Surgical Management of Rabbit Ear Disease

Refractory otitis media and otitis externa in a koala (Phascolarctos cinereus) treated with total ear canal ablation and lateral bulla osteotomy

BACKGROUND

To the authors' knowledge, this is the first report fully describing the surgical and medical management of otitis media and otitis externa in the koala (Phascolarctos cinereus) treated by total ear canal ablation and lateral bulla osteotomy.

CASE REPORT

An adult male koala captured as part of a monitoring project in South East Queensland was diagnosed with chlamydial cystitis. Purulent discharge from the right ear was also observed; diagnostic imaging was consistent with otitis media and otitis externa. Yokenella regensburgei was repeatedly cultured from the site. Clinical signs resolved with topical antibiotic therapy; however, recrudesced following cessation of antibiotics. A total ear canal ablation and lateral bulla osteotomy was performed, followed by an extended period of systemic antibiotic therapy. Mild facial nerve paresis was observed for 4 weeks postoperatively and resolved spontaneously. The koala remained clinically healthy for the 6 months it was monitored following release.

CONCLUSION

Total ear canal ablation combined with lateral bulla osteotomy appears to be an appropriate surgical intervention for otitis media combined with otitis externa refractory to medical management in the koala. Transient postoperative facial nerve paresis is a possible complication, as documented in other species. To the authors' knowledge this is the first case of Yokenella regensburgei infection outside of humans and American alligators (Alligator mississippiensis); the clinical significance of this pathogen in the koala remains unknown.

Encephalitozoon cuniculi Infection of Domestic Rabbits (Oryctolagus cuniculus) in Slovenia between 2017 and 2021

Encephalitozoon cuniculi is a microsporidial parasite that primarily infects domestic rabbits (Oryctolagus cuniculus). It is the causative agent of encephalitozoonosis, a disease with an internationally recognized seroprevalence among rabbits. This study determines the presence, clinical manifestation, and serological status of encephalitozoonosis in pet rabbits in Slovenia using various diagnostic procedures. From 2017 to 2021, 224 pet rabbit sera were collected and tested for encephalitozoonosis with the indirect immunofluorescence assay. Immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies against E. cuniculi were confirmed in 160 (65.6%) cases. Most seropositive rabbits suffered from neurological clinical signs or signs of gastrointestinal disorders such as recurrent hypomotilities, chronic weight loss, cachexia, or anorexia, and fewer showed clinical signs related to the urinary system or phacoclastic uveitis. A quarter of the positively tested rabbits presented without clinical signs. Hematological and biochemical blood analysis confirmed that seropositive animals had elevated globulin and deviated albumin levels in comparison to the normal reference values of non-infected animals. Furthermore, rabbits with neurological clinical signs showed statistically significant higher levels of globulins and total protein. Sixty-eight whole-body radiographs and thirty-two abdominal ultrasound reports were analyzed, looking for changes in the shape or size of the urinary bladder, presence of urinary sludge or uroliths, and any abnormalities related to the kidneys (shape, size, or nephrolites). The results suggest that neurological defects in the urinary bladder caused by E. cuniculi lead to a distended urinary bladder and consequently dysuria, incontinence, urine scalding, and sludgy urine.

Perioperative complications and outcomes following partial ear canal ablation and lateral bulla osteotomy in pet rabbits: 20 cases (2009-2021)

OBJECTIVE

To investigate the perioperative complications and outcomes of rabbits undergoing partial ear canal ablation and lateral bulla osteotomy for treatment of chronic otitis.

MATERIALS AND METHODS

Surgical logbooks were searched to identify rabbits that underwent partial ear canal ablation and lateral bulla osteotomy between December 2009 and September 2021. Data collected included signalment, history, clinical signs, historical and current medical management, physical examination findings, preoperative diagnostic imaging and aural bacterial culture results, surgical procedure information, duration of hospitalisation, complications and final outcome.

