Feline vestibular disorders. Part I: anatomy and clinical signs

An understanding of the anatomy of the feline vestibular system is essential for interpretation of the clinical signs associated with vestibular dysfunction, for precise lesion localisation, and for accurate interpretation of results of diagnostic imaging. Appropriate recognition and interpretation of the clinical signs of vestibular disease is also an essential aspect of the precise diagnosis of the cause of vestibular dysfunction in cats. The objectives of this review are to provide an overview of the anatomy of the feline vestibular system, and to review the clinical signs of peripheral and central vestibular dysfunction of cats.     

VESTIBULAR DISEASE, AND ITS RELATIONSHIP TO FACIAL PARALYSIS IN THE HORSE: A CLINICAL STUDY OF 7 CASES

The signs observed in 6 cases of peripheral vestibular disease included incoordination, head tilt and nystagmus. The intensity of the signs varied greatly with duration of the disease, and in 3 cases facial paralysis was also present. Tympanosclerosis was demonstrable in all cases subject to radiology. Trauma was the causative factor in most cases. The causes of, and relationships between, vestibular dysfunction and concomitant facial paralysis are discussed. The exact etiology of the tympanosclerosis is unknown.     

Inner ear fluid‐attenuated inversion recovery MRI signal intensity in dogs with vestibular disease

The inner ear contains endolymph and perilymph. The second is comparable and in continuity with the cerebrospinal fluid (CSF) so it is expected to suppress in fluid‐attenuated inversion recovery (FLAIR) magnetic resonance imaging (MRI) if normal. Even though inner ear FLAIR abnormalities have been extensively described in humans with inner ear disease, its diagnostic value in dogs is yet to be proven. The goal of this retrospective cohort study was to investigate the diagnostic utility of FLAIR MRI in dogs with vestibular disease. A review of medical records identified 101 dogs that had brain MRI performed because of vestibular signs. Based on the final diagnosis, patients were allocated to three groups: otitis media/interna, idiopathic vestibular disease, and central vestibular disease. Additionally, a control group (n = 73) included dogs with normal MRI and without vestibular signs. Inner ears were delineated using a region of interest, and signal intensity was measured in FLAIR and T2‐weighted images. The percentages of suppression in FLAIR were calculated and compared between affected and unaffected sides of each individual and between groups using a general linear mixed model. Correlation between suppression and CSF cell count and protein concentration was assessed. Affected inner ears in dogs with otitis media/interna had decreased suppression in FLAIR compared to the unaffected side (P < .001), and all other groups (P < .01). No significant correlation was detected between CSF results and suppression. These results show the diagnostic value of FLAIR in otitis media/interna due to lack of suppression in the affected inner ear.     

Adenocarcinoma of the middle ear with osteolysis of the tympanic bulla in a cat.

Peripheral vestibular disease and lethargy were attributed to an adenocarcinoma in the middle ear of a 10-year-old cat. The tumor was invasive, inducing severe lysis of the tympanic bulla and adjacent temporal bone. Direct invasion to the meninges and brainstem also was observed. Neoplasms of the middle ear are rare in cats, with squamous cell carcinomas reported most commonly, but should be considered as causes of chronic otitis or signs of peripheral vestibular disease.     

Intracranial metastases from an ovarian dysgerminoma in a 2-year-old dog.

A 2-year-old, intact female rottweiler was presented for signs of lethargy. A mass was ultrasonographically observed, cranial and lateral to the left kidney. Exploratory laparotomy revealed a mass in the left ovary that was diagnosed histopathologically as an ovarian dysgerminoma. Two weeks after surgery, the dog was readmitted with signs of peripheral vestibular disease that progressed to central vestibular disease. Magnetic resonance imaging of the brain revealed the presence of a mass in the caudal fossa. The histopathological diagnosis of the mass was metastases from the ovarian dysgerminoma.     

Survival of Dictyocaulus viviparus infection on pasture.

Congenital and probable developmental vestibular disease is reported in a litter of English cocker spaniel puppies. The syndrome was marked by loss of balance and ataxia initially, but subsequent compensation has left only one individual with "permanent" head tilt.     

