- Email: [email protected]
Total Ear Canal Ablation and Temporary Bulla Fenestration for Treatment of Otitis Media in a Chinchilla (Chinchilla Laniger)
Accepted Manuscript
Total ear canal ablation and temporary bulla fenestration for treatment of otitis media in a chinchilla (Chinchilla laniger) Kelly Rockwell DVM , Amy Wells DVM, MPVM , Michael Dearmin DVM, MS, Dip. ACVS PII: DOI: Reference:
S1557-5063(18)30251-9 https://doi.org/10.1053/j.jepm.2018.11.005 JEPM 50186
To appear in:
Journal of Exotic Pet Medicine
Received date: Revised date: Accepted date:
20 October 2018 11 November 2018 21 November 2018
Please cite this article as: Kelly Rockwell DVM , Amy Wells DVM, MPVM , Michael Dearmin DVM, MS, Dip. ACVS , Total ear canal ablation and temporary bulla fenestration for treatment of otitis media in a chinchilla (Chinchilla laniger), Journal of Exotic Pet Medicine (2018), doi: https://doi.org/10.1053/j.jepm.2018.11.005
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Case Report Total ear canal ablation and temporary bulla fenestration for treatment of otitis media in a chinchilla (Chinchilla laniger)
From Pet Specialists of Monterey, Monterey, CA.
CR IP T
Kelly Rockwell, DVM, Amy Wells, DVM, MPVM, and Michael Dearmin, DVM, MS, Dip. ACVS
Address Correspondence to: Kelly Rockwell, DVM, School of Veterinary Medicine, Louisiana State University, 1 Skip Bertman Drive, Baton Rouge, LA, USA 70803. E-mail: [email protected].
AN US
Abstract
A 6-year old neutered male chinchilla (Chinchilla laniger) presented for surgical consultation for chronic left-sided otitis externa. A computed tomography (CT) scan showed diffuse soft tissue opacity of the left external canal and tympanic bulla consistent with otitis
M
media associated with concurrent otitis externa. A modified total ear canal ablation and temporary fenestration of the caudodorsal and rostroventral chambers of the bulla was
ED
performed. The patient required a temporary tarsorrhaphy due to post-operative facial nerve
PT
palsy, but otherwise recovered without any complications. The temporary fenestration windows remained open for approximately five weeks which allowed for routine flushing and medicating
CE
with topical antibiotics (based on culture and susceptibility results). Recheck CT scan showed reoccurence of soft tissue opacity within the bulla. Despite diagnostic imaging results, the patient
AC
has shown no return of clinical signs to date. Therefore, this procedure is considered a success and the first published report of this technique being used for this disease in a chinchilla. Chinchillas present a unique surgical challenge due in part to the anatomy of their tympanic bulla.
ACCEPTED MANUSCRIPT
Keywords: Chinchilla; Chinchilla laniger; otitis externa; otitis media; fenestration; computed tomography
CR IP T
This is an original case report.
A 6-year-old neutered male chinchilla (Chinchilla laniger) was referred to Pet Specialists of Monterey (Monterey, CA, USA) for diagnostic imaging and surgical consultation for a sixyear history of chronic otitis externa. As a neonate, his mother was known to chew on his
AN US
external pinnae causing permanent deformation (Figure 1). As a result, the left external ear canal swelled and became impacted with caseous debris when the animal was 10 days old. Warm compressing and surgical debridement of the left ear canal was performed. Additionally,
M
medicated eardrops and systemic antibiotics based on culture and sensitivity results were implemented. Despite therapy, the animal continued to develop reoccurring infections that were
ED
only temporarily resolved with medical management. After a year of treatment, the left ear canal was stenotic and often had to be surgically opened for medicating purposes over the following
PT
five years. The patient became increasingly painful and sensitive post treatment, evidenced by
CE
significant weight loss over a several month period. Based on lack of resolution with medical management and deteriorating clinical appearance, surgical intervention was considered.
