Introduction
A 9-year-old 13.6-kg neutered male mixed-breed brachycephalic dog was referred because of a 3-week history of ataxia and an acute-onset, nonprogressive, right-sided head tilt and a 6-month history of visual and hearing impairment and ocular discharge. Previous medical history included otitis externa of the right ear. Results of a physical examination were unremarkable except for reduced tear production in the right eye, as determined with a Schirmer tear test (right eye, 8 mm/min; left eye, 20 mm/min).
Assessment
Anatomic diagnosis
The absent menace response and palpebral reflex in the right eye with a normal pupillary light reflex and vision were suggestive of a lesion involving the right facial nerve (cranial nerve VII). Reduced tear production in the right eye could be attributed to a lesion involving the same nerve, especially a lesion of the parasympathetic portion of cranial nerve VII (major petrosal nerve). The head tilt was most likely associated with a disorder affecting the vestibular system. The animal’s decreased hearing on the right was attributed to a lesion involving the right cochlea or the cochlear portion of cranial nerve VIII.
Likely location of a single lesion
The animal’s presenting clinical signs and neurologic examination findings were compatible with a lesion involving the right peripheral vestibular system (right inner ear, right vestibulocochlear nerve, or both) and right facial nerve.
Etiologic diagnosis
Potential differential diagnoses for a 9-year-old dog with peripheral vestibular syndrome include inflammatory or infectious disorders (eg, otitis media, otitis interna, and nasopharyngeal polyps), neoplasia (eg, primary aural tumors and peripheral nerve tumors), and, less likely, idiopathic vestibular disease or metabolic disease (eg, hypothyroidism). There was no history of toxicosis or a traumatic event, so these were considered unlikely causes. The initial diagnostic plan included a CBC, serum biochemistry and electrolyte analysis, T4/thyroid-stimulating hormone measurement and urinalysis, followed by MRI study of the head and CSF analysis, if indicated. If material was found within the middle ear, video-otoscopic examination and myringotomy would be appropriate.
Diagnostic Test Findings
The initial diagnostic plan included a CBC, serum biochemical panel including measurement of electrolyte concentrations, measurement of serum thyroxine and thyroid-stimulating hormone concentrations, and a urinalysis, followed by MRI of the head with analysis of a CSF sample, if indicated. If material were found within the middle ear, video-otoscopy and myringotomy would be performed.
Results of the CBC, serum biochemical panel, thyroid function testing, and urinalysis were unremarkable. MRI of the head was performed with a 1.5-T scanner (Magnetom; Siemens), and the following sequences were obtained: T2-weighted (T2W) images in the sagittal, transverse, and dorsal planes; T1-weighted (T1W) images before and after administration of gadopentetate dimeglumine (Magnevist); FLAIR images; and T2-weighted gradient echo images in the transverse plane. MRI revealed abnormal material in the right tympanic bulla that was heterogeneously hyperintense, compared with adjacent gray matter, on T2W and FLAIR images and iso- to hypointense on T1W images (Figure 1). The material extended dorsally toward the right oval foramen and inner ear, with hyperintensity on T2W images also apparent within the right lateral pterygoid muscle. On T1W images, the right tympanic bulla was obliterated, with expansion and discontinuation of its ventrolateral wall. After IV administration of contrast medium, there was a marked rim enhancement of the inner tympanic bulla wall and heterogeneous contrast enhancement of the dorsal aspect of the middle-ear material at the level of the oval foramen, in addition to asymmetric contrast enhancement of the right trigeminal, facial, and vestibulocochlear nerves (Figure 2). Pachymeningeal enhancement was also reported along the ventral aspect of the right temporal lobe and pons. These findings were consistent with right-sided otitis media and interna with associated focal meningitis and right lateral pterygoid myositis and neuritis of cranial nerves V, VII, and VIII.
