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EQUINE VETERINARY EDUCATION / AE / MARCH 2015
Original Article The role of head computed tomography in equine practice
G. Manso-Díaz*, J. M. García-López†, L. Maranda‡ and O. Taeymans† Department of Animal Medicine and Surgery, School of Veterinary Medicine, Universidad Complutense de Madrid, Madrid, Spain; †Department of Clinical Sciences, Cummings School of Veterinary Medicine, Tufts University, Massachusetts, USA; and ‡Department of Quantitative Health Sciences, University of Massachusetts Medical School, Massachusetts, USA. *Corresponding author email:
gmanso@ucm.es
Keywords: horse; skull; CT; dental; sinus
Summary This retrospective study describes the computed tomography (CT) findings in 59 horses presented with diseases of the head over 8 years that underwent CT examination of this region, including dental or sinonasal diseases (Group A) (n = 42), osseous and/or articular diseases (Group B) (n = 11) and soft tissue diseases (Group C) (n = 6). For Group A, radiographic and CT findings comparison was possible. Computed tomography had higher sensitivity (100%) and specificity (96.7%) than radiography in diagnosing dental disease. Compared to CT, radiographic identification of sinus involvement was less sensitive, particularly for ventral conchal and sphenopalatine sinuses and presented an overall sensitivity of 43.5 and 16.7%, respectively. In Group B CT allowed identification of a higher number of bone fragments and fractures in the maxillary, lacrimal, sphenoidal, temporal and zygomatic bones not identified radiographically. Accurate identification of CT changes in the temporomandibular joint and temporohyoid articulation was also possible. Group C included both intra- and extra-cranial disease, retrobulbar masses being the most representative pathology (n = 3). In this group, CT was considered the gold standard for detection of periorbital diseases. We conclude that CT is an imaging technique with high diagnostic value for evaluating the equine head, yielding additional information over multiple radiographic views, which may alter the outcome of the case. Additionally, this paper reports several conditions not previously described using CT.
Introduction
The equine head is a complex anatomic area (Smallwood et al. 2002). Diseases involving the head are frequently encountered in horses and require imaging studies for further work-up (Tucker and Farrell 2001). Historically, radiography has been the primary imaging technique for assessing the skull, nasal cavity, dental structures and paranasal sinuses (Wyn-Jones 1985a,b; Tremaine and Dixon 2001a). However, the anatomic complexity and superimposition of the osseous, dental and soft tissue structures complicate radiographic interpretation (Tucker and Farrell 2001). Cross-sectional imaging modalities, such as computed tomography (CT) and magnetic resonance imaging (MRI), are therefore particularly useful for this area (Kraft and Gavin 2001; Solano and Brawer 2004). Several studies report the use of CT for a wide array of diseases, both intra- and extra-cranially (Tietje et al. 1996; Henninger et al. 2003; Hilton et al. 2009; Sogaro-Robinson et al. 2009; Lacombe et al. 2010; Pownder et al. 2010; Huggons et al.
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Computed tomography examination For CT studies, horses were examined under general anaesthesia in dorsal recumbency on a custom-built CT table. A single slice CT scanner (PQ5000)3 was used for 31 cases and a 16 slice CT scanner (Toshiba Aquilion 16)4 used for the remainder of the horses. The scanning protocol for the first scanner consisted of
nonhelical contiguous 5–8mm transverse slices using a bone algorithm, with a second acquisition of additional thinner slices (3 mm) through the abnormal region. The scanning protocol for the second scanner consisted of helical 0.5mm slice acquisition. Images were reconstructed as contiguous 5mm slice thickness in 3 orthogonal planes (transverse, dorsal and sagittal), using both soft tissue and bone reconstruction algorithms, displayed using standard bone and soft tissue window levels and widths. Thinner slices (1 mm) were also reconstructed through the abnormal region using the initial
2011; Cissell et al. 2012; Textor et al. 2012). However, most studies were restricted to certain pathologies and/or had a limited number of cases. The purpose of the present study was to describe the CT
features of the most common equine head disorders of a large number of cases and compare them with radiographs when available.
Materials and methods
Case selection A retrospective search of the medical records database from 2004 to 2012 at a referral centre was performed. Inclusion criteria were a final diagnosis of head disease and a CT scan of the head for the same reason. Three groups were established. Horses included in the first
group (Group A) presented for dental or sinonasal disease. The second group (Group B) included horses that were presented for osseous or articular disease and horses in the third group (Group C) for soft tissue, orbital or cerebral pathologies.
Radiographic examination All horses from Group A and most from Group B had a radiographic examination consisting of a lateral, dorsoventral and one or both oblique projections (dorsolateral- ventrolateral or ventrolateral-dorsolateral depending on the location of the disease). Radiographs were acquired either with 14 x 17" computed radiography cassettes (Kodak CR 850 System)1, or using a 14 x 17" direct radiography flat panel (Eklin Mark 5 System)2.
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