Computed tomography and magnetic resonance imaging of the equine head

An application of the density standard and scaled-pixel-counting protocol to assess the radiodensity of equine incisor teeth affected by resorption and hypercementosis: preliminary advancement in dental radiography

BACKGROUND

Equine Odontoclastic Tooth Resorption and Hypercementosis (EOTRH) syndrome is a dental disease where the radiographic signs may be quantified using radiographic texture features. This study aimed to implement the scaled-pixel-counting protocol to quantify and compare the image structure of teeth and the density standard in order to improve the identification of the radiographic signs of tooth resorption and hypercementosis using the EOTRH syndrome model.

METHODS AND RESULTS

A detailed examination of the oral cavity was performed in 80 horses and maxillary incisor teeth were evaluated radiographically, including an assessment of the density standard. On each of the radiographs, pixel brightness (PB) was extracted for each of the ten steps of the density standard (S1-S10). Then, each evaluated incisor tooth was assigned to one of 0-3 EOTRH grade-related groups and annotated using region of interest (ROI). For each ROI, the number of pixels (NP) from each range was calculated. The linear relation between an original X-ray beam attenuation and PB was confirmed for the density standard. The NP values increased with the number of steps of the density standard as well as with EOTRH degrees. Similar accuracy of the EOTRH grade differentiation was noted for data pairs EOTRH 0-3 and EOTRH 0-1, allowing for the differentiation of both late and early radiographic signs of EOTRH.

CONCLUSION

The scaled-pixel-counting protocol based on the use of density standard has been successfully implemented for the differentiation of radiographic signs of EOTRH degrees.

Correlation between computed tomography, magnetic resonance imaging and cross-sectional anatomy of the head of the guinea pig (Cavia porcellus, Linnaeus 1758)

The current work aimed to study the anatomical features of the guinea pig's head by two medical imaging techniques: computed tomography (CT) and magnetic resonance imaging (MRI), and their correlation with the anatomical cross-sectional images. Six adult healthy guinea pigs were used in the present study. Two heads were imaged by CT scanner and then by MRI. The examined heads were cut sagittally and transversely, and two skulls were macerated. The anatomical features were identified on the anatomical sections and compared with the tomographic and MRI images obtained. Data were presented as three-dimensional reconstructed images of the head. In addition, representative combinations of the sagittal and transverse anatomical sections and the corresponding CT scans and MRI images were also presented. Reconstruction of CT images enabled the visualization of different bony structures and airways of the guinea pig head. In addition, skull bones were easily visualized on CT scans, while different parts of the brain were identified on MRI images. Air cavities could be identified by their different contrast on the CT scans and their low intensity on MRI images. The study showed that guinea pig had poorly developed paranasal sinus system represented by rostral and caudal maxillary sinuses. On the contrary, the guinea pig had two tympanic bullae: a small dorsal and a large ventral bulla. In conclusion, this study provides one of the first investigations that uses the multislice CT scans and MRI to study the guinea pig's head and their correlation with the corresponding anatomical sections.

Correlated Imaging of the Equine Hyoid Apparatus Using CT, Micro-CT, and Histology

Background: Detailed radiological evaluation of the normal hyoid apparatus by computed tomography (CT) has not yet been conducted. Thus, it is unclear what type of junction connects the different parts of the equine hyoid apparatus.

Objectives: To describe the normal CT anatomy of the equine hyoid apparatus, and to determine the junction type that connects the different parts of the hyoid apparatus.

Study Design: Combination of retrospective study and prospective cadaver study.

Methods: The medical records of horses that underwent head CT scans from 2009 to 2018 were retrieved. Inclusion criteria for the CT scans were visibility of at least two of the four junctions of the hyoid apparatus. CT images were analyzed in three different planes. Additionally, 10 cadaver heads were processed using CT, micro-CT of selected joints, and histology of all joints.

Results: CT scans of 200 horses fulfilled the inclusion criteria. The tympanohyoid cartilage consisted of hyaline cartilage. Areas of mineralization within the cartilage were visible on CT scans as early as 2 years of age. The epihyoid was not fused with the stylohyoid in one-third of the horses. All horses younger than 2.5 years showed three ossification centers of the basihyoid, and all horses younger than 1.5 years had a non-fullydeveloped lingual process. In total, 10 of 11 horses between 1.5 and 3 years had separate ossification centers of the lingual process. We found a synchondrosis between the styloid process and the stylohyoid bone. The basihyoid and thyrohyoid, as well as the stylohyoid and epiyhoid were connected by a synostosis in two-thirds of the horses. The remaining parts were connected to one another by synovial joints.

