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A Technique for Examining the External Ear Canal in Standing Sedated Horses
Journal of Equine Veterinary Science 33 (2013) 1124–1130
Contents lists available at SciVerse ScienceDirect
Journal of Equine Veterinary Science journal homepage: www.j-evs.com
Original Research
A Technique for Examining the External Ear Canal in Standing Sedated Horses Sophia Sommerauer DVM, Alice Snyder DVM, Julia Breuer DVM, Gerald F. Schusser DVM, DECEIM * Department of Large Animal Medicine, Faculty of Veterinary Medicine, University of Leipzig, Leipzig, Germany
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 February 2013 Received in revised form 11 April 2013 Accepted 24 April 2013 Available online 24 June 2013
In this study ultrasonography, local anesthesia, and endoscopy were performed in both ears of 23 horses. The aim was to find a reliable technique for examination of the external ear canal in standing sedated horses and to create a grading of debris and the occurrence of abnormalities in clinically healthy horses. Local blockage of the great and internal auricular nerves was performed after caudal palpation at the base of the ear and ultrasonographic assessment of the styloid process of the auricle as a reference point for the needle placement. The otoscopic examination was accomplished with two flexible video endoscopes with 2- and 7-mm tip diameters. The depth of the styloid process varied ultrasonographically from 2.08 to 2.73 cm on the left side and from 2.04 to 2.76 cm on the right side. Local anesthesia was successful in all sedated horses, without any long-term complications. The grading of endoscopic appearance of the skin, epithelium, and ceruminous and cell debris in the cartilaginous and osseous part including tympanic membrane of the equine external ear canal ranged from I to III. Abnormalities like osteoma, granuloma, hemorrhagic or erythematous areas, and narrowing of the osseous part of the external ear canal due to stenosis (exostosis) were seen in 10 of 23 horses. The tympanic membrane was visualized in 20 of 23 horses. Local blockage of the great and internal auricular nerves was found to be a reliable method for equine ear anesthesia. Ó 2013 Elsevier Inc. All rights reserved.
Keywords: Horse Local anesthesia External ear canal Endoscopy
1. Introduction Diseases of the equine external ear canal are considered uncommon or are not described accurately. Some of the diseases described include external otitis, inflammatory aural polyps, aural neoplasia, auricular chondrosis, and parasites, such as ear mites [1-3]. Furthermore, pathological stenosis in the external ear canal can appear due to temporohyoid osteoarthropathy [4,5]. Additionally, the phenomenon of headshaking could be associated with diseases of the equine ear [6,7]. Horses with sudden shying * Corresponding author at: Gerald F. Schusser, DVM, DECEIM, Department of Large Animal Medicine, Faculty of Veterinary Medicine, University of Leipzig, An den Tierkliniken 11, 04103 Leipzig, Germany. E-mail address: [email protected] (G.F. Schusser). 0737-0806/$ – see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jevs.2013.04.015
or older horses might suffer from hearing loss. In such cases, however, endoscopy of the external auditory meatus could be an important diagnostic tool. The equine external ear canal is divided into a pigmented cartilaginous and nonpigmented osseous part [8]. The osseous part is described by the use of computed tomography to have an hourglass shape, angled in a dorsolateral-to-ventromedial direction and narrowing up to 4.6-4.7 mm with a length of 25.2-26.5 mm. That is why endoscopic instruments are usually too large to reach the level of the tympanic membrane [9]. Moreover, the sensitivity of many horses makes otoscopic evaluations quite difficult. Cole [16] describes the normal external ear canal in small animals as smooth, light pink, and containing minimal debris, such as hair, ceruminoliths or foreign bodies. The tympanic membrane is divided into the upper
S. Sommerauer et al. / Journal of Equine Veterinary Science 33 (2013) 1124–1130
pars flaccida and the lower pars tensa. It is translucent, and the stria mallearis should be visible. The stria mallearis describes the attachment of the manubrium of the malleus. The sensitive innervation of the outer and inner surfaces of the auricle is mediated by the great auricular nerve, a branch of the second cervical nerve (CII). The external ear canal is sensitively innervated by the internal auricular nerve, a branch of the facial nerve (CN VII) [10]. The great auricular nerve runs subcutaneously from the second cervical vertebra to the caudal aspect of the base of the ear. The internal auricular nerve runs underneath the parotid gland, next to the lateral recess of the guttural pouch and enters the auricle at its deepest point, adjacent to the styloid process [11]. Local anesthesia techniques of the equine head are mainly performed for procedures such as eyelid, dental and paranasal sinus surgery, mandibular fracture repairs and transendoscopic laser surgery [12]. McCoy et al. [13] described a technique for blockage a horse’s ear based on palpation of the great auricular nerve on the caudal aspect of the base of the auricle. A cadaver head study about an anesthesia technique of the great and internal auricular nerve has recently been published by the authors [14]. Video endoscopy of the external ear canal, including the tympanic membrane, has so far only been performed on the heads of cadavers [9] or under general anesthesia [2,15]. The aim of this study was to develop an examination technique of the external ear canal in standing sedated horses. A further purpose of this study was to describe the degree of ceruminous debris in the cartilaginous part, cell debris and epithelium color in the osseous part, appearance of the tympanic membrane and additional abnormalities.
2. Material and Methods 2.1. Animals The pigmented cartilaginous and nonpigmented osseous parts of the external ear canal were examined endoscopically in 23 Warmblood Horses. Endoscopy of the osseous part and evaluation of the structure of the tympanic membrane were done under local anesthesia. Local ear anesthesia was performed under ultrasound guidance. The trials were approved by the Commission of Animal Welfare. There were 3 stallions, 16 geldings and 4 mares. The ages of the horses ranged from 10 to 25 years old (median, 16 years old). All horses were stabled in inside boxes and turned out daily. None of the horses had a history of ear disease or headshaking or showed other neurological symptoms. The horses were moved into stocks and sedated at the beginning of manipulation. Sedation was accomplished with detomidine (0.02 mg/kg of body weight [bw], IV [Cepesedan; CP Pharma, Burgdorf, Germany]) and butorphanol (0.01-0.05 mg/kg bw, IV [Alvegesic; Virbac Schweiz AG, Glattbrugg, Germany]). The skin over the palpable great auricular nerve and the styloid process of the auricular cartilage was clipped and aseptically prepared. All of the horses were closely monitored for the next 2 weeks to facilitate the detection of possible complications.