RESULTS

Twenty rabbits with chronic, medically unresponsive otitis underwent 27 partial ear canal ablation and lateral bulla osteotomies. Ten rabbits had pre-existing neurologic deficits and 17 had an ear base abscess at the time of surgery. A total of 13 (65%) rabbits developed at least one complication, either in the perioperative period or between discharge and recheck. Three of these rabbits (15%) underwent revision surgery for persistent or recurrent ear base abscess. Complete resolution of clinical signs ultimately occurred in 12 (60%) rabbits. Three (15%) rabbits showed improved but not completely resolved clinical signs (three facial asymmetry). Five (25%) rabbits died of causes potentially related to chronic otitis and/or partial ear canal ablation and lateral bulla osteotomy; two of these rabbits had undergone revision surgery.

CLINICAL SIGNIFICANCE

Although this study reports a high complication rate (65%), most complications resolved, with 15 (75%) rabbits having a good to excellent final outcome. Since the majority of rabbits in this study had chronic and severe ear disease, further studies are required to determine if surgical intervention earlier in the disease process could result in a lower complication rate.

Endoscope and image-guided ventral bulla osteotomy in the dog: A cadaveric and patient study

BACKGROUND

Surgery of the bulla in the dog can be difficult and associated with suboptimal resolution of disease and risk of complications, particularly in treatment of cholesteatoma. We explored use of image guidance and endoscopic assistance in ventral bulla osteotomy (VBO), initially with cadaveric studies and subsequently on dogs with cholesteatoma.

METHODS

For surgical approach we used cone beam CT with an optical image navigation system. For endoscopic surgery we used 4 mm and 2.7 mm diameter endoscopes and a camera viewing system, with micro-instruments for dissection.

RESULTS

Image guidance allowed us to accurately identify and approach the bulla in cadavers (n = 2) and patients (n = 2). The endoscope enabled us to define detailed endoscopic anatomy in cadaveric canine heads (n = 15), and in patients (n = 5) it enabled reliable and safe removal of pathological tissue.

CONCLUSION

Image and endoscopic assistance could be a significant advance to the reliability and safety of VBO. Our techniques may be applicable to other indications and species.

3D Printed Biomimetic Rabbit Airway Simulation Model for Nasotracheal Intubation Training

Rabbit inhalation anesthesia by endotracheal intubation involves a higher risk among small animals owing to several anatomical and physiological features, which is pathognomonic to this species of lagomorphs. Rabbit-specific airway devices have been designed to prevent misguided intubation attempts. However, it is believed that expert anesthetic training could be a boon in limiting the aftermaths of this procedure. Our research is aimed to develop a novel biomimetic 3D printed rabbit airway model with representative biomechanical material behavior and radiodensity. Imaging data were collected for two sacrificed rabbit heads using micro-computed tomography (μCT) and micro-magnetic resonance imaging for the first head and cone beam computed tomography (CBCT) for the second head. Imaging-based life-size musculoskeletal airway models were printed using polyjet technology with a combination of hard and soft materials in replicates of three. The models were evaluated quantitatively for dimensional accuracy and radiodensity and qualitatively using digital microscopy and endoscopy for technical, tactic, and visual realism. The results displayed that simulation models printed with polyjet technology have an overall surface representation of 93% for μCT-based images and 97% for CBCT-based images within a range of 0.0-2.5 mm, with μCT showing a more detailed reproduction of the nasotracheal anatomy. Dimensional discrepancies can be caused due to inadequate support material removal and due to the limited reconstruction of microstructures from the imaging on the 3D printed model. The model showed a significant difference in radiodensities in hard and soft tissue regions. Endoscopic evaluation provided good visual and tactile feedback, comparable to the real animal. Overall, the model, being a practical low-cost simulator, comprehensively accelerates the learning curve of veterinary nasotracheal intubation and paves the way for 3D simulation-based image-guided interventional procedures.

Injection techniques for auricular nerve blocks in the rabbit cadaver

OBJECTIVE

To describe the landmarks for localization and to determine the methodology and volume of methylene blue dye to adequately stain the auricular nerves in rabbit cadavers.

STUDY DESIGN

Prospective, randomized, cadaveric study.

