Total ear canal ablation and lateral bulla osteotomy for treatment of otitis externa and media in a rabbit

Lateral ear canal resection and bulla osteotomy with marsupialization to treat otitis media in rabbits: forty-eight procedures

OBJECTIVE

Describe lateral ear canal resection and bulla osteotomy with marsupialization (LECARBOM) in rabbits with otitis media (OM), and report outcomes, complications, bacteria cultured from middle ears, and their antimicrobial susceptibility testing (AST) results.

STUDY DESIGN

Retrospective clinical case series; single referral hospital.

ANIMALS

Forty-two rabbits with naturally occurring OM.

METHODS

Medical records (2011-2021) of rabbits with CT-confirmed OM undergoing surgery were reviewed for outcomes, complications, bacteria cultured from middle ears, and AST.

RESULTS

Surgery was performed on 48 ears, and outcomes determined 21 days postoperatively. All rabbits survived the procedure. Otitis externa resolved in all lop-eared rabbits. Of 29 ears with OM-associated head tilt, eight (28%) resolved, nine (31%) improved, seven (24%) remained unchanged and five (17%) worsened. Outcome was not associated with head tilt duration nor OM severity. Postoperative complications occurred in 12 (25%) cases, seven of which had wound margin dehiscence that healed by 21 days. The most frequent bacteria isolated were Pasteurella multocida (16%), Bordetella bronchiseptica (14%) and Staphylococcus aureus (14%). Bacteria were sensitive to azithromycin, marbofloxacin or enrofloxacin and resistant to penicillin.

CONCLUSION

LECARBOM is a well-tolerated surgical procedure to treat OM. It also improved or stabilized 83% of cases with head tilt and resolved all cases with otitis externa.

CLINICAL SIGNIFICANCE

LECARBOM with administration of an AST-sensitive antibiotic, or azithromycin when no AST is performed, should be effective in rabbits with OM. Postsurgically, it resolves or alleviates most secondary conditions such as otitis externa, head tilt and facial nerve paralysis.

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.

TOTAL EAR CANAL ABLATION AND LATERAL BULLA OSTEOTOMY (TECA-LBO) IN ATLANTIC HARBOR SEALS (PHOCA VITULINA CONCOLOR) FOR SUCCESSFUL SURGICAL MANAGEMENT OF OTITIS MEDIA

Chronic, severe otitis media was diagnosed in four Atlantic harbor seals (Phoca vitulina concolor), three of which were stranded animals undergoing rehabilitation. All seals presented with unilateral purulent aural discharge that would intermittently recur despite prolonged topical and systemic antimicrobial therapy. Aerobic culture from aural discharge isolated multidrug-resistant organisms in all seals, including Pseudomonas aeruginosa, Staphylococcus pseudintermedius, Klebsiella pneumoniae, and/or Enterococcus faecalis. Computed tomography was used in three cases to confirm otitis media and positive contrast ear canalography was used in one case to confirm tympanic membrane rupture. Given the persistent nature of otitis, surgical intervention in the form of a total ear canal ablation and lateral bulla osteotomy (TECA-LBO) was indicated. Surgery was successful in achieving complete clinical resolution of otitis in all seals. Postoperative complications included temporary unilateral paralysis of the left nare (2/4) and a transient left ptosis (1/4). Partial to complete surgical site dehiscence occurred in all cases; however, complete healing was achieved by second intention in 60 d or less. One rehabilitated seal was fitted with a satellite tag that confirmed normal swimming and diving patterns post release. In harbor seals, TECA-LBO can be performed safely to treat persistent cases of otitis media and should be considered in cases of chronic otitis that are not responsive to medical management.