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2.2. Ultrasonography The entrance point of the internal auricular nerve into the auricle is formed by the styloid process. As this is also the area where local anesthesia should be performed this cartilaginous process was seen as the desired landmark. The close proximity of the internal auricular nerve to the parotid gland and the guttural pouch warrants ultrasonographic evaluation prior to local anesthesia. With the help of ultrasonography, the enhanced vascularity of the parotid gland was pictured to avoid vessel puncture. Furthermore the border of the guttural pouch can be seen, which prevents the loss of anesthetic due to an accidental puncture. The region of interest was shaved and cleaned with alcohol. The examination was accomplished with a 10-MHz rectal probe (GE Logiq 5 Expert; Scil, GmbH, Viernheim, Germany) with 40-mm penetration depth, which appeared to be most suitable for this region. The probe was placed in a vertical plane directed caudal of the zygomatic process of the temporal bone and in extension to the longitudinal axis of the auricle for localizing the styloid process (Fig. 1). 2.3. Local Anesthesia Local anesthesia of the great auricular and internal auricular nerves was performed in 23 horses, providing full desensitization of the auricle and the external ear canal for endoscopic evaluation of the tympanic membrane. A 21-G needle (Sterican B; Braun Melsungen AG, Berlin, Germany) was used for the injection. The great auricular nerve was palpable subcutaneously at the caudal aspect of the base of the ear (Fig. 1). The local blockage was performed with 2 ml of lidocaine hydrochloride (Xylocitin, loc 2%; Mibe GmbH, Brehna, Germany). The internal auricular nerve was blocked right at the styloid process using 3 ml lidocaine hydrochloride. Desensitization of the external ear canal was tested five minutes later by inserting a cotton bud. Defense reactions were observed and the result of the local anesthesia technique was evaluated. If necessary, the injection had to be repeated. As soon as no signs of
Fig. 1. Right side of the head. Placement of the probe in a vertical plane caudal to the zygomatic process of the temporal bone and in extension to the longitudinal axis of the auricle to localize the styloid process. C, indicates landmarks for local anesthesia of the great and internal auricular nerve.
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discomfort occurred (e.g., headshaking), anesthesia was regarded as successful. 2.4. Endoscopy The chemical restraint of the horses was supplemented with a twitch. Endoscopy was accomplished with a flexible video endoscope (Karl Storz GmbH, Tuttlingen, Germany) with a 7-mm diameter tip. Another flexible video endoscope with 2 mm diameter tip from the same company was used in order to become familiar with normal structures of the tympanic membrane and thus to identify any abnormalities in the deeper region of the osseous part which was not seen in every detail by the first scoping. The desired landmarks were formed by the junction between the pigmented cartilaginous part and the nonpigmented osseous part of the external auditory meatus, and finally, the tympanic membrane. The skin and epithelium color as well as the degree of debris both of the cartilaginous and the osseous part of the external ear canal together with the translucent tympanic membrane were evaluated. Based on these findings a tentative grading description including abnormalities was made, which is characterized in Table 1. 2.5. Statistical Analysis Calculation was performed using Excel version 12.0 (Microsoft, Redmond, WA) and PASW version 18.0 software. Results were reported as ranges and medians. The correlation of the degree of debris between the cartilaginous and osseous parts was analyzed using the Spearman correlation coefficient. Significance was set at a P value of <.05. 3. Results 3.1. Ultrasonography The cartilage of the auricle and the parotid gland were pictured in both ears of 23 horses. The ear cartilage was traced to its end, where the styloid process became visible. It appeared as a thin hyperechoic line and its tissue depth
varied from 2.08 to 2.73 cm on the left side (median, 2.44) and from 2.04 to 2.76 cm on the right side (median, 2.45). The enhanced vascularity of the parotid gland was pictured by the use of Doppler ultrasonography (Fig. 2). The boundary of the air-filled guttural pouch was marked ultrasonographically. 3.2. Local Anesthesia Nerve blocks of the great and internal auricular nerves were carried out on 23 sedated horses. The needle placement was very well tolerated, and no signs of discomfort appeared. Based on the Doppler ultrasonography a vessel puncture in the parotid gland was avoided in every case. Desensitization of the auricle and the external ear canal in both ears of 20 of the horses occurred 5 minutes postinjection of local anesthesia. In the other three horses, no or only slight desensitization of the external ear canal occurred, which required a repeated injection of internal auricular nerve anesthesia with 2 ml of the local anesthetic. The great auricular nerve was successfully anesthetized in these cases. However, these horses had mildly drooping ears and ptosis due to bilateral facial nerve paralysis simultaneously with the onset of anesthesia, which persisted for 4 hours. Therefore, eye ointment (Kerato Biciron 5%; SK Pharma GmbH, Herford, Germany) was administered in three occasions. 3.3. Endoscopy The horse’s ear in each case was held with one hand, and the endoscope was carefully inserted in a vertical direction (Fig. 3). In this way, using the flexible video endoscopes with 2- or 7-mm tip diameter, the cartilaginous part lined with pigmented skin, covered with fine hairs and brownish or black ceruminous debris became visible. As a result, the junction with the nonpigmented osseous part of the external ear canal was exposed (Figs. 4 and 5). The highest degree of ceruminous and cell debris was found in this area in all horses (Figs. 6 and 7). The epithelium of the osseous part of the equine external ear canal appeared to be light pink (Fig. 5). The grading of endoscopic appearance
Table 1 Grading of endoscopic appearance of the skin, epithelium and ceruminous and cell debris in the cartilaginous and osseous part of the equine external ear canal and assessment of abnormalities Grading of Endoscopic Appearance
Cartilaginous Part
I
Pigmented skin is visible; a small amount of ceruminous debris is closely attached to the pigmented skin and little dust on hair Pigmented skin is hardly visible, and dirt formations, dust on hair, and several free ceruminous debris formations are observed
II
III
Abnormalities
Osseous Part
Junction is clearly contoured; light pink epithelium; visible translucent tympanic membrane characterized by central visible stria mallearis Junction surrounded by a rim of cell debris; light pink epithelium; several free ceruminous and cell debris formations and dirt particles; translucent tympanic membrane is characterized by central stria mallearis, hardly visible Pigmented skin not visible; presence of dirt formations, dust Partially or completely obstructed junction is the result of and dirt, with sticky hair, and massive ceruminous debris ceruminous and cell debris including dirt accumulation; formations tympanic membrane is not visible For example, erythematous and/or hemorrhagic lesions, granulomas, osteomas, stenosis (exostosis), foreign bodies, blood accumulations, exudations, parasites (ear mites, mosquitoes, ticks, ants, insects), congenital defects
S. Sommerauer et al. / Journal of Equine Veterinary Science 33 (2013) 1124–1130
Fig. 2. Ultrasonographic evaluation of the depth of the styloid process of a 17-year-old Warmblood gelding, using a 10-MHz rectal probe with 40-mm penetration depth. The blood flow in the parotid gland was pictured by the use of Doppler ultrasonography.