ANIMALS

A total of 26 rabbit cadavers (Dutch-Belted and New Zealand White breeds).

METHODS

Part I: anatomical dissections were performed to identify the sensory auricular nerves and to establish the ideal injection approach and volume of dye required for nerve staining. Part II: a single injection technique using 0.1 mL kg^-1 dye was evaluated for staining the greater auricular nerve and two techniques (perpendicular and angled needle approaches) using 0.075 mL kg^-1 dye were evaluated for the auriculotemporal nerve. Dye spread was evaluated through cadaveric dissections and nerve staining graded using a 0-2 point scale. Injections were considered successful if the nerve was stained circumferentially. Cadavers were assessed for staining of the mandibular nerve owing to the close proximity to the auriculotemporal nerve. Fisher's exact test and mixed effects logistic regression model were used for statistical analysis.

RESULTS

The greater auricular nerve was stained in 24/27 (88.9%) injections. The auriculotemporal nerve was stained in 7/12 injections (58.3%) with the perpendicular needle approach; staining success increased to 80% (12/15 injections) with the angled needle approach; however, this difference was not statistically significant (p = 0.228). Mandibular nerve staining occurred on seven auriculotemporal injections with no statistically significant difference in the incidence of nerve staining between techniques.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that the auricular nerves in rabbit cadavers can be successfully located and stained using anatomic landmarks and the described injection techniques.

Lop-eared rabbits have more aural and dental problems than erect-eared rabbits: a rescue population study

This research aimed to assess whether rabbits having lop ears, an artificially selected conformation, compromises welfare. We investigated the occurrence of aural and dental pathology in lop-eared compared with erect-eared rabbits. Thirty rabbits (15 lop-eared and 15 erect-eared) from a rabbit-only rescue shelter were examined. An otoscope was used to visualise the ear canals and mouth. Samples were taken from each ear to examine for mites, bacteria and yeast. Medical records were also examined. Lop-eared rabbits showed statistically significantly more frequent ear canal stenosis, higher scores of cerumen and erythema and more frequent potential pain response during ear examination, compared with erect-eared rabbits. We also found statistically significantly more frequent incisor pathology, molar overgrowth, molar sharpness, molar spurs and history of veterinary dental treatment in lop-eared compared with erect-eared rabbits. The effect sizes were often large. Age was not statistically significant between the lop-eared and erect-eared rabbit groups. Thus, lop-eared rabbits were at an increased risk of aural and dental pathology in this study. This brings into debate the ethics of breeding and buying lop-eared rabbits, as they are more likely to suffer conditions that negatively impact welfare, such as pain, and potentially deafness and difficulty eating.

What Makes a Rabbit Cute? Preference for Rabbit Faces Differs according to Skull Morphology and Demographic Factors

Domesticated rabbits typically exhibit shorter, flatter skulls than their wild counterparts (brachycephalism). However, brachycephaly is associated with considerable health problems, including problems with dentition. The aim of this study was to establish which type of rabbit face people prefer, with a particular emphasis on skull morphology and brachycephaly. We grouped 25 images of rabbit faces by cephalic degree based on ratings assigned by 134 veterinary professionals. An online questionnaire was then launched, in which people could rate each of the 25 images according to preference for the rabbits' faces, and a total of 20,858 questionnaires were completed globally. Repeated-measure, multi-level general linear modelling revealed mildly-brachycephalic rabbits to be the most preferred type of rabbit, and moderately-dolichocephalic (longer skulled) rabbits to be the least preferred. The preference for brachycephalic rabbits was stable across continents, and as such it is highly plausible that human preference has been a driver for the shortening of the skull typically seen in domestic rabbits, perhaps as a result of the 'baby-schema'. Additional features of rabbit faces that were preferred include a soft, medium-light fur appearance and being generally short-furred. These novel insights may prove useful in the improvement of the public understanding of rabbit health and welfare. The relationship between preference and skull shape is particularly pertinent to future work concerning rabbit health, given the cross-species evidence that having a flat face is associated with chronic health conditions.

