Computed tomographic anatomy of the canine inner and middle ear

Aural CT characteristics of American Cocker Spaniels have features of both mesaticephalic and brachycephalic breeds

Otitis externa and otitis media are common in American Cocker Spaniels, however breed-specific aural CT descriptions are currently lacking. This prospective and retrospective, observational, analytical study aimed to describe quantitative CT characteristics of the horizontal ear canal and the tympanic bulla in American Cocker Spaniels versus similar-sized mesaticephalic dogs. We prospectively performed clinical examinations and aural CT scanning for 38 American Cocker Spaniels. Computed tomographic transverse area of the osseous horizontal ear canal (TA1), transverse area of the widest air-filled part of the cartilaginous horizontal ear canal (TA2), tympanic bulla volume, and tympanic bulla wall thickness were measured. The TA1 and TA2 measurements were compared with those of 23 retrospectively recruited, similar-sized mesaticephalic dogs that had undergone CT-scanning of the head for non-ear-related reasons. The TA1 and TA2 did not differ for healthy American Cocker Spaniels and mesaticephalic dogs. Severely affected American Cocker Spaniels had significantly smaller TA2 (P < .001). The intraclass correlation coefficient for intraobserver and interobserver repeatability was 0.972 and 0.983 for TA1 and 0.994 and 0.998 for TA2, respectively. Variation between individuals was subjectively noted in healthy and affected American Cocker Spaniels, but mean tympanic bulla volume was slightly smaller in relation to body weight, and the tympanic bulla wall was thicker than in previous reports for mesaticephalic dogs. The tympanic bulla wall appeared thicker rostro-ventrally than caudo-ventrally in 44% of the dogs. Our results imply that a relatively thick tympanic bulla wall may be a normal CT variation and should be interpreted cautiously in this breed.

Cholesteatoma in a cat

Case summary

A 14-year-old neutered female Burmese cat was referred for investigation of a caudal oropharyngeal mass. CT showed a thin walled cyst-like structure filling and expanding from the right tympanic bulla. Histopathology showed fragments of mildly dysplastic squamous epithelium and aggregates of keratin. These findings were considered consistent with a diagnosis of cholesteatoma.

Relevance and novel information

To the best of our knowledge, this is the first reported case of a cholesteatoma in a cat. Cholesteatoma should be considered a differential diagnosis for cats presenting with a caudal oropharyngeal mass, a history of chronic ear disease or a history of previous, surgically managed middle ear disease. Advanced imaging and biopsies should be considered important in the diagnosis of these lesions.

Middle ear polyps: results of traction avulsion after a lateral approach to the ear canal in 62 cats (2004–2014)

Objectives

The objective of this study was to report the surgical outcome and complication rate of deep traction avulsion (TA) of feline aural inflammatory polyps after a lateral approach (LA) to the ear canal.

Methods

This was a retrospective analysis of data retrieved from an electronic database of 62 cats treated with TA after an LA (TALA) for removal of ear canal polyps. Long-term outcome was assessed via a telephone questionnaire survey with the owners.

Results

Domestic shorthair cats (48%) and Maine Coons (37%) were over-represented. The most common presenting clinical signs were otorrhoea, ear scratching and head shaking. Video-otoscopic examination confirmed a polypous mass in the ear canal in all patients. All 62 cats underwent TALA, with a mean surgical time of 33 mins for experienced surgeons (n = 4) and 48 mins (n = 12) for less experienced surgeons. The recurrence rate of polyp regrowth for experienced surgeons was 14.3% vs 35% for the less experienced surgeons. Postoperative complications included Horner’s syndrome (11.5%) and facial nerve paralysis (3%). Otitis interna was not observed.

Conclusions and relevance

A lateral approach to the ear canal in combination with deep TA of an aural inflammatory polyp is an effective first-line technique that results in a low recurrence and complication rate.

MRI findings of a middle ear cholesteatoma in a dog

This article describes the MRI features of a middle ear cholesteatoma in an 8 yr old flat-coated retriever. Physical examination revealed pain on opening the jaw, and otoscopic examination showed tympanic membrane rupture associated with hyperplastic tissue at the entrance of the middle ear. Standard MRI sequences allowed for the identification of a severely expanded bulla containing material that was isointense to brain tissue on T1-weighted images and of mixed intensity on T2-weighted and fluid-attenuated inversion recovery sequences. No postcontrast enhancement of the content was present, but the lining of the bulla was partially enhanced. The images allowed evaluation of the surgical margins and the secondary changes due to the expansion of the mass. Surgery was performed and histopathology confirmed the presumptive diagnosis of cholesteatoma. In the present case, MRI appeared to serve as a good alternative to computed tomography for the diagnosis of cholesteatoma.

