ULTRASONOGRAPHY VERSUS RADIOGRAPHY FOR DETECTION OF FLUID IN THE CANINE TYMPANIC BULLA

The tympanic bullae of 20 previously healthy cadaver animals were randomly filled with sterile saline or air. The heads were positioned using tape ties and a rostrocaudal open mouth radiograph taken. The resulting radiographs were assessed by a blinded ECVDI diplomate, with each tympanic bulla being recorded as being either air or fluid filled. Ultrasound examination of the bullae was performed, by a blinded assessor, using a B-mode 5 mHz sector probe (Sonotron-VingMed Sound A/S, PO Box 141, N3191, Horten, Norway) operating at 3 mHz. Each bulla was recorded as being either air or fluid filled. Results of radiography and ultrasonography were each compared to the actual status of the bulla in a chi square analysis. Sensitivity of radiography was 80%, with specificity of 65%. Ultrasonographic sensitivity was 100% and specificity 100%. Ultrasonography may in future provide a cheap, noninvasive, rapid and widely available method for diagnosing otitis media in clinical cases.     

Virtual otoscopy for evaluating the inner ear with a fluid-filled tympanic cavity in dogs

The feasibility of virtual otoscopy (VO) imaging was evaluated in five dogs with experimentally induced otitis media, two control dogs, and two canine patients with otitis media. VO images of the tympanic cavity and ossicles were generated with commercially available software using raw computed tomography (CT) data. Eight out of 10 ears inoculated with pathogen exhibited obvious clinical signs associated with otitis externa. CT images revealed soft tissue density material occupying the tympanic bulla compatible with otitis media in three dogs with experimentally induced otitis media and two patients. No remarkable features were observed on the radiographs. Four different VO views (ear canal, tympanic bulla, eustachian tube, and ossicular chain) were created. Promontory, cochlea window, tympanic, and septum bulla as well as ossicles were easily and clearly distinguished except for the incus and stapes of the clinical patients. VO images were not more suitable than images created with conventional CT for accurately diagnosing otitis media in this study. However, it appears that VO could be more feasible for assessing the complex structure of the inner ear in dogs with fluid-filled tympanic cavities since fluid accumulation within the tympanic bulla did not affect the evaluation of bony tissue in the middle ear on VO images.     

ULTRASONOGRAPHIC EVALUATION OF THE EXTERNAL EAR CANAL AND TYMPANIC MEMBRANE IN DOGS

Ultrasonographic imaging of the canine external ear canal, tympanic membrane, and tympanic bulla was described in five healthy beagle dogs before and after infusion of saline into the ear canal. Saline served as an acoustic window. With this method, the external ear canal, and tympanic bulla were visible in the same imaging plane and the integrity of the tympanic membrane could be evaluated indirectly by confirming an intact tympanic membrane, which appeared at the end of the ear canal as a hyperechoic line with reverberation. Experimentally, perforated tympanic membrane could be evaluated by identifying anechoic saline in the tympanic bulla lumen. The air and fluid-filled tympanic bulla were also visualized. Ultrasonography with saline as an acoustic window appears to be helpful for the evaluation of the external ear canal, tympanic membrane, and tympanic bulla and it may have the potential to be a useful clinical tool in evaluation of integrity of the tympanic membrane.     

