Ear Canal Of Dogs Research Articles

In vitro efficacy of lavender oil, otological gel and gentamicin to eradicate biofilm produced by Pseudomonas aeruginosa.

Otitis externa (OE) is one of the most frequently diagnosed dermatological diseases in dogs, having a multifactorial aetiology. Among the bacterial agents associated with canine OE, Pseudomonas aeruginosa is of special concern owing to its frequent multidrug resistance profile and ability to form biofilms related to the infection's chronicity and recurrence. The main objective of this study was to evaluate and compare the antibiofilm activity of two innovative antimicrobials-an otological gel containing a synthetic antimicrobial peptide and Lavandula angustifolia essential oil-with gentamicin (a conventional antibiotic) using biofilm-producing P. aeruginosa isolates obtained from dogs with OE. The biofilm eradication capacity of gentamicin, otological gel and lavender oil was determined against a collection of 12 P. aeruginosa biofilm-producers among 35 clinical isolates obtained from the ear canals of dogs with OE. Also, the antimicrobial activity of the otological gel against P. aeruginosa biofilms was assessed in an invitro model of dog cerumen. Lavender oil showed the best effectiveness after 30 min of contact, eradicating 58.3% (seven of 12) of the isolates, and gentamicin showed full eradication (12 of 12) after 24 h. The otological gel acted more slowly than the lavender oil; yet at 24 h, the antibiofilm capacity of both compounds was similar, with no significant difference between them. It also was found that triglycerides from synthetic cerumen earwax had antipseudomonal activity and, when combined with the otological gel, led to the full eradication of P. aeruginosa. The results of this invitro study indicate that lavender oil and the otological gel may be effective topical treatments for canine OE promoted by P. aeruginosa biofilm-producers, as alternatives to gentamicin.

Action of mycocins produced by Wickerhamomyces anomalus on Malassezia pachydermatis isolated from the ear canal of dogs

This study aims to examine the effectiveness of mycocins produced by Wickerhamomyces anomalus in inhibiting Malassezia pachydermatis, a yeast commonly found in the ear canal of dogs. M. pachydermatis has a zoophilic origin and can be found in mammals, and frequently in dogs, where it mainly colonizes the ear canal region and the skin, leading to lesions that are difficult to treat. The antimicrobial mechanism was evaluated using dilutions of supernatant with enzymatic activity, which may include β-glucanases, glycoproteins known to act on microorganism cell walls. However, it is important to note that this supernatant may contain other compounds as well. β-glucanases in the mycocins supernatant were found at a concentration of 0.8 U/mg. The susceptibility of M. pachydermatis isolates was tested using the microdilution method. The isolates suffered 100% inhibition when tested with the culture supernatant containing mycocins. In the proteinases production test, 44% of the isolates tested were strong proteinases producers. Subsequently all these isolates suffered inhibition of their activity when tested in research medium containing mycocins supernatant at a subinhibitory concentration of β-glucanases. This shows that mycocins can inhibit the production of proteinases, a virulence factor of M. pachydermatis. The viability test showed the antifungal action of mycocins in inhibiting the viability of M. pachydermatis cells after a period of 8 hours of contact. These results support the antimicrobial potential of mycocins and their promise as a therapeutic option.

