by chelonians and turtles.
Abscessation of middle ear is relative common clinical problem by chelonians and free lived eastern box turtles (Terrapene carolina).
The predisposing factors is as suboptimal husbandry conditions as immunosuppression caused by other disease processes.
Anatomy and physiology of ear
The ear of turtles and chelonians is located caudoventral to the eye and isn't really conspicuous. The reptilan ear is divided to the external, the middle and the inner ear like by mammals.
Every part of an ear has a important function. The external ear collects sound waves from environment, the middle ear transmits and amplifies these sound waves into vibrations of chains of ossicles and finally the inner ear transmits these vibration to a fluid medium that causes movement of cochlear hair cells, these movements are transmitted by the vesibulocochlear nerve to the brain for interpretation.
By chelonians and turtles is absent the external ear. The chelonian and turtles tympanum is flush with the surrounding skin. The middle ear consist of the tympanic membrane, the ossicular chain ( included Columella and Extracolumella), the tympanic cavity, the oval window of the cochlea on which the ossicular chain inserts. The tympanic cavity is large and extends caudally into a blind-ended sac, named tymanic bulla.
For compare with mammal's ossicular chain the stapes presented the columella as its elongated version together with extracolumella, a cartilaginous expansion of the distal part of columella. Both the mallelus and incus are absent.
The inner ear consist of the cochlear duct, the scala vestibuli (periotic cistern), the scala tympani ( periotic sac) , the round window and the insert of vestibulocholear nerve. The function of inner ear is auditory and equilibrium.
Etiopathogenesis
Aural abscesses is a pathological process, which based on multifactorial cause. Predisposing factors are stress caused by crowded husbandry, suboptimal temperatures, husbandry inappropriate for the species, inadequate nutrition, hypovitaminosis A and by free lived box turtles organochlorine, which retarded metabolism of vitamin A.
Hypovitaminosis A caused lesions of tympanic epithelium like hyperemia, hyperplasia, squamous metaplasia, cellular sloughing, granulomatous inflamation. These processes promoted bacterial infection and inflammation.
A very important cause of aural abscesses is immunodeficiency with secondary opportunistic infection or infection with bacteria, which flourish by bad hygienic condition in environment. In this case is often way of infection from esophagus through tuba auditiva into the middle ear.
Systemic illness is also reason for immunodeficiency, therefore is necessary close clinical examination as well hematology and biochemistry tests by patients with aural abscesses.
* The cell-mediated immunologic response to a bacterial inflammatory process within the middle ear is manifested as an accumulation of granulocytes and histiocytes. As a result of the relative or absolute lack of lysozymes in granulotic leukocytes the inflammatory exudate tends to be caseous. Caseous exudate can be palpable as firm to semi firm swelling. As the process becomes more chronic the response becomes more mononuclear, increased chronicity result in the presence of multinucleated giant cells. The formation of a fibrous connective tissue capsule is possible. The abscesses center is avascular, that is the reason, why parenterally administred antibiotics can't work.
Diagnosis
As by every patient is very important its case history. Exactly ask about water source, frequency of water changes, water bowl disinfection, temperature, nutritional review, vitamin A application or beta-carotenoid content of the diet, patient's activity and behaviour.
After the anamnesis must follow complete clinical examination of entire patient, in order to detect other illnesses and affections as result of suboptimal conditions.
Otitis media can't be clinical detected by beginning process. Later come to a formation of an auricular abscesses. This can be obtained as firm to semifirm swelling unilateral or bilateral. This status is painful and without treatment threaten to rupture of the tympanic membrane.
Option of ancillary diagnostic is fine-needle aspiration of the swelling. In the aspirat are represented varying numbers of granulocytes, macrophages and eosiniphilic proteinaceous material. Samples for culture and sensitivity testing should be achieve via centesis or at the time of surgical debridement. Microorganisms don't have to be identified.
For a imagination a video from youtube:
Guy's report about aural abscess by his Trachemys scripta elegans
Therapy
The only promising treatment of aural abscess is a surgery.
Patients may benefit from delay of surgical intervention and start of stabilizations therapy. This therapy included systemic antibiotics to alleviate an inflammatory process in a organism, fluids to stabilize acidobasic and electrolyte balance and help by possible dehydratation. When was observed a anorexia, can be started appropriate supportive care for 3 or 4 days. All these therapy may enhance patient's ability to tolerate a general anesthesia.
As general anesthesia may be used total intravenous anesthesia with propofol or inhalations anesthesia with isofluran. By very good cooperating patients is possible only very good local anesthesia and surgical intervention by full obtained conscious. As recommended is using of propofol as induction to anesthesia, continuing anesthesia with isofluran, intratracheal tube may help by prevention of aspiration.
By all anesthesia protocols is analgesia important!
Surgery intervention started with incision through tympanic membrane in rostrocaudal direction. A incision by the lenght of the neck is important for healing of wound and protection of neck musculature. A present debris may be removed with small curette. As next ear may be flushed with NaCl solution to remove all debris form ear and auditive tube too. I this phase occur a high risk of aspiration, so is recommended to control more times. After appropriate bebridement may flushed the ear with antimicrobial agent.
Povidone-iodine is not recommended, because this solutions killed fibroblasts what has negative influence to healing process. Free iodine is inactive in the presence of a serum proteins. As good option appear ethacridin lactat, on the market known as rivanol. The incision may be allowed to heal with secondary intention.
After surgery should be managed analgesia, systemic antibiotic therapy, a treatment of other present illnesses, appropriate feeding with consideration for vitamin A concentration, if necessary repeat a rivanol flushing.
Prognosis
After adequate debridement, improving of husbandry and environmental conditions, successful treatment of other illnesses is the prognosis ad vitam very good.
Prognosis ad functionem, that means auditory capability is uncertain. The substantial fibrotic changes in the tympanic cavity injure the function of the transmission of sound to the inner ear. This is expected by completely undamaged columella too. These facts let's assume that auditory capability isn't remaining.
REFERENCES
Reptile medicine and surgery by Douglas R. Mader, Saunders Elsevier (2006)
BSAVA manual of reptile by Simon Girling, Paul Raiti, British Small Animal Veterinary
Krankheiten der Heimtiere by Karl Gabrisch, Peernel Zwart, Schlütersche (2007)
PubMed.gov :
Diagnosis, treatment, and outcome of eastern box turtles (Terrapene carolina carolina) presented to a wildlife clinic in Tennessee, USA, 1995-2007.
Relationships among aural abscesses, organochlorine compounds, and vitamin a in free-ranging eastern box turtles (Terrapene carolina carolina).
Inability to induce tympanic squamous metaplasia using organochlorine compounds in vitamin A-deficient red-eared sliders (Trachemys scripta elegans).
Characterization of the bacterial microflora of the tympanic cavity of eastern box turtles with and without aural abscesses.
Pathology of aural abscesses in free-living Eastern box turtles (Terrapene carolina carolina).
Epidemiologic determinants of aural abscessation in free-living eastern box turtles (Terrapene carolina) in Virginia.
Morbidity and mortality of reptiles admitted to the Wildlife Center of Virginia, 1991 to 2000.
Aural abscesses in wild-caught box turtles (Terapene carolina): possible role of organochlorine-induced hypovitaminosis A.