AC
On presentation, the chinchilla was in good body condition (5/9), had notably deformed external pinnae (left worse than right) with a completely stenotic left external canal. The right external canal was visibly open and apparently normal. All other systems were apparently normal and the animal was in otherwise good health. Anesthesia was induced and then maintained with isoflurane (IsoFlo; Abbott Laboratories, North Chicago, IL, USA) in oxygen by
ACCEPTED MANUSCRIPT
facemask for imaging purposes. A computed tomography (CT) scan was performed. Diffuse soft tissue opacity of the left external canal and within the tympanic bulla was consistent with otitis media associated with concurrent otitis externa, shown in Figure 2. The left tympanic bulla also had a thickened wall. The right bulla and canal were normal. An intravenous catheter was not
CR IP T
placed and contrast was not administered, as images were diagnostic without this additional tool. One month later, the patient was admitted for surgery. At time of surgery, he weighed 488.0 grams. Buprenorphine (Buprenex; Reckitt Benckiser Pharmaceuticals, Inc, Slough,
Berkshire, UK) (0.04 mg/kg) and midazolam hydrochloride (Midazolam; Hospira, Inc, Lake
AN US
Forest, IL, USA) (0.6 mg/kg) were administered intramuscularly as premedication. Anesthesia was induced and then maintained at a surgical plane with isoflurane in oxygen by facemask. The patient was placed in right lateral recumbency and the surgical area was clipped and scrubbed
M
with chlorhexadine scrub (Hibiclens; Mölnlycke Health Care, Gothenburg, Sweden). An elliptical incision was made around the remaining left pinna. Monopolar electrocautery with
ED
needle tip electrode, blunt, and sharp dissection were used to dissect the muscular attachments away from the ear canal to the level of the horizontal ear canal. This was followed until the bulla
PT
was visualized, Figure 3. The facial nerve was easily visualized and protected during the
CE
surgical procedure. The canal was sharply transected at the level of the bulla and removed. A moderate amount of purulent material was observed within the bulla and removed. Initial
AC
material present within the bulla opening was removed with Frazier suction tip and halstead mosquito hemostats. The lining of the tympanic cavity was removed via gentle elevation and retraction. The incision was extended dorsally to expose the caudodorsal chamber of the tympanic bulla. A 0.062” K-wire was used by hand to establish several holes in the caudodorsal aspect of the bulla region. Micro-Friedman rongeurs were then used to expand the holes and
ACCEPTED MANUSCRIPT
remove the lateral aspects of the caudodorsal bulla to expose each chamber (Figure 4). The area was thoroughly flushed and lavaged with sterile 0.9% sodium chloride irrigation (Baxter Healthcare Corporation, Deerfield, IL, USA). The original incision was then extended ventrally to expose the rostroventral chamber of the bulla and this was fenestrated in similar manner.
CR IP T
Material was removed from each chamber with a combination of mosquito forceps, freer
elevator, house curette, right angle probe, and Frazier suction tip. The area was thoroughly
flushed and lavaged. Skin surrounding the opening left from the horizontal canal was closed over the tympanic bulla using 4-0 polydioxanone suture (PDS, Johnson and Johnson) simple
AN US
continuous. The openings of both the caudodorsal and rostroventral chambers were left open for postoperative flushing and draining, as shown in Figure 5. A post-operative CT scan showed that the majority of the soft tissue opacity was removed from the bulla and that the deep petrous bone
M
of the tympanic bulla was still intact (Figure 6).
The day following surgery, the patient was stable, able to prehend food, and running on a
ED
wheel provided in his cage. He had a diminished blink reflex of the left eye due to presumptive facial nerve palsy. A temporary tarsorrhaphy was performed three days postoperative due to no
PT
improvement in blink reflex. The ear surgical site was warm compressed daily and the bulla was
CE
flushed with sterile saline (VetOne; MWI Animal Health Veterinary Supply Co., Boise, ID, USA) through both the caudodorsal and rostroventral openings. Aerobic culture of samples taken
AC
peri-operatively from the bulla grew Pseudomonas that was only sensitive to amikacin and gentamicin as well as Escherichia coli. The patient was started on topical Gentamicin Sulfate Ophthalmic Solution USP 0.3% (Bausch and Lomb, Bridgewater, NJ, USA) on the open surgical site four times daily for two weeks. Almost three weeks following surgery, the opening to the rostroventral chamber had closed and very minimal discharge was noted. No discharge was seen
ACCEPTED MANUSCRIPT
from the surgical site one month following surgery and only a small opening remained. The tarsorrhaphy was removed at this time and full blink reflex of the left eye was observed. A follow-up CT was performed at a two-month recheck. As shown in Figure 7, radiodense material was present within the left bullae. Due to the chronic nature of this patient’s
CR IP T
disease, it was not expected for the entire cavity to empty and resemble a healthy bulla. The owner reported normal behavior with no clinical signs since the procedure in addition to
significant weight gain. Despite diagnostic imaging findings, as the patient’s signs improved
still alive and showing no clinical signs.