Cytological and microbiotic aspects of the diagnosis of otitis externa in dogs

The purpose of the study was to compare cytological samples from two consecutive swabs obtained from ear canals of dogs with otitis externa and to determine the minimum number of samples required to obtain up-to-date information on the degree of microbiological contamination of the affected ear canals. Samples were obtained using sterile applicators with a cotton tip, which were sequentially inserted into ear canal until slight resistance (the junction between vertical and horizontal parts of ear canal), after making a circular motion, the applicator was removed and the material from the tip was applied to the glass slide with rolling movements so that on each slide there were four single parallel smears - two from each ear of the dog. The slides were air dried for one hour and stained using the standard Diff-Quick method. The actual counting was carried out at 1000 magnification (at a high magnification field). Bacteria were differentiated according to their shape into cocci and bacilli. The numbers of bacteria and fungi in the two samples were compared using the Wilcoxon matched pair test. Qualitative agreement between two consecutive swabs was determined using the k-test. Among the studied animals, a breed predisposition to otitis externa was revealed in Cocker Spaniels and French Bulldogs, and an anatomical predisposition in animals with drooping auricles. There was no significant difference in the number of microorganisms present in two ear cytology samples taken consecutively from the same ear at the same site in the external auditory canal, and there was significant agreement between the results of two consecutive smears for the presence of cocci and rods. For yeast, the agreement was only moderate. The data obtained indicate that in cases of otitis externa in dogs, reproducibility of cytological pattern with a single sample of material, as a rule, reflects current stage of pathogenesis of the disease and provides the best opportunity to detect local proliferative activity of opportunistic microbiota and corresponding inflammatory response of the macroorganism.

Tolerability of Otic Solutions Containing Different Enrofloxacin Concentrations in Dogs with Healthy Ears.

Otitis externa (OE) is a common disease in dogs, and topical medications are the preferred treatment. Compounded solutions of enrofloxacin are commonly used in practice to treat bacterial OE; however, the tolerability of different concentrations of this antibiotic in the ear canals of dogs has not been evaluated. The objective of this study is to determine if a higher concentration of enrofloxacin applied to the external ear canal is clinically tolerated in dogs with healthy ears. Sixteen client-owned dogs with bilateral healthy ears and no previous history of OE were enrolled. Injectable enrofloxacin 2.27% diluted with sterile sodium chloride in 1:1 (11.35 mg/mL) and 2:1 (15 mg/mL) ratios were applied into the dogs' right and left ears, respectively, q 12 hr for 14 days. Based on video otoscopic examination, clinical score for canine OE (OTIS3) results before application were ≤1 for all dogs. During the study and at the conclusion, all scores remained ≤2, which is considered normal. No cytologic inflammatory cells were seen in any of the dogs' ears throughout the study. Different concentrations of enrofloxacin solution applied topically were well tolerated by dogs with healthy ears and can be considered for the treatment of dogs with bacterial OE.

Antimicrobial resistance and genotyping of Pseudomonas aeruginosa isolated from the ear canals of dogs in Japan.

The strong bond between dogs and their owners creates a close association that could result in the transfer of antibiotic-resistant bacteria from canines to humans, potentially leading to the spread of antimicrobial resistance genes. Pseudomonas aeruginosa, a common causative agent of persistent ear infections in dogs, is often resistant to multiple antibiotics. Assessing the antimicrobial resistance profile and genotype of P. aeruginosa is crucial for the appropriate use of veterinary pharmaceuticals. However, in recent years, few studies have been conducted on this bacterium in Japan. We determined the antimicrobial resistance profile and genotype of P. aeruginosa isolated from the ear canal of dogs in Japan in 2020. Analysis of antimicrobial resistance using disk diffusion tests indicated a high frequency of resistance to most antimicrobial agents. Particularly, 29 isolates from the ear canals of the 29 affected dogs (100%) were resistant to cefovecin, cefpodoxime, and florfenicol; however, they were susceptible to cefepime and piperacillin/tazobactam. Only 3.4, 10.3, and 10.3% of the isolates were resistant to ceftazidime, tobramycin, and gentamicin, respectively. Furthermore, upon analyzing the population structure using multilocus sequence typing, a considerably large clonal complex was not observed in the tested isolates. Three isolates, namely ST3881, ST1646, and ST532, were clonally related to the clinically isolated sequence types in Japan (such as ST1831, ST1413, ST1812, and ST1849), which is indicative of dog-to-human transmission. Considering the variation in antibiotic resistance compared to that reported by previous studies and the potential risk of dog-to-human transmission, we believe that the survey for antimicrobial resistance profile and population structure should be continued regularly. However, the prevalence of multidrug-resistant P. aeruginosa in dogs in Japan is not a crisis.