Computed tomographic features of feline nasopharyngeal polyps

The computed tomographic (CT) findings of histopathologically confirmed nasopharyngeal polyps are described in 13 cats. Most polyps were mildly hypoattenuating to adjacent muscles and isoattenuating to soft-tissue (n= 13), homogeneous (n = 12) and with ill-defined borders (n = 10) on precontrast images. After contrast medium administration, the polyps were homogeneous (n = 11), with well-defined borders (n = 13), oval (n = 13), and had rim enhancement (n = 13). Nasopharyngeal polyps were pedunculated in 11 cats with a stalk-like structure connecting the polyp through the auditory tube to an affected tympanic bulla. All cats had at least one tympanic bulla severely affected, with CT images identifying: (1) complete (n = 12) or partial (n = 1) obliteration of either the dorsal or ventral compartments with soft-tissue attenuating material; (2) pathologic expansion (n = 13) with wall thickening (n = 10) that was asymmetric in nine cats; and (3) identification of a polyp-associated stalk-like structure (n = 11). Nine cats had unilateral tympanic bulla disease ipsilateral to the polyp, and four cats had bilateral tympanic bulla disease, most severe ipsilateral to the polyp with milder contralateral pathologic changes. Two cats had minimal osteolysis of the tympanic bulla. Enlargement of the medial retropharyngeal lymph node was seen commonly (n = 8), and in all cats it was ipsilateral to the most affected tympanic bulla. One cat had bilateral lymphadenopathy. CT is an excellent imaging tool for the supportive diagnosis of nasopharyngeal polyps in cats. CT findings of a well-defined mass with strong rim enhancement, mass-associated stalk-like structure, and asymmetric tympanic bulla wall thickening with pathologic expansion of the tympanic bullae are highly indicative of an inflammatory polyp.     

ASSESSMENT OF THREE RADIOGRAPHIC PROJECTIONS FOR DETECTION OF FLUID IN THE RABBIT TYMPANIC BULLA

Otitis media in the rabbit commonly results in fluid accumulation in the tympanic bulla. Radiographic detection of fluid in the tympanic bulla is only moderately sensitive in the dog and cat. The purpose of this study was to investigate the accuracy of radiographic detection of fluid in the rabbit tympanic bulla for three different radiographic projections. Forty rabbit cadavers were used. Half of the tympanic bullae were randomly allocated to be filled with soft tissue material. Following this procedure, each specimen was radiographed in three projections: dorsoventral (DV), rostro 40° ventral-caudodorsal (R40°V-CdDO), and left and right latero 40° ventral-laterodorsal (Lat40°V-LatDO). After imaging, each specimen was frozen and sectioned to determine the content of the tympanic bullae. Images were interpreted and scored independently by two board-certified radiologists. There was no significant difference in sensitivity or specificity between the three projections when compared with the gross findings following sectioning, but observer confidence was highest for the DV projection. Accuracy of radiographic fluid detection was similar to that reported in the dog and cat. The DV and R40°V-CdDO allow comparison of both tympanic bullae on a single radiograph, but the DV was subjectively easier to position, while the Lat40°V-LatDO requires two radiographs for comparison.     

COMPARISON BETWEEN COMPUTED TOMOGRAPHIC CHARACTERISTICS OF THE MIDDLE EAR IN NONBRACHYCEPHALIC AND BRACHYCEPHALIC DOGS WITH OBSTRUCTIVE AIRWAY SYNDROME

Prevalence of subclinical middle ear lesions in dogs that undergo computed tomography (CT) and magnetic resonance imaging of the head has been reported up to 41%. A predisposition in brachycephalics has been suggested, however evidence‐based studies are lacking. Aims of this retrospective cross‐sectional study were to compare CT characteristics of the middle ear in groups of nonbrachycephalic and brachycephalic dogs that underwent CT of the head for conditions unrelated to ear disease, and test associations between thickness of the soft palate and presence of subclinical middle ear lesions. One observer recorded CT findings for each dog without knowledge of group status. A total of 65 dogs met inclusion criteria (25 brachycephalic, 40 nonbrachycephalic). Brachycephalic dogs had a significantly thicker bulla wall (P = 2.38 × 10^?26) and smaller luminal volume (P = 5.74 × 10^?20), when compared to nonbrachycephalic dogs. Soft palate thickness was significantly greater in the brachycephalic group (P = 2.76 × 10^?9). Nine of 25 brachycephalic dogs had material in the lumen of the tympanic cavity, compared to zero of 45 of nonbrachycephalics. Within the brachycephalic group, a significant difference in mean soft palate thickness was identified for dogs with material in the middle ear (12.2 mm) vs. air‐filled bullae (9 mm; P = 0.016). Findings from the current study supported previous theories that brachycephalic dogs have a greater prevalence of subclinical middle ear effusion and smaller bulla luminal size than nonbrachycephalic dogs. Authors recommend that the bulla lumen volume formula previously developed for mesaticephalic dogs, (?0.612 + 0.757 [lnBW]) be adjusted to 1/3(?0.612 + 0.757 [lnBW]) for brachycephalic breeds.     