A Pharmacokinetic-Pharmacodynamic Study of Intravenous Midazolam and Flumazenil in Adult New Zealand White-Californian Rabbits (Oryctolagus cuniculus)

Flumazenil, a competitive GABAA receptor antagonist, is commonly used in rabbits to shorten sedation or postanesthetic recovery after benzodiazepine administration. However, no combined pharmacokinetic (PK) and pharmacodynamic (PD) data are available to guide its administration in this species. In a prospective, randomized, blinded, crossover study design, the efficacy of IV flumazenil (FLU; 0.05 mg/kg) or saline control (SAL; equal volume) to reverse the loss of righting reflex (LORR) induced by IV midazolam (1.2 mg/kg) was investigated in 15 New Zealand white rabbits (2.73 to 4.65 kg, 1 y old). Rabbits were instrumented with arterial (central auricular artery) and venous (marginal auricular vein) catheters. After baseline blood sampling, IV midazolam was injected (T0). Flumazenil or saline (FLU/SAL) was injected 30 s after LORR. Arterial blood samples were collected at 1 and 3 min after midazolam injection, and at 1, 3, 6, 10, 15, 21, 28, 36, 45 and 60 min after injection with flumazenil. Plasma samples for midazolam, 1-OH-midazolam and flumazenil were analyzed using high performance liquid chromatography-high-resolution mass spectrometry and the time to return of righting reflex (ReRR) was compared between groups (Wilcoxon test). FLU terminal half-life, plasma clearance and volume of distribution were 26.3 min [95%CI: 23.3 to 29.3], 18.74 mL/min/kg [16.47 to 21.00] and 0.63 L/kg [0.55 to 0.71], respectively. ReRR was 25 times faster in rabbits treated with FLU (23 [8 to 44] s) compared with SAL (576 [130 to 1141] s; 95%CI [425 to 914 s]). Return of sedation (lateral recumbency) occurred in both groups (7/13 in FLU; 12/13 in SAL) with return of LORR in a few animals (4/13 in FLU; 7/13 in SAL) at 1540 [858 to 2328] s. In the population and anesthesia protocol studied, flumazenil quickly and reliably reversed sedation induced by midazolam injection. However, the potential return of sedation after flumazenil administration warrants careful monitoring in the recovery period.

Efficacy of greater auricular and auriculotemporal nerve blocks performed in rabbits

OBJECTIVE

To evaluate the efficacy, duration and safety of greater auricular and auriculotemporal nerve blocks in rabbits.

STUDY DESIGN

Prospective, randomized, crossover, experimental study.

ANIMALS

A total of 11 healthy adult Dutch-belted rabbits.

METHODS

The rabbits underwent general anesthesia and injections of the greater auricular and auriculotemporal nerves using either bupivacaine (0.3 mL kg^-1, 0.5%) or the same volume of saline. After anesthesia, the efficacy and duration of nerve blocks were assessed using analgesiometry forceps on the pinna and cotton-tipped applicators within the vertical ear canal. Rabbits were monitored for abnormal carriage of the ear and auriculopalpebral nerve block of the ipsilateral eye. Body weight, food intake, fecal output and fecal pellet diameter were measured daily for 6 days after the nerve blocks were performed and compared with baseline to assess short-term effects.

RESULTS

The greater auricular nerve was successfully blocked in 12/16 (75%) ears for mean ± standard deviation duration of 88 ± 52 minutes. In successfully blocked ears, altered ear position was noted in five/16 (31%) cases. The auriculotemporal nerve was blocked in one/16 ears for 120 minutes. The auriculopalpebral nerve was inadvertently blocked in three/16 ears. Food intake and fecal output decreased significantly during the treatment day but returned to pretreatment values after 24 hours. There was no change in body weight or fecal pellet diameter for either treatment.

CONCLUSIONS AND CLINICAL RELEVANCE

The results suggest that duration of the greater auricular nerve block with 0.5% bupivacaine was short-lived in the live rabbit. Auriculotemporal nerve block was only achieved in one ear; therefore, further studies are warranted to evaluate the contribution of these blocks in the pain management of rabbits undergoing auricular surgery.

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.

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.