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Ear surgery in rabbits Charly PIGNON, DVM, Dip ECZM (Small Mammal)Clinical Associate ProfessorHead of the Exotics Medicine ServiceAlfort Teaching HospitalEcole Nationale Vétérinaire d‘Alfort, 7 Avenue du Général de Gaulle, 94700 Maisons-Alfort, Francecharly.pignon@vet-alfort.frEars are an important organ and an anatomical characteristic of rabbits. In his artificial selection work, man has created rabbits with larger ears than the wild rabbits (Belgium hare breed), with very small ears (dwarf Polish breed), or even droopy ears (lop breeds). They can represent up to 12% of the surface of the body in some breeds.The rabbits’ ears allow them to perceive the finest sounds and to anticipate the aggression of predators. Rabbits don’t have sweat glands and cannot thermo regulate by sweating or panting, as dogs do. Ears play a major role in the thermoregulation (1) of the rabbit, their important vascularity allowing them to evacuate excessive heat by a counter current system.Anatomy The ear comprises three parts (2). The outer ear consists of the pinna and the ear canal, which extends distally to the tympanic membrane. The ear cartilage is the supporting structure of the pinna and gives its shape. Unlike in dogs, the ear canal is does not consist of a vertical and a horizontal portion. The shape of the ear canal in rabbits is like a J and there is no histological difference between the vertical and the curved part of the ear canal. The first part of the ear canal’s shape (vertical part) is given by the tragus, the helix and the scutiform cartilage and the second part (curved), by the annular cartilage. The arterial network of the pinna comes from the caudal auricular artery, branch of the external carotid artery. It divides successively to give lateral, intermediate and medial auricular branches. These branches feed the outer face of the pinna. The superficial temporal artery, also derived from the external carotid artery, gives rise to the rostral atrial artery that supplies the rostral part of the pinna. The venous network is satellite of the arterial network, the rostral atrial vein emerges in the superficial temporal vein and the caudal auricular vein flows into the maxillary vein.The tympanic membrane of rabbits is elliptical and consists of distinct portions, the larger pars tensa located ventrally and the smaller pars flaccida located dorsally. It is located just deep to the annular cartilage making it difficult to visualize in upright-eared breeds and impossible in lop-eared breeds, without sedation or general anesthesia. The tympanic bulla is proportionally larger in rabbits compared with dogs and cats. The bone is thicker on the lateral and rostral aspects of the bullae and thinner ventrally. The facial nerve lies very close to the tympanic bulla (1, 2). The nerve enters the facial canal on the medial aspect of the bulla and exits the skull immediately caudal to the bulla, through the stylomastoid foramen coursing along the ventral surface of the tympanic bullae.The inner ear is at the level of the petrous part of the temporal bone. It includes the cochlear and vestibular apparatus. The bony labyrinth consists of the semicircular ducts, the cochlea, the utricle and the vestibule. The bony walls delimit a space filled with a liquid called perilymph, and a membrane within this space forms the membranous labyrinth, which contains the endolymph. The vestibular apparatus comprises the semicircular ducts connected to the utricle by the ampoulea, and then to the saccule. The vestibular ramp communicates with the cochlear ramp by a foramen called helicotrema. The organ of Corti, located along the cochlea canal, is the organ that allows the transformation of the vibrations transmitted by the fluid of the inner ear into electrical information transmitted to the branch of the vestibulo-cochlear nerve (nerve VIII).OtectomyIndicationsRabbits’ ear can be seriously injured during a fight between mates, followed by bites. Lacerations of the ear are possible following an ear stuck in the cage of the animal. If the cartilage is severely affected or if the loss of skin is too great, an otectomy has to be considered. Some cases of serious frostbite have also been reported in animals living outside. In this case, the purpose of the otectomy is to prevent any spread of necrosis. The presence of a tumor is also an indication for an otectomy. Squamous cell carcinoma and lymphoma have also been described in laboratory rabbit.Surgical Technique To perform an otectomy, also called pinnectomy, the animal is anesthetized, then the ear is totally shaved (3). The cutaneous incision is previously marked with a marker to ensure a harmonious contour of the ear. The ear is surgically prepared. The vascularization of the ear can be visualized using a transilluminator. It is possible to mark the ear vessels with a marker to prevent any accidental section of these during the surgery. To prevent bleeding, ligations of the most important vessels are performed