Discussion
AN US
postoperatively, this procedure was considered a success. At time of publication, this patient is
M
Otitis externa is uncommon in chinchillas, and often occurs secondary to otitis media caused by bacterial translocation from the Eustachian tube.1, 2 Predisposing factors of middle ear
ED
disease include dysfunction of the Eustachian tube due to viral or bacterial infections, altered upper respiratory tract flora, insufficient immune response, or concurrent disease.1 The
PT
Eustachian tube connects the oropharynx to a uniquely large and complex tympanic bulla. The
CE
tympanic bullae in chinchillas are divided into ventral and dorsal bulla, which are separated by multiple bony septa. The larger ventral bulla extends rostrally while the dorsal bulla reaches the
AC
inner side of the meatus1, 3. Due to this unique anatomy, multiple approaches into these subchambers of the bulla must be made during surgery in order to flush and remove all debris.3 Otitis media can be diagnosed with a combination of physical exam findings, diagnostic
imaging, and cytological and microbiological sampling of middle ear effusion. Systemic therapy based on culture and sensitivity can be successful, although effusion and inflammation can
ACCEPTED MANUSCRIPT
persist for weeks. Additionally, medical management can be difficult if abscessation has already occurred. As chinchillas have heterophils, which lack myeloperoxidase, the enzyme responsible for liquefying purulent material, they tend to develop thick and caseous abscesses.4 This material is nearly impossible to resolve without surgical debridement.
CR IP T
This case presents a unique presentation of primary otitis externa from trauma with
secondary otitis media. Medical management was unable to prevent progression of the ascending infection, leading to ear canal stenosis and a space-filling mass effect within the tympanic bulla. Surgical intervention was required to completely remove the infected tissue. To prevent post-
AN US
operative abscess formation, temporary fenestration of the bulla was performed to allow for repeated flushing and direct medication application. This is the first published case report of a total ear canal ablation with temporary lateral bulla fenestration in a chinchilla. Total ear canal
M
ablation and bulla osteotomy (TECABO) is more common in dogs than chinchillas or other small exotic mammals, although there has been reported success of the same or similar surgical
ED
techniques in rabbits for treatment of chronic otitis externa and/or media.5, 6 Chronic primary otitis externa in dogs stimulates hyperplasia of the ceruminous glands, which can progress to
PT
stenosis of the external ear canal and development of otitis media. In dogs with end-stage and
CE
non-responsive otitis externa and media, total ear canal ablation with concurrent bulla osteotomy is often indicated to alleviate chronic pain and discomfort.7 As chinchillas more commonly
AC
develop otitis media without otitis externa, this type of surgical approach is often not indicated. However, in this case, it was the appropriate step to alleviate a chronic infection for this patient. Rabbits undergo a similar approach to the TECABO as dogs and cats, however unlike these animals, they only possess a vertical ear canal that contains multiple cartilaginous plates. Unlike chinchillas, they contain a bony duct distal to the tympanic membrane that requires removal as
ACCEPTED MANUSCRIPT
well as a thickened lateral aspect of the tympanic membrane. Similar to chinchillas, they produce caseous exudate that often requires the use of antibiotic-impregnated beads following the procedure to completely eliminate infections.8, 9 Comparitively, in this case, it was opted to leave the surgical site open via temporary lateral fenestration for continual lavage and drainage. This
CR IP T
case report shows the successful use of a modified total ear canal ablation and temporary bulla osteotomy procedure in a chinchilla. Indications for this technique include chronic otitis media with concurrent otitis externa as well as neoplasia.
It is important to note the complications and risks associated with this procedure,
AN US
including facial nerve palsy, Horner’s syndrome, vestibular disease, reoccurrence of infection, and anesthesia-induced complications. Facial nerve palsy results from facial nerve damage or neuropraxia secondary to manipulation during the procedure and is often temporary. Clinical
M
signs include loss of the palpebral reflex and inability to move the muscles of the face and blink. In this case, the patient developed facial nerve palsy despite identification and avoidance of the
ED
facial nerve during the procedure. His clinical signs resolved within one-month. During the procedure, the patient also experienced cardiac arrest on two separate occasions, but was
PT
resuscitated with appropriate administration of emergency medications and chest compressions.