Advanced imaging: use and misuse

SUMMARY

The primary purpose of diagnostic imaging is to enable clinicians to make correct decisions about a patient's diagnosis and severity of its condition and, thereby, to contribute to effective and efficient treatment. Advanced imaging modalities are inherently better detectors of morphological lesions than radiography; hence, they offer the possibility of more accurate diagnosis and staging, with correspondingly better patient outcomes. However, there is a lack of evidence that better outcomes are being realised for veterinary patients. Furthermore, increased use of advanced imaging carries the possibility of increased misuse, primarily through unnecessary studies that contribute little to patient management other than increased costs.

SCOPE

This article is intended to be relevant to all veterinary species. Advanced imaging of cats is not sufficiently developed as a specific discipline that a balanced review could be based purely on feline examples or references.

Computed tomography in small animals – Basic principles and state of the art applications

Since its clinical introduction, computed tomography (CT) has revolutionized veterinary medicine and is considered to be one of the most valuable tools for the imaging work-up of neurological, oncological and orthopaedic canine and feline patients. In small animals with acute trauma, particularly those involving complex anatomic areas such as the head, spine or pelvis, CT has been established as a standard imaging method. With the increasing availability of radiation therapy in veterinary medicine, CT has also become the principal tool to stage a tumour, assess response, and guide radiation therapy. The increasing availability of helical CT in veterinary medicine has allowed novel techniques such as spiral CT angiography and high-resolution CT. This review provides a brief overview of the historical and technical development of CT and literature reviews of the major clinical CT applications in small animals such as intracranial and extracranial lesions, the spine, the appendicular skeleton, and abdominal and thoracic diseases.

Computed Tomographic Anatomy of the Canine Temporal Bone

This study aims to identify and describe structures of the temporal bone in normal dogs that can be depicted using computed tomography (CT). Five normal dogs of different breeds and both sexes ranging from 0.5 to 8 years were used as the study material. CT images of 2 mm thickness without abnormalities in the temporal bone were reviewed and analysed in bone and soft tissue settings. All images were compared with corresponding E 12 plastic-embedded cross sections of 3 mm thickness, which were acquired from anatomic cross sections of frozen beagles. The sections were provided from the Department of Pathobiology (Institute of Anatomy). CT is able to image all relevant bony structures within the temporal bone. Concerning soft tissue structures, CT allows their localization by using bony markers, i.e. the internal acustic meatus for the cranial nerves VII and VIII or the canals for the internal carotid artery and the temporal sinus. The provided reference images are meant to improve orientation within the complex anatomy of the temporal bone. On condition that slice thickness is equal to or smaller than 2 mm and bony setting is supplied, CT is able to visualize all relevant structures within the temporal bone. However, in clinical settings the combined look on air, liquids and bone as well as the contrast enhancement of soft tissues might prefer magnetic resonance imaging to CT.

MEASUREMENT OF NORMAL MIDDLE EAR CAVITY VOLUME IN MESATICEPHALIC DOGS

Water-filling and serial computed tomographic (CT) imaging techniques were used to measure normal middle ear cavity volume (MECV) in 18 dogs (10 live dogs, eight cadavers; 36 ears in total). The specific aims of this study were to (1) compare MECV measurements by water-filling and CT techniques and (2) define a model of MECV vs. body weight (BW) from CT values. There was a significant difference between the two techniques (P = 0.02). The volume obtained by water filling was consistently greater than that obtained by computed tomography. MECV (expressed in ml) increased with BW (expressed in kg) according to the following formula: MECV = -0.612 + 0.757 (In BW) (P<0.01, R2 = 0.74).

ANATOMICAL STUDY OF CRANIAL NERVE EMERGENCE AND SKULL FORAMINA IN THE DOG USING MAGNETIC RESONANCE IMAGING AND COMPUTED TOMOGRAPHY

Twenty-two magnetic resonance imaging (MRI) brain studies of different breeds of dogs were reviewed to assess the anatomy of cranial nerve (CN) origins and associated skull foramina. These included five anatomic studies of normal brains using 2-mm-thick slices and 17 studies using conventional clinical protocols with 3- or 4-mm slices on both normal and abnormal brains. Images were obtained in transverse, sagittal, and dorsal planes to allow a thorough comparison between studies. CNs II, III, V (and its divisions), and VIII were observed consistently on conventional studies. On the thin-slice studies, the origins and proximal portions of CNN IV, VII, and the group of IX, X, and XI could be seen. The origins of CNN VI and XII were not observed with certainty. In parallel, a computed tomography study of an isolated skull was performed with a thin copper wire within each of the skull foramina to determine precisely each CN exit and to facilitate recognition of the course of CNs when exiting the skull on MRI images.