Prevalence and infestation degree of yeast in canine otitis externa

Otitis externa is a persistent and recurrent problem, and the resistance of the involved pathogens to conventional drugs has made this a serious issue in veterinary medicine. This is an inflammation of the external ear canal in dogs that can be caused by bacteria or yeast. Often, these two causative agents are isolated together in combination. This study aimed to determine the prevalence of yeast and the degree of infestation of the isolated pathogens in canine otitis externa at veterinary clinics for small pets at the Department of Veterinary Medicine, University of Novi Sad, Serbia. Samples were taken from 60 dogs with clinical symptoms of otitis externa using a sterile swab and sent to laboratory for further mycological and bacteriological examination. In order to isolate the bacteria and yeast, conventional methods were used under aerobic conditions. Of the total samples, 53 (88.33%) were positive for at least one of the causative agents of otitis externa. Yeasts were isolated from 36 (52.94%) samples. The study showed that in comparing mixed and independent types of infection, in most cases 15/23 (65.22%) the degree of infestation with yeast was highest when the infectionwas mixed with bacteria. In relation to dog breeds, their ear forms and type of infection, more yeast samples (either as solo or mixed infection) were isolated from dogs with pendulous ears. It has been confirmed that Malassezia pachydermatis is the most common yeast pathogen of otitis externa in dogs, compared to other species of this genus, and it occurs in a higher degree of infestation in mixed infections than in solo infections. Dog breeds with pendulous ear form are more predisposed to yeast otitis externa than erect eared dog breeds.

Onychomycosis Caused by Malassezia pachydermatis in a Dog

Background: Malassezia species are commensal skin organisms of warm-blooded vertebrates that can act as opportunistic pathogens. Malassezia pachydermatis is of importance in both veterinary and human medicine. Recognised initially as causes of infection of the skin, they are now known to be superficial commensals as well as potential causes of infections in domestic animals and more serious human conditions such as fungemia. They have also been implicated in the pathogenesis of allergic and other inflammatory diseases. Onychomycosis is defined as fungal infection of the claw (nail disease) caused by dermatophytes (Microsporum and Trichophyton genus), non-dermatophyte molds (hyaline and dematiaceous) and/or yeasts. The objective of this work was to report a case of canine onychomycosis by Malassezia pachydermatis based on reference standard diagnostics of this pathology.Case: A 9-year-old male West Highland White Terrier presented history of claw abnormality: brown staining and partly brittle. The dog has no apparent history of trauma on the affected claw and no skin disease was reported. Direct examination of claw was performed using the tape strip technique revealed Malassezia organisms. Nail fragments were cultured onto Sabouraud Dextrose Agar with Chloramphenicol and Cycloheximide. After 10 days of incubation (32ºC) nail fragments allowed the isolation of pure colonies of Malassezia pachydermatis. The histopathological evaluation was performed by Sector of Veterinary Clinical Pathology, Faculdade de Veterinária (FAVET/UFRGS) and fungal infection due to Malassezia pachydermatis was confirmed by histopathologic examination (Hematoxylin and eosin and Grocott’s methenamine silver stain) of the nail, that revealed abundant yeasts (blastoconidia).Discussion: Fungal infection of the skin, hair and nails are common and are primary caused by the dermatophyte molds. Non-dermatophyte molds isolated from nails constitute a long list, but only a few species cause onychomycoses. These include Scopulariopsis brevicaulis, Fusarium sp., Acremonium spp., Aspergillus spp., Penicillium spp. Yeasts like Malassezia and Candida spp. are saprophytes and usually represent incidental contaminants associated with a non-sterile specimen at mycological culture, however in some cases they may parasite the nails and become an etiological agent of the disease. M. pachydermatis, normally present on the skin and in the ear canal of dogs and cats, can act as opportunistic pathogenic microbe and frequently causes dermatitis and otitis in mammals. In the case of onychomycosis, there is little evidence that Malassezia yeasts are implicated in nail plate invasion, although this may be a rare occurrence. All species of the genus are obligatory lipid-dependent forms, with the exception of M. pachydermatis, as well as absence of keratinolytic ability. Malassezia organisms were commonly retrieved from the subungual claw fold region of normal healthy dogs (should be considered resident microflora of the normal canine claw fold). Some authors suggests that high numbers of yeast can be detected on cytological evaluation of the skin surface of the canine claw fold from allergic dogs in both the absence and presence of concurrent signs of pruritus and paronychia.

