Optimising magnetic resonance image quality of the ear in healthy dogs

Evaluation of canine tympanic membrane integrity using positive contrast computed tomography canalography

Introduction

The assessment of the integrity of the tympanic membrane (TM) can be a diagnostic challenge in patients with otitis externa and/or otitis media (OM) under an otoscopic examination. In computed tomography (CT), the TM is not always visualized. However, a positive contrast canalography using conventional radiography has been previously described to evaluate the TM integrity.

Objective

This single-center study aimed to describe the positive contrast canalography technique in CT and its usefulness in identifying TM integrity in 11 dogs.

Methods

Dogs with clinical signs of ear disease underwent CT canalography following a systematic protocol.

Result

The presence of contrast medium and contrast homogeneity within the tympanic cavity was assessed, confirming TM rupture when contrast medium was present in the tympanic cavity. CT canalography was performed in 16 ears, and in 7 of the 16 ears (44%), there was a contrast in the tympanic cavity, confirming TM rupture (positive CT canalography result). In two of the seven cases (29%), rupture of the TM was identified in both otoscopic and CT canalography. In the remaining five of the seven (71%) positive CT canalography results, tympanic membrane rupture was identified only by CT canalography.

Discussion

In conclusion, a positive contrast CT canalography is a complementary and safe technique to assess TM integrity, with a potentially higher sensitivity than otoscopic examination for the diagnosis of TM rupture in dogs.

Bacterial meningitis secondary to otogenic infection in 10 French bulldogs: A retrospective case series

Background

There is limited published information to guide the clinical management of bacterial meningitis/encephalitis in dogs.

Methods

This was a retrospective case series comprising 10 French bulldogs from two referral centres. The cases were diagnosed with bacterial meningitis/encephalitis suspected secondary to otogenic infection based on detection of abnormal fluid/soft tissue opacity within the middle/inner ear, associated meningeal/intracranial involvement through MRI, the findings of cerebro-spinal fluid (CSF) analysis suggestive of sepsis and/or clinical improvement following antibiosis.

Results

Ten dogs were included (three female and seven male), with a median age of 60 months. Dogs presented with acute onset (median 2 days), progressive history of vestibular signs and/or intra-oral or cervical pain. Five dogs had gross signs of concurrent otitis externa. Common MRI findings included material within the tympanic bulla with adjacent meningeal enhancement. Analysis of CSF documented pleocytosis in all eight dogs, intracellular bacteria seen in three with positive bacteriological culture in two dogs. One dog was euthanised following diagnosis. Nine remaining dogs received antimicrobial therapy and six underwent surgical management. Three dogs treated surgically were neurologically normal within 2 weeks and the remaining three improved. Two dogs treated medically improved and one had complete resolution reported within a 4-week follow-up period. Study limitations include its retrospective nature and small sample size with minimal longer term follow-up.

Conclusions

Bacterial meningitis/encephalitis in French bulldogs can require both medical and surgical treatment to achieve a favourable outcome.

Anatomy of the rabbit inner ear using computed tomography and magnetic resonance imaging

Anatomically, the inner ear is a highly complex organ of intricate design, composed of a bony labyrinth that encases the same-shaped membranous labyrinth. It is difficult to study the three-dimensional anatomy of the inner ear because the relevant structures are very small and embedded within the petrous temporal bone, one of the densest bones in the body. The current study aimed to provide a detailed anatomic reference for the normal anatomy of the rabbit's inner ear. As a study model, ten healthy adults New Zealand White rabbit heads were used. Six heads were used for macroscopic evaluation of the bony and membranous labyrinths. The remaining four heads were evaluated radiographically, where 3D images were generated of the bony and membranous labyrinths using data sets from computed tomography (CT) and magnetic resonance imaging (MRI), respectively. The anatomical structures were identified and labelled according to NominaAnatomicaVeterinaria (NAV). Our study revealed that CT and MRI are the optimal cross-sectional imaging modalities for investigating such tiny and often inaccessible inner ear structures. As high-quality scanners are not readily available to veterinarians, the CT and MRI images generated by this research were of lower quality; therefore, high-quality dissections were used to identify/support structures seen in these images. In conclusion, this study provides one of the first investigations that uses multislice CT scans and MRI to study the rabbit's inner ear and its correlation with the corresponding anatomical images. Both anatomical, CT and MRI images will serve as a reference for interpreting pathologies relative to the rabbit's inner ear.

Functional magnetic resonance imaging of the ascending stages of the auditory system in dogs

Background

Functional magnetic resonance imaging (fMRI) is a technique able to localize neural activity in the brain by detecting associated changes in blood flow. It is an essential tool for studying human functional neuroanatomy including the auditory system. There are only a few studies, however, using fMRI to study canine brain functions. In the current study ten anesthetized dogs were scanned during auditory stimulation. Two functional sequences, each in combination with a suitable stimulation paradigm, were used in each subject. Sequence 1 provided periods of silence during which acoustic stimuli could be presented unmasked by scanner noise (sparse temporal sampling) whereas in sequence 2 the scanner noise was present throughout the entire session (continuous imaging). The results obtained with the two different functional sequences were compared.

Results

This study shows that with the proper experimental setup it is possible to detect neural activity in the auditory system of dogs. In contrast to human fMRI studies the strongest activity was found in the subcortical parts of the auditory pathways. Especially sequence 1 showed a high reliability in detecting activated voxels in brain regions associated with the auditory system.

Conclusion

These results indicate that fMRI is applicable for studying the canine auditory system and could become an additional method for the clinical evaluation of the auditory function of dogs. Additionally, fMRI is an interesting technique for future studies concerned with canine functional neuroanatomy.