Diagnostic imaging of peripheral vestibular disease in a Chinese goose (Ansev cygnoides).
Key words: brainstem auditory evoked response test, otitis interna, vestibular disease, avian, Chinese goose, Anser cygnoides
A 5-kg, 20-year-old male Chinese domestic goose (Anser cygnoides) presented to the Zoological Service at the University of Georgia College of Veterinary Medicine (Athens, GA, USA) for a severe left-sided head tilt and circling to the left. The bird was housed in an outdoor pen with other healthy waterfowl, and its diet consisted of 50% grain, 20% Mazuri waterfowl pellets (Purina Animal Nutrition, St Louis, MO, USA), 25% turnip greens, and 5% wheat bread. The bird had been seen by a referring veterinarian during the past year for the head tilt but had shown substantial deterioration in the last month. A month before admission at the University of Georgia, the referring veterinarian had performed a physical examination, complete blood count, plasma biochemical profile, skull radiographs, ear cytologic examination, and aerobic culture of the left external ear canal. The only abnormal findings at that time were mild thickening and outward bulging of the left tympanic membrane when compared with the right. Culture of the ear canal was negative for bacterial growth. The bird received enrofloxacin (9 mg/kg PO q12h x 14 days: Baytril, Bayer Corp, Pittsburgh, PA, USA) and meloxicam (0.5 mg/kg PO q24h x 7 days; Metacam, Boehringer Ingelheim Vetmedica Inc, St Joseph, MO, USA) with no improvement.
On initial presentation, the bird had a severe left-sided head tilt and torticollis with the left side of its face rubbing against the left side of the body. On neurological examination, the bird's mentation was normal. On analysis of gait, the goose was circling to the left with a left-sided vestibular ataxia. Postural reactions such as hopping responses and proprioceptive placing of the pelvic limbs appeared normal bilaterally. Strength and muscle mass of the pelvic limbs were preserved. Withdrawal reflexes were normal bilaterally. Cranial nerve examination revealed a resting rotatory nystagmus with the fast phase to the right. Based on the left-sided head tilt, vestibular ataxia, abnormal nystagmus, and normal postural reactions, the neuroanatomic diagnosis was consistent with left-sided peripheral vestibular dysfunction. (1) On physical examination, the carpi had abrasions on the lateral aspect bilaterally. Ophthalmologic examination revealed bilateral multifocal punctate nuclear cataracts that were thought to be related to nutritional factors. Additionally, a corneal ulcer of the left eye was present and most likely associated with trauma from the torticollis. Differential diagnoses at this time included otitis due to active infection or chronic inflammation, neoplasia, or idiopathic vestibular disease. The goose was fasted overnight before anesthesia for otoscopy and cross-sectional imaging, and treatment with diazepam (0.5 mg/kg PO q12h) was begun to help with anxiety while hospitalized.
Anesthesia was induced with isoflurane administered by facemask followed by intubation with a 5.5-mm uncuffed endotracheal tube. A 22-gauge catheter was placed in the left metatarsal vein for intraoperative fluid support of lactated Ringer's solution at 10 mL/kg per hour. A 2.7-mm x 18-cm, 30-degree rigid endoscope (Karl Storz Veterinary Endoscopy, Goleta, CA, USA) was used to visualize a ruptured tympanic membrane in the left ear, but evidence of active inflammation was absent. The right ear was normal. The bird was given a bolus of lactated Ringer's solution (100 mL IV) and then allowed to recover from anesthesia. Two hours later, the bird was premedicated with ketamine (20 mg/kg IM) and midazolam (1 mg/kg IM) and then anesthetized as before for magnetic resonance imaging (MRI) of the head.