Main limitations: The junctions studied by histologic examination were from older horses, therefore growing patterns of different bones could not be totally clarified.

Conclusion: The temporohyoid joint is a synchondrosis. The epihyoid is an ossification center of the stylohyoid and fuses with the stylohyoid in two-thirds of horses. The lingual process has a separate ossification center.

Position of the midline septum of the guttural pouches in horses subjected to computed tomography

Standing computed tomographic (CT) examination of the equine guttural pouch frequently reveals deviation of the midline septum. The significance of deviation is currently unknown. The aims of this retrospective, single-centre study were to determine the prevalence of deviation of the midline septum of the guttural pouch and determine whether there was an association between the presence and degree of deviation of the septum, and guttural pouch disease. Case records were reviewed, identifying 95 horses that had undergone a standing, sedated, head CT and guttural pouch endoscopy. The presence, laterality, subjective degree and angle of deviation of the midline septum on CT was recorded. A total of 69 (72.6%) horses were identified with deviation of the midline septum, with the mean angle of deviation 13.4^o and a maximum deviation of 52.6^o. No significant association between the presence of deviation of the midline septum (P = .722) or severity of deviation (P = .428) and an endoscopic abnormality within the guttural pouch was found. The laterality of deviation and guttural pouch abnormalities were also not associated (P = .000). Deviation of the midline septum of the guttural pouch is a common finding on CT examination, and does not have clinical significance in this study.

Multidetector CT and cone-beam CT have substantial agreement in detecting dental and sinus abnormalities in equine cadaver heads

The performance of cone-beam CT (CBCT) systems compared to conventional helical multidetector CT (MDCT) imaging of the equine head is unknown. The aim of this prospective, method-comparison study was to compare the ability of CBCT and MDCT to detect abnormalities in equine cadaver heads. Eleven equine cadaver heads were scanned using a CBCT scanner and a 64-slice MDCT scanner. Consensus evaluations for CBCT and MDCT scans were performed by three observers. Identified abnormalities were grouped into subcategories with a focus on dental abnormalities. Kappa agreement values between detected abnormalities for CBCT and MDCT methods were calculated. Of 468 teeth evaluated, 122 (26.1%) were found to have abnormalities (including in 58 infundibula and 7 pulps) using MDCT and 105 (22.4%) were found to have abnormalities (including in 52 infundibula and 2 pulps) using CBCT. The agreement between CBCT and MDCT was almost perfect for overall detection of dental abnormalities (k = 0.90) with k = 1 for diastema k = 0.95 for clinical crown abnormalities, and k = 0.93 for infundibular abnormalities. However, the detection of pulp changes by CBCT was only moderate k = 0.44. Increased scatter radiation, non-calibrated Hounsfield Unit and artefacts in CBCT images made accurate identification of the pulp density difficult. In conclusion, CBCT results were similar to conventional MDCT for the majority of dental abnormalities, however, pulp abnormalities were not reliably identified using CBCT, potentially limiting its clinical use for detecting endodontic disease in its current form. Further comparison with more cases with confirmed dental disease and studies in clinical cases are warranted.

Macroscopic anatomy, radiography and computed tomography of normal paranasal sinuses of the adult one-humped dromedary (Camelus dromedarius)

In order to improve the current knowledge of the topography and the anatomy of the paranasal sinuses of the one‐humped dromedary (Camelus dromedarius), we applied both conventional and advanced imaging techniques, namely, radiography and computed tomography (CT). Twelve heads of healthy dromedaries were used; eight heads were dissected to obtain skulls for the fenestration of the sinuses, two heads underwent anatomical sections, and two heads were imaged respectively by radiography and CT. Sinus fenestration allowed observation of sinuses and their communications. In each dissected dromedary's head, the frontal sinus is a large compartment delimited by thick partitions. The sphenoid sinus is divided into small compartments by bony plates. The lacrimal sinus occupies a small cavity in the rostro‐medial lacrimal bone of the orbit. In all dissected heads, there was neither palatal sinus nor ventral conchal sinus. Five images obtained by CT were selected with an excellent correspondence with the anatomical sections. These images allowed a good differentiation between bones and sinus cavities. The visualisation of the sinus cavities and their anatomical limits has better quality using the CT compared to the radiography. Radiographic and CT images are therefore very useful for the interpretation of clinical imaging studies of the dromedary's paranasal sinuses.

