EQUINE VETERINARY EDUCATION / AE / AUGUST 2019


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a) A C D B C D


Fig 4: Diamond block. Needle setting on a) skull and b) head for diamond block (A, supraorbital nerve; B, lacrimal nerve; C, infratrochlear nerve; D, zygomatofacial nerve).


(Beukers et al. 2016). The hyperechoic structures are the fascicles of the nerves; the hypoechoic background reflects the connective tissue between neuronal structures. The nerve’s image is sensitive to the angle of insonation because of the presence of fat (Re et al. 2016).


Maxillary nerve block Ultrasound guidance for the maxillary nerve block has been described both in man (Bouzinac et al. 2014) and in horses (O’Neill et al. 2014). In the study by Bouzinac et al. (2014) efficacy of the block was not tested by pinpricks since the patients were under general anaesthesia, but ultrasound guidance allowed for accurate placement of the needle by visible spreading of the local anaesthetic into the pterygopalatine fossa. O’Neill et al. (2014) described the


a)


technique both in equine cadavers and in a number of clinical cases in a standing procedure. Ultrasound permits identification of the bony landmarks of the pterygopalatine fossa that can guide the needle towards the maxillary nerve and determination of the position of the needle relative to the greater vascular structures accompanying the maxillary nerve (deep facial vein, infraorbital artery, descending palatine artery). Puncturing of these vascular structures can cause serious side-effects such as temporary blindness, haemorrhage and severe swelling. Ultrasonography can be very helpful in improving the safety and efficacy of maxillary nerve blocks (Fig 5) and has proven to be an accurate and precise technique without any complications in clinical cases (O’Neill et al. 2014), compared to the blind technique (Bardell et al. 2010). Colour flow Doppler can be very useful


b) B


b) A


c)


d)


C A C E F D


Fig 5: a) and b) relative positioning of the ultrasound probe and the needle for ultrasound-guided maxillary nerve block. c) masseter muscle (A) and underlying extraperiorbital fat tissue (B) with the deep facial vein (C) embedded in the extraperiorbital fat tissue and the maxillary nerve situated deeper (D), in close proximity of the infraorbital artery (E) and the descending palatine artery (F). d) Ultrasound with colour Doppler image showing the maxillary nerve at the needle tip (white arrow) and associated vascular structures (C, deep facial vein, red and blue Doppler traces are infraorbital artery and the descending palatine artery; G, tuberosity of the maxillary bone).


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