Images of the head of a 9-year-old mixed-breed dog with a 3-week history of ataxia and an acute-onset, nonprogressive, right-sided head tilt and a 6-month history of visual and hearing impairment and ocular discharge. A—Transverse T2-weighted MRI image at the level of the tympanic bulla (arrowheads); notice the hyperintense material within the right tympanic bulla and expansion of the ventrolateral aspect of the bulla. B and C—Precontrast (B) and postcontrast (C) transverse T1-weighted (T1W) MRI images at the level of the thalamus. Notice the meningeal contrast enhancement of the temporal lobe (arrow) and right lateral pterygoid myositis. D and E—Precontrast (D) and postcontrast (E) transverse T1W MRI images at the level of the pons. Hyperintense material is seen within the right tympanic bulla, with marked rim enhancement of the inner tympanic bulla wall and enhancement of the dorsal aspect of the material at the level of the oval foramen on postcontrast images (arrows). F and G—Transverse CT images at the level of the tympanic bulla displayed in soft tissue (F) and bone (G) windows. Non–contrast-enhancing material is present in the right tympanic bulla, with markedly lytic changes affecting the ear canal (arrows) and adjacent brain.
Citation: Journal of the American Veterinary Medical Association 260, 13; 10.2460/javma.21.12.0529
Additional images of the dog in Figure 1. A through C—Precontrast transverse T1W MRI images obtained at the level of cranial nerves VIII (A; small arrow), VII (B; small arrow), and V (C; small arrow). D through F—Postcontrast transverse T1W MRI images at the level of cranial nerves VIII (D; large arrow), VII (E; large arrow), and V (F; large arrow). Notice the contrast enhancement of the cranial nerves on postcontrast images.
Citation: Journal of the American Veterinary Medical Association 260, 13; 10.2460/javma.21.12.0529
Video-otoscopy of the right ear did not reveal any obvious alterations of the external ear canal. Myringotomy was performed, but no debris was retrieved despite copious flushing. Results of cytologic examination of samples collected from the external ear canal and middle ear were unremarkable. The patient was discharged with treatment for suspected otitis media-interna with bacterial meningitis secondary to a presumptive cholesteatoma.
On reexamination 4 weeks later, the right-sided head tilt remained static. Neurologic findings were the same as before, except that anisocoria with miosis of the right eye was also present. Worsening of tear production in the right eye was detected (Schirmer tear test, 0 mm/min) along with ipsilateral xeromycteria. These findings led to the diagnosis of neurogenic keratoconjunctivitis sicca likely associated with neuritis of the facial nerve. The anisocoria was interpreted as partial Horner syndrome affecting the right eye.
CT of the head was performed as part of surgical planning and revealed markedly lytic and proliferative right middle and inner ear changes with extension into the external ear canal and brain (Figure 1). The tympanic bulla was filled with non–contrast-enhancing material. There was marked lysis of the right bony labyrinth, petro-occipital canal, jugular and stylomastoid foramina, and right trigeminal canal, with contrast enhancement of the brain parenchyma at this level. Video-otoscopy confirmed the presence of keratinized material in the middle ear. Findings were consistent with chronic otitis media-interna and secondary bacterial meningoencephalitis. Additionally, the CT findings were deemed pathognomonic for a diagnosis of cholesteatoma.
Treatment
The patient underwent a total ear canal ablation and lateral bulla osteotomy. Results of histologic examination of the external ear canal and bacterial culture and antimicrobial susceptibility testing were consistent with chronic otitis externa caused by Pseudomonas aeruginosa. Histologic examination of the mass was not performed.
The dog was discharged from the hospital 2 days after surgery for ongoing postoperative management at home. Four months after initial diagnosis, the dog experienced an episode of collapse at home, and the owners elected to have the dog euthanized.