CE
Although preoperative intubation and intravenous catheter placement was not performed in this case, it is worthwhile investing time to perform these prior to invasive, long surgical procedures
AC
to help limit the risk of cardiopulmonary arrest. Exotic patients are typically a higher anesthesia risk, with a reported eight times higher anesthetic and sedation-related death in rabbits than dogs in the United Kingdom.10 Because of this, careful consideration should be made when deciding if a patient is a candidate for this procedure.
ACCEPTED MANUSCRIPT
References 1. Mans C, Donnelly TM. Update on disease of chinchillas. Vet Clin Exot Anim 16:383-406, 2013.
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2. Mans C, Donnelly TM. Disease problems of chinchillas. In Quesenberry KE, Carpenter JW (ed): Ferrets, rabbits, and rodents: clinical medicine and surgery. St Louis, MO, Saunders/Elsevier, 311–25, 2012. 3. Browning GG, Granich MS. Surgical anatomy of the temporal bone in the chinchilla. Ann Otol Rhinol Laryngol 87(6):875-882, 1978 4. Riggs SM, Mitchell MA. Chinchillas. In Mitchell MA, Tully TN (ed): Manual of Exotic Pet Practice. St. Louis, MO, Saunders/Elsevier, 474-492, 2009.
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5. Chow EP, Bennett RA, Whittington JK. Total ear canal ablation and lateral bulla osteotomy for treatment of otitis externa and media in a rabbit. J Am Ve Med Assoc 239(2):228-232, 2011. 6. Eatwell K, Mancinelli E, Hedley J, Keeble E, Kovalik M, Yool DA. Partial ear canal ablation and lateral bulla osteotomy in rabbits. J Small Anim Pract 54(6):325-330, 2013.
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7. Medleau L, Hnilica KA (ed): Small Animal Dermatology, A Color Atlas and Therapeutic Guide. St. Louis, MO, Saunders/Elsevier, 2006. 8. Chow EP. Surgical management of rabbit ear disease. J Exot Pet Med 20(3):182-187, 2011.
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9. Csomos R, Bosscher G, Mans C, Hardie R. Surgical management of ear disease in rabbits. Vet Clin North Am Exot Anim Pract 19(1):189-204, 2016.
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CE
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10. Allweiler SI. How to improve anesthesia and analgesia in small mammals. Vet Clin Exot Anim 19:361-377, 2016.
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ACCEPTED MANUSCRIPT
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Figure 1. Permanent deformation of the left external pinna (arrow) appreciated prior to surgery
AC
CE
PT
ED
M
with surgical field shaved. Cr = cranial, Cd = caudal.
ED
M
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ACCEPTED MANUSCRIPT
PT
Figure 2. Series of axial images from pre-operative CT scan showing extensive soft tissue
CE
opacity and thickened wall of the left (L) tympanic bulla. Right (R) bulla is normal. 1 = most
AC
cranial, 3 = most caudal.
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CR IP T
ACCEPTED MANUSCRIPT
Figure 3. Surgical approach to the left tympanic bulla, denoted by the arrow. The external ear
M
canal and pinna (EC) is almost completely removed, exposing the bulla cavity filled with
AC
CE
PT
ED
purulent discharge. Cr = cranial, Cd = caudal.
AN US
CR IP T
ACCEPTED MANUSCRIPT
Figure 4. The left external canal has been fully removed and the tympanic bulla is exposed (denoted by the arrow). Fenestration of the caudodorsal chamber has been achieved, exposing
AC
CE
PT
ED
M
one of several septa within the chamber (*). Cr = cranial, Cd = caudal.
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ACCEPTED MANUSCRIPT
Figure 5. Post operative image while patient recovers. Total ear canal ablation approach is closed
M
(denoted by the arrow) while temporary fenestration of the caudodorsal (*) and rostroventral (**)
AC
CE
PT
ED
chambers have been left open for draining and medicating purposes. Cr = cranial, Cd = caudal.
AN US
CR IP T
ACCEPTED MANUSCRIPT
M
Figure 6. Immediate postoperative axial CT scan showing a large amount of soft tissue opacity removed from the left (L) bulla while the right (R) remains normal. Note that the patient was
AC
CE
PT
cranial, 2 = most caudal.