using a PDS 4.0. The skin is incised on each side following the predefined line. The cutaneous bleeding is stopped by pressure gauze soaked with a few drops of adrenaline. The skin is dissected five millimeters to the base of the ear to separate it from the cartilage. The cartilage is cut five millimeters back from the skin using scissors. The skin is then sutured using an interrupted pattern with PDS 3.0.Post-operative caresA bandage is made to protect the sutures. Gauzes are rolled on themselves and placed inside the ear. The ear is "wrapped" around the gauzes. A band of gauze outside of the pinna sticks the ear on the gauzes, these are fixed by a tape.The animal is discharged under analgesic (meloxicam 1mg / kg / 12h for one week). A wound check and a bandage change are performed on day 7 and day 14. The stitches are removed on day 14 if they have not plicationsThe wound can dehisce if the cartilage has not been shortened enough from the skin. In this case, the cartilage expresses too much pressure on the surgical wound which prevent good healing.Ear hematomaEtiologyThe othematoma or ear hematoma seems infrequent in the rabbit (4). The cause is most often due to self-injury when the animal scratches or shakes his ears. The underlying causes may be an inflammatory process, a parasitic infection, a foreign body. These causes must be treated to avoid any recurrence. The hematoma usually appears on the inner surface of the ear.The branches of the caudal auricular artery that penetrates inside the cartilage are often the source of the bleeding. Bleeding continues as long as there is no pressure balance between blood pressure and pressure within the hematoma. This painful process causes an increase in pruritus, the animal shakes more and more ears which increases the pressure in the hematoma and eventually stop the bleeding. The mature hematoma, fibrin is lysed leading to the formation of a sero-hemorrhagic fluid. If the othematoma is not treated, it can lead to thickening and significant deformation of the ear.Surgical TechniqueOn an anesthetized animal, the ears are shaved and then surgically prepared (3, 4). The blood vessels are spotted with a transilluminator and marked. The skin on the side of the hematoma is incised along its entire length. Sero-hemorrhagic fluid and fibrin are removed. The inside of the wound is rinsed with warm saline fluid. If needed, a flap of skin is excised along the incision so that the edges can properly face each other when they are affixed to the cartilage. Single points crossing the ear from side to side are made using a wide diameter non resorbable sutures (2.0). The stiches are made parallel to the major axis of the ear over the entire area that has been separated from the cartilage. The incised skin is left open in order to drain any new collections.Post-operative caresA bandage similar to that used during the otectomy is made. The bandage is changed daily until there is no more sero-hemorrhagic fluid production and then the bandage is changed every 3 days. The bandage and the stitches are removed 14 days after the plicationsA perforation of the vessels of the ear can happen when the stiches are placed. If the underlying cause of the othematoma has not been treated or if the number of stiches is not enough to be able to flatten the skin on the cartilage, then, the othematoma may recur.Partial resection of the ear canalIndicationsAblation of the first portion of the ear canal is indicated for external otitis not responding to medical treatment, particularly in the case of severe ear infections with an important accumulation of pus which is often difficult to extract (5). The diagnosis of otitis externa is made using an otoscope or an endoscope. Because of their particular anatomy, lop breeds have more chance to develop this kind of complication. Indeed, in these rabbits, the auricular pinna is obstructing the opening of the ear canal, the air circulation and the evacuation of cerumen is more difficult. The presence of mass (neoplasia) obstructing the auditory canal may also require the completion of this surgery.Surgical Technique (6, 7)The rabbit is anesthetized and placed in lateral decubitus. The base of the ear is shaved just behind the lateral cantus of the eye and up to the end of the pinna. This area is prepared aseptically. A surgical drape is placed in order to have access to the opening of the ear canal, as well as to the base of the ear. Two parallel skin incisions are made from the base of the ear along the long axis of the pinna. The subcutaneous tissues of this flap are dissected, separated from the cartilage and then pulled back rostrally. Scissors are used to create two parallel incisions of the ear canal thus cutting the scutiform cartilage. Special attention is paid to avoid cutting the rostral and caudal auricular vein during this step. The cartilage flap is repulsed rostrally, then incised at its base at the opening of the vertical part of the ear canal. The curved part of the ear canal is then highlighted by the visualization