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the CT images. Toth and Hollerrieder (2013) also have described an ultrasound-guided retrobulbar block in horses with a similar approach (Fig 6), followed by CT assessment of local anaesthetic spread. They describe the use of Tuohy needles to advance a catheter into the retrobulbar intraconal location for repeated injections.


Internal auricular nerve block To enable otoscopic examination of the equine external ear canal including the tympanic membrane in sedated standing horses, the internal auricular nerve block can be performed. Sommerauer et al. (2012) provided a detailed anatomical dissection of the equine external ear canal and its nerve supply and described anaesthesia of the equine external ear canal by desensitising the internal auricular nerve. Ultrasound- guided localisation of the styloid process of the auricular cartilage was described as a reliable landmark for desensitisation of the internal auricular nerve, which is a branch of the facial nerve that provides most of the sensory innervation to the equine external ear canal.


Advanced imaging guided procedures


The role of modern imaging techniques, such as CT and magnetic resonance imaging in equine medicine, has expanded in the last decades and these techniques are becoming more widely available for clinical use. For


visualisation of the equine skull and the related perineural anaesthetic techniques, CT imaging can especially be very helpful as has been stressed in various review studies (Porter and Werpy 2014; Manso-Dıaz et al. 2015). The introduction of sliding gantry CT scanners that allow for standing procedures in sedated horses without exposure of personnel, has further increased the possibilities to use this technique without significant risks for the patient (such as complications related to general anaesthesia). These imaging techniques are very useful for assisting with locoregional techniques as well. This clinical application is still under development and should be explored further. Tomaszewska et al. (2014), used a CT scan to determine


anatomical landmarks for localisation of the greater palatine foramen in man. CT scans have been used to compare two different techniques for maxillary nerve blocks in horses and yielded very useful information on anatomical landmarks for these techniques (Staszyk et al. 2008). These authors assessed a modified superficial (extra periorbital fat body) technique, in which the needle is not inserted up to the palatine bone (where the maxillary nerve is located) and showed it to be effective and safer than the more conventional palatine bone technique. The cadaveric and CT images from this study provide invaluable information about the regional anatomy of the maxillary nerve in relation to accompanying structures such as blood vessels (Fig 7). CT has also been used to aid maxillary nerve block placement in a human


ipc po pb in dfv PBI EFBI dpa a) 20 mm b) ia mm m 20 mm dpa c) m 20 mm


Fig 7: Regional anatomy of the maxillary nerve in cadaveric specimens and matching CT scans. a) Transverse section through the left pterygopalatine fossa of a deep frozen specimen, rostral view. The inset indicates the section plane at the level of the caudal third of the eyeball. The lines indicate the position of the tip of the needle for performing a maxillary block (x). The needle was inserted either until its tip touched the palatine bone (PBI: Palatine Bone Insertion) or the needle was inserted only for 15–20 mm into the extraperiorbital fat body (EFBI: Extraorbital Fat Body Insertion). b) The same picture as in (a) to demonstrate selected anatomical landmarks. The transition from the masseter muscle (mm) to the extraperiorbital fat body (epfb) is clearly visible. c) CT image corresponding to (a) and (b). The periorbita (po) separates the extraperiorbital fat body (epfb) from the intraperiorbital compartment (ipc). Note that the infraorbital nerve (in) is located directly next to the palatine bone (pb). The infraorbital nerve is accompanied by the infraorbital artery (ia) laterally and by the descending palatine artery (dpa) ventrally. The deep facial vein (dfv) is embedded in the extraperiorbital fat body (epfb). ba – buccal artery; pb – perpendicular plate of the palatine bone; za – zygomatic arch; m – mandible; bo – bulbus oculi. Reproduced with permission by Staszyk et al. (2008).


© 2017 EVJ Ltd epfb ba ia dfv epfb mm za pb in za


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