Magnetic resonance imaging was performed with a 3.0T GE HDx MRI unit (GE Healthcare, Waukesha, WI, USA) using an 8-channel wrist array coil. The following sequences were acquired in 3 planes: 2-mm-thick slices through the head in T2-weighted, T2-weighted fluid-attenuated inversion recovery (FLAIR), T1-weighted FLAIR precontrast sequences, and 3-dimensional fast imaging employing steady state acquisition. For contrast imaging, T1-weighted FLAIR sequences also were obtained after administration of gadopentetate dimeglumine (0.1 mmol/kg IV; Magnevist, Bayer Healthcare Pharmaceuticals Inc, Wayne, NJ, USA). Results showed the pneumatic cavity of the left quadrate bone was filled with material that was homogeneously hypointense to fat and hyperintense to muscle (Fig 1). The material did not suppress on T2-weighted FLAIR images. Subjectively, there was no contrast enhancement of the material within the left quadrate bone on the postcontrast T1-weighted FLAIR images. The cortex of the quadrate bone and surrounding soft tissues were normal. On T2-weighted images, the normal high signal intensity of the fluid in the cochlea was visible bilaterally. Additionally, a small volume of noncontrast-enhancing material in the left frontal sinus was visible, which was mildly hypointense to vitreous humor on T2-weighted images and isointense to muscle on T1-weighted images. The brain was normal.
Based on results of the MRI and the otoscopic examination, an infectious cause was suspected for the peripheral vestibular disease. Flowever, neoplastic infiltration of the quadrate bone could not be excluded from consideration. The patient made an uneventful recovery from anesthesia on oxygen and after receiving 1 dose of flumazenil (0.05 mg/ kg IV).
The next day, a brainstem auditory evoked response was performed to assess the function of the auditory system. The goose was premedicated with butorphanol (1 mg/kg IV), midazolam (0.5 mg/kg IV), and glycopyrrolate (0.006 mg/kg IV). Anesthesia was induced with ketamine (10 mg/kg IV). The patient was maintained on isoflurane, a constant rate infusion of butorphanol for analgesia (1 mg/kg per hour IV), and crystalloid fluids (10 ml/kg per hour IV). Tubal inserts were placed in the external ear canals. Subcutaneously placed 26-gauge needle electrodes were used to acquire differential recordings. The negative electrodes were placed ventral to the external meatus of the ears bilaterally. The positive electrode was placed on the dorsal midline of the head and a ground electrode was placed on the dorsal aspect of the neck. A square-wave broadband click stimulus of 100 ps duration was used at a rate of 21.1 Hz. The center frequency of the click was approximately 3-4 kHz. The stimulus intensity was 85 db nHL with a 60-db nHL masking noise in the contralateral ear. Recordings from the left ear were consistent with sensorineural hearing loss (Fig 2).
To further characterize the osseous structures and pneumatic spaces, computed tomography (CT) of the head was performed during the same anesthetic episode. One-millimeter helical transverse images of the head were acquired before and after administration of iohexol (880 mgI/kg IV; Omnipaque 350 mgI/mL, GE Healthcare Inc, Princeton, NJ, USA). In the left quadrate bone, the cavity was replaced diffusely with homogeneously hyperattenuating (230-290 Hounsfield units) material that did not contrast enhance. The right quadrate bone was normal, with a gas-filled
central cavity with numerous, thin, mineral-attenuating trabeculae. Compared with the right quadrate bone, the cortex of the left quadrate bone was thicker and more hyperattenuating, consistent with sclerosis (Fig 3). A small amount of fluid-attenuating, noncontrast-enhancing material was present in the left frontal sinus. Imaging findings were consistent with left-sided quadrate osteitis with dense cellular or proteinaceous deposition and frontal sinusitis.
Subsequent to the CT, debridement of the infected material and flushing of the left middle ear was performed. A 2-cm incision was made rostral to the left external auditory opening. The tissue was dissected to approach the quadrate bone, avoiding the closely associated facial nerve and extensive vasculature. A pneumatic drill was used to bore a small hole in the lateral cortex of the quadrate bone. Material from within the cavity of the quadrate bone was removed and submitted for aerobic and anaerobic cultures and for histopathologic evaluation. The cavity was flushed and then packed with 150 mg of clindamycin powder, and the soft tissues were closed with 3-0 antibacterial poliglecaprone 25 (Monocryl Plus; Ethicon Inc, Somerville, NJ, USA). The bird recovered uneventfully from anesthesia. Postoperatively, the bird was treated with clindamycin (60 mg/kg PO q12h x 4 weeks), meloxicam (0.5 mg/kg 1M q24h x 2 days), and diazepam (0.5 mg/kg PO q12h x 3 days). Additionally, the bird was treated with daily nutraceuticals (Pine Bark with Pure-way C, Imuno-2865, Neuro-Plex; Animal Necessity LLC, New York, NY, USA; and with Ocu-GLO Rx, Animal HeathQuest, Bellingham, WA, USA). (2-5) The bird was sent home with all of these medications, with the exception of meloxicam, which was replaced with firocoxib (5.7 mg/kg PO q12h x 4 weeks; Previcox, Merial, Duluth, GA, USA) for ease of administration. Petroleum ophthalmic ointment was to be applied topically to the corneal ulcer (OS q8h x 4 weeks).