of the annular cartilage. The cutaneous flap is then incised and removed. The skin as well as the subcutaneous tissue are sutured with some PDS 4.0 at the edge of the annular cartilage marking the opening of the equivalent of the horizontal canal. The remaining ear canal is then cleaned and rinsed with warm saline of its purulent debris. The free edge of the vertical portion of the ear remaining canal is sutured to the skin using single interrupted pattern with the same suture than previously. During this step, it is important to check that the remaining part of the scutiform cartilage does not exert too much tension on the sutures. If necessary, it is dissected, and a thin flap is removed. At the end of the surgery, the basis of the ear canal (the curved part of the J) is in direct communication with the external environment, reducing the accumulation of debris and thus allowing easier plicationsThe wound facing the cartilage can dehisced if it has not been cut short enough and exerts too much pressure on the sutures. There is a risk of hemorrhage if the rostral or caudal auricular veins are punctured. If pressure hemostasis is not possible, ligation of these vessels may result in necrosis of the ear. Therefore pressure, or the use of hemostatic sponges should be preferred.Postoperative caresPostoperative care consists of analgesia, systemic and local antibiotic therapy. The remaining part of the ear canal is rinsed using a fine syringe to remove the crusts and the remaining pus.The animal needs to be seen in consultation one week after surgery to check the healing of the surgical wound and to remove, after moistening with warm saline, the accumulation of crusts around the sutures. The sutures can be removed 2 weeks after the surgery if they have not resorbed themselves.Ear canal ablation and lateral bulla osteotomyIndicationsOtitis externa can progress and reach the middle ear. The other etiology of a middle ear infection is a contamination of the tympanic bulla from the upper respiratory system through the eustachian tube. This infection includes the eardrum and the tympanic bulla. Otitis media is considered very painful for rabbits like for other animals. The complaint could be only depression and anorexia. Palpation of the base of the ear may indicate acute pain. Rabbits could present a vestibular syndrome (meaning that the inner ear is also affected) that is not always the case. The diagnosis of otitis media could be made by endoscopic examination. In this case, the tympanic membrane is visualized with by transparency pus seen in the tympanic bulla. The tympanic membrane could also be ruptured and direct visualization of pus in the tympanic bulla could be seen. But sometime, because of the thickness of the pus, and the inflammation of the ear canal, this examination is sometime impossible. A CT scan of the skull is the diagnostic of choice to allow the visualization of the bulla (8). Medical treatment is often disappointing, requiring the use of surgery to treat otitis media.Surgical Technique: Partial Eran Canal Ablation and Bulla osteotomy (PECALBO) (7, 9)As this is a painful surgery, a proper analgesic protocol must be performed. The use of a continuous rate infusion of fentanyl, lidocaine and ketamine usually provide a suitable analgesia.The animal is anesthetized and placed in lateral decubitus. The base of the ear is shaved and surgically prepared. The beginning of the surgery technique follows the previously technique of the partial resection of the ear canal, up to the exposure of the curved part of the J shape ear canal. Then, the remaining part of the ear canal is dissected minutely until it joins the tympanic bulla. This operation requires patience and skill because the facial nerve, the rostral and caudal auricular arteries and veins run in this area. It is recommended to use lone star retractors? in order to retract the skin and to facilitate the visualization of the tissues to dissect. The remaining part the auditory canal is separated at its base. The acoustic meatus is visualized and enlarged by performing an osteotomy using a fine bone rongeur forceps. Once the tympanic bulla has been sufficiently opened, it is gently cleaned with a fine Volkmann curette to remove as much pus as possible. The tympanic bulla is then gently flushed with warm saline. The cutaneous and subcutaneous tissue surrounding the vertical part of the ear canal is then sutured with interrupted pattern (PDS 4.0). Tissues surrounding the opening of the tympanic bulla are marsupialized with interrupted pattern (PDS 4.0).Alternative Surgical techniquesClosed surgical wound Another slightly PECALBO technique was described (10). In this case series, the surgeon made a single cutaneous vertical incision over the base of the ear canal. The surgical technique is then the same than presented previously up to the flush of the tympanic bulla. But after the stage, the tissues over the bulla are closed with resorbable sutures. The mucosa of the distal incision in the ear canal is closed with a