LOW-FIELD MAGNETIC RESONANCE IMAGING OF THE CANINE MIDDLE AND INNER EAR

A series of low-field magnetic resonance images of the normal canine middle and inner ear are presented to serve as a reference. A completely balanced steady-state gradient echo pulse sequence with a slice thickness of 0.9 mm can be used to acquire images of the relevant structures within and neighboring the inner ear. These were the cochlear duct, semicircular ducts, vestibule, facial and vestibulocochlear nerves, as well as the temporal sinus. Within the middle ear, no applied sequence was able to allow identification of the auditory ossicles or the tympanic membrane.

Diagnostic imaging of the canine and feline ear

Radiographic evaluation of the tympanic bulla is limited. Improper obliquity or angulation of the skull for radiographs or malpositioning of the tongue can result in an inadequate study [4]. Additionally, because of the complex anatomy of the canine and feline skull, with superimposition of multiple osseous structures, radiography can result in false-negative examinations or understimation of the disease present [2]. When compared with surgical findings of 19 clinical cases of presumptive middle ear disease, false-negative radiographic findings were found in 25% of the surgically confirmed cases of otitis media [4]. Therefore, radiographs are not considered to be a highly sensitive mode of diagnosing otitis media. Radiographs may be helpful in determining lysis associated with neoplasia; however, the extent of involvement is still underestimated. In a study comparing CT and radiographic evaluation of otitis media, CT was determined to be more sensitive but less specific than radiography [11]. CT is the preferred modality for the evaluation of the tympanic bulla at our institution. This opinion may be biased by the fact that most cases are presented for recurrent or chronic otitis. Although radiography is more accessible, the availability of CT in local referral settings is increasing as opposed to being limited to university settings. After the cost (i.e., anesthesia, radiographs) and amount of time necessary to make optimum radiographic studies are taken into account, a CT study may actually be faster and more informative. Given our preference for the CT examination, the cost of the examination has been adjusted to make it more appealing to the owner and clinician. For example, a bulla CT study is only 1.3 times the cost of a radiographic bulla study. In conclusion, imaging of the ear canal can provide important information about ear disease, including unilateral or bilateral ear disease, the degree of middle or inner ear involvement, peripheral versus central vestibular disease, an infectious or inflammatory versus neoplastic process, the chronicity of the disease process, involvement of adjacent structures, and postsurgical complications.

INFLAMMATORY POLYP IN THE MIDDLE EAR WITH SECONDARY SUPPURATIVE MENINGOENCEPHALITIS IN A CAT

A 15-month-old male Maine Coon Cat presented with persistent auricular discharge and progressive head tilt, ataxia, and loss of blink on the right side. Using computed tomography a hyperattenuating, contrast-enhancing material within a thickened right tympanic bulla and contrast enhancement of the adjacent cerebellum were identified. Marked suppurative inflammation was identified on cerebrospinal fluid analysis with no growth on bacterial culture. Ventral bulla osteotomy was performed to remove a soft tissue mass, and an inflammatory polyp with chronic severe suppurative inflammation was confirmed using histology. Staphylococcus auricularis was grown on aerobic culture and Fusobacterium necrophorum and Peptostreptococcus anaerobius were grown on anaerobic culture. The cat was treated for 10 weeks with amoxicillin/clavulinic acid and metronidazole. Dramatic improvement in body weight, appetite, energy level, balance, and resolution of right-sided facial paralysis were noted, but the cat retained a head tilt.

Review of diagnostic imaging of ear diseases in the dog and cat

Diagnostic imaging techniques (conventional radiography, computed tomography and magnetic resonance imaging) are an essential tool in the diagnostic work-up of ear diseases. Conventional radiography is commonly used, but often lacks sensitivity. Computed tomography (CT) and magnetic resonance (MR) are complementary imaging studies of the middle ear, labyrinth, internal auditory canal and their contents. CT provides excellent images of bony structures and is indicated where osseous changes are of greatest diagnostic importance. MR is superior in imaging soft tissue components including intralabyrinthine fluid. Therefore, more than one of these imaging techniques may be required in order to make a diagnosis.

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.