Equine Imaging: Computed Tomography Interpretation

Computed tomography (CT) has revolutionized the veterinarian's ability to image the equine skull and led to improved diagnostic accuracy and clarity for surgical planning. The increased cost for this evaluation is offset by more accurate diagnosis and targeted therapy. As novel technology is developed that allows for increased availability of equine head, the price will continue to decrease and more examinations will be performed. New skills are needed for the veterinarian to accurately interpret this modality. This article reviews the normal CT appearance of the equine skull and presents examples and key features of several common diseases.

Description of normal head structures of the one-humped camel (Camelus dromedarius) by magnetic resonance imaging, computed tomography, and cross-sectional anatomy

Aim:

This study was designed for the 1^st time to describe the normal head structures of one-humped camel (Camelus dromedarius) using both magnetic resonance imaging (MRI) and computed tomography (CT) as well as cross-sectional anatomy.

Materials and Methods:

Five fresh cadaver heads were collected from clinically normal camels and then subjected to T1-weighted MR and CT imaging. Afterward, these examined heads were transversely sliced to obtain seven crossing levels.

Results:

The obtained structures per each crossing level were matched with their relevant sorted images of T1-weighted MRI and CT, then identified and labeled accordingly.

Conclusion:

The data shown herein expand our knowledge of the normal head structures of the camel and could be used as a reference for ultimate diagnosis of the surgical affections of head using MRI and/or CT.

Computed tomography characteristics of equine paranasal sinus cysts

BACKGROUND

Computed tomography (CT) is commonly used to investigate equine paranasal sinus disease, however, only limited information is available in the literature about the detailed CT appearance of equine paranasal sinus cysts.

OBJECTIVES

To investigate if paranasal sinus cysts have specific characteristics in CT images that allow differentiation from other sinus diseases.

STUDY DESIGN

Retrospective observational study.

METHODS

Evaluation and comparison of CT studies of eight horses with surgically and/or histopathologically confirmed paranasal sinus cysts and 10 horses with other confirmed paranasal sinus diseases.

RESULTS

A discrete hyperattenuating wall-like structure was detected in the periphery of the sinus lesion in precontrast acquisition in 7/8 horses with paranasal sinus cysts. A similar wall-like structure was detected in 3/10 horses with other sinus diseases, however, in contrast to horses with paranasal sinus cysts, two of these also had hyperattenuating regions within the contents of the sinus lesion. Bone destruction and formation affecting cancellous and cortical bone and dental disease were frequent in horses with paranasal sinus cysts. No significant difference in attenuation values was found when the fluid/soft tissue attenuation contents of lesions in horses with paranasal sinus cysts (mean 28.9 ± SD 9.2 HU) were compared with other sinus diseases when ethmoid haematomas were excluded (30.4 ± 12.9 HU, P = .8).

MAIN LIMITATIONS

Low number of cases.

CONCLUSIONS

Detection of a hyperattenuating cystic wall is a helpful feature for identifying paranasal sinus cysts in CT images of horses. In contrast, measurement of attenuation values of the soft tissue/fluid contents of the sinus lesions was not helpful in identifying paranasal sinus cysts.