resorbable suture ensuring the mucosa was accurately apposed. A single, horizontal mattress suture is placed across the incised cartilage of the vertical canal to close it. The remaining soft tissues are opposed, and the skin is closed using a subcuticular pattern. The main difference with the previously described technique is that the skin is closed on the surgical site. According to the literature in dogs and cats, the main complication is a dehiscence of the surgical wound due to some remaining infected tissues left in the surgical site (11). It realistically very complicated in rabbits to be sure to remove all the affected tissue when doing an ear canal surgery. The risk of having some remaining infected tissue is high. Some authors recommend to place polymethylmethacrylate (PMMA) beads mixed with antibiotics (12) but because the result of the culture and the sensitivity is taking days to be released after the surgery, there is a possibility that bacteria could be resistant to the selected antibiotic. By using a marsupialization and flushing the wound daily, anaerobes bacteria could be killed, and the flush can mechanically clean the wound from debris. Total Era Canal Ablation and Lateral Bulla Osteotomy (TECALBO)Some authors described a total ear canal ablation technique in addition to the lateral bulla osteotomy similar to what was described in dogs and cats (11, 13). AT-shaped skin incision is made with the horizontal component parallel and ventral to the dorsal edge of the tragus. A vertical incision is made from the midpoint of the horizontal incision extending ventral to the right tympanic bulla. The horizontal incision was extended circumferentially around the opening of the external ear canal. Loose connective tissue is bluntly dissected until the lateral aspect of the vertical canal was exposed. The cartilage of the acoustic meatus and the scutiform cartilage are dissected from surrounding tissues. The canal attachment to the bony acoustic duct is excised, and the entire external ear canal with cartilage plates is removed. Soft tissues are bluntly dissected and elevated from the tympanic bulla. Lempert rongeurs are used to remove the lateral aspect of the bony acoustic duct and to perform an osteotomy at the lateral aspect of the bulla. Cotton-tipped applicators and a curette are used to remove the caseous debris and epithelial lining within the bulla. PMMA beads are mixed with antibiotics are placed together in the bulla and surrounding soft tissues to fill the surgically created dead space. The subcutaneous and subcuticular layers are closed with 3-0 polydioxanone suture in a simple continuous pattern. This technique is more invasive than the previous one which leads to the risk of more traumatize on the surrounding tissues such as blood vessels, and nerves. It also increases the difficulty to manage medically the pain. In non-lop breed, the total ablation of the ear canal could also induce a pending ear after the surgery. Another main difference is that the surgical wound is closed at the end of the surgery with the same limitation than discussed previously.Post-operative caresPain treatment must be continued and reevaluated daily until the animal eats by himself. The continuous perfusion of fentanyl, lidocaine, ketamine is gradually decreased during one to two days, and if the animal is comfortable, a relay could be performed with buprenorphine. In addition, the animal receives some meloxicam. Waiting for the result of the culture and sensitivity, wide spectrum of antibiotics (Penicillin SC, azithromycin PO) are provided. The surgical wound is gently flushed with saline twice daily. The average time of hospitalization is 3 days (14). The rabbit is discharged, under pain medication, antibiotics and surgical wound flush, only when he is able to eat by himself and he is comfortable. Weekly recheck are made to monitor the surgical wound plicationsMultiple complications are described after this type of surgery. It is important to take the time to discuss with the owner about this point. The risks related to this surgery are a lesion of the facial nerve, leading to a hemiparalysis of the face, a lesion of the vestibular apparatus during the curettage of the tympanic bulla leading to a vestibular syndrome and hemorrhage by lesion of the rostral veins or auricular arteries leading to a necrosis of the ear. If a head tilt is already present, there is also a risk that the head tilt does not fully improved or do not improve at all. In the author experience, longer the delay between the beginning of the clinical signs and the surgery is, less likely the animal is to fully recover from his head tilt. Overall, the rate of complication is lower than in dogs (14). Ventral bulla osteotomy (VBO) (15, 16)The indication for a VBO is an otitis media without otitis externa, and with no osteolysis of the tympanic bulla. A VBO is performed in dorsal recumbency with the neck fully extended. Because of the presence of a prominent semicircular mandibular angle in rabbits, the bulla cannot be