based on our evaluation (Table 1) varied between I and III in the cartilaginous parts (median: II), and in the osseous parts (median: I). Statistically all variables were not normally distributed. There was a significant positive correlation between the debris of the cartilaginous and osseous part within one ear as well on the left (0.539) as on the right side (0.436). So it is safe to assume that horses with a severe pollution of the cartilaginous part also suffer from
Fig. 3. Vertical insertion of the flexible video endoscope with 2-mm tip diameter in the right external ear canal after local anesthesia.
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Fig. 4. Right external ear canal of a 15-year-old Warmblood gelding. The junction between the pigmented cartilaginous and the nonpigmented osseous part of the equine external ear canal is visualized with a flexible video endoscope. Endoscopic appearance with a grade I of the external ear canal.
severe debris in the osseous part of the external ear canal, even if an advancing of the endoscope in a deeper position is not possible. An obstructed osseous part was found bilaterally in 3 of 23 horses (Fig. 7). The following detected abnormalities were described: a light pink, pinhead-sized mass (approximately 2 mm) like an osteoma right next to the pars tensa of the tympanic membrane at the bottom of the osseous part was seen in one external ear canal of one horse (1 of 23) (Fig. 8). An inflamed area like a granuloma (1 of 23) or hemorrhagic area (1 of 23) (Fig. 9) were only seen unilaterally. However, a narrowing of the osseous part of the external ear canal like an exostosis was shown bilaterally in 7 of 23 horses and was considered an abnormality (Fig. 5). Compared to the horses which were considered to have a normal condition, no significant difference in the grade of pollution was seen.
Fig. 5. Left external ear canal of a 10-year-old Warmblood mare. Translucent tympanic membrane with the centered stria mallearis is seen at the bottom of the osseous part, light pink epithelium with delicately colored vessels, visualized with a flexible video endoscope. Endoscopic appearance of grade I and an abnormality like an exostosis at the bottom of the osseous part on the right side of the picture is visible.
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Fig. 6. Right external ear canal of a 16-year-old Warmblood gelding. The junction between the cartilaginous and osseous part is surrounded by inflamed, swollen, bloody skin; the entrance of the osseous part is partially obstructed, and the tympanic membrane is not visible (grading III).
Because of the described anatomical conditions of the equine external ear canal it was only possible to advance the flexible endoscope with 2 mm diameter tip into the osseous part, which enabled the exposure and examination of the tympanic membrane. The normal tympanic membrane characterized by the central stria mallearis, which is formed by the manubrium of the malleus, the pars flaccida (upper region) and the translucent pars tensa could have been pictured in both external ear canals of 20 Warmblood horses (Fig. 10). In the other three cases, the visualization of the tympanic membrane was prevented from severe accumulation of ceruminous and cell debris. No complications such as permanent facial nerve paralysis or parotid gland fistulas were detected in any horse after local anesthesia or external ear canal endoscopy during the next 2 weeks. 4. Discussion
Fig. 8. Suspected osteoma at the bottom of the left osseous part next to the pars tensa of the tympanic membrane of a 15-year-old Warmblood gelding.
It was possible to anesthetize both external ear canals of 23 horses. The proximity of the parotid gland and the guttural pouch to the internal auricular nerve was considered a problem in performing local anesthesia. Feared complications included local pain, swelling, infection, facial nerve paralysis, or the development of parotid gland fistulas. The development of salivary fistulas is described in some cases as a result of parotid gland traumas [19]. In the present study, none of the horses acquired parotid gland abnormalities. Facial nerve paralysis is described in relation to inner ear diseases and facial nerve inflammation occurs in the course of middle ear diseases, followed by contralateral hemifacial muscle activity [20]. As a matter of fact, it is assumed that increased tissue pressure as a result of the lidocaine hydrochloride injection may also be a reason for facial nerve paralysis or inflammation. None of the horses in this study developed hemifacial spasm following local anesthesia, however, mild bilateral facial nerve paralysis occurred in three horses. These were the horses which received 2 ml of lidocaine hydrochloride as the second injection. The paralysis was evident mainly in reduced
The present study is the first report describing an examination of the external ear canal in the standing horse.
Fig. 7. Right external ear canal of a 16-year-old Warmblood gelding. Obstructed osseous part is caused by ceruminous and cell debris; the tympanic membrane is not visible (grade III).
Fig. 9. Right external ear canal of a 10-year-old Warmblood mare. Hemorrhagic lesion is seen in the osseous part of the ear canal. Visible at the bottom of the osseus part are the tympanic membrane with stria mallearis (center, white), the pars flaccida (upper right, white), and the pars tensa (translucent, lower left).