Abnormalities of the brainstem auditory response of the dog associated with equilibrium deficit and seizure

The brainstem auditory evoked response (BAER) was recorded from 20 dogs, 10 exhibiting vestibular deficit, and 10 presented with a history of seizures. Two dogs exhibited both types of signs. Abnormalities of the BAER, prolonged interwave latency, were seen in 8 of the 10 animals with vestibular problems, and in 7 of the 10 animals with seizure history. Several different diagnosis were associated with BAER abnormalities in both groups of animals. In 55.5% of the cases exhibiting abnormalities of the BAER, postmortem evidence of brainstem pathology was not detected. The electroencephalogram (EEG) was normal in three instances of abnormalities of the BAER. The BAER was normal in three dogs with abnormalities of the EEG. The BAER is presented as a useful diagnostic tool for brain lesions in animals with vestibular deficit and seizure history, but appears most useful when used in conjuction with the EEG. Correlations of abnormalities of the BAER and clinical course of disease are discussed.Publication No. 1707, School of Veterinary Medicine, Auburn University, AL 36849     

MRI utricle diameter asymmetry is significantly greater in dogs with idiopathic vestibular syndrome compared with unaffected dogs

Idiopathic vestibular syndrome (IVS) is the most common cause of acute unilateral peripheral vestibular dysfunction in older dogs. The purpose of this retrospective, cross‐sectional study was to characterize morphological changes in the utricle of dogs affected by IVS, using MRI. To evaluate differences between affected and unaffected utricles, the ratio of the largest to the smallest utricle diameter was obtained, as measured on transverse T2‐weighted images, and defined as the utricle asymmetricity ratio (UAR). Out of 137 patients diagnosed with IVS after excluding other vestibular diseases by MRI, 101 were eligible for inclusion. Additionally, 31 older dogs with no signs of vestibular disorders or other intracranial diseases were included as a control group. The disease group was divided into two subgroups in which the direction of head tilt and nystagmus symptoms versus the decreased utricle diameters were consistent or inconsistent. The medians of UARs of the IVS and control groups were 0.83 (range 0.37‐1.00) and 0.98 (0.70‐1.00), respectively. The medians of the UARs of the consistent and inconsistent IVS subgroups were 0.82 (0.37‐0.99) and 0.90 (0.74‐1.00), respectively. The UAR of the IVS group was significantly decreased than that of the control group and UAR of the consistent sub‐group was significantly decreased than that of the inconsistent sub‐group (P < .01). In conclusion, significant asymmetry of utricle diameter was identified in dogs with IVS versus unaffected dogs. We propose that canine IVS may possibly be correlated with structural atrophy of the vestibular system.     

Signs of neurologic dysfunction in dogs with central versus peripheral vestibular disease

OBJECTIVE: To determine the frequency of specific signs of neurologic dysfunction in dogs with central vestibular disease (CVD) or peripheral vestibular disease (PVD) and whether the degree of head tilt, rate of nystagmus, and number of beats of postrotatory nystagmus can be used to help distinguish CVD from PVD. DESIGN: Prospective clinical study. ANIMALS: 40 client-owned dogs with vestibular system dysfunction. PROCEDURE: A standard neurologic examination was performed, along with an expanded vestibular system examination that assessed the degree of head tilt, rate of nystagmus, and number of beats of postrotatory nystagmus. RESULTS: Dogs with CVD were significantly more likely to be nonambulatory than were dogs with PVD. Dogs with PVD were significantly more likely to veer or lean in 1 direction and to have resting nystagmus than were dogs with CVD. Median rate of resting nystagmus was significantly higher for dogs with PVD, but no significant differences between groups were detected in regard to presence or degree of head tilt, presence of positional ventral strabismus, and number of beats of postrotatory nystagmus. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that nonambulatory tetraparesis is significantly more common in dogs with CVD and veering and leaning are significantly more common in dogs with PVD. Although neither the degree of head tilt nor the number of beats of postrotatory nystagmus could be used to distinguish CVD from PVD, rate of resting nystagmus may be useful in distinguishing the 2 conditions.     

Clinical presentation of pituitary adenomas in rats.

This article describes the clinical presentation of central vestibular disease secondary to pituitary adenoma as it manifested in six rats. Prognosis is poor. Recommendations are made regarding questions to ask and advice to offer owners when dealing with cases.     

Toxicity of aminoglycoside antibiotics.

In cats, aminoclycosides cause vestibular damage followed in a few days by renal damage. The reverse is true in the dog, except that streptomycin causes vestibular damage prior to renal damage. To avoid toxicities, therapeutic doses of aminoglycosides should not be given longer than a week and they should be given cautiously in animals with renal impairment. Failure of the kidneys to eliminate aminoglycosides will result in very high blood levels, even with therapeutic doses, that can cause further renal and vestibular damage. The oral administration of aminoglycosides is seldom dangerous when normal therapeutic doses are employed. Although it is remote, the possibility exists that animals with renal impairment and intestinal obstruction may become intoxicated. Kanamycin is less nephrotoxic to dogs than neomycin and it is less destructive to the auditory nerve than vestibular damage than streptomycin. Gentamicin in cats is twice as toxic to the vestibular apparatus as streptomycin and more toxic to the cochlea than streptomycin or dihydrostreptomycin. Neomycin is more toxic than kanamycin, gentamicin, and streptomycin to both cats and dogs. Amikacin causes renal damage in dogs similar to other aminoglycosides. It also causes vestibular damage.     