Standing CT of the equine head: Reducing radiation dose maintains image quality

Multiple published studies involving computed tomographic (CT) examinations of the equine head utilise a wide range of mAs parameters for image acquisition. This prospective, experimental study assessed the effects of lowering mAs during CT image acquisition on image quality and scatter radiation on 10 cadaver equine heads. Each head was scanned three times at 300, 225, and 150 mAs, with all other scanning parameters remaining constant between series. An anthropomorphic phantom was positioned adjacent to each equine head during image acquisition, mimicking a human bystander, with an ionization chamber attached to the phantom at eye level. Each series was reconstructed using filtered back projection, using medium (H30) and high (H80) frequency reconstruction algorithms. Quantitative image quality assessment was performed by calculating signal to noise ratio (SNR) and contrast to noise ratio (CNR). Two qualitative image quality assessments were performed independently by three blinded board certified veterinary radiologists with a 4 week interval, using a visual grade analysis model adapted from peer reviewed medical literature. Ionization chamber measurements, calculated volume CT dose index (CTDIvol), and dose-length product (DLP) were recorded. Halving radiation dose during image acquisition from 300 to 150mAs resulted in comparable image quality between series. There was a statistically significant and linear relationship between mAs and scatter radiation to the bystander; halving mAs during image acquisition resulted in halving of scatter radiation. Results of this cadaveric study support the use of lower mAs settings during standing CT examinations of the equine head.

Neuroanatomy of the equine brain as revealed by high-field (3Tesla) magnetic-resonance-imaging

In this study, the morphology of the horse brain (Equus caballus) is decribed in detail using high field MRI. The study includes sagittal, dorsal, and transverse T2-weighted images at 0.25 mm resolution at 3 Tesla and 3D models of the brain presenting the external morphology of the brain. Representative gallocyanin stained histological slides of the same brain are presented. The images represent a useful tool for MR image interpretation in horses and may serve as a starting point for further research aiming at in vivo analysis in this species.

Intra-arterial versus intra venous contrast-enhanced computed tomography of the equine head

Background

The anatomical complexity of the horse’s head limits the abilities of radiography. Computed tomography (CT) in combination with contrast enhanced CT is used more often for diagnosing various head pathology in horses. The objective of this study was to compare intravenous and intra-arterial contrast-enhancement techniques and describe normal and abnormal contrast enhancement in the horse’s head.

Results

All 24 horses included in the study recovered without complication from the procedures. Compared to the pre-contrast studies, post-contrast studies showed significant contrast enhancement in the pituitary gland (IA: p < 0.0001; IV: p < 0.0001), IA nose septum (p = 0.002), nose mucosa (IA: p < 0.0001; IV: p = 0.02), parotid salivary gland (IA: p < 0.0001; IV p < 0.0001), cerebrum (IA: p < 0.0001; IV: p < 0.0001), rectus capitis muscle (IA: p < 0.0001; IV p = 0.001), IA temporal muscle (p < 0.0001), IA masseter muscle (p <0.0001) and IV brainstem (p = 0.01). No significant contrast enhancement was seen in the eye (IA: p = 0.23; IV p = 0.33), tongue (IA p = 0.2; IV p = 0.57), IA brainstem (p = 0.88), IV nose septum (p = 0.26), IV temporal muscle (p = 0.09) and IV masseter muscle (p = 0.46). Three different categories of abnormal enhancement were detected: a strong vascularised mass, an enhanced rim surrounding an unenhanced structure and an inflamed anatomical structure with abnormal contrast enhancement.

Conclusion

Using the intra-arterial technique, similar contrast enhancement is achieved using less contrast medium compared to the intravenous technique. And a potential major advantage of the IA technique is the ability to evaluate lesions that are characterized by increased blood flow. Using the intravenous technique, a symmetrical and homogenous enhancement is achieved, however timing is more crucial and the contrast dosage is more of influence in the IV protocol. And a potential major advantage of the IV technique is the ability to evaluate lesions that are characterized by increased vascular permeability. Knowing the different normal contrast enhancement patterns will facilitate the recognition of abnormal contrast enhancements.

Radiographic, computed tomographic and surgical anatomy of the equine sphenopalatine sinus in normal and diseased horses

REASONS FOR PERFORMING STUDY

Knowledge of imaging anatomy, surgical anatomy and disorders affecting the sphenopalatine sinus are currently lacking.

OBJECTIVES

To describe the computed tomographic (CT) and surgical anatomy of the sphenopalatine sinus and diagnosis, treatment and outcome in clinical cases with sphenopalatine sinus disease.

STUDY DESIGN

Cadaver observational study and retrospective case series.

METHODS

The sphenopalatine sinuses of 10 normal cadaver heads were examined with digital radiography, CT and sinoscopic examination prior to anatomical sectioning. Sphenopalatine sinus anatomy was described and compared between cadaver specimens across the imaging modalities. Medical records (January 2004-2014) of cases diagnosed with sphenopalatine sinus disease were reviewed.