Report of Mollicutes in the Ear Canal of Domestic Dogs in Brazil

Several microorganisms as bacteria, fungi, yeast and ectoparasites compose canine ear canal microbiota. These agents can be native or invasive pathogens that cause clinical otitis. The aim of this study was to associate Mollicutes in external ear canal with clinical otitis. 41 domestic dogs were examined, and a total of 82 otologic samples were collected using sterile swabs, placed in a plastic storage tube containing 2 milliliters of sterile phosphate buffer saline (PBS, pH 7.2) and appropriately labeled. The samples were processed for isolation of Mollicutes using Hayflick’s medium. The frequency of Mollicutes class in the isolation was 32.9% (27/82). 14.8% (4/27) of the dogs, which were positive for Mollicutes, had external otitis and 85.2% (23/27) were healthy dogs. The genus Mycoplasma spp. was detected in 7.4% (2/27) by digitonin test. It was the first isolation of Mollicutes from the external ear canal in dogs. Although there have been important findings in this study, the presence of these bacteria cannot indicate the onset and perpetuation of external otitis in dogs.

Comparative Analysis of Protein Profiles of Malassezia Pachydermatis Strains Isolated from Healthy Dogs and Dogs with Otitis Externa

Abstract The study included 40 strains of Malassezia pachydermatis obtained in pure culture from external ear canal of dogs and the reference strain. Protein fractions were received by mechanical disruption of the fungal cells. Denaturing protein electrophoresis was performed according to Laemmli method. More than 90% of the all tested strains were characterised by the presence of the following protein fractions: 83.0; 77.0; 59.0; 55.0; 48.0; 38.0; 35.0; 28.0, and 27.0 kDa. In other regions of electrophoregrams, a relatively high differentiation was observed. The strains isolated from animals with otitis externa were characterised by the presence of the following protein fractions: 75.0; 61.0; 52.0; 36.0; 19.5; 16.0; 13.8, and 13.0 kDa. These fractions were absent in the commensal strains. The use of statistical analysis confirmed the obtained results and allowed to generate dendrogram grouping potentially pathogenic and commensal strains on two different branches. Such results may indicate significant differences between protein profiles of strains of M. pachydermatis isolated from healthy and diseased animals.

High prevalence of Enterococcus spp. from dogs with otitis externa

Otitis externa (OE) is a frequent disease in the ear canals of dogs. To identify the pathogens causing OE in dogs and to determine their antimicrobial resistances, specimens were collected from animal hospitals in Daejeon. The isolates were examined by morphological and biochemical tests, 16S rRNA analysis and antimicrobial susceptibility tests. We analyzed correlation between the isolated pathogens and external factors of dogs such as breed, age, gender, ear mite, hair in ears and experience with antibiotic therapy. Thirty three strains of bacteria were isolated from 26 of the 68 heads of dogs with OE. The most isolated bacteria were Enterococcus faecalis (E. faecalis) followed by Staphylococcus aureus (Sta. aureus), Sta. pseudointermedius, E. faecium, E. avium and Streptococcus canis (Strep. canis) in order of frequency of occurrence. Isolation frequency of Enterococcus spp. and Staphylococcus spp. were 51.5% and 45.5%, respectively. E. faecalis and E. faecium isolates showed VanB phenotype, which is resistant to vancomycin but sensitive to teicoplanin were 58% and 25%, respectively. Nine isolates among total twelve isolates of E. faecalis were isolated from the dogs treated with antibiotics. There was no methicillin-resistant Sta. aureus (MRSA), but were MR-Sta. pseudointermedius (MRSP) (57.1%) and vancomycin-resistant (VR)-Sta. pseudointermedius (14.3%) (VRSP) showing VanB phenotype. However, vanA, vanB and vanC genes were not detected in VR isolates from the dogs. Taken together, VR-Enterococcus spp. (VRE) is one of the major pathogens in domestic animals, as well as community-and hospital-acquired infection.