A surgical technique for implantation of the vibrant soundbridge middle ear implant in dogs

Objective: To report a surgical implantation of the Vibrant Soundbridge (VSB) middle ear implant in dogs. Study Design: Pilot study. Animals: Dogs (n=3). Methods: A lateral approach to the tympanic bulla was used to insert the floating mass transducer of the VSB into the tympanic bulla. Using microscopic guidance the transducer was moved to and inserted into the round window niche by manipulation through the acoustic bony meatus, after reflection of the tympanic membrane. VSB position was confirmed by computed tomography (CT) imaging. Results: No intraoperative complications occurred and CT images confirmed correct placement of the VSB. Conclusions: A VSB can be safely implanted in the middle of dogs.     

VIRTUAL CT OTOSCOPY OF THE MIDDLE EAR AND OSSICLES IN DOGS

Virtual otoscopy enables noninvasive 3D endoluminal imaging of the middle ear through postprocessing of computed tompgraphy (CT) data. A standardized imaging approach for the middle ear was established in six normal dogs in an attempt to optimize the clinical application and student education. High‐resolution CT data were obtained. Virtual otoscopic images of the middle ear cavity and ossicles were generated using commercially available software. The views of the four different directions (the ear canal, tympanic bulla, eustachian tube, and ossicular chain) were made for virtual otoscopy. The promontory, cochlea window, tympanic bulla, septum bulla, and auditory tube were distinguished easily and clearly. One of the ossicles, the malleus, was visualized accurately. However, small structures such as the incus and stapes always could not be seen. The main advantage of virtual otoscopy is not only to provide diagnostic information but also to enhance the quality and efficiency of student education, because it contributes to an understanding of the anatomy of the middle ear. We describe the normal topographical 3Dimages of the middle ear of the dog using virtual otoscopy.     

Computed tomographic evidence of bulla effusion in cats with sinonasal disease: 2001-2004

BACKGROUND: Sinonasal disease is common in cats; chronic inflammatory disease and neoplasia are diagnosed most frequently. Radiographic and computed tomographic (CT) findings in nasal disease have been reported, although involvement of other cranial structures has not been fully described to our knowledge. HYPOTHESIS: We hypothesized that neoplastic or inflammatory obstruction of the auditory tube associated with sinonasal disease could result in CT evidence of effusive bulla disease in affected cats. ANIMALS: 46 cats with sinonasal disease, 18 control cats. METHODS: CT images acquired in cats with (n = 46) and without (n = 18) sinonasal disease were reviewed for evidence of concurrent bulla effusion. CT findings of soft tissue or fluid opacity within the tympanic bulla or thickening of the bone of the bullae were considered evidence of effusive bulla disease. RESULTS: The prevalence of bulla effusion in cats with sinonasal disease was 28% (13/46) and was significantly higher than that observed in cats without sinonasal disease (1/18, P = .043). CT findings that were found in association with effusive bulla disease included imaging features of sinusitis and nasopharyngeal disease. The most common neoplasm associated with bulla effusion was nasopharyngeal lymphoma. Bulla effusion was not observed in any cat with nasal carcinoma. CONCLUSIONS AND CLINICAL IMPORTANCE: Findings of this study suggest that auditory canal dysfunction may play a larger role in feline sinonasal disease than was previously recognized. The implications of these findings for management of cats with chronic inflammatory or neoplastic sinonasal disease require further investigation.     