RESULTS

The anatomy of the sphenopalatine sinus was variable. The borders of the sphenopalatine sinus were not identifiable on plain radiographs, whereas CT provided useful anatomical information. The palatine portion of the sphenopalatine sinus was consistently accessible sinoscopically and the sphenoidal portion was accessible in 6/10 cadaver heads. Fourteen cases of sphenopalatine sinus disease were identified, presenting with one or more clinical signs of exophthalmos, blindness, unilateral epistaxis or unilateral nasal discharge. Diagnoses included neoplasia (7), progressive ethmoidal haematoma (4), sinus cyst (2) and empyema (1). Computed tomography provided diagnostic information but could not differentiate the nature of soft tissue masses. Standing sinoscopic access to the palatine portion of the sphenopalatine sinus was possible for evaluation, biopsy and resection of abnormal soft tissues. Surgical access to the sphenoidal portion was limited. Eight horses were alive at 1 year after diagnosis, with a worse outcome associated with CT evidence of bone loss and a diagnosis of neoplasia.

CONCLUSIONS

Sphenopalatine sinus disease should be considered a rare cause of the clinical signs described. Knowledge of the anatomical variation of the sphenopalatine sinus is vital for interpreting CT images. A combination of CT and sinoscopy provides the most comprehensive approach for diagnosis and treatment of sphenopalatine sinus disease.

Seizures in horses: diagnosis and classification

Seizures are a diverse and very common set of chronic neurologic disorders in humans and dogs but are less common in horses. Seizures refer to a specific clinical event (described as sudden and severe) regardless of the etiology, which includes both intracranial and extracranial causes. Therefore, after briefly reviewing some definitions, this article aims to describe the use of a standardized classification, which could facilitate a logical approach for the clinician to establish a diagnosis, as well as to use a consistent mode of communication. For instance, seizures can be classified by type (ie, focal vs generalized) or etiology (ie, reactive, symptomatic, cryptogenic, idiopathic). In particular, epilepsy, a brain disorder characterized by recurrent seizures can be classified as primary (ie, genetic origin) or secondary (ie, acquired). This review further discusses the limitations associated with the clinical workup of horses with seizures. This is germane to the fact that the identification of the underlying cause remains challenging due to the technical limitations of imaging the equine adult brain. Indeed, as in man and dogs, epilepsies of unknown cause (ie, cryptogenic) account for the majority of all epilepsies. Therefore, although electroencephalography and advanced brain imaging techniques (eg, computed tomography and magnetic resonance imaging) are becoming increasingly available, information obtained from the history, physical, and neurologic examinations and progression of clinical signs and response to treatment remain essential in the workup of horses with seizures.

Update on disorders and treatment of the guttural pouch

The most common disorders of the equine guttural pouches are empyema, tympany, mycosis, and temporohyoid osteoarthropathy. Diagnosis of these conditions is made primarily by imaging with endoscopy, radiographs, computed tomography, and/or MRI. Medical treatment with anti-inflammatories, antimicrobials, and/or antifungals may be successful in some cases, but many of these disorders necessitate surgical intervention. Direct surgical approaches to the guttural pouch are difficult because of their complex anatomy and relationship with important structures, thus precipitating a move toward minimally invasive procedures when possible.

Magnetic resonance imaging features of sinonasal disorders in horses

Diseases of paranasal sinuses and nasal passages in horses can be a diagnostic challenge because of the complex anatomy of the head and limitations of many diagnostic modalities. Our hypothesis was that magnetic resonance (MR) imaging would provide excellent anatomical detail and soft tissue resolution, and would be accurate in the diagnosis of diseases of the paranasal sinuses and nasal passages in horses. Fourteen horses were imaged. Inclusion criteria were lesions located to the sinuses or nasal passages that underwent MR imaging and subsequent surgical intervention and/or histopathologic examination. A low field, 0.3 tesla open magnet was used. Sequences in the standard protocol were fast spin echo T2 sagittal and transverse, spin echo T1 transverse, short-tau inversion recovery (STIR) dorsal, gradient echo 3D T1 MPR dorsal (plain and contrast enhanced), spin echo T1 fatsat (contrast enhanced). Mean scan time to complete the examination was 53 min (range 39-99 min). Lesions identified were primary or secondary sinusitis (six horses), paranasal sinus cyst (four horses), progressive ethmoid hematoma (two horses), and neoplasia (two horses). The most useful sequences were fast spin echo T2 transverse and sagittal, STIR dorsal and FE3D MPR (survey and contrast enhanced). Fluid accumulation, mucosal thickening, presence of encapsulated contents, bone deformation, and thickening were common findings observed in MR imaging. In selected horses, magnetic resonance imaging is a useful tool in diagnosing lesions of the paranasal sinuses and nasal passages.

