube, is a small tube inserted into the tympanic membrane to improve the environment of the middle ear, allowing drainage of fluid and debris. This may be required
when a patient needs frequent myringotomy. Myringotomy is a procedure in which a small incision is made in the tympanic membrane to allow active or passive drainage of the middle ear. This opening is temporary, usually lasting about two weeks and, therefore, frequent operations may be necessary if the problem persists.
Breeds such as Cavalier King Charles spaniels are susceptible to ‘glue ear, which is a build-up of fluid in the ear; and myringotomy may benefit these cases, although the technique is in the early stages of development.
Complications
Apart from reduced hearing, other complications may arise from aural surgery, especially where the lateral wall is resected.
Facial nerve paralysis
This is usually transient and is the result of bruising and inflammation. It can occur in as many as 20 per cent of patients. Drooping of the lip and eyelid, including a reduced palpebral reflex on the surgical side, may be evident. Eye lubrication and care with feeding may be required until it resolves, usually after four to six weeks.
Excessive haemorrhage
Excessive haemorrhage may occur from the large blood vessels around the surgical area (Figure 7).
Figure 7: Ear bandage
Vestibular syndrome
If damage occurs to the vestibules within the inner ear during surgery, the patient may suffer from vestibular syndrome. This may be transient or permanent. On recovery from anaesthesia these patients will require careful nursing, as they may be ataxic, nauseated and disorientated.
Postoperative infections
Postoperative infections are a potential risk of this surgery, given the pathogens present and the difficulty of aseptic preparation.
Horner’s syndrome
Horners syndrome may occur, but it is often transient and causes no ill effects.
Summary
Ear disease is a very common problem which can arise for a number of reasons and surgical intervention is normally the preferred treatment option. However, the procedures are often painful for the patient and good nursing skills and observation are needed to ensure that these patients are comfortable, and to minimise the potential for complications arising as a result of the surgery.
Author
Josephine Killner DipAVN(Surg)DipAVN(Med)RVN/MBVNA
Josey qualified as a veterinary nurse in 1988. She continued to work in primary care practice for 22 years, gaining the Advanced Diploma in Surgical Nursing (DipAVNSurg) and NVQ Assessor qualification in 2001, and the Advanced Diploma in Medical Nursing (DipAVNMed) in 2006. In'2007, she joined Fitzpatrick Referrals, as head of training.
To cite this article use either
DOI: 10.1111/j.2045-0648.2012.00199.x or Veterinary Nursing Journal Vol 27 pp 299-302
Further reading
SMALL ANIMAL EAR DISEASE: AN ILLUSTRATED GUIDE, 2nd EDITION [2005] Elsevier & Saunders.
• VOL 27 • August 2012 • Veterinary Nursing Journal