Comparison of ultrasonography, radiography and a single computed tomography slice for fluid identification within the feline tympanic bulla

Evaluation of the tympanic bulla (TB) in cases of acute feline otitis media can be a diagnostic challenge, although a feature often associated with this condition is the accumulation of fluid or material within the middle ear cavity. A technique is reported allowing optimum imaging of the feline TB using ultrasound (US) and recording of the appearance of gas and fluid-filled TB. A random number of bullae in 42 feline cadavers were filled with lubricant and rostroventral-caudodorsal oblique radiographs, single slice computed tomography (CT) images and US images were created and interpreted by blinded operators. The content (fluid or gas) of each TB was determined using each technique and the cadavers were then frozen and sectioned for confirmation. CT remained the most accurate diagnostic method, but US produced better results than radiology. Given the advantages of US over other imaging techniques, these results suggest that further work is warranted to determine applications of this modality in the evaluation of clinical cases of feline otitis media.     

Comparison of computed tomography and routine radiography of the tympanic bullae in the diagnosis of otitis media in the calf

Background: Otitis media is difficult to diagnose antemortem. Case reports have described computed tomography (CT) in the diagnosis, but not all cases were confirmed. Hypothesis: CT is a sensitive and specific imaging modality of the tympanic bullae and can be used as the gold standard for the diagnosis of otitis media. Animals: Sixteen Holstein calves 5–7 weeks of age were included. Methods: Prospective study. All calves were sedated with IV xylazine (0.05–0.15 mg/kg) for routine radiography (3 views) and CT of the tympanic bullae followed by necropsy. Results: Based upon necropsy findings, 10 of 16 calves were affected with otitis media, 4 unilaterally and 6 bilaterally. Imaging changes associated with otitis media included increased soft tissue opacity within the bulla, thickening of the bulla wall, enlarged bulla, and osteolysis of the bulla wall and trabeculations. The most frequent radiographic changes were lysis of trabeculations and increased soft tissue opacity, which were present in 56.3% of affected bullae. On CT, increased soft tissue opacity within the bulla was present in 93.8% of affected bullae. Sensitivity of radiography and CT was 68.8 and 93.8% and specificity was 50 and 100%, respectively. The κ value between radiography and CT with necropsy diagnosis was 0.19 for radiography, indicating poor agreement, and 0.94 for CT, indicating excellent agreement. Conclusion: CT is more specific, more sensitive, and easier to interpret than radiography and can be used as the gold standard in the diagnosis of otitis media in the calf.     

Comparison of ultrasonography, radiography and a single computed tomography slice for the identification of fluid within the canine tympanic bulla

Fluid accumulation within the tympanic bulla (TB) is an important diagnostic indicator in clinical cases of canine otitis media although its identification can be a challenge using currently available imaging techniques. The aim of this study was to compare ultrasound with radiography and a single computed tomography (CT) slice for the identification of fluid within the TB of canine cadavers. A random number of TB in 66 cadavers were filled with ultrasound gel. Rostrocaudal open mouth (RCdoM) radiographs and CT images were interpreted by 2 blinded radiologists and ultrasound examinations were performed by 2 blinded sonographers. The heads were then frozen and sectioned to confirm the contents of each TB. Although CT remained the most accurate method, comparable results were obtained by one of the sonographers and even the inexperienced sonographer produced results superior to radiography. Ultrasound has several advantages over the other imaging techniques and this study suggests that it may have an application in the investigation of canine otitis media although further work in live animals would be required to confirm this.     

MAGNETIC RESONANCE IMAGING FEATURES OF BRAIN STEM ABSCESSATION IN TWO CATS

Premortem magnetic resonance imaging (MRI) was performed in two cats with brain stem abscessation confirmed post mortem by histology and recovery of multiple bacterial species. The MRI features of the abscesses were distinctive and included a thick and marked enhancement of the abscess capsule and extension of the lesion from a tympanic bulla in one cat. A focal area of increased signal intensity was present on T2-weighted images. A circumscribed area of decreased signal intensity was surrounded by a ring of increased signal intensity on precontrast T1-weighted images. A center of decreased signal intensity with a thick, markedly enhanced abscess capsule was observed on post contrast T1-weighted images. These findings are compared to the current experimental and clinical literature of brain abscess. The underlying pathogenesis of MRI features is reviewed.     

