Page 75 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery

Even with improved visual access, the diagnosis of OM 2007). MRI is the modality of choice for differentiation
can be quite challenging in the face of an intact tympanum. of central vestibular disease and peripheral vestibular
VetBooks.ir otomy when necessary) has been shown to be the most sation or meningoencephalitis as a sequela to OM/OI is
disease, and is also indicated when intracranial absces-
Collection of a culture sample from the bulla (via myring-
suspected (Bischoff and Kneller, 2004; Sturges et al.,
reliable method for diagnosis of bacterial or fungal otitis
media, and superior to imaging techniques (Cole et al.,
2002). Sampling via myringotomy may be safely achieved 2006; Martin-Vaquero et al., 2011).
by passing a sterile spinal needle through a sterilized oto-
scopic speculum to puncture the tympanic membrane. Medical treatment
Samples for cytology and culture/sensitivity testing are Medical regimens for the successful treatment of infec-
then collected from the tympanic bulla in a similar manner, tious otitis may vary widely, depending upon the degree of
using a micro-tip culturette. The external canal should be pathological changes of the external ear canals, the status
lavaged with sterile saline to clear exudates prior to of the tympanic membranes and the specific microorgan-
passage of the speculum, to maintain as much asepsis isms involved. Chronic OM is especially problematic, as
of its internal surface as possible. impaction of the bulla can be difficult to resolve, and these
cases often involve antibiotic-resistant bacteria. The con-
Indications for advanced imaging tinuing emergence of resistant Pseudomonas aeruginosa
and Staphylococcus spp. is one of the most threatening
Imaging studies can be helpful in any patient with chronic factors to the successful practice of otology, and the spec-
OE, particularly those with chronic pathological changes of trum of antimicrobial drugs capable of eliminating these
the ear canals (e.g. glandular and epidermal hyperplasia, organisms has been decreasing.
stenosis, suspected mineralization of the soft tissues of In addition to specific antimicrobial therapy, lavage of
the ear canal) to evaluate for evidence of OM or osteomy- the middle ear cavity via a polypropylene or red rubber
elitis of the tympanic bulla: fluid within the tympanic bulla, catheter inserted through the external auditory canal is
sclerosis, or lysis/erosion of the wall of the tympanic considered by most veterinary dermatologists to be an
bulla (Doust et al., 2007). Advanced imaging studies are important adjunct in the management of OM. In the case
also useful to determine the presence or extent of sus- of bulla impaction with inflammatory exudates and debris,
pected or known obstructive masses (i.e. neoplastic medical failure is virtually guaranteed without a thorough
masses or inflammatory polyps), extension of middle ear lavage. Prior to the advent of fibreoptic otoscopes, many
disease to the petrous temporal bone or temporoman - cases of chronic OM with impaction or resistant bacterial
di bular joint (particularly in patients presenting with reluc- infection were subjected to bulla osteotomy for curettage
tance to chew or open the mouth) or communication and lavage. However, fibreoptic otoscopes allow more effi-
between abscesses or fistulous tracts and the ear canal cient high-flow lavage through a working channel in the
(Bischoff and Kneller, 2004; Doust et al., 2007). Other speculum. Additionally, an arthroscopic attachment will
indications for advanced imaging include neurological allow direct visualization of the bulla interior. Aggressive
signs consistent with OM/otitis interna (OI) (vestibular bulla lavage, when followed by long-term high-volume
dysfunction, facial nerve paresis or paralysis, Horner’s topical therapy, generally together with systemic anti-
syndrome) or suspicion of brainstem abscessation or microbials based on middle ear culture and susceptibility,
meningoencephalitis secondary to OM/OI (altered men- has been associated with an 82% rate of resolution for
tation, multiple cranial nerve deficits, seizures, gait abnor- chronic OM, with a median time to resolution of 117 days
malities) (Sturges et al., 2006; Martin-Vaquero et al., 2011). (Palmeiro et al., 2004). In some cases of OM associated
Advanced imaging is also indicated to confirm middle ear with multi drug-resistant bacteria (particularly P. aerugi-
effusion in Cavalier King Charles Spaniels with suspected nosa), oral antimicrobial options can be limited. In these
PSOM. Clinical signs suspicious for PSOM may include cases, bulla lavage coupled with long-term high-volume
head shaking or ear scratching, hearing loss, peripheral topical therapy alone can be effective for resolution of
vestibular signs, facial nerve paresis or paralysis, frequent chronic OM (Palmeiro et al., 2004).
yawning, or bulging of the pars flaccida on otoscopic
examination (Cole, 2012); affected dogs may present with
only some of these clinical signs. Indications for surgery
Available imaging modalities include bulla radiographs, Despite the best efforts of the veterinary surgeon and
computed tomography (CT), magnetic resonance imaging owner, some cases will progress to end-stage otitis (Figure
(MRI) or ultrasonography. CT is typically considered to be 5.5) due to progressive pathological changes that result in
the ideal imaging modality to assess the tympanic bulla irreversible stenosis of the external auditory canals, and
(Bischoff and Kneller, 2004). Radiography of the tympanic tissue ablation will then be necessary. Medically intrac-
bulla is widely available, even to clinicians in primary care table OM due to impaction or resistant infection is also
practice, but its utility may be limited to evaluation for an indication for surgical intervention. For example, the
mineralization of the ear canal or changes to the bone of American Cocker Spaniel is especially problematic. This
the tympanic bulla. Interpretation of radiographs may be breed is not only predisposed to allergic skin disease and
difficult owing to the need for precise positioning and the idiopathic seborrhoea (both of which often contribute to
potential for superimposition of soft tissue structures (King intractable inflammation), but also responds to the inflam-
et al., 2007). Ultrasonography is also a readily available mation differently from other breeds. These spaniels
tool, and can potentially be performed without the need rapidly develop marked glandular hyperplasia of the exter-
for sedation or general anaesthesia. The repeatability of nal canals and may progress to end-stage otitis in as little
ultrasound examination for detection of fluid within the as 2–3 months.
tympanic bulla or changes to the bulla wall may be poor, For any dog with end-stage OE, a total ear canal abla-
however, and in cats visualization of the dorsal compart- tion (TECA) is the preferred method of treatment. Con-
ment of the tympanic bulla via ultrasonography may be current bulla osteotomy is mandatory, as persistent OM
limited (Dickie et al., 2003; Doust et al., 2007; King et al., will continue to produce inflammatory exudates that no

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