ED
placed in right lateral recumbency for CT images while recovering from anesthesia. 1 = most
CE
PT
ED
M
AN US
CR IP T
ACCEPTED MANUSCRIPT
Figure 7. Two month recheck axial CT scan images. A soft tissue opacity is seen within the left
AC
(L) tympanic bulla compared to the unaffected right (R) bulla. Bone removed from the temporary fenestration sites is most apparent in image 2 and 3. As the owner reported no relapse of clinical signs since the procedure, surgery was considered successful despite these findings. 1 = most cranial, 3 = most caudal.
Total ear canal ablation and temporary bulla fenestration for treatment of otitis media in a chinchilla (Chinchilla laniger) Kelly Rockwell DVM , Amy Wells DVM, MPVM , Michael Dearmin DVM, MS, Dip. ACVS PII: DOI: Reference:
S1557-5063(18)30251-9 https://doi.org/10.1053/j.jepm.2018.11.005 JEPM 50186
To appear in:
Journal of Exotic Pet Medicine
Received date: Revised date: Accepted date:
20 October 2018 11 November 2018 21 November 2018
Please cite this article as: Kelly Rockwell DVM , Amy Wells DVM, MPVM , Michael Dearmin DVM, MS, Dip. ACVS , Total ear canal ablation and temporary bulla fenestration for treatment of otitis media in a chinchilla (Chinchilla laniger), Journal of Exotic Pet Medicine (2018), doi: https://doi.org/10.1053/j.jepm.2018.11.005
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Case Report Total ear canal ablation and temporary bulla fenestration for treatment of otitis media in a chinchilla (Chinchilla laniger)
From Pet Specialists of Monterey, Monterey, CA.
CR IP T
Kelly Rockwell, DVM, Amy Wells, DVM, MPVM, and Michael Dearmin, DVM, MS, Dip. ACVS
Address Correspondence to: Kelly Rockwell, DVM, School of Veterinary Medicine, Louisiana State University, 1 Skip Bertman Drive, Baton Rouge, LA, USA 70803. E-mail: [email protected].
AN US
Abstract
A 6-year old neutered male chinchilla (Chinchilla laniger) presented for surgical consultation for chronic left-sided otitis externa. A computed tomography (CT) scan showed diffuse soft tissue opacity of the left external canal and tympanic bulla consistent with otitis
M
media associated with concurrent otitis externa. A modified total ear canal ablation and temporary fenestration of the caudodorsal and rostroventral chambers of the bulla was
ED
performed. The patient required a temporary tarsorrhaphy due to post-operative facial nerve
PT
palsy, but otherwise recovered without any complications. The temporary fenestration windows remained open for approximately five weeks which allowed for routine flushing and medicating
CE
with topical antibiotics (based on culture and susceptibility results). Recheck CT scan showed reoccurence of soft tissue opacity within the bulla. Despite diagnostic imaging results, the patient
AC
has shown no return of clinical signs to date. Therefore, this procedure is considered a success and the first published report of this technique being used for this disease in a chinchilla. Chinchillas present a unique surgical challenge due in part to the anatomy of their tympanic bulla.
ACCEPTED MANUSCRIPT
Keywords: Chinchilla; Chinchilla laniger; otitis externa; otitis media; fenestration; computed tomography
CR IP T
This is an original case report.
A 6-year-old neutered male chinchilla (Chinchilla laniger) was referred to Pet Specialists of Monterey (Monterey, CA, USA) for diagnostic imaging and surgical consultation for a sixyear history of chronic otitis externa. As a neonate, his mother was known to chew on his
AN US
external pinnae causing permanent deformation (Figure 1). As a result, the left external ear canal swelled and became impacted with caseous debris when the animal was 10 days old. Warm compressing and surgical debridement of the left ear canal was performed. Additionally,
M
medicated eardrops and systemic antibiotics based on culture and sensitivity results were implemented. Despite therapy, the animal continued to develop reoccurring infections that were
ED
only temporarily resolved with medical management. After a year of treatment, the left ear canal was stenotic and often had to be surgically opened for medicating purposes over the following
PT
five years. The patient became increasingly painful and sensitive post treatment, evidenced by
CE
significant weight loss over a several month period. Based on lack of resolution with medical management and deteriorating clinical appearance, surgical intervention was considered.
