Otitis media

From Dog
Otoscopic examination of the tympanic membrane in a dog with otitis media[1]

Otitis media is defined as inflammation of the middle ear between the tympanic membrane and the labyrinths, and may involve the auditory canal (eustachian tube) and tympanic bulla.

The middle ear of the dog is classified into three sections - the epitympanic bulla, which is the most dorsal space in the middle ear, housing the ossicles, the tympanic cavity immediately medial to the tympanum and the tympanic bulla which is immediately ventral to this and is partially separated from the tympanic cavity in the dog by a ridge of bone (variable width from individual to individual).

The middle ear is lined by ciliated columnar epithelial cells with intermittent mucous-producing goblet cells. The middle ear has a normal bacterial flora, which usually arises from colonization of the auditory tube via the pharynx.

The middle ear communicates with the back of the pharynx through the auditory canal (originates in the anterior medial aspect of the epitympanic recess) which allows for equalization of air pressure across the tympanum.

In dogs, otitis media is usually due to:

Clinically affected dogs usually present with ipsilateral head tilting, variable degrees of ear pain, Horner's syndrome and circling to the affected side. Complications such as keratoconjunctivitis sicca, retrobulbar abscess[9] and xeromycteria (unilateral drying and hyperkeratosis of the planum nasale on the affected side) have also been reported. Seizures are rarely reported except in cases where infection has resulted in otitis interna, with secondary meningitis.

Otoscopic examination of the ear often reveals bulging of the tympanic membrane due to effusive fluid accumulation. With chronicity, the epithelial lining of the middle will potentially become markedly hyperplastic and may be responsible for much of the soft tissue density seen within the bulla on radiographic or CT/MRI examination. These changes may require considerable time to regress.

Cholesteatoma are formed when the tympanum is pushed into the bulla by usually dry concretions. Epithelial debris continues to accumulate within this "pouch" until it fills the entire bulla. With time, pressure may be placed on the bulla wall to result in thinning of the bone and an actual expansion of the bulla.

Treatment usually involves aggressive and prolonged antimicrobial therapy with drugs such as clindamycin, enrofloxacin or amoxycillin/clavulanate.

In unresponsive cases, total ear canal ablation and/or bulla osteotomy is indicated as a salvage procedure[10].

References

  1. Flowertown Animal Hospital
  2. Henneveld K et al (2012) Corynebacterium spp. in dogs and cats with otitis externa and/or media: a retrospective study. J Am Anim Hosp Assoc 48(5):320-326
  3. Gatineau M et al (2010) Multiple follicular cysts of the ear canal in a dog. J Am Anim Hosp Assoc 46(2):107-114
  4. Schuenemann RM & Oechtering G (2012) Cholesteatoma after lateral bulla osteotomy in two brachycephalic dogs. J Am Anim Hosp Assoc 48(4):261-8
  5. Harran NX et al (2012) MRI findings of a middle ear cholesteatoma in a dog. J Am Anim Hosp Assoc 48(5):339-343
  6. Hayes GM et al (2010) Relationship between pharyngeal conformation and otitis media with effusion in Cavalier King Charles spaniels. Vet Rec 167(2):55-58
  7. Cole LK (2012) Primary secretory otitis media in Cavalier King Charles spaniels. Vet Clin North Am Small Anim Pract 42(6):1137-1142
  8. Hordeaux J et al (2011) Histopathologic changes of the ear in canine models of mucopolysaccharidosis types I and VII. Vet Pathol 48(3):616-626
  9. Kraijer-Huver IM et al (2009) Peri- and retrobulbar abscess caused by chronic otitis externa, media and interna in a dog. Vet Rec 165(7):209-211
  10. Smeak DD (2011) Management of complications associated with total ear canal ablation and bulla osteotomy in dogs and cats. Vet Clin North Am Small Anim Pract 41(5):981-994