ESTUDO CLÍNICO E MICROBIOLÓGICO DE OTITE EXTERNA DE CÃES ATENDIDOS EM HOSPITAL VETERINÁRIO DO NOROESTE PAULISTA

A canine otitis is the most common disease of the ear canal in dogs and represents 8-15% of cases treated in the medical clinic of small animals. This study aimed to do a retrospective evaluation of 274 medical records of dogs with external otitis treated at the “Dr Halim Atique” Hospital during the period of January 2006 to August 2010. It was performed the analysis of paper and electronic records in way to examine the influence of sex, age and breed of animals in external otitis. After that, it was done the description of etiologic agents and sensibility test for antimicrobials. Two hundred and fourteen cultures were positive (78.68%) for the growth of microorganisms, and 60 (21.32%) were negative. Regarding to culture growth, the frequency of Staphylococcus spp. was 47.08%; Proteus spp. of 14.39%; Pseudomonas spp. 13.23%; 10.31% of Escherichia coli and others. Bigger bacterial isolation was described in the age group of 0-3 years (p = 0.059), accounting for 89 cases (32.04%). Regarding the breed, 59 (21.24%) were mongrel dogs and 40 Poodles (14.40%). There was no statistical difference between the microorganism isolation and the sex. The distribution of external otitis according to sex and monomicrobial infection in females was of 113 cases (41.22%) and 63 males (22.97%). Monomicrobial infection was significantly higher compared to polymicrobial (p < 0.0001). There was a higher sensitivity, a statistically significant of Staphylococcus spp., cephalexin (60.86%), ciprofloxacin (59,09%) and enrofloxacin (59,09%) were statistically significant compared to trimethoprim-sulfamethoxazole (16.66%). Keywords: External otitis, dogs, Staphylococcus spp.

Malassezia and seborrhoeic dermatitis

During the last 20 years, the yeast Malassezia pachydermatis has been acknowledged as a relatively common cause of dermatitis in dogs. The organism occurs naturally on the skin, mucosal surfaces and in the ear canals of dogs, but it can proliferate in response to abnormalities, for example, associated with allergic diseases, keratinisation defects and hormone disturbances.

Subtotal Ear Canal Ablation in 18 Dogs and One Cat With Minimal Distal Ear Canal Pathology

A modified technique for performing total ear canal ablations is described. This technique requires less dissection than the standard technique and maintains a portion of the distal vertical ear canal. Subtotal ear canal ablations were performed in 18 dogs and one cat for the treatment of otitis externa or masses of the horizontal ear canal. Animals with otitis externa had minimal involvement of the distal ear canal. Dermatological problems associated with the remaining ear canal and pinnae occurred in eight animals and resolved with medical management. Normal ear carriage was maintained in all animals with erect ears. Further investigation is required before the procedure can be recommended as a treatment for otitis externa not caused by masses or anatomical abnormalities of the horizontal ear canal in dogs with pendulous ears.