Histopathologic evaluation of the quadrate bone was consistent with normal bone. Anaerobic culture of the material removed from the quadrate bone grew a gram-positive anaerobic bacillus that was sensitive to clindamycin. However, further characterization of the organism was not achieved.
At recheck evaluation 4 weeks after surgery, the bird had slightly improved. The head tilt was still present, but the goose was able to hold its head upright for increased periods of time. The bird was able to walk without circling, although it still had a vestibular ataxia and difficulty walking forward. The diet had been changed to Mazuri waterfowl diet with an increased amount of greens and decreased wheat bread. The corneal ulcer was smaller, and the cataracts were unchanged. Given the improvement in the neurological dysfunction, the clindamycin was continued for an additional 4 weeks. The surgical site had healed, and the firocoxib was discontinued at this time. At 8 weeks after surgery, the bird was showing continued improvement. It had a mild head tilt and was able to walk forward normally but had to be encouraged and pushed to walk. Results of a complete blood count and chemistry profile performed at this visit were unremarkable. The clindamycin was discontinued at this time, while the puralube and nutraceuticals were continued. At 16 weeks, the animal continued to show mild improvement and started to ambulate forward more normally. One year after initial presentation, the owner reported that the bird still had a slight head tilt but otherwise walked normally. At this time, both eyes remained sighted. The cataract in the right eye remained stable, and the left eye developed subcapsular lenticular opacities and corneal scarring associated with the previous corneal ulceration. Two years after initial presentation, the bird's vestibular disease had not progressed.
This case demonstrates peripheral vestibular disease in a goose and successful treatment after thorough diagnostic testing. While the diagnostic tools used in this case are used frequently in dogs and cats, their use in diagnosing peripheral vestibular disease in avian patients is still relatively uncommon. Additionally, the anatomy of the avian ear in relation to peripheral vestibular disease has not been described in a clinical setting.
In all species, a head tilt, abnormal nystagmus, vestibular ataxia, and circling are classic signs of vestibular dysfunction. The neuroanatomic basis for vestibular dysfunction is divided into disease affecting the vestibular system in the peripheral nervous system (peripheral vestibular disease) or in the central nervous system (central vestibular disease). Central vestibular disease is caused by a lesion in the medulla oblongata or cerebellum, whereas peripheral vestibular disease is caused by a lesion affecting the vestibular branch of cranial nerve VIII or its receptors. (1) Unique to most birds, almost all of the bones of the skull are pneumatic, and therefore intimately connected. (6,7) One of the challenges of this case was determining which structures were affected and how they related to the clinical signs. The MRI and CT scans were instrumental in identifying the bones, cavities, and communications affected. These imaging modalities have proven very effective at diagnosing middle ear disease in dogs and cats, (8,9) but their use in evaluating avian otic and vestibular disease has not been previously reported. Otitis media in dogs and cats has a characteristic appearance on MRI and CT, consisting of material filling the tympanic bulla. (10,11) There are no imaging changes consistent with otitis interna in dogs, so the diagnosis is made based on clinical signs of vestibular disease and a concurrent diagnosis of otitis media seen on imaging. (10) Birds, however, do not possess a tympanic bulla, which is the structure most commonly associated with otitis media in dogs and cats. (7,9) Advanced imaging in this patient revealed an accumulation of material similar to that seen in the bulla of dogs and cats but located in the quadrate bone. Changes of the quadrate bone, the ruptured tympanic membrane, and the clinical signs of vestibular disease were supportive of otitis media and interna.