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A study in dogs showed that an accumulation of ceruminous debris within the ear canal also significantly affects hearing ability [21]. Cerumen impaction describes the accumulation of ear wax in the ear canal and occurs mostly in elderly human beings [22]. The partial obstruction described at the entrance point (Fig. 6) or the total obstructed osseous part (Fig. 7), because of severe ceruminous and cell debris formation, may have caused hearing loss in the two horses. Due to the relatively homogenous age of the animals examined, no statement about the different degree of debris of the external ear canals in miscellaneous age classes can be made. Further studies of more animals will be necessary to describe the occurrence of pathologies of the external ear canal including tympanic membrane of horses. 5. Conclusions
Fig. 10. Left external ear canal of a 16-year-old Warmblood gelding. The tympanic membrane is shown.
eyelid and ear reflexes. None of the other horses, however, showed similar symptoms, so the paralysis was clearly attributable to the larger amount of local anesthetic and was transient for the duration of local anesthesia. Other feared complications, such as inflammation of the injection side, were not reported within the following two weeks. The entire external ear canals, including the tympanic membrane, were visualized by the use of two flexible video endoscopes. The tympanic membrane with the central stria mallearis could be more accurately examined with the video endoscope with 2 mm tip diameter, due to the anatomic conditions of the equine external ear canal. The advantages of using a video endoscope in comparison to a handheld otoscope for the otoscopic examination include the high degree of magnification, and the greater visualization of the osseous part and tympanic membrane with a more detailed resolution. Furthermore, images of the external ear canal and the tympanic membrane may be captured and saved during any procedure [16]. However, it is important to standardize the orientation of the video endoscope in relation to the position of the animal. Otherwise it can be difficult to recognize abnormalities in the ear [17]. A recent report even describes the treatment of external otitis by the use of video otoscopy [18]. The degree of resolution of the video endoscopes used in the present study was accurate to identify normal findings like ceruminous and cell debris, and abnormalities like osteoma, granuloma, hemorrhage, and exostosis. Exostoses were defined as bony neoformations within the osseous part of the external ear canal while stenoses were assumed to be caused by tissue swellings in either one of the parts. In this study abnormalities like osteoma, granuloma, and hemorrhage occurred unilaterally, wherever ceruminous and cell debris and the abnormalities like exostoses occurred bilaterally. The missing histological differentiation of the described masses is clearly a limitation of this study, because suspected diagnoses could not have been confirmed.
Combined with local anesthesia endoscopy is a reliable technique to visualize the external ear canal, including the tympanic membrane, in standing sedated horses. Endoscopic examination of the external ear canal should be carried out on skittish horses or horses with symptoms of ear rubbing, aural discharge or headshaking, on horses with a history of facial asymmetry including keratoconjunctivitis or of head trauma, followed by ataxia and head tilt or at least on horses which have a high startle response. After this evaluation of external ear canals a different accumulation of ceruminous and/or cell debris in the osseous part and pollution in the cartilaginous part were seen in all horses with normal condition. In cases with increased grading of ceruminous and/or cell debris removal of debris with an ear wick or with a foreign body forceps through an endoscope is recommended. References [1] Fjordbakk CT, Kenney DG, Rodriguez-Palacios A, Keller S, Stalker M. Inflammatory aural polyp in a horse. Can Vet J 2006;47:65–6. [2] Oosterlaan-Mayer B, Van der Kolk JH. Endoscopically guided thermocautery and laser removal of an inflammatory polyp associated with chronic otitis externa in a pony. Equine Vet Educ 2006;18: 256–9. [3] Bowers JR, Slocombe RF. Auricular chondrosis in a horse. Aust Vet J 2009;87:219–21. [4] Hughes KJ, Hodgson DR. Unilateral ataxia and head tilt in a 7-yearold thoroughbred stallion. Aust Vet J 2006;84:139–42. [5] Aleman M, Puchalski SM, Williams DC, Kass PH, Holliday TA. Brainstem auditory-evoked responses in horses with temporohyoid osteoarthropathy. J Vet Intern Med 2008;22:1196–202. [6] Davis EG. Headshaking. In: Proceedings of North American Veterinary Conference 2005;143–144. [7] Schüle E, Herling A. Headshaking of horsesda review. Pferdeheilkunde 2006;22:281–95. [8] Dyce KM, Sack WO, Wensing CJG. Sense organs. In: Dyce KM, Sack WO, Wensing CJG, editors. Textbook of veterinary anatomy. 4th ed. St. Louis, MO: Saunders Elsevier; 2010. p. 332–53. [9] Sargent SJ, Frank LA, Buchanan BR, Donnell RL, Morandi F. Otoscopic, cytological and microbiological examination of the equine external ear canal. Vet Dermatol 2006;3:175–81. [10] Dyce KM, Sack WO, Wensing CJG. The head and ventral neck of the horse. In: Dyce KM, Sack WO, Wensing CJG, editors. Textbook of veterinary anatomy. 4th ed. St. Louis, MO: Saunders Elsevier; 2010. p. 501–31. [11] Budras KD, Sack WO, Röck S. Head. In: Budras KD, Sack WO, Röck S, editors. Anatomy of the horse. 5th ed. Hannover, Germany: Schlütersche Verlagsgesellschaft; 2009. p. 32–52.
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[12] Tremaine, H. Regional analgesia for the horse’s head. In: Proceedings of 49th British Equine Veterinary Association Congress 2010; 174. [13] McCoy AM, Schaefer E, Malone E. How to perform effective blocks of the equine Ear. In: Proceedings of annual convention of the American Association of Equine Practitioner 2007; 397–8 [14] Sommerauer S, Mülling CKW, Seeger J, Schusser GF. Anatomy and anesthesia of the equine external ear canal. Anat Histol Embryol 2012;41:395–401. [15] Hassel DM, Schott HC, Tucker RL, Hines MT. Endoscopy of the auditory tube diverticula in four horses with otitis media/interna. J Am Vet Med Assoc 1995;207:1081–4. [16] Cole LK. Otoscopic evaluation of the ear canal. Vet Clin Small Anim Pract 2004;34:397–410.
