EQUINE VETERINARY EDUCATION / AE / FEBRUARY 2018


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Le Vet


room of hospitals (Weninger et al. 2007). Studies have found that the use of CT as a primary investigation of trauma patients reduces both missed injury rates and delays to definitive management (Hilbert et al. 2007; Wurmb et al. 2009; Lawson et al. 2011; Sierink et al. 2012). Before the invention of standing CT in horses, the risk and


cost of a GA was a major disadvantage of CT in horses. These risks are justified when specific treatment can be advised (MacKay 2004; Jose-Cunilleras and Piercy 2007), but greatly reduced now that the technology permits scanning the standing horse. Unfortunately, this is not practical in young foals due to their size, or in neurologically compromised individuals due to safety. Findings of the ultrasound study performed two days after


Fig 4: Longitudinal ultrasonograph of the left SS tendon near its insertion. Cranial is to the left. The normal longitudinal fibre pattern of the tendon is reduced cranially and absent cranial to a linear hyperechoic zone (red arrow).


the new owner’s veterinarian not to be showing any appreciable abnormalities.


Discussion


Nuchal ligament and semispinalis capitis injury There have been no previous reports of acute injury to the NL or SS in foals. There is one previous description of chronic avulsion of the tendon of the right SS muscle in a textbook description of CT images (Saunders et al. 2011). Laceration and avulsion fractures of the nuchal crest are


common when horses flip over backwards (Ragle 1993). In a previous case series of two horses with nuchal crest avulsion fractures, both horses had sustained trauma to the poll region (Voigt et al. 2009). It is likely that the mechanism for injury in the case described was blunt trauma when the foal’s poll collided with a manger.


Imaging The decision to perform a CT as a primary diagnostic step in this case was well justified. It allowed for a rapid and accurate assessment of a young potentially neurologically compromised foal. A radiograph may have allowed visualisation of some of the changes seen on CT and ultrasound, such as air within the soft tissues and fragments of bone. Whilst radiography is useful in assessment of traumatic injuries of the equine head it does have limitations. It cannot allow evaluation of intracranial structures and in one study by Feary et al. (2007) radiographs failed to identify 50% of fractures of the calvarium, including basilar bone fractures (Ramirez et al. 1998; Feary et al. 2007; Kinns and Pease 2009). The benefits of CT for assessment of trauma patients are


well acknowledged in human medicine (Chan 2009) where there is great emphasis on recognising and treating injuries within the ‘golden hour’ (Saltzherr et al. 2013) and it is becoming routine to install CT machines in the emergency


presentation correlated well with those of the CT. An ultrasound examination at presentation may have provided an accurate diagnosis. However, ultrasonographic examination and interpretation in this area is difficult (Dyson 2011a). Furthermore, a thorough investigation would have been hindered in this case by subcutaneous air, haemorrhage, soft tissue disruption and the demeanour of the foal. Ultrasonography lacks sensitivity for the detection of many other types of lesions that CT may have detected and both Nowak (2001) and Dyson (2011a) have previously suggested that CT is the most sensitive modality to recognise lesions of either the NL or border of insertion of SS.


Neurological findings The CT failed to identify a lesion of the central nervous system (CNS). The head tilt and altered head carriage were likely a result of the trauma to the soft tissues supporting the head, pain or a combination of both. Treatment with hypertonic saline was initiated immediately after injury due to concerns about potential brain injury. This was discontinued following CT.


Compared with magnetic resonance imaging (MRI), CT is


less sensitive for the detection of lesions of the CNS and may have failed to identify a lesion in our case (Gilman 1998). In human medicine MRI is the preferred modality for most neurological diseases except for abnormal calcification, disorders of bones and joints and acute subarachnoid haemorrhage (Gilman 1998; Sogaro-Robinson et al. 2009). In addition, beam-hardening artefact in the caudal fossa between the temporal bones can limit assessment of the brain parenchyma (Sogaro-Robinson et al. 2009; Hecht 2011). Magnetic resonance imaging is limited in its availability for most of the horse population, suffers from much longer scan times and is not as effective as CT for detecting acute subarachnoid haemorrhage (Gilman 1998; Kinns and Pease 2009). Intravenous iodinated contrast medium can be used to


enhance vascular mass lesions and to aid detection of inflammation and diseases that disrupt the blood-brain barrier on CT images (Kraft and Gavin 2001; MacKay 2004) and may have helped identify a lesion. However, in one study of 57 horses affected by neurological disorders, the use of contrast identified lesions in only one horse for which a lesion had not been diagnosed or suspected on plain CT (Sogaro-Robinson et al. 2009). At the time of CT diagnosis we thought that the prognosis


was fair. A previous report describes a series of two cases of Thoroughbred horses developing head-shaking as a result of nuchal crest avulsion fractures, both of which were assumed to be caused by trauma to the poll region (Voigt et al. 2009).


© 2016 EVJ Ltd


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