PATHOLOGIC BASIS FOR RIM ENHANCEMENT OBSERVED IN COMPUTED TOMOGRAPHIC IMAGES OF FELINE NASOPHARYNGEAL POLYPS

In postcontrast computed tomographic (CT) images, feline nasopharyngeal polyps typically demonstrate enhancement of the peripheral rim. Computed tomographic images and histologic specimens of a case series of 22 cats with surgically removed nasopharyngeal polyps were reviewed retrospectively in an attempt to elucidate the origin of rim enhancement. Polyps were present in the tympanic cavity in 15 (68%) cats (three with extension into the nasopharynx), only in the nasopharynx in four (18%) cats, and only in the external ear canal in the remaining three (14%) cats. All polyps had variable degrees of epithelial injury. Hemorrhage and inflammatory infiltration were significantly more marked in the superficial stroma whereas edema was significantly more marked in the core stroma. In noncontrast CT images (n = 22), the tympanic bulla was thickened in all 15 cats with a polyp in the tympanic cavity and enlarged in eight (53%) of these cats. In postcontrast CT images (n = 15), an outer zone of relatively increased attenuation compatible with a rim was observed in 11 (73%) polyps. The magnitude and extent of rim enhancement in CT images was positively correlated with the histologic grade of inflammation in the superficial stroma and negatively correlated with the grade of edema in the superficial stroma. It appears that inflammation is the major determinant of contrast medium accumulation in feline nasopharyngeal polyps, and the tendency for inflammation to affect predominantly the superficial layers explains the frequent observation of a rim in postcontrast CT images.     

A COMPARISON OF THE ROSTROCAUDAL OPEN MOUTH AND ROSTRO 10° VENTRO-CAUDODORSAL OBLIQUE RADIOGRAPHIC VIEWS FOR IMAGING FLUID IN THE FELINE TYMPANIC BULLA

Fluid within the tympanic bulla is an indication of middle ear disease. Radiography has a relatively low accuracy for the detection of soft tissue opacification in the tympanic bulla, and the most useful radiographic projection, the rostrocaudal open mouth (RCd (open mouth)), is technically difficult to perform in dogs and cats. An alternative projection for the feline tympanic bulla, the rostro 10 degrees ventro-caudodorsal oblique (R10 degrees V-CdDO), was compared to the RCd (open mouth) in 41 feline cadaver heads with the tympanic bullae randomly filled with KY jelly. Computed tomography was used as the gold standard. Each tympanic bulla was recorded as being positive or negative for soft tissue opacification. Although there was no significant difference between the accuracy of the two views, the R10 degrees V-CdDO was subjectively more accurate and easier to perform, and in a live patient may be performed without the need for general anesthesia. The R10 degrees V-CdDO projection is a good alternative to the RCd (open mouth) projection for detecting otitis media in the cat.     

COMPUTED TOMOGRAPHY FEATURES OF MIDDLE EAR CHOLESTEATOMA IN DOGS

We describe the computed tomography (CT) findings in 11 dogs with middle ear cholesteatoma. The cholesteatoma appeared as an expansile tympanic cavity mass with a mean attenuation value of 55.8±4.2 Hounsfield units. There was no appreciable contrast enhancement of the tympanic bulla contense but ring enhancement was seen in four dogs. Due to the slow progressive growth, the lesion causes severe bone changes at the contour of the tympanic bulla, including osteolysis, osteoproliferation and osteosclerosis, expansion of the tympanic cavity, and sclerosis or osteoproliferation of the ipsilateral temporomandibular joint and paracondylar process. Cholesteatoma can cause lysis of the petrosal part of the temporal bone, leading to intracranial complications. Although not definitive, CT provides useful information for distinguishing a middle ear cholesteatoma from otitis media and neoplasia. In otitis media, enlargement of the tympanic cavity is not routinely observed. In tumors that primarily affect the middle or inner ear, the predominant signs are lysis of the contour of the tympanic bulla or the petrosal part of the temporal bone, soft tissue swelling around the middle ear and marked contrast enhancement. In tumors that arise from the external ear, a soft tissue mass is visible within the external acusticus meatus, and the middle ear is only involved secondarily.     