[17] Angus JC, Campbell KL. Uses and indications for video-otoscopy in small animal practice. Vet Clin Small Anim Pract 2001;31:809–28. [18] Usui R, Usui R, Fukuda M, Fukui E, Hasegawa A. Treatment of canine otitis externa using video otoscopy. J Vet Med Sci 2011;73:1249–52. [19] Rakestraw PC. Pathology of the salivary glands and esophagus. In: Proceedings of 8th congress on Equine Medicine and Surgery, Geneva, Switzerland, 2003. [20] Cook LB. Neurologic evaluation of the ear. Vet Clin Small Anim Pract 2004;34:425–35. [21] Eger CE, Lindsay P. Effects of otitis on hearing in dogs characterized by brainstem auditory evoked response testing. J Small Anim Pract 1997;38:380–6. [22] Roland PS, Smith TL, Schwartz SR, Rosenfeld RM, Ballachanda B, Earll JM, et al. Clinical practice guideline: Cerumen impaction. Otolaryngol Head Neck 2008;139:1–21.
Contents lists available at SciVerse ScienceDirect
Journal of Equine Veterinary Science journal homepage: www.j-evs.com
Original Research
A Technique for Examining the External Ear Canal in Standing Sedated Horses Sophia Sommerauer DVM, Alice Snyder DVM, Julia Breuer DVM, Gerald F. Schusser DVM, DECEIM * Department of Large Animal Medicine, Faculty of Veterinary Medicine, University of Leipzig, Leipzig, Germany
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 February 2013 Received in revised form 11 April 2013 Accepted 24 April 2013 Available online 24 June 2013
In this study ultrasonography, local anesthesia, and endoscopy were performed in both ears of 23 horses. The aim was to find a reliable technique for examination of the external ear canal in standing sedated horses and to create a grading of debris and the occurrence of abnormalities in clinically healthy horses. Local blockage of the great and internal auricular nerves was performed after caudal palpation at the base of the ear and ultrasonographic assessment of the styloid process of the auricle as a reference point for the needle placement. The otoscopic examination was accomplished with two flexible video endoscopes with 2- and 7-mm tip diameters. The depth of the styloid process varied ultrasonographically from 2.08 to 2.73 cm on the left side and from 2.04 to 2.76 cm on the right side. Local anesthesia was successful in all sedated horses, without any long-term complications. The grading of endoscopic appearance of the skin, epithelium, and ceruminous and cell debris in the cartilaginous and osseous part including tympanic membrane of the equine external ear canal ranged from I to III. Abnormalities like osteoma, granuloma, hemorrhagic or erythematous areas, and narrowing of the osseous part of the external ear canal due to stenosis (exostosis) were seen in 10 of 23 horses. The tympanic membrane was visualized in 20 of 23 horses. Local blockage of the great and internal auricular nerves was found to be a reliable method for equine ear anesthesia. Ó 2013 Elsevier Inc. All rights reserved.
Keywords: Horse Local anesthesia External ear canal Endoscopy
1. Introduction Diseases of the equine external ear canal are considered uncommon or are not described accurately. Some of the diseases described include external otitis, inflammatory aural polyps, aural neoplasia, auricular chondrosis, and parasites, such as ear mites [1-3]. Furthermore, pathological stenosis in the external ear canal can appear due to temporohyoid osteoarthropathy [4,5]. Additionally, the phenomenon of headshaking could be associated with diseases of the equine ear [6,7]. Horses with sudden shying * Corresponding author at: Gerald F. Schusser, DVM, DECEIM, Department of Large Animal Medicine, Faculty of Veterinary Medicine, University of Leipzig, An den Tierkliniken 11, 04103 Leipzig, Germany. E-mail address: [email protected] (G.F. Schusser). 0737-0806/$ – see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jevs.2013.04.015
or older horses might suffer from hearing loss. In such cases, however, endoscopy of the external auditory meatus could be an important diagnostic tool. The equine external ear canal is divided into a pigmented cartilaginous and nonpigmented osseous part [8]. The osseous part is described by the use of computed tomography to have an hourglass shape, angled in a dorsolateral-to-ventromedial direction and narrowing up to 4.6-4.7 mm with a length of 25.2-26.5 mm. That is why endoscopic instruments are usually too large to reach the level of the tympanic membrane [9]. Moreover, the sensitivity of many horses makes otoscopic evaluations quite difficult. Cole [16] describes the normal external ear canal in small animals as smooth, light pink, and containing minimal debris, such as hair, ceruminoliths or foreign bodies. The tympanic membrane is divided into the upper
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pars flaccida and the lower pars tensa. It is translucent, and the stria mallearis should be visible. The stria mallearis describes the attachment of the manubrium of the malleus. The sensitive innervation of the outer and inner surfaces of the auricle is mediated by the great auricular nerve, a branch of the second cervical nerve (CII). The external ear canal is sensitively innervated by the internal auricular nerve, a branch of the facial nerve (CN VII) [10]. The great auricular nerve runs subcutaneously from the second cervical vertebra to the caudal aspect of the base of the ear. The internal auricular nerve runs underneath the parotid gland, next to the lateral recess of the guttural pouch and enters the auricle at its deepest point, adjacent to the styloid process [11]. Local anesthesia techniques of the equine head are mainly performed for procedures such as eyelid, dental and paranasal sinus surgery, mandibular fracture repairs and transendoscopic laser surgery [12]. McCoy et al. [13] described a technique for blockage a horse’s ear based on palpation of the great auricular nerve on the caudal aspect of the base of the auricle. A cadaver head study about an anesthesia technique of the great and internal auricular nerve has recently been published by the authors [14]. Video endoscopy of the external ear canal, including the tympanic membrane, has so far only been performed on the heads of cadavers [9] or under general anesthesia [2,15]. The aim of this study was to develop an examination technique of the external ear canal in standing sedated horses. A further purpose of this study was to describe the degree of ceruminous debris in the cartilaginous part, cell debris and epithelium color in the osseous part, appearance of the tympanic membrane and additional abnormalities.