Computed tomographic grading of middle ear disease in domestic rabbits (Oryctolagus cuniculi)

Ear disease, involving the middle and external ear, is commonly reported in pet rabbits, with lop-eared breeds predisposed. CT is the most reliable imaging modality for identifying otitis media (OM) in rabbits. This study aimed to develop a CT-based grading scale to classify the severity of CT changes in rabbits with presumed OM. Three observers independently reviewed CT images of 36 rabbits with OM. For both OM and material within the external ear canal, a grade of I to IV was used, (I=mild, IV=severe disease) and the level of agreement between reviewers was statistically evaluated. The study demonstrated that grades from the three reviewers showed a strong level of interobserver agreement. Comparisons between clinical signs and CT grade were also evaluated. Rabbits with grade IV OM had a high grade of material in the external ear canal. A high proportion of rabbits (83 per cent) underwent CT scanning conscious, demonstrating that diagnostic quality CT images are achievable without the need for anaesthetic intervention, minimising patient risk. This novel CT-based grading scale provides a methodology to correlate grade of disease with clinical signs, ear canal cytology, predisposing factors, treatment options and outcomes for rabbits with ear disease.

Surgical Treatment of Facial Abscesses and Facial Surgery in Pet Rabbits

Odontogenic facial abscesses associated with periapical infections and osteomyelitis of the jaw represent an important part of the acquired and progressive dental disease syndrome in pet rabbits. Complications such as retromasseteric and retrobulbar abscesses, extensive osteomyelitis of the mandible, and empyemas of the skull are possible sequelae. Standard and advanced diagnostic imaging should be pursued to make a detailed and proper diagnosis, and plan the most effective surgical treatment. This article reviews the surgical anatomy, the pathophysiology, and the classification of abscesses and empyemas of the mandible, the maxilla, and the skull. It also discusses surgical techniques for facial abscesses.

Surgical Management of Ear Diseases in Rabbits

Otitis externa and media are frequently diagnosed disorders in rabbits and are particularly common in lop-eared breeds because of the specific anatomy of the ear canal. Medical management for otitis externa and media often provides only a temporary improvement in clinical signs. Surgery by means of partial or total ear canal ablation (PECA or TECA) combined with lateral bulla osteotomy (LBO) represents a feasible approach that is well tolerated and provides a good clinical outcome. Short-term complications associated with PECA/TECA-LBO include facial nerve paralysis and vestibular disease.

Diagnosis and surgical treatment of a malignant trichoepithelioma of the ear canal in a pet rabbit (Oryctolagus cuniculus)

CASE DESCRIPTION

A 10-year-old spayed female Holland Lop-mix pet rabbit (Oryctolagus cuniculus) was evaluated because of purulent-hemorrhagic discharge from the right ear canal and a suspected mass within that ear canal.

CLINICAL FINDINGS

Results of contrast-enhanced CT, video otoscopy, and histologic examination of endoscopic tissue biopsy samples indicated severe otitis media and externa and a benign trichoepithelioma of the right ear canal.

TREATMENT AND OUTCOME

Total ear canal ablation and lateral bulla osteotomy were performed. Histologic examination of a surgical biopsy sample of the mass indicated malignant trichoepithelioma. Tumor recurrence was detected 22 weeks after surgery. The rabbit was euthanized 33 weeks after surgery because of the large size of the recurrent tumor and declining quality of life. Necropsy findings indicated a malignant trichoepithelioma with local and lymphatic invasion into the right mandibular lymph node.

CLINICAL RELEVANCE

This was the first report of the clinical diagnosis, surgical treatment, and outcome for a domestic rabbit with a diagnosis of a malignant trichoepithelioma of the ear canal and associated otitis media and externa. Neoplasia should be included as a differential diagnosis for pet rabbits with otitis externa and media. Although such tumors are typically benign, trichoepitheliomas in rabbits can be malignant. Computed tomography and histologic examination of tissue samples were useful diagnostic techniques, but histologic examination of an endoscopic biopsy sample did not allow identification of malignant characteristics of the trichoepithelioma.