Page 1140 - Small Animal Internal Medicine, 6th Edition

1112 PART IX Nervous System and Neuromuscular Disorders

BOX 63.2
VetBooks.ir Disorders Causing Head Tilt

Peripheral Vestibular Disease
Otitis media-interna
Neoplasia in middle ear
Feline nasopharyngeal polyps in middle ear
Geriatric canine vestibular disease
Feline idiopathic vestibular syndrome
Trauma
Congenital vestibular syndromes
Aminoglycoside ototoxicity
Chemical ototoxicity
Hypothyroid neuropathy
A
Central Vestibular Disease
Trauma or hemorrhage
Infectious disorders
Granulomatous meningoencephalitis (dogs)
Necrotizing leukoencephalitis (dogs)
Primary or metastatic neoplasia
Vascular infarct
Thiamine deficiency
Neurodegenerative disorders
Metronidazole intoxication

Diagnostic evaluation of patients with peripheral ves-
tibular signs should include external palpation of the
bullae for asymmetry or pain. If ototoxic drugs or treat-
ments have been administered, these should be discon- B
tinued and improvement monitored over 24 to 48 hours.
Systemic evaluation for inflammatory, neoplastic, or meta- FIG 63.4
bolic disease (including hypothyroidism in dogs) should be (A) Adult Cocker Spaniel with left peripheral vestibular
considered. Radiographs, computed tomography (CT), or disease caused by otitis media-interna. (B) Radiograph
magnetic resonance imaging (MRI) of the tympanic bullae reveals thickening of the left bulla wall, with an increase in
(middle ear) should be evaluated. CT and MRI are much density within the bulla. Osteotomy of the ventral bulla
more sensitive for detection of subtle abnormalities than revealed bilateral otitis media-interna.
radiography. When warranted based on the results of oto-
scopic examination or imaging, a myringotomy can be used
to collect a sample from the middle ear for cytologic analysis otoscopic examination and an intact tympanum at the time
and culture. of diagnosis, necessitating further testing.
Bulla radiographs, CT, or MRI may reveal fluid or soft
OTITIS MEDIA-INTERNA tissue accumulations with the bullae as well as secondary
Otitis media-interna (OM-OI) is one of the most common reactive or remodeling changes. When performing a radio-
causes of peripheral vestibular signs in dogs and cats. Con- graphic bulla series, rostrocaudal open-mouth radiograph
current facial nerve paralysis or Horner syndrome affecting and oblique views taken under general anesthesia are most
the same side is sometimes apparent (Figs. 63.3 and 63.4). often diagnostic (see Figs. 66.7 and 63.4). CT and MRI are
All dogs and cats with peripheral vestibular disease should more sensitive than radiography for evaluating the bullae in
be evaluated for ear disease. Most animals develop OM-OI patients with OM-OI. Typical MRI findings include hyper-
as an extension of obvious otitis externa, and many have a intense material within the tympanic bulla on T2-weighted
tympanic membrane that appears abnormal or ruptured. images, isointense material within the tympanic bulla on
Otoscopic diagnosis of OM-OI can, however, be difficult T1-weighted images, and gadolinium ring enhancement
when chronic otitis externa results in stenosis or hyperplasia along the inner margin of the tympanic bulla. Animals with
of the external ear canal, making visualization of the tym- inner ear disease may also have loss of the normally visible
panic membrane and sampling of the middle ear cavity intralabyrinthine fluid signal and contrast enhancement in
impossible. Rarely, animals with OM-OI will have a normal the petrous portion of the temporal bone. While the animal