In the bird, the external ear is surrounded by the quadrate, zygomatic, and temporal bones. The outer ear consists only of a short external acoustic meatus, starting at the circular external auditory orifice and terminating at the tympanic membrane. (6,7,12) The middle ear and inner ear are embedded in the temporal bone, which is pneumatic. The middle ear cavity contains air and communicates with the pneumatic spaces in the bones of the skull. (6,7,12) The middle ear also communicates with the pharyngeal cavity via the auditory tube. The semicircular canals and the vestibule of the bony labyrinth of the temporal bone, the utriculus, saccule, and semicircular ducts of the membranous labyrinth of the inner ear, and the vestibular division of cranial nerve VIII are responsible for balance and equilibrium. They are set in the os oticum, which is part of the temporal bone. The temporal bone articulates with the quadrate bone, which is the bone of interest in our patient. (6'12) In some birds the ligamentum columello-squamosum originates from the tympanic process, a continuation of the stapes, and crosses the middle ear cavity to insert on the ventral edge of the otic process of the quadrate bone. It creates a direct connection between the middle and outer ear. (7)
There are several routes of infection that can potentially lead to otitis media and interna, including extension of otitis externa through the tympanic membrane, aspiration of pharyngeal contents through the auditory tube, and hematogenous spread and extension of infection through the pneumatic bones. (7,8) Because of the chronicity of the current case, the exact route of infection could not be determined. Although it is possible that the initial otitis media and interna occurred via extension from otitis externa, at initial presentation to the referring veterinarian the tympanic membrane was intact. Regardless of the cause, treatment for patients with otitis media and interna is similar. It includes surgical removal of infected, necrotic material and tissues and administering appropriate antibiotics. (8,9)
Standard surgical treatment for otitis media in dogs and cats is a ventral bulla osteotomy, which involves surgical drainage of abscessed material from the tympanic bullae. (8,9) The surgical technique described in this report is analogous to a ventral bulla osteotomy, although the quadrate bone was drained and Hushed since birds do not possess a tympanic bulla. If the tympanic membrane had been intact and evidence of active infection was visible on otoscopic examination of this bird, perhaps myringotomy would have been effective for relieving clinical signs. However, more aggressive therapy was needed based on the imaging performed. Extrapolating from dogs and cats, prognosis for a bird with middle or inner ear disease is fair if aggressive surgical and medical therapy is attempted. (9) The neurologic signs may be permanent, and the bird in this report still maintains a slight head tilt but has learned to function normally. Follow-up imaging was not attempted in this bird because of the significant clinical improvement but would be beneficial to document clearance of the infection from the quadrate bone. Reinfection is a possible risk because of the ruptured tympanic membrane, which should be discussed with owners before treatment in similar cases.
Inner ear and intracranial disease should be considered in a bird presenting with a head tilt. Thorough imaging and diagnostic testing are recommended to establish the cause and to define an appropriate treatment course. While an infection is a common cause of inner ear disease, diagnostic imaging using MRI and CT are helpful to rule out other soft tissue causes of vestibular disease such as neoplasia or a brain abscess. (8) Magnetic resonance imaging is best suited to evaluate ear anatomy, the brainstem, and the cerebellum in veterinary patients with vestibular disease. (10) Computed tomography is often employed to evaluate osseous and gas-filled structures of the middle ear. (8) The unique advantages of each of these imaging modalities were similarly applicable in this Chinese goose and should be considered for modality selection in future patients.
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Katie W. Delk, DVM, Johanna Mejia-Fava, DVM, David A. Jimenez, DVM, Dipl ACVR, Marc Kent, DVM, Dipl ACVIM, Kathern Myrna, DVM, MS, Dipl ACVO, Joerg Mayer, DVM, MS, Dipl ABVP, Dipl ECZM, and Stephen Divers, BVetMed, DZooMed, Dipl ACZM, Dipl ECZM, FRCVS
From the Department of Small Animal Medicine and Surgery (Delk, Mejia-Fava, Kent, Myrna, Mayer, Divers), and the Department of Veterinary Biosciences and Diagnostic Imaging (Jimenez), College of Veterinary Medicine, The University of Georgia, 501 DW Brooks Dr, Athens, GA 30602, USA. Present address (Delk): Veterinary Teaching Hospital, University of California, Davis, One Shields Ave, Davis, CA 95616, USA.
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|Title Annotation:||Clinical Reports|
|Author:||Delk, Katie W.; Mejia-Fava, Johanna; Jimenez, David A.; Kent, Marc; Myrna, Kathern; Mayer, Joerg; Di|
|Publication:||Journal of Avian Medicine and Surgery|
|Date:||Mar 1, 2014|
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