AC
On presentation, the chinchilla was in good body condition (5/9), had notably deformed external pinnae (left worse than right) with a completely stenotic left external canal. The right external canal was visibly open and apparently normal. All other systems were apparently normal and the animal was in otherwise good health. Anesthesia was induced and then maintained with isoflurane (IsoFlo; Abbott Laboratories, North Chicago, IL, USA) in oxygen by
ACCEPTED MANUSCRIPT
facemask for imaging purposes. A computed tomography (CT) scan was performed. Diffuse soft tissue opacity of the left external canal and within the tympanic bulla was consistent with otitis media associated with concurrent otitis externa, shown in Figure 2. The left tympanic bulla also had a thickened wall. The right bulla and canal were normal. An intravenous catheter was not
CR IP T
placed and contrast was not administered, as images were diagnostic without this additional tool. One month later, the patient was admitted for surgery. At time of surgery, he weighed 488.0 grams. Buprenorphine (Buprenex; Reckitt Benckiser Pharmaceuticals, Inc, Slough,
Berkshire, UK) (0.04 mg/kg) and midazolam hydrochloride (Midazolam; Hospira, Inc, Lake
AN US
Forest, IL, USA) (0.6 mg/kg) were administered intramuscularly as premedication. Anesthesia was induced and then maintained at a surgical plane with isoflurane in oxygen by facemask. The patient was placed in right lateral recumbency and the surgical area was clipped and scrubbed
M
with chlorhexadine scrub (Hibiclens; Mölnlycke Health Care, Gothenburg, Sweden). An elliptical incision was made around the remaining left pinna. Monopolar electrocautery with
ED
needle tip electrode, blunt, and sharp dissection were used to dissect the muscular attachments away from the ear canal to the level of the horizontal ear canal. This was followed until the bulla
PT
was visualized, Figure 3. The facial nerve was easily visualized and protected during the
CE
surgical procedure. The canal was sharply transected at the level of the bulla and removed. A moderate amount of purulent material was observed within the bulla and removed. Initial
AC
material present within the bulla opening was removed with Frazier suction tip and halstead mosquito hemostats. The lining of the tympanic cavity was removed via gentle elevation and retraction. The incision was extended dorsally to expose the caudodorsal chamber of the tympanic bulla. A 0.062” K-wire was used by hand to establish several holes in the caudodorsal aspect of the bulla region. Micro-Friedman rongeurs were then used to expand the holes and
ACCEPTED MANUSCRIPT
remove the lateral aspects of the caudodorsal bulla to expose each chamber (Figure 4). The area was thoroughly flushed and lavaged with sterile 0.9% sodium chloride irrigation (Baxter Healthcare Corporation, Deerfield, IL, USA). The original incision was then extended ventrally to expose the rostroventral chamber of the bulla and this was fenestrated in similar manner.
CR IP T
Material was removed from each chamber with a combination of mosquito forceps, freer
elevator, house curette, right angle probe, and Frazier suction tip. The area was thoroughly
flushed and lavaged. Skin surrounding the opening left from the horizontal canal was closed over the tympanic bulla using 4-0 polydioxanone suture (PDS, Johnson and Johnson) simple
AN US
continuous. The openings of both the caudodorsal and rostroventral chambers were left open for postoperative flushing and draining, as shown in Figure 5. A post-operative CT scan showed that the majority of the soft tissue opacity was removed from the bulla and that the deep petrous bone
M
of the tympanic bulla was still intact (Figure 6).
The day following surgery, the patient was stable, able to prehend food, and running on a
ED
wheel provided in his cage. He had a diminished blink reflex of the left eye due to presumptive facial nerve palsy. A temporary tarsorrhaphy was performed three days postoperative due to no
PT
improvement in blink reflex. The ear surgical site was warm compressed daily and the bulla was
CE
flushed with sterile saline (VetOne; MWI Animal Health Veterinary Supply Co., Boise, ID, USA) through both the caudodorsal and rostroventral openings. Aerobic culture of samples taken
AC
peri-operatively from the bulla grew Pseudomonas that was only sensitive to amikacin and gentamicin as well as Escherichia coli. The patient was started on topical Gentamicin Sulfate Ophthalmic Solution USP 0.3% (Bausch and Lomb, Bridgewater, NJ, USA) on the open surgical site four times daily for two weeks. Almost three weeks following surgery, the opening to the rostroventral chamber had closed and very minimal discharge was noted. No discharge was seen
ACCEPTED MANUSCRIPT
from the surgical site one month following surgery and only a small opening remained. The tarsorrhaphy was removed at this time and full blink reflex of the left eye was observed. A follow-up CT was performed at a two-month recheck. As shown in Figure 7, radiodense material was present within the left bullae. Due to the chronic nature of this patient’s
CR IP T
disease, it was not expected for the entire cavity to empty and resemble a healthy bulla. The owner reported normal behavior with no clinical signs since the procedure in addition to
significant weight gain. Despite diagnostic imaging findings, as the patient’s signs improved
still alive and showing no clinical signs.