Comparison of ultrasonography, radiography and a single computed tomography slice for the identification of fluid within the tympanic bulla of rabbit cadavers

Evaluation of the tympanic bulla (TB) in cases of otitis media in the rabbit can be a diagnostic challenge, although a feature often associated with the condition is the accumulation of fluid or material within the TB. Randomly selected TB from 40 rabbit cadavers were filled with a water-based, water-soluble jelly lubricant. A dorsoventral radiograph and single computed tomography (CT) slice were taken followed by an ultrasound (US) examination. Image interpretation was performed by blinded operators. The content of each TB was determined (fluid or gas) using each technique and the cadavers were frozen and sectioned for confirmation. CT was the most accurate diagnostic method, but US produced better results than radiography. Given the advantages of US over the other imaging techniques, the results suggest that further work is warranted to determine US applications in the evaluation of the rabbit TB and clinical cases of otitis media in this species.     

Ultrasound imaging of the canine tympanic bulla

A procedure for imaging the canine tympanic bulla, external ear canal and adjacent structures using currently available ultrasound equipment was established. Lateral and ventral transducer positions were identified for this purpose and a 6.5 MHz curvilinear transducer was considered to be optimal. The sonographic appearance of these structures in cadavers and live dogs unaffected by ear disease is documented. Fluid was introduced into the tympanic bullae of the cadavers and its presence could be identified through the bony wall of the bulla. The ability of ultrasound to differentiate between gas and fluid within the bulla has important clinical implications as this is a common occurrence in dogs with middle ear disease. Ultrasound has several advantages over other imaging modalities and the examination procedure was well tolerated by unsedated dogs.     

PREVALENCE AND CHARACTERIZATION OF SMALL TYMPANIC BONE SPICULES AND DRUMSTICK‐LIKE HYPEROSTOTIC TYMPANIC BONE SPICULES IN THE MIDDLE EAR CAVITY OF DOGS

Rounded, sessile, hyperattenuating structures detected in computed tomography (CT) studies of canine tympanic bullae have been termed “otoliths.” These have been proposed to represent dystrophic mineralizations or heterotopic bone formations in the middle ear that are potentially related to chronic otitis media. Aims of the current study were to describe the prevalence, macroscopic, and histological features of structures consistent with “otoliths” in the canine tympanic cavity. Tympanic bullae from 50 routinely necropsied dogs and 139 retrospectively retrieved CT scans of canine clinical cases were examined. Small tympanic bone spicules with pointed or clubbed tips essentially arising from the free margin of the septum bullae were bilaterally present in the tympanic cavities of all 50 of the necropsied dogs. In 48% of the dogs, “otolith”‐like CT‐detectable bone spicules carrying drumstick‐like hyperostoses that were 1–6 mm in diameter were also present. In the retrospective survey of bulla CT scans of 139 cases, the prevalence of hyperostotic tympanic bone spicules (HTBS) was 20%. Findings from the current study indicated that the presence of small tympanic bone spicules in adult dogs is most likely due to physiological bone growth in the septum bullae and that HTBS represent osseous proliferations of small tympanic bone spicules. However, the factors inducing formation of hyperostotic spicules from small tympanic bone spicules remain unknown. The high prevalence of HTBS displaying a similar appearance in bulla CT scans in dogs suggests that these spicules should be included in a differential diagnosis list for “otoliths.”