Topographic comparative study of paranasal sinuses in adult horses by computed tomography, sinuscopy, and sectional anatomy

Clinical and radiographic investigations of paranasal sinuses in horses are difficult due to the complex anatomy of these regions, the lack of patognomonic symptoms, and the low sensitivity of conventional diagnostic techniques. The aim of this study was to produce an anatomical atlas to support computed tomography (CT) and sinuscopy of the paranasal sinuses of the adult horse. Transverse, sagittal, and dorsal CT images were acquired, and sinuscopy with both rigid and flexible endoscopes was performed. The heads were frozen and sectioned using a band saw, with the cuts aligned as close as possible with the CT transverse slices. Each CT image was compared with its corresponding anatomical section and sinuscopy image to assist in the accurate identification of specific structures.

Factors predictive of abnormal results for computed tomography of the head in horses affected by neurologic disorders: 57 cases (2001-2007)

OBJECTIVE

To determine neurologic indications associated with abnormal results for computed tomography (CT) imaging of the head of horses affected by neurologic disorders.

DESIGN

Retrospective case series.

ANIMALS

57 horses.

PROCEDURES

Signalment, history, clinical abnormalities, and clinicopathologic findings were obtained from medical records of horses examined because of neurologic disorders, and precontrast and postcontrast CT images of the head were reviewed. Data were analyzed by use of univariate and multivariate logistic regression.

RESULTS

For a horse with abnormal mentation, odds of having abnormal results for CT imaging of the head was 30 times (95% confidence interval [CI], 2.36 to 374.63) the odds for a similar horse without abnormal mentation. For a horse with cranial nerve deficits, odds of having abnormal results for CT imaging of the head was 11 times (95% CI, 1.00 to 127.96) the odds for a similar horse without cranial nerve deficits. For a horse with seizure-like activity, odds of having abnormal results for CT imaging of the head was 0.05 times (95% CI, 0 to 0.90) the odds for a similar horse without seizures.

CONCLUSIONS AND CLINICAL RELEVANCE

These results suggested that alterations in consciousness and cranial nerve deficits were strong predictors of abnormal CT findings for the head of affected horses. Thus, CT can be a useful complementary diagnostic test in horses with these neurologic deficits. In contrast, alternative diagnostic tests (eg, electroencephalography and magnetic resonance imaging) should be considered in horses with seizure-like activity that do not have head trauma or cranial nerve deficits.

Magnetic Resonance Imaging of the Canine Shoulder: An Anatomic Study

OBJECTIVES

To describe the normal anatomy of the soft tissue stabilizing components of the canine shoulder identified by magnetic resonance imaging (MRI) and to evaluate specific acquisition sequences and planes for observing structures of diagnostic interest.

STUDY DESIGN

Descriptive study.

ANIMAL

Canine cadavers (n=3).

METHODS

T1-weighted, proton density fat saturation (PD), and T2(*)-weighted gradient echo (GE) MRI sequences were obtained in the sagittal, transverse, and dorsal planes of the left shoulder of 3 canine cadavers. After imaging, each shoulder was embedded and thin sectioned. The corresponding right shoulder was frozen and thick sectioned. The anatomic structures on the histologic and frozen thick sections were visually correlated with the MR images.

RESULTS

The sagittal plane provided a longitudinal view of the bicep, infraspinatus, and supraspinatus tendons. The biceps, supraspinatus, infraspinatus, and subscapularis tendons, and the medial and lateral glenohumeral ligaments were identified in the transverse and dorsal planes. The dorsal plane allowed for the bicep tendon to be evaluated transversely as it passed over the humeral head. The GE sequence was more useful in identifying tendons and ligaments. The PD sequence was more helpful in identifying fluid accumulations in the joint and around tendons.