Multilobular tumour of the caudal cranium causing severe cerebral and cerebellar compression in a dog

Multilobular tumour of bone (MTB) is an uncommon tumour and is usually located in the skull. A 13-year-old mixed breed dog was presented with a two-week history of progressively worsening vestibular dysfunction and cognitive abnormalities; it appeared demented and showed asymmetric ataxia and hypermetria of all limbs. The owner opted to have the animal euthanised. Necropsy revealed a large mass occupying the right occipital, parietal and temporal bones, severely compressing the cerebellum and the right occipital lobe. Histologically, it was characterised by the presence of multiple lobules containing osteoid or cartilage and separated by fibrous septae, features typical of MTB. Lung metastases were evident. To our knowledge, this is the first report of an MTB causing both severe cerebral and cerebellar compression and the second detailed report of an MTB of the occipital bone. MTB should be included in the differential diagnosis of bone tumours as well as in cases with central vestibular disease.     

OTOLITHIASIS IN THREE DOGS

Mineral opacities within the tympanic bullae, termed otoliths, were detected in three dogs by means of radiography and computed tomography. Radiographic signs of otitis externa were present in two dogs. One dog had clinical signs of vestibular disease, whereas the other two dogs had no clinical evidence of ear disease. Otolithiasis may represent mineralized necrotic material of a current or previous case of otitis media.     

Otitis media/interna and suppurative meningoencephalomyelitis associated with Listeria monocytogenes infection in a llama

Listeria monocytogenes was found to be the cause of fatal suppurative meningoencephalomyelitis in a 3.5-month-old cria. The cria initially had clinical signs of unilateral peripheral vestibular disease, but on the following day, the cria developed progressive signs of encephalitis. Treatment with antibiotics, flunixin meglumine, and anticonvulsant drugs failed to stop progression of the disease, and the cria was euthanatized. Post-mortem examination revealed otitis media-interna and diffuse suppurative meningoencephalomyelitis. Listeria monocytogenes was isolated from CSF and brain tissue.     

Feline vestibular disorders. Part II: diagnostic approach and differential diagnosis

Results of a neurological examination usually permit localisation of a vestibular disorder to either the central or peripheral parts of the vestibular system. Many different disorders located in the same part of the vestibular system will produce similar clinical signs. Therefore, additional diagnostic tests beyond a neurological examination are required in order to make an accurate diagnosis. The objectives of this review are to outline a diagnostic approach for disorders affecting the feline vestibular system, and to summarise the clinically important features of frequently diagnosed diseases affecting the vestibular system of cats.     

Gemistocytic astrocytoma in a one-month-old llama

A tumor involving the caudal portion of the brainstem was detected at necropsy after euthanasia of a 1-month-old llama with clinical signs consistent with vestibular disease. Gemistocytic astrocytoma of the medullary mass was the histopathologic diagnosis. Regardless of age, neoplasia should be included in differential diagnosis in animals with signs referable to the CNS.     

Vestibular syndrome associated with an ependymoma in a cat

An ependymoma was diagnosed in a 4.5-year-old spayed Siamese cat with clinical signs of vestibular disease. Diagnosis was based on history, results of neurologic examination, and the finding of neoplastic cells in CSF. Necropsy revealed an ependymoma arising from the fourth ventricle of the ventricular CNS and involving the left medullary and cerebellar areas.     

Cerebrospinal elaphostrongylosis in sheep in northern Norway.

Pathologic examination of four sheep from northern Norway exhibiting neurologic signs of paresis, paralysis and vestibular system disease revealed nematodes in the central nervous system (CNS). The worms were identified as Elaphostrongylus rangiferi Mitskevich, 1960, the elaphostrongylid nematode of reindeer (Rangifer tarandus tarandus). Microscopic lesions found in the CNS were focal traumatic encephalomyelomalacia caused by migrating worms, eosinophilic meningitis and choroiditis, lymphohistiocytic and nematode granulomas, and perineural infiltrations. The disease occurred in November and December 1990, after the sheep had been on pasture in areas frequented by considerable numbers of reindeer.     

Histochemical studies on the dependence of secretory function of the major vestibular gland (Bartholin's gland) on ovarian steroid hormones in the cat.

The dependency of the secretory function of the feline major vestibular gland (Bartholin's gland) on the ovarian steroid hormones was studied histochemically. After estrogen (estradiol-17 beta or diethylstilbestrol), progesterone or a combination of these was administered to cats which were previously ovariohysterectomized, the major vestibular glands were removed, embedded in paraffin, sectioned, and stained by alcian blue, periodic acid-Schiff or peroxidase-labeled lectin (peanut agglutinin and wheat germ agglutinin). The vividly positive reactions to the stainings applied were observed in the secretory epithelial cells of the major vestibular glands in the estrogen treated animals. The dependency of the secretory function of the major vestibular glands on the estrogen was demonstrated in this study.