Comments
Cholesteatomas (also referred as tympanokeratomas) are nonneoplastic, cystic, expansile lesions within the middle ear that have been reported in association with or consequent to chronic otitis media-externa in dogs.1 They have been reported in both humans and dogs and may be congenital or acquired. The congenital form is thought to develop secondary to dysfunction of the eustachian tube and chronic hypoventilation of the auditory tube, which in turn leads to invagination of the tympanic membrane into the bulla, whereas the acquired form is characterized by an intense inflammatory response that results in lysis of the surrounding tissues.2,3 Breed and sex predisposition have not been reported. Affected animals typically present with a history of chronic otitis, pain associated with the temporomandibular joint, and discomfort on opening the mouth but can also have neurologic signs such as a head tilt, vestibular ataxia, and facial paralysis.3
The cystic portion of a cholesteatoma is lined by keratinizing squamous epithelium and central accumulation of granulation tissue containing inflammatory cells and keratin debris.2 The continuous production of keratin leads to enlargement of the cyst and destruction of adjacent tissues, especially bone.1,3
A diagnosis of cholesteatoma can be made with advanced imaging. CT is most commonly used to differentiate cholesteatomas from other middle ear diseases; however, MRI findings associated with cholesteatomas have also been reported.4 Radiography, video-otoscopy, bacterial culture, and histologic examination can also aid in the diagnosis of a cholesteatoma.3
On CT images, cholesteatomas typically appear as expansile tympanic cavity masses with severe changes of the tympanic bulla (eg, expansion, osteoproliferation, osteolysis, and osteosclerosis), usually without contrast enhancement within the inner ear. Peripheral ring enhancement of the tympanic bulla has been reported. These changes in the bone seem to occur consequently to the inflammatory process with associated production of keratin and cytokines and increased pressure in the tympanic bulla.5
MRI images of cholesteatomas have been reported less frequently, but they have been described as expansile masses arising from the middle ear that are isointense to the brain on T1W images with no contrast enhancement. Partial contrast enhancement of the inner lining of the bulla on T1W images has also been reported.4 Contrast enhancement of the ipsilateral perilesional meninges has also been described in a dog with a cholesteatoma and meningoencephalitis associated with chronic otitis externa.1
Surgical removal of the lesion and management of the underlying infection are the advised treatment approaches for dogs with cholesteatomas, with possible curative effects with early intervention but a high risk of recurrence in advanced cases.3 Development of neurologic signs can affect the prognosis of surgical treatment, with a higher risk of recurrence after surgery.2 In the dog described in the present report, there was no definitive confirmation of the diagnosis by means of histologic analysis; therefore, other neoplastic middle ear masses cannot be definitively ruled out. However, the clinical signs alongside the MRI and CT features and video-otoscopy findings supported a presumptive diagnosis of cholesteatoma.
In summary, cholesteatoma is a benign, keratinizing growth of the middle ear and should be considered as a differential in dogs with peripheral vestibular syndrome.
Acknowledgments
The authors declare that there were no conflicts of interest.
References
- 1. ↑
Newman AW, Estey CM, McDonough S, Cerda-Gonzalez S, Larsen M, Stokol T. Cholesteatoma and meningoencephalitis in a dog with chronic otitis externa. Vet Clin Pathol. 2015;44(1):157–163.
- 2. ↑
Risselada M. Diagnosis and management of cholesteatomas in dogs. Vet Clin North Am Small Anim Pract. 2016;46(4:623–634.
- 3. ↑
Greci V, Travetti O, Di Giancamillo M, et al. Middle ear cholesteatoma in 11 dogs. Can Vet J. 2011;52(6:631–636.
- 4. ↑
Harran NX, Bradley KJ, Hetzel N, Bowlt KL, Day MJ, Barr F. MRI findings of a middle ear cholesteatoma in a dog. J Am Anim Hosp Assoc. 2012;48(5:339–343.
- 5. ↑
Travetti O, Giudice C, Greci V, Lombardi R, Mortellaro M, Di Giancamillo M. Computed tomography features of middle ear cholesteatoma in dogs. Vet Radiol Ultrasound. 2010;51(4:374–379.