CONCLUSIONS

The tendinous and ligamentous structures that stabilize the canine shoulder joint can be readily identified with MRI.

CLINICAL RELEVANCE

MRI has the potential to be a useful tool in the diagnosis of canine soft tissue shoulder injuries.

Infections of the Head and Ocular Structures in the Horse

Infectious conditions of the equine head are commonly encountered in clinical practice. Pathogenic bacterial, viral, and fungal organisms may localize in the extensive nasal passages, paranasal sinuses, and guttural pouches, creating a range of clinical signs and conditions that can be severe enough to lead to unexpected fatality. Renewed interest in equine dentistry has led to a greater recognition of dental disease that is associated with infection. This article focuses on bacterial and fungal infections of the main anatomic regions of the equine head, where advances in diagnosis and management have been made or consolidated in recent years. It also addresses recent advances made in the area of infectious equine corneal disease, including bacterial, viral, and fungal etiologies. Recent developments in equine recurrent uveitis as it relates to infectious diseases and ocular manifestations of systemic disease are also discussed.

A review of equine dental disorders

Equine dentistry is a very important but until recently rather neglected area of equine practice, with many horses suffering from undiagnosed, painful dental disorders. A thorough clinical examination using a full mouth speculum is a pre-requisite to performing any equine dental procedure. Common incisor disorders include: prolonged retention of deciduous incisors, supernumerary incisors and overjet--the latter usually accompanied by cheek teeth (CT) overgrowths. Overjet can be surgically corrected, but perhaps should not be in breeding animals. In younger horses, traumatically fractured incisors with pulpar exposure may survive by laying down tertiary dentine. Loss or maleruption of incisors can cause uneven occlusal wear that can affect mastication. Idiopathic fractures and apical infection of incisors are rare. The main disorder of canine teeth is the development of calculus of the lower canines, and occasionally, developmental displacements and traumatic fractures. The main indications for extraction of "wolf teeth" (Triadan 05s) are the presence of displaced or enlarged wolf teeth, or their presence in the mandible. Developmental abnormalities of the CT include; rostral positioning of the upper CT rows in relation to the lower CT rows--with resultant development of focal overgrowths on the upper 06s and the lower 11s. Displaced CT develop overgrowths on unopposed aspects of the teeth and also develop periodontal disease in the inevitable abnormal spaces (diastemata) that are present between displaced and normal teeth. Diastemata of the CT due to excessive developmental spacing between the CT or to inadequate compression of the CT rows is a common but under diagnosed problem in many horses and causes very painful periodontal disease and quidding. Supernumerary CT mainly occur at the caudal aspect of the CT rows and periodontal disease commonly occurs around these teeth. Eruption disorders of CT include prolonged retention of remnants of deciduous CT ("caps") and vertical impaction of erupting CT that may lead to large eruption cysts and possibly then to apical infections. Disorders of wear, especially enamel overgrowths ("enamel points"), are the main equine dental disorder and are believed to be largely due to the dietary alterations associated with domestication. If untreated, such disorders will eventually lead to more severe CT disorders such as shearmouth and also to widespread periodontal disease. More focal dental overgrowths will develop opposite any CT not in full opposition to their counterpart, e.g., following maleruption of or loss of a CT. Because of the great length of reserve crown in young (hypsodont) CT, apical infections usually cause infection of the supporting bones and depending on the CT involved, cause facial swellings and fistulae and possibly sinusitis. Diagnosis of apical infection requires radiography, and possibly scintigraphy and other advanced imaging techniques in some early cases. When possible, oral extraction of affected CT is advocated, because it reduces the costs and risks of general anaesthesia and has much less post-extraction sequelae than CT repulsion or buccotomy.