2. Material and Methods 2.1. Animals The pigmented cartilaginous and nonpigmented osseous parts of the external ear canal were examined endoscopically in 23 Warmblood Horses. Endoscopy of the osseous part and evaluation of the structure of the tympanic membrane were done under local anesthesia. Local ear anesthesia was performed under ultrasound guidance. The trials were approved by the Commission of Animal Welfare. There were 3 stallions, 16 geldings and 4 mares. The ages of the horses ranged from 10 to 25 years old (median, 16 years old). All horses were stabled in inside boxes and turned out daily. None of the horses had a history of ear disease or headshaking or showed other neurological symptoms. The horses were moved into stocks and sedated at the beginning of manipulation. Sedation was accomplished with detomidine (0.02 mg/kg of body weight [bw], IV [Cepesedan; CP Pharma, Burgdorf, Germany]) and butorphanol (0.01-0.05 mg/kg bw, IV [Alvegesic; Virbac Schweiz AG, Glattbrugg, Germany]). The skin over the palpable great auricular nerve and the styloid process of the auricular cartilage was clipped and aseptically prepared. All of the horses were closely monitored for the next 2 weeks to facilitate the detection of possible complications.
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2.2. Ultrasonography The entrance point of the internal auricular nerve into the auricle is formed by the styloid process. As this is also the area where local anesthesia should be performed this cartilaginous process was seen as the desired landmark. The close proximity of the internal auricular nerve to the parotid gland and the guttural pouch warrants ultrasonographic evaluation prior to local anesthesia. With the help of ultrasonography, the enhanced vascularity of the parotid gland was pictured to avoid vessel puncture. Furthermore the border of the guttural pouch can be seen, which prevents the loss of anesthetic due to an accidental puncture. The region of interest was shaved and cleaned with alcohol. The examination was accomplished with a 10-MHz rectal probe (GE Logiq 5 Expert; Scil, GmbH, Viernheim, Germany) with 40-mm penetration depth, which appeared to be most suitable for this region. The probe was placed in a vertical plane directed caudal of the zygomatic process of the temporal bone and in extension to the longitudinal axis of the auricle for localizing the styloid process (Fig. 1). 2.3. Local Anesthesia Local anesthesia of the great auricular and internal auricular nerves was performed in 23 horses, providing full desensitization of the auricle and the external ear canal for endoscopic evaluation of the tympanic membrane. A 21-G needle (Sterican B; Braun Melsungen AG, Berlin, Germany) was used for the injection. The great auricular nerve was palpable subcutaneously at the caudal aspect of the base of the ear (Fig. 1). The local blockage was performed with 2 ml of lidocaine hydrochloride (Xylocitin, loc 2%; Mibe GmbH, Brehna, Germany). The internal auricular nerve was blocked right at the styloid process using 3 ml lidocaine hydrochloride. Desensitization of the external ear canal was tested five minutes later by inserting a cotton bud. Defense reactions were observed and the result of the local anesthesia technique was evaluated. If necessary, the injection had to be repeated. As soon as no signs of
Fig. 1. Right side of the head. Placement of the probe in a vertical plane caudal to the zygomatic process of the temporal bone and in extension to the longitudinal axis of the auricle to localize the styloid process. C, indicates landmarks for local anesthesia of the great and internal auricular nerve.
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discomfort occurred (e.g., headshaking), anesthesia was regarded as successful. 2.4. Endoscopy The chemical restraint of the horses was supplemented with a twitch. Endoscopy was accomplished with a flexible video endoscope (Karl Storz GmbH, Tuttlingen, Germany) with a 7-mm diameter tip. Another flexible video endoscope with 2 mm diameter tip from the same company was used in order to become familiar with normal structures of the tympanic membrane and thus to identify any abnormalities in the deeper region of the osseous part which was not seen in every detail by the first scoping. The desired landmarks were formed by the junction between the pigmented cartilaginous part and the nonpigmented osseous part of the external auditory meatus, and finally, the tympanic membrane. The skin and epithelium color as well as the degree of debris both of the cartilaginous and the osseous part of the external ear canal together with the translucent tympanic membrane were evaluated. Based on these findings a tentative grading description including abnormalities was made, which is characterized in Table 1. 2.5. Statistical Analysis Calculation was performed using Excel version 12.0 (Microsoft, Redmond, WA) and PASW version 18.0 software. Results were reported as ranges and medians. The correlation of the degree of debris between the cartilaginous and osseous parts was analyzed using the Spearman correlation coefficient. Significance was set at a P value of <.05. 3. Results 3.1. Ultrasonography The cartilage of the auricle and the parotid gland were pictured in both ears of 23 horses. The ear cartilage was traced to its end, where the styloid process became visible. It appeared as a thin hyperechoic line and its tissue depth
varied from 2.08 to 2.73 cm on the left side (median, 2.44) and from 2.04 to 2.76 cm on the right side (median, 2.45). The enhanced vascularity of the parotid gland was pictured by the use of Doppler ultrasonography (Fig. 2). The boundary of the air-filled guttural pouch was marked ultrasonographically. 3.2. Local Anesthesia Nerve blocks of the great and internal auricular nerves were carried out on 23 sedated horses. The needle placement was very well tolerated, and no signs of discomfort appeared. Based on the Doppler ultrasonography a vessel puncture in the parotid gland was avoided in every case. Desensitization of the auricle and the external ear canal in both ears of 20 of the horses occurred 5 minutes postinjection of local anesthesia. In the other three horses, no or only slight desensitization of the external ear canal occurred, which required a repeated injection of internal auricular nerve anesthesia with 2 ml of the local anesthetic. The great auricular nerve was successfully anesthetized in these cases. However, these horses had mildly drooping ears and ptosis due to bilateral facial nerve paralysis simultaneously with the onset of anesthesia, which persisted for 4 hours. Therefore, eye ointment (Kerato Biciron 5%; SK Pharma GmbH, Herford, Germany) was administered in three occasions. 3.3. Endoscopy The horse’s ear in each case was held with one hand, and the endoscope was carefully inserted in a vertical direction (Fig. 3). In this way, using the flexible video endoscopes with 2- or 7-mm tip diameter, the cartilaginous part lined with pigmented skin, covered with fine hairs and brownish or black ceruminous debris became visible. As a result, the junction with the nonpigmented osseous part of the external ear canal was exposed (Figs. 4 and 5). The highest degree of ceruminous and cell debris was found in this area in all horses (Figs. 6 and 7). The epithelium of the osseous part of the equine external ear canal appeared to be light pink (Fig. 5). The grading of endoscopic appearance
