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Fig 5: Transverse CT images of the brain of a foal pre- (a) and post contrast injection (b) (right is to the left). A noncontrast enhancing curvilinear hyperattenuating band is observed between the brain and osseous structures on the right side (asterisks), corresponding to a subdural haematoma. There is swelling of the subcutaneous soft tissues on the left side of the head (arrowheads).
exophthalmos was observed in all cases. One case had a ring-shaped contrast enhancement confirmed to be an abscess. Squamous cell carcinoma was the final diagnosis in the other 2 cases. One had intracranial invasion with lysis of the presphenoid and temporal bones. Computed tomography findings for acute subdural haematoma consisted of a curvilinear hyperattenuating area between the brain and osseous structures, with an average CT attenuation value of 75 HU and no contrast enhancement (Fig 5). There was also swelling of the subcutaneous soft tissues on the left side of the head. Abnormalities for the case of nuchal bursitis included
dystrophic mineralisation dorsal to the atlas and atlanto-occipital junction and marked distension of the cranial nuchal bursa. It appeared as a large fluid pocket (9 HU) extending from the foramen magnum up to the cranial portion of the second cervical vertebra. A focal mineralisation was also detected within the nuchal ligament dorsal to the distended bursa. The parotid mucocele consisted of a rounded and well-defined fluid pocket lateral to the parotid gland, with an average density of 14 HU. The remaining parotid gland volume appeared reduced.
Discussion
Computed tomography is commonly used to obtain images of the head in horses with a wide array of conditions. The aim of the present study was to describe the CT features of the most common equine head disorders and compare them with other imaging modalities when available. The most prevalent condition was dental disease. Radiographic (Wyn-Jones 1985a; Gibbs and Lane 1987; Townsend et al. 2011) and CT (Henninger et al. 2003; Veraa et al. 2009) features of this condition have previously been described. Radiography is currently still the most commonly employed diagnostic imaging modality for investigating dental disorders (Townsend et al. 2011). However, this technique is not a very reliable method for the diagnosis of dental disease in the horse, especially in cases of periapical infection. Previous studies estimated the sensitivity for the
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diagnosis of periapical infection between 50 (Gibbs and Lane 1987) and 57% (Tremaine and Dixon 2001a). The slightly higher sensitivity using radiography observed in this study could be explained by the use of digital radiography or may merely reflect a difference of population. A comparative study between radiography and scintigraphy showed the latter had a high sensitivity but low specificity (Weller et al. 2001). However, no studies comparing radiography and CT are available. Using both modalities, we agreed in identification of affected teeth in 16 of 32 cases (50%) and disagreed on the identification of all clinically relevant teeth in 7 cases (22%). With CT we were able to identify all clinically affected teeth, but in 5 horses the use of CT resulted in identifying abnormalities in more teeth than clinically detectable. The importance of this finding remains questionable and further investigation on the long-termclinical outcome of these teeth is necessary. One of these horses was rescanned for nasal discharge one year later and showed severe changes in one tooth previously described as abnormal by CT. However, mild changes in teeth, such as nondetectable lamina dura, have been observed using CT in horses without dental clinical signs (Bühler et al. 2014). Availability of standing CT units would make it more feasible to follow-up these subtle findings, avoiding general anaesthesia, which is one of the main limitations of this modality. This would increase the understanding of whether these findings progress over time. More dental abnormalities, such as disruption of the lamina
dura and tooth fractures, were found with CT (Fig 6); CT being, for example, superior at detection of pulp and infundibular abnormalities. Detailed examination of the internal structure of the tooth is important in deciding on its treatment. The use of thin slices (1 mm) and multiplanar reconstructions assisted with the identification of mild changes. Infundibular abnormalities, such as hypoattenuation in the infundibulum, must be studied carefully in each case. This can represent air or necrotic cementum. A recent study reported the relationship between infundibular caries and the frequency of CT changes within the infundibulum, but a direct relationship between the 2 processes has not been established (Veraa et al. 2009). In another study, infundibular changes occurred as a single CT feature not associated significantly with CT signs of apical
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