Discussion
AN US
postoperatively, this procedure was considered a success. At time of publication, this patient is
M
Otitis externa is uncommon in chinchillas, and often occurs secondary to otitis media caused by bacterial translocation from the Eustachian tube.1, 2 Predisposing factors of middle ear
ED
disease include dysfunction of the Eustachian tube due to viral or bacterial infections, altered upper respiratory tract flora, insufficient immune response, or concurrent disease.1 The
PT
Eustachian tube connects the oropharynx to a uniquely large and complex tympanic bulla. The
CE
tympanic bullae in chinchillas are divided into ventral and dorsal bulla, which are separated by multiple bony septa. The larger ventral bulla extends rostrally while the dorsal bulla reaches the
AC
inner side of the meatus1, 3. Due to this unique anatomy, multiple approaches into these subchambers of the bulla must be made during surgery in order to flush and remove all debris.3 Otitis media can be diagnosed with a combination of physical exam findings, diagnostic
imaging, and cytological and microbiological sampling of middle ear effusion. Systemic therapy based on culture and sensitivity can be successful, although effusion and inflammation can
ACCEPTED MANUSCRIPT
persist for weeks. Additionally, medical management can be difficult if abscessation has already occurred. As chinchillas have heterophils, which lack myeloperoxidase, the enzyme responsible for liquefying purulent material, they tend to develop thick and caseous abscesses.4 This material is nearly impossible to resolve without surgical debridement.
CR IP T
This case presents a unique presentation of primary otitis externa from trauma with
secondary otitis media. Medical management was unable to prevent progression of the ascending infection, leading to ear canal stenosis and a space-filling mass effect within the tympanic bulla. Surgical intervention was required to completely remove the infected tissue. To prevent post-
AN US
operative abscess formation, temporary fenestration of the bulla was performed to allow for repeated flushing and direct medication application. This is the first published case report of a total ear canal ablation with temporary lateral bulla fenestration in a chinchilla. Total ear canal
M
ablation and bulla osteotomy (TECABO) is more common in dogs than chinchillas or other small exotic mammals, although there has been reported success of the same or similar surgical
ED
techniques in rabbits for treatment of chronic otitis externa and/or media.5, 6 Chronic primary otitis externa in dogs stimulates hyperplasia of the ceruminous glands, which can progress to
PT
stenosis of the external ear canal and development of otitis media. In dogs with end-stage and
CE
non-responsive otitis externa and media, total ear canal ablation with concurrent bulla osteotomy is often indicated to alleviate chronic pain and discomfort.7 As chinchillas more commonly
AC
develop otitis media without otitis externa, this type of surgical approach is often not indicated. However, in this case, it was the appropriate step to alleviate a chronic infection for this patient. Rabbits undergo a similar approach to the TECABO as dogs and cats, however unlike these animals, they only possess a vertical ear canal that contains multiple cartilaginous plates. Unlike chinchillas, they contain a bony duct distal to the tympanic membrane that requires removal as
ACCEPTED MANUSCRIPT
well as a thickened lateral aspect of the tympanic membrane. Similar to chinchillas, they produce caseous exudate that often requires the use of antibiotic-impregnated beads following the procedure to completely eliminate infections.8, 9 Comparitively, in this case, it was opted to leave the surgical site open via temporary lateral fenestration for continual lavage and drainage. This
CR IP T
case report shows the successful use of a modified total ear canal ablation and temporary bulla osteotomy procedure in a chinchilla. Indications for this technique include chronic otitis media with concurrent otitis externa as well as neoplasia.
It is important to note the complications and risks associated with this procedure,
AN US
including facial nerve palsy, Horner’s syndrome, vestibular disease, reoccurrence of infection, and anesthesia-induced complications. Facial nerve palsy results from facial nerve damage or neuropraxia secondary to manipulation during the procedure and is often temporary. Clinical
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signs include loss of the palpebral reflex and inability to move the muscles of the face and blink. In this case, the patient developed facial nerve palsy despite identification and avoidance of the
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facial nerve during the procedure. His clinical signs resolved within one-month. During the procedure, the patient also experienced cardiac arrest on two separate occasions, but was
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resuscitated with appropriate administration of emergency medications and chest compressions.