Table 1 Grading of endoscopic appearance of the skin, epithelium and ceruminous and cell debris in the cartilaginous and osseous part of the equine external ear canal and assessment of abnormalities Grading of Endoscopic Appearance
Cartilaginous Part
I
Pigmented skin is visible; a small amount of ceruminous debris is closely attached to the pigmented skin and little dust on hair Pigmented skin is hardly visible, and dirt formations, dust on hair, and several free ceruminous debris formations are observed
II
III
Abnormalities
Osseous Part
Junction is clearly contoured; light pink epithelium; visible translucent tympanic membrane characterized by central visible stria mallearis Junction surrounded by a rim of cell debris; light pink epithelium; several free ceruminous and cell debris formations and dirt particles; translucent tympanic membrane is characterized by central stria mallearis, hardly visible Pigmented skin not visible; presence of dirt formations, dust Partially or completely obstructed junction is the result of and dirt, with sticky hair, and massive ceruminous debris ceruminous and cell debris including dirt accumulation; formations tympanic membrane is not visible For example, erythematous and/or hemorrhagic lesions, granulomas, osteomas, stenosis (exostosis), foreign bodies, blood accumulations, exudations, parasites (ear mites, mosquitoes, ticks, ants, insects), congenital defects
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Fig. 2. Ultrasonographic evaluation of the depth of the styloid process of a 17-year-old Warmblood gelding, using a 10-MHz rectal probe with 40-mm penetration depth. The blood flow in the parotid gland was pictured by the use of Doppler ultrasonography.
based on our evaluation (Table 1) varied between I and III in the cartilaginous parts (median: II), and in the osseous parts (median: I). Statistically all variables were not normally distributed. There was a significant positive correlation between the debris of the cartilaginous and osseous part within one ear as well on the left (0.539) as on the right side (0.436). So it is safe to assume that horses with a severe pollution of the cartilaginous part also suffer from
Fig. 3. Vertical insertion of the flexible video endoscope with 2-mm tip diameter in the right external ear canal after local anesthesia.
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Fig. 4. Right external ear canal of a 15-year-old Warmblood gelding. The junction between the pigmented cartilaginous and the nonpigmented osseous part of the equine external ear canal is visualized with a flexible video endoscope. Endoscopic appearance with a grade I of the external ear canal.
severe debris in the osseous part of the external ear canal, even if an advancing of the endoscope in a deeper position is not possible. An obstructed osseous part was found bilaterally in 3 of 23 horses (Fig. 7). The following detected abnormalities were described: a light pink, pinhead-sized mass (approximately 2 mm) like an osteoma right next to the pars tensa of the tympanic membrane at the bottom of the osseous part was seen in one external ear canal of one horse (1 of 23) (Fig. 8). An inflamed area like a granuloma (1 of 23) or hemorrhagic area (1 of 23) (Fig. 9) were only seen unilaterally. However, a narrowing of the osseous part of the external ear canal like an exostosis was shown bilaterally in 7 of 23 horses and was considered an abnormality (Fig. 5). Compared to the horses which were considered to have a normal condition, no significant difference in the grade of pollution was seen.
Fig. 5. Left external ear canal of a 10-year-old Warmblood mare. Translucent tympanic membrane with the centered stria mallearis is seen at the bottom of the osseous part, light pink epithelium with delicately colored vessels, visualized with a flexible video endoscope. Endoscopic appearance of grade I and an abnormality like an exostosis at the bottom of the osseous part on the right side of the picture is visible.
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Fig. 6. Right external ear canal of a 16-year-old Warmblood gelding. The junction between the cartilaginous and osseous part is surrounded by inflamed, swollen, bloody skin; the entrance of the osseous part is partially obstructed, and the tympanic membrane is not visible (grading III).
Because of the described anatomical conditions of the equine external ear canal it was only possible to advance the flexible endoscope with 2 mm diameter tip into the osseous part, which enabled the exposure and examination of the tympanic membrane. The normal tympanic membrane characterized by the central stria mallearis, which is formed by the manubrium of the malleus, the pars flaccida (upper region) and the translucent pars tensa could have been pictured in both external ear canals of 20 Warmblood horses (Fig. 10). In the other three cases, the visualization of the tympanic membrane was prevented from severe accumulation of ceruminous and cell debris. No complications such as permanent facial nerve paralysis or parotid gland fistulas were detected in any horse after local anesthesia or external ear canal endoscopy during the next 2 weeks. 4. Discussion
Fig. 8. Suspected osteoma at the bottom of the left osseous part next to the pars tensa of the tympanic membrane of a 15-year-old Warmblood gelding.
It was possible to anesthetize both external ear canals of 23 horses. The proximity of the parotid gland and the guttural pouch to the internal auricular nerve was considered a problem in performing local anesthesia. Feared complications included local pain, swelling, infection, facial nerve paralysis, or the development of parotid gland fistulas. The development of salivary fistulas is described in some cases as a result of parotid gland traumas [19]. In the present study, none of the horses acquired parotid gland abnormalities. Facial nerve paralysis is described in relation to inner ear diseases and facial nerve inflammation occurs in the course of middle ear diseases, followed by contralateral hemifacial muscle activity [20]. As a matter of fact, it is assumed that increased tissue pressure as a result of the lidocaine hydrochloride injection may also be a reason for facial nerve paralysis or inflammation. None of the horses in this study developed hemifacial spasm following local anesthesia, however, mild bilateral facial nerve paralysis occurred in three horses. These were the horses which received 2 ml of lidocaine hydrochloride as the second injection. The paralysis was evident mainly in reduced
The present study is the first report describing an examination of the external ear canal in the standing horse.