Mycologic Disorders of the Skin

Cutaneous tissue can become infected when fungal organisms contaminate or colonize the epidermal surface or hair follicles. The skin can be a portal of entry for fungal infection when the epithelial barrier is breached or it can be a site for disseminated, systemic fungal disease. The two most common cutaneous fungal infections in small animals are dermatophytosis and Malassezia dermatitis. Dermatophytosis is a superficial cutaneous infection with one or more of the fungal species in the keratinophilic genera Microsporum, Trichophyton, or Epidermophyton. Malassezia pachydermatis is a nonlipid dependent fungal species that is a normal commensal inhabitant of the skin and external ear canal in dogs and cats. Malassezia pachydermatis is the most common cause of Malassezia dermatitis. The diagnosis and treatment of these cutaneous fungal infections will be discussed.

Malassezia pachydermatis: enzymes production in isolates from external ear canal of dogs with and without otitis

The relationship between production of enzymes and pathogenicity of Malassezia pachydermatis strains was studied. Thirty strains of M. pachydermatis isolated from dogs were used: 15 originating from animals with external otitis and 15 obtained from ears of asymptomatic dogs. The samples, obtained by introduction of a sterile swab into the auditory canal after cleaning the auricle with alcohol-ether solution, were seeded onto Sabouraud dextrose agar with chloramphenicol (100mg/l) and were incubated at 37°C for up to two weeks. The colonies were identified according to their macro-and-micromorphology. All strains were investigated for the production of chondroitin-sulphatase, hyaluronidase, phospholipase and proteinase. Most of the strains showed a high production of the four enzymes. Statistical analysis did not show any differences in the enzymatic activity among the strains. M. pachydermatis originating in normal microbiota as well as in otic secretion from dogs with otitis could produce the four researched enzymes. Probably M. pachydermatis has other virulence factors that are involved in the parasitism.

Genetic typing of Malassezia pachydermatis from different domestic animals

In the present study, random amplification of polymorphic DNA, which detects DNA polymorphism in fungal genomic DNA, was applied for genetic typing of Malassezia pachydermatis isolates. Fifty-five isolates from different domestic animals and body sites and the neotype strain CBS 1879 were characterized. Primers M13 and OPT-20 were used to analyse their genetic relatedness and similarity. This technique allowed us to distinguish four different genetic types. The predominant genetic type was observed in isolates recovered from different anatomical locations in all animals. It was the only genetic type found in cats, horse, goat and pig. The other three genetic types were observed only in isolates from external ear canals of dogs. Types II and IV were only recovered from external otitic ears and type III from healthy ears. An animal was colonised by more than one type of M. pachydermatis and different genetic types were detected in the same body site. Some genetic types were only isolated from diseased skin.

FC‐46 Methicillin‐resistant Staphylococcus intermedius organisms from the vertical ear canal of dogs with end‐stage otitis externa

Methicillin‐resistant staphylococci (MRS) have been isolated from the ears of dogs with otitis externa; however, the specific location of the sample and the condition of the ear were not disclosed. The purpose of this study was to identify MRS from the vertical ear canal in dogs with end‐stage otitis externa. Swab samples were obtained from one vertical ear canal of 26 dogs undergoing a total ear canal ablation and bulla osteotomy. Swab samples were routinely processed for bacterial culture. No topical or oral antimicrobial agents had been administered within 24 h of obtaining the sample. Testing for oxacillin (methicillin) resistance was performed with the disk diffusion test (DD) and confirmed with the oxacillin screen agar test (OSA) for staphylococcal organisms. Twenty‐three staphylococcal organisms [21 Staphylococcus intermedius (SI), 2 coagulase‐negative staphylococci (CNS)] were isolated from 17 dogs. On the DD, 15 organisms were susceptible (13 SI, two CNS), one was intermediate (SI), and seven were resistant (all SI) to methicillin. On the OSA, one SI that was intermediate on DD was susceptible, and of the seven that were resistant on DD, five SI were susceptible and two SI were resistant to methicillin. Both methicillin‐resistant S. intermedius (MRSI) were susceptible to chloramphenicol, polymyxin B and trimethoprim‐sulfadiazine. In dogs with end‐stage otitis externa, MRSI may be an important pathogen. Had OSA not been performed to confirm MRS, five of seven staphylococcal organisms would have been erroneously reported as resistant to certain antibiotics, which may have affected antibiotic selection and treatment of the otitis. Funding: Bayer Animal Health, The Ohio State University Canine Research Fund, American College of Veterinary Dermatology, Ohio Animal Health Foundation.