directly palpated until the overlying muscles are partially dissected. A 4–5 cm skin incision is made parallel and medial to the mandible. The incision is continued through the platysma muscle medial to the mandibular salivary gland. The digastricus muscle is dissected from the hyoglossus and styloglossus muscles taking care to avoid the hypoglossal nerve coursing lateral to the hyoglossus muscle. Lone star retractors are used to provide exposure of underlying tissues throughout the procedure. The bulla is palpated between the jugular process of the skull and mandibular angle. Using a Freer periosteal elevator, blunt dissection is continued until the ventral surface of the bulla is exposed. The bulla is entered on the ventral aspect with a Steinmann pin and hand chuck. The osteotomy is extended circumferentially with rongeurs or a pneumatic burr to allow adequate access and drainage. The bulla is carefully curetted to remove any debris as well as the epithelium lining the middle ear. Samples for culture and susceptibility and histopathology are obtained as necessary and the site lavaged with sterile saline. Antibiotic-impregnated PMMA beads are placed in the surgical field (16). The surgical site is closed in a routine fashion using 4–0 or smaller absorbable suture material for the muscle and subcutaneous tissue and 4–0 or smaller nonabsorbable suture material for the skin. An alternative to the use of PMMA is to place a drain and to rinse the bulla using the drain (9).Myringotomy (17)In case of otitis media without otitis externa, an endoscopic examination of the tympanic bulla could be performed. Depending to the size of the rabbit, a 5mm otoscope optic, a 2.7mm 30° or a 1.9 mm 30° optic with their operating channel sheath could be used. The external ear canal needs to be thoroughly cleaned and flushed with sterile saline. The tympanic membrane is visualized and is perforated with a myringotomy needle. The content is aspirated and sampled to send for a bacterial culture and sensitivity. Then, the tympanic bulla is flushed with sterile saline. A large incision of the tympanic membrane is often necessary, to allow adequate lavage of debris and exudate from the middle ear. As the rabbits’ pus often present in the middle ear is thick, it could be challenging to fully clean the tympanic bulla during the first procedure. The author recommends repeating this procedure once a week until the tympanic bulla is perfectly clean.References1 O’Malley B; Section four, Rabbits. In: O’Malley. Clinical anatomy and physiology of exotic species, Structure and function of mammals, birds, reptiles, and amphibians. Ed. Elsevier et Saunders WB, Saint Louis. 2005:163-2612 Popesko P., Rajtova V., Jindrich Horak J. A Colour Atlas of Anatomy of Small Laboratory Animals: Volume 1 Rabbit, Guinea pig. Saunders. London 19923 Handerson R., Horne R. Pinna in Slatter Texterbook of small animal surgery section 14: ear.3rd Edition. Saunders. New York. 2002:1737-17464 Manjunatha D, Mahesh V, Ranganath L. Surgical management of aural hematoma in Russian grey giant rabbit. Int J Agric Sc Vet Med 2014;2(3):37–85 Harcour Brown F.: Otitis externa in Textbook of rabbit medicine. Butterworth imprint of Elsevier, Oxford UK. 2002:232-2336 Krahwinkel D. External ear canal in in Slatter Texterbook of small animal surgery section 14: ear. 3rd Edition. Saunders. New York. 2002: p1746-17567 Capello V. Treatment of the otitis externa and media in pet rabbit. Exotics DVM. 2004;6.3:15-218 de Matos R, Ruby J, Van Hatten RA, et al. Computed tomographic features of clinical and subclinical middle ear disease in domestic rabbits (Oryctolagus cuniculus): 88 cases (2007-2014). J Am Vet Med Assoc 2015;246(3):336–343.9 White R. Midle ear in in Slatter Texterbook of small animal surgery section 14: ear. 3rd Edition. Saunders. New York. 2002:1757-176610 Eatwell K, Mancinelli E, Hedley J, et al. Partial ear canal ablation and lateral bulla osteotomy in rabbits. J Small Anim Pract 2013;54(6):325–3011 Smeak D. Management of Complications Associated with Total Ear Canal Ablation and Bulla Osteotomy in Dogs and Cats. Vet Clin Small Anim. 2011;41:981–99412 Chow EP, Benett RA, Whittington JK. Total ear canal ablation and lateral bulla osteotomy for treatment of otitis externa and media in a rabbit, J. Am. Vet. Med. Assoc. 2011;239(2): 228-23213 Chow EP. Surgical management of rabbit ear disease. J Exot Pet Med 2011;20(3):182–714 Pignon C, Hyunh M, Coquelle M, et al. Assessment of tympanic bulla osteotomy for treatment of middle ear disease in 8 domestic rabbits. Proc ICARE 2013. Wiesbaden. 19115 Chow EP, Benett RA, Dustin L. Ventral Bulla Osteotomy for Treatment of Otitis Media in a Rabbit, J. of Exotic Pet Med. 2009;18(4):299-30516 Csomos R., Bosscher G., Mans C., Surgical management of ear disease in rabbits. Vet Clin Exot Anim. 2016;19(1):189–20417 Jekl V, Hauptman K, Knotek Z. Video otoscopy in exotic companion mammals. Vet Clin North Am Exot Anim Pract. 2015;18(3):431–445 ................
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