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Although preoperative intubation and intravenous catheter placement was not performed in this case, it is worthwhile investing time to perform these prior to invasive, long surgical procedures
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to help limit the risk of cardiopulmonary arrest. Exotic patients are typically a higher anesthesia risk, with a reported eight times higher anesthetic and sedation-related death in rabbits than dogs in the United Kingdom.10 Because of this, careful consideration should be made when deciding if a patient is a candidate for this procedure.
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References 1. Mans C, Donnelly TM. Update on disease of chinchillas. Vet Clin Exot Anim 16:383-406, 2013.
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2. Mans C, Donnelly TM. Disease problems of chinchillas. In Quesenberry KE, Carpenter JW (ed): Ferrets, rabbits, and rodents: clinical medicine and surgery. St Louis, MO, Saunders/Elsevier, 311–25, 2012. 3. Browning GG, Granich MS. Surgical anatomy of the temporal bone in the chinchilla. Ann Otol Rhinol Laryngol 87(6):875-882, 1978 4. Riggs SM, Mitchell MA. Chinchillas. In Mitchell MA, Tully TN (ed): Manual of Exotic Pet Practice. St. Louis, MO, Saunders/Elsevier, 474-492, 2009.
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5. Chow EP, Bennett RA, Whittington JK. Total ear canal ablation and lateral bulla osteotomy for treatment of otitis externa and media in a rabbit. J Am Ve Med Assoc 239(2):228-232, 2011. 6. Eatwell K, Mancinelli E, Hedley J, Keeble E, Kovalik M, Yool DA. Partial ear canal ablation and lateral bulla osteotomy in rabbits. J Small Anim Pract 54(6):325-330, 2013.
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7. Medleau L, Hnilica KA (ed): Small Animal Dermatology, A Color Atlas and Therapeutic Guide. St. Louis, MO, Saunders/Elsevier, 2006. 8. Chow EP. Surgical management of rabbit ear disease. J Exot Pet Med 20(3):182-187, 2011.
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9. Csomos R, Bosscher G, Mans C, Hardie R. Surgical management of ear disease in rabbits. Vet Clin North Am Exot Anim Pract 19(1):189-204, 2016.
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10. Allweiler SI. How to improve anesthesia and analgesia in small mammals. Vet Clin Exot Anim 19:361-377, 2016.
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Figure 1. Permanent deformation of the left external pinna (arrow) appreciated prior to surgery
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with surgical field shaved. Cr = cranial, Cd = caudal.
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Figure 2. Series of axial images from pre-operative CT scan showing extensive soft tissue
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opacity and thickened wall of the left (L) tympanic bulla. Right (R) bulla is normal. 1 = most
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cranial, 3 = most caudal.
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Figure 3. Surgical approach to the left tympanic bulla, denoted by the arrow. The external ear
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canal and pinna (EC) is almost completely removed, exposing the bulla cavity filled with
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purulent discharge. Cr = cranial, Cd = caudal.
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Figure 4. The left external canal has been fully removed and the tympanic bulla is exposed (denoted by the arrow). Fenestration of the caudodorsal chamber has been achieved, exposing
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one of several septa within the chamber (*). Cr = cranial, Cd = caudal.
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Figure 5. Post operative image while patient recovers. Total ear canal ablation approach is closed
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(denoted by the arrow) while temporary fenestration of the caudodorsal (*) and rostroventral (**)
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chambers have been left open for draining and medicating purposes. Cr = cranial, Cd = caudal.
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Figure 6. Immediate postoperative axial CT scan showing a large amount of soft tissue opacity removed from the left (L) bulla while the right (R) remains normal. Note that the patient was
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cranial, 2 = most caudal.
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placed in right lateral recumbency for CT images while recovering from anesthesia. 1 = most
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Figure 7. Two month recheck axial CT scan images. A soft tissue opacity is seen within the left
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(L) tympanic bulla compared to the unaffected right (R) bulla. Bone removed from the temporary fenestration sites is most apparent in image 2 and 3. As the owner reported no relapse of clinical signs since the procedure, surgery was considered successful despite these findings. 1 = most cranial, 3 = most caudal.