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The Nasolacrimal Duct of the Mule: Anatomy and Clinical Considerations M

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The Nasolacrimal Duct of the Mule: Anatomy and Clinical Considerations M 636 EQUINE VETERINARY EDUCATION / AE / DECEMBER 2013 Original Article The nasolacrimal duct of the mule: Anatomy and clinical considerations M. F. Adams*, J. R. Castro, F. Morandi†, R. E. Reese and R. B. Reed‡ Departments of Large Animal Clinical Sciences, †Small Animal Clinical Sciences, and ‡Biomedical and Diagnostic Sciences, College of Veterinary Medicine, University of Tennessee, USA. *Corresponding author email: [email protected] Keywords: horse; mule; nasolacrimal duct; donkey; anatomy; computed tomography; dacryocystography Summary Mules were administered detomidine hydrochloride 1 This study investigated the location of the nasolacrimal orifice (Dormosedan) (0.015 mg/kg bwt i.v.) to facilitate (NLO) and course of the nasolacrimal duct in the mule examination. Each nasal vestibule was examined to using visual examination, gross dissection and computed determine the location of the NLO. The nasolacrimal duct of 9 tomography (dacryocystography [CT-DCG]) and concluded mules was lavaged using a technique previously described for 2 that the location of the NLO is distinct from that described for the horse (Michau 2005). Lidocaine hydrochloride gel was horses and donkeys and is easily located, by visual applied to the NLO prior to inserting a 14 cm (5.5 inch), 3.5 Fr, 3 examination alone, within the internal cutaneous tissue of the open-end, tomcat catheter . Once catheterised, the duct lateral wall of the external nares. The course of the was occluded with digital pressure and lavaged in retrograde 4 nasolacrimal duct caudal to the nasal vestibule is similar to fashion with 6–10 ml of sterile, eye irrigating solution injected that of the horse. slowly until the solution flowed from the medial canthus. Introduction Computed tomography - dacryocystography The 4 university owned mules were subjected to euthanasia The equine lacrimal system consists of both secretory and immediately before CT-DCG and the heads removed at drainage portions and is composed of the lacrimal gland, 2 the atlanto-occipital joint. The specimens were positioned lacrimal puncta, 2 canaliculi, a lacrimal sac, the nasolacrimal on the CT table in ventral recumbency and CT-DCG was duct and NLO (Latimer et al. 1984). The anatomy of the performed using a previously published technique (Nykamp nasolacrimal duct of the horse and the donkey has been et al. 2004), which entailed inserting a 14 cm (5.5 inch), 3.5 Fr, previously described (Said et al. 1977; Latimer et al. 1984) and open-end, tomcat catheter3 into the NLO of the right and left several variations exist, most notably the location of the nares and injecting a radiographic contrast medium (Optiray nasolacrimal orifice (NLO). The NLO of the horse is located on 350; Ioversol 350 mg/ml organically bound iodine)5 into the floor of the nasal vestibule near the mucocutaneous the nasolacrimal duct until it exited the lacrimal puncta. junction (Latimer et al. 1984), whereas the NLO of the donkey The volume of contrast medium injected depended on the is located in cutaneous tissue in the dorsal external nares (Said size of the head and ranged from 1.0 ml (6-month-old, et al. 1977). Anecdotally, the location of the NLO of the mule miniature mule) to 5.5 ml (7-year-old, gaited-horse mule). Thin (Equus asinus x caballus) has been described as highly section, transverse images were obtained before and variable and difficult to locate visually. The aims of this study immediately after injecting the contrast medium using a were to determine the location of the NLO in a population of 40 slice multidetector CT scanner (DS Brilliance 40 Hybrid mules, to describe landmarks for locating the NLO, and to CT system)6 and the following imaging parameters: 40 × determine the course of the nasolacrimal duct of the mule 0.625 mm collimation, 0.474 pitch, 0.5 s rotation time, 120 kV, using gross dissection and CT-DCG. 2509 mAs/slice. Data were reconstructed using edge enhancing and standard algorithms. Edge enhancing was Materials and methods used to optimise evaluation of osseous structures and standard algorithms were used to optimise evaluation of soft tissues. Visual examination and nasolacrimal lavage Results were displayed with bone windows (window width: The left and right external nares of 40 mules were examined to 2600, window level: 660) and with soft tissue windows (window establish the location of the NLO and determine if retrograde width: 350, window level: 50). Images were evaluated using a lavage of the nasolacrimal duct was possible. Thirty-six mules dedicated workstation (Philips Extended Brilliance Workspace were privately owned and the cohort included mules 4.5) and multiplanar and 3D images were reformatted, as of varying age, sex and breed (gaited-horse mules, needed, from the transverse thin section data. Measurements nongaited-horse mules and draught mules). The remaining 4 were obtained on transverse images oriented 90° to the hard mules were university owned, including a 6-month-old, palate. miniature mule, one yearling mule and two 7-year-old gaited-horse mules. All mules were in good body condition, had no evidence of ocular or respiratory disease and Gross dissection appeared clinically healthy. All procedures performed on The tomcat catheter3 was left in place following CT-DCG and mules were approved by the University of Tennessee’s the left and right nasolacrimal ducts of each of the 4 heads Institutional Animal Care and Use Committee. were injected retrograde with red latex casting material7 until © 2013 EVJ Ltd EQUINE VETERINARY EDUCATION / AE / DECEMBER 2013 637 Fig 1: Left naris of mule showing placement of hand prior to eversion of naris. The NLO is located opposite the tip of the index finger within the nasal vestibule. Fig 2: Everted left naris of mule demonstrating the NLO (arrow) in Location A. observed to flow from the lacrimal puncta. The lacrimal puncta and NLOs were clamped with haemostats to prevent loss of casting material prior to polymerisation. The specimens caudomedial from the lateral edge of the naris (Fig 2). In 4/40 were injected with 10% formalin via the common carotid mules (10%), the NLO was observed on the floor of the nasal arteries, submerged in 10% formalin and refrigerated at 7°C for vestibule (Location B). One mule (2.5%) had a NLO in Location 7 days to allow the latex to solidify. The specimens were A and in Location B in both nares. hemisected longitudinally on the median plane using an Catheterisation and retrograde lavage of the nasolacrimal electric band saw before dissecting the nasolacrimal duct duct was performed in 9 mules. In these mules, including 3 with < from either a medial or lateral approach. The rostral and a NLO 1 mm, the tomcat catheter was inserted easily and caudal maxillary sinuses of 2 specimens were trephined using a with little resistance (Figs 3 and 4) and lavage was performed 2.54 cm (1 inch) Galt trephine8 using previously published without difficulty. landmarks for sinusotomy in the horse (Perkins et al. 2009). Multiple NLOs were identified in 5/40 mules (12.5%). In 4 of the 5 mules, 2 orifices, approximately 5–10 mm apart, were found bilaterally, although not always bilaterally symmetrical in Results location or in size. Of the 4 mules, 2 mules had double orifices Visual examination and nasolacrimal lavage in Location A and 2 mules had double orifices in Location B (Fig 5). In one of these mules, a Jones Test (passage of The NLO of the mule was easily located with visual fluorescein stain to the NLO after topical application to the examination in all 40 mules (36 live and 4 cadaver specimens). eye) was performed to evaluate patency and produced stain The average diameter of the NLO was about 1 mm but varied from both orifices of the right naris in approximately 5–6 min. between 0.25 and 4 mm. The most common location One mule had one orifice in Location A and one in Location B observed in 35/40 mules (87.5%) was in the internal cutaneous in both external nares. In this mule, catheterisation of both tissue of the lateral wall of the external nares. This location orifices revealed communication with each other and the (Location A) was easily visualised when the thumb was placed main nasolacrimal duct, allowing for retrograde lavage of the in the most dorsal aspect of the external naris, the index finger duct via either of the NLOs. was placed 6 cm in a caudolateral direction from the thumb towards the direction of the caudal border of the false nostril and the internal surface of the naris was everted (Fig 1). The Gross dissection orifice was found at the level of the tip of the index finger in the The right and left NLO of all 4 heads were found within the internal cutaneous tissue at the junction where the lateral wall cutaneous tissue of the lateral wall of the external naris (i.e. curved to meet the floor of the nostril, approximately 3.5–5 cm Location A). Within the tissue of the external naris, the duct was © 2013 EVJ Ltd 638 EQUINE VETERINARY EDUCATION / AE / DECEMBER 2013 Fig 3: Nasolacrimal catheterisation of the left naris using 5.5 inch 3.5 Fr tomcat catheter. Note the lateral location of the NLO in the cutaneous tissue of the external naris. Fig 5: Double NLO (arrows) observed in Location A of right naris of mule. to be visualised. When the duct reached the level of the caudal maxillary sinus, it entered the lacrimal bone where it was encased in a substantial amount of bone preventing its visualisation without further dissection. While passing through the dorsolateral aspect of the maxillary sinus, the nasolacrimal duct is located dorsal to the recommended site of maxillary sinus trephination in the horse (Fig 8).
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