Canalographic evaluation of the external ear canal in dogs.

Canalography was performed to measure the diameter of the horizontal ear canal and to assess the clinical relevance of the measurements in identifying abnormalities of the ear canal. The diameter of the proximal and distal end of the annular cartilage in the horizontal ear canal was measured using canalography in 222 ears. The tympanic membrane could not be visualized with otoscopic examination in 70 ears even after ear cleansing. These canals were classified as being stenotic. The diameter of the proximal annular cartilage in the stenotic canals ranged from 0.8 to 3.1 mm (mean = 2.6 +/- 0.8 mm). The proximal annular cartilage was consistently smaller in diameter than the distal annular cartilage. The ratio between the diameter of the proximal and distal annular cartilage varied between dogs. In stenotic ear canals (70 ears) the ratio was less than 0.65. Total ear canal ablations and histopathological analysis were performed in 70 ear canals classified as stenotic after canalography. Hyperplasia of the epidermal layer was found in 56 stenotic canals. Stenosis of the canal due to otitis externa was found in the other 14 canals. Three canals with severe otitis externa were also diagnosed with canalography as having a ruptured tympanic membrane. The results suggest that canalography can be used to measure the diameter of the horizontal ear canal and to assess whether or not the tympanic membrane is ruptured prior to conservative or surgical therapy.

Evaluation of dogs and cats with tumors of the ear canal: 145 cases (1978-1992)

Objective To characterize the frequency, clinical signs, biologic behavior, and response to treatment of tumors of the ear canal in dogs and cats. Design Retrospective analysis of medical records. Animals Medical records of 81 dogs (48 malignant tumors, 33 benign tumors) and 64 cats (56 malignant tumors, 8 benign tumors). Procedure Data were analyzed for cats and dogs with malignant tumors, and risk factors were analyzed for their potential impact on survival time. Results Malignant tumor types most commonly reported included ceruminous gland adenocarcinoma, squamous cell carcinoma, and carcinoma of undetermined origin. Median survival time of dogs with malignant aural tumors was &gt; 58 months, whereas that of cats was 11.7 months. A poor prognosis was indicated by extensive tumor involvement (dogs) and by neurologic signs at time of diagnosis, diagnosis of squamous cell carcinoma or carcinoma of undetermined origin, and invasion into lymphatics or blood vessels (cats). Clinical Implications Malignant tumors of the ear canal in dogs and cats have a propensity for local invasion, but tend not to metastasize. Squamous cell carcinoma and carcinoma of undetermined origin were the most locally aggressive tumors. Malignant tumors of the ear canal are best managed by aggressive surgical excision. Radiotherapy may be useful when tumors cannot be completely removed. (J Am Vet Med Assoc 1996;208:1413-1418)

The pathology of the external ear canal in dogs and cats.

A survey of factors which predispose the canine ear to otitis externa is presented. In resected ear specimens of 106 dogs, otitis externa without tumour was found on 58 occasions. In 46 dogs tumours were diagnosed in 15 cases with an otitis externa. In two dogs an inflammatory polyp was found. In the resected ear specimens of 48 cats, otitis externa was diagnosed 27 times, in 6 cases combined with an inflammatory polyp. In 21 cases neoplasia was present. The otitis externa was mainly a chronic proliferative inflammation characterised by hyperkeratinization, hyperplasia of the sebaceous and ceruminous glands, fibrosis and infiltration with plasma cells, lymphocytes and macrophages, often containing ceroid pigment.