Fig. 7. Right external ear canal of a 16-year-old Warmblood gelding. Obstructed osseous part is caused by ceruminous and cell debris; the tympanic membrane is not visible (grade III).
Fig. 9. Right external ear canal of a 10-year-old Warmblood mare. Hemorrhagic lesion is seen in the osseous part of the ear canal. Visible at the bottom of the osseus part are the tympanic membrane with stria mallearis (center, white), the pars flaccida (upper right, white), and the pars tensa (translucent, lower left).
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A study in dogs showed that an accumulation of ceruminous debris within the ear canal also significantly affects hearing ability [21]. Cerumen impaction describes the accumulation of ear wax in the ear canal and occurs mostly in elderly human beings [22]. The partial obstruction described at the entrance point (Fig. 6) or the total obstructed osseous part (Fig. 7), because of severe ceruminous and cell debris formation, may have caused hearing loss in the two horses. Due to the relatively homogenous age of the animals examined, no statement about the different degree of debris of the external ear canals in miscellaneous age classes can be made. Further studies of more animals will be necessary to describe the occurrence of pathologies of the external ear canal including tympanic membrane of horses. 5. Conclusions
Fig. 10. Left external ear canal of a 16-year-old Warmblood gelding. The tympanic membrane is shown.
eyelid and ear reflexes. None of the other horses, however, showed similar symptoms, so the paralysis was clearly attributable to the larger amount of local anesthetic and was transient for the duration of local anesthesia. Other feared complications, such as inflammation of the injection side, were not reported within the following two weeks. The entire external ear canals, including the tympanic membrane, were visualized by the use of two flexible video endoscopes. The tympanic membrane with the central stria mallearis could be more accurately examined with the video endoscope with 2 mm tip diameter, due to the anatomic conditions of the equine external ear canal. The advantages of using a video endoscope in comparison to a handheld otoscope for the otoscopic examination include the high degree of magnification, and the greater visualization of the osseous part and tympanic membrane with a more detailed resolution. Furthermore, images of the external ear canal and the tympanic membrane may be captured and saved during any procedure [16]. However, it is important to standardize the orientation of the video endoscope in relation to the position of the animal. Otherwise it can be difficult to recognize abnormalities in the ear [17]. A recent report even describes the treatment of external otitis by the use of video otoscopy [18]. The degree of resolution of the video endoscopes used in the present study was accurate to identify normal findings like ceruminous and cell debris, and abnormalities like osteoma, granuloma, hemorrhage, and exostosis. Exostoses were defined as bony neoformations within the osseous part of the external ear canal while stenoses were assumed to be caused by tissue swellings in either one of the parts. In this study abnormalities like osteoma, granuloma, and hemorrhage occurred unilaterally, wherever ceruminous and cell debris and the abnormalities like exostoses occurred bilaterally. The missing histological differentiation of the described masses is clearly a limitation of this study, because suspected diagnoses could not have been confirmed.
Combined with local anesthesia endoscopy is a reliable technique to visualize the external ear canal, including the tympanic membrane, in standing sedated horses. Endoscopic examination of the external ear canal should be carried out on skittish horses or horses with symptoms of ear rubbing, aural discharge or headshaking, on horses with a history of facial asymmetry including keratoconjunctivitis or of head trauma, followed by ataxia and head tilt or at least on horses which have a high startle response. After this evaluation of external ear canals a different accumulation of ceruminous and/or cell debris in the osseous part and pollution in the cartilaginous part were seen in all horses with normal condition. In cases with increased grading of ceruminous and/or cell debris removal of debris with an ear wick or with a foreign body forceps through an endoscope is recommended. References [1] Fjordbakk CT, Kenney DG, Rodriguez-Palacios A, Keller S, Stalker M. Inflammatory aural polyp in a horse. Can Vet J 2006;47:65–6. [2] Oosterlaan-Mayer B, Van der Kolk JH. Endoscopically guided thermocautery and laser removal of an inflammatory polyp associated with chronic otitis externa in a pony. Equine Vet Educ 2006;18: 256–9. [3] Bowers JR, Slocombe RF. Auricular chondrosis in a horse. Aust Vet J 2009;87:219–21. [4] Hughes KJ, Hodgson DR. Unilateral ataxia and head tilt in a 7-yearold thoroughbred stallion. Aust Vet J 2006;84:139–42. [5] Aleman M, Puchalski SM, Williams DC, Kass PH, Holliday TA. Brainstem auditory-evoked responses in horses with temporohyoid osteoarthropathy. J Vet Intern Med 2008;22:1196–202. [6] Davis EG. Headshaking. In: Proceedings of North American Veterinary Conference 2005;143–144. [7] Schüle E, Herling A. Headshaking of horsesda review. Pferdeheilkunde 2006;22:281–95. [8] Dyce KM, Sack WO, Wensing CJG. Sense organs. In: Dyce KM, Sack WO, Wensing CJG, editors. Textbook of veterinary anatomy. 4th ed. St. Louis, MO: Saunders Elsevier; 2010. p. 332–53. [9] Sargent SJ, Frank LA, Buchanan BR, Donnell RL, Morandi F. Otoscopic, cytological and microbiological examination of the equine external ear canal. Vet Dermatol 2006;3:175–81. [10] Dyce KM, Sack WO, Wensing CJG. The head and ventral neck of the horse. In: Dyce KM, Sack WO, Wensing CJG, editors. Textbook of veterinary anatomy. 4th ed. St. Louis, MO: Saunders Elsevier; 2010. p. 501–31. [11] Budras KD, Sack WO, Röck S. Head. In: Budras KD, Sack WO, Röck S, editors. Anatomy of the horse. 5th ed. Hannover, Germany: Schlütersche Verlagsgesellschaft; 2009. p. 32–52.
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