Ophthalmic imaging

The availability of advanced imaging modalities in veterinary medicine has greatly widened the diagnostic imaging capabilities possible. Ultrasonography provides a rapid noninvasive modality that provides detailed examination and resolution of the intraocular structures and soft tissues surrounding the orbit of opaque eyes. Ultrasonography is cost-effective and widely available to practitioners,referral centers, and academic institutions. In many areas,mobile specialist ultrasonographers are available to supplement the equipment and skills of the practitioner. The added strengths of CT and MRI lie in their cross-sectional capability and better image quality. Unfortunately, the cost of CT and MRI currently limits their availability to referral centers and academic institutions. Primarily because of financial considerations, CT is currently more widely available for evaluation of equine disorders than MRI. A thorough evaluation of the multiple images and an understanding of normal anatomy and abnormal tissue patterns are indicated to maximize the use of each modality. Unlike ultrasonography, which can be performed in awake horses, the costs and contraindications of general anesthesia in some critical patients should also be considered when using CT and MRI. Finally, imaging artifacts are frequently encountered with each of these modalities. Thus, a thorough understanding of the various types of artifacts that occur is important so as to avoid interpretation pitfalls.

Magnetic resonance imaging of a brain abscess in a 10-month-old filly

The purpose of this paper was to correlate the magnetic resonance imaging (MRI) characteristics of a mature brain abscess in a horse with histopathologic alterations of brain tissue. Eight months after the onset of clinical signs, MRI of the brain of a 10-month-old filly was performed. A large space-occupying lesion in the right cerebral hemisphere was identified. This space-occupying lesion was delineated by a thick and well-defined capsule that was isointense to brain parenchyma on the T1-weighted images and with a markedly hypointense on the T2-weighted images. The identification of such a capsule is highly diagnostic of a mature brain abscess. The lesion seen on MR images was confirmed at necropsy where a large abscess of the right hemisphere was observed. Streptococcus zooepidemicus and Pseudomonas aeruginosa were isolated from the abscess. Based on histopathologic examination, the signal characteristics of the capsule on T1-weighted and T2-weighted images were found to be due to the presence of numerous hemosiderin-laden macrophages. These results are in agreement with previous studies on human patients. This report confirms the value of MRI in the diagnosis of equine brain diseases.

Thick-section reformatting of thinly collimated computed tomography for reduction of skull-base-related artifacts in dogs and horses

Computed tomography (CT) of the caudal fossa of 10 canine and nine equine cadaver heads was performed with conventional slice widths of 5 and 10 mm, respectively, and with thin collimations of 1 and 2 mm, respectively. Reformatting of thinly collimated slices was done by addition of thinly collimated slices to section thicknesses of 5 and 10 mm, respectively. Seventy-six pairs of conventional and reformatted images of identical anatomic locations were evaluated for magnitude of skull-base-related artifacts and image noise. A film-based subjective evaluation of artifact and noise was performed by four radiologists on a five-point score system. There was a statistically significant reduction of artifacts of canine and equine heads by 33% and 50%, respectively, on reformatted images compared with conventional ones but no difference in image noise. On objective artifact assessment based on the magnitude of standard deviation of attenuation values in the interpetrosal region, there was a statistically significant reduction of artifacts of canine and equine heads by 23% and 39%, respectively, on reformatted images. Thick-section reformatting significantly improves image quality of CT scans of the caudal fossa in dogs and horses.

Assessment of the accuracy of computed tomography for measurement of normal equine pituitary glands

OBJECTIVE

To describe the anatomic features of the pituitary gland region in horses via computed tomography (CT) and determine the accuracy of CT for estimating normal equine pituitary gland dimensions.

ANIMALS

25 adult horses with no clinical signs of pituitary disease.

PROCEDURE

Transverse CT images and gross transverse tissue sections were compared in 2 horses. Contrast-enhanced CT of the pituitary gland region was performed postmortem in 23 horses with 4 slice thickness and interval settings (10-mm contiguous or overlapping slices and 4-mm contiguous or overlapping slices). Gross and CT estimates of pituitary gland dimensions were compared via ANOVA. Accuracy of CT estimates was calculated with gross pituitary gland measurements as the known value.

RESULTS

Pituitary glands were located between the temporomandibular joints and had contrast enhancement. Mean gross dimensions were length, 2.11 cm; width, 2.16 cm; height, 0.98 cm; and volume, 2.66 cm3. Gross measurements and CT estimates of pituitary gland length from 10-mm contiguous and overlapping slices did not differ. Gross measurements and CT estimates of pituitary gland width from 4-mm contiguous and overlapping slices did not differ. Estimates of height and volume from all CT techniques differed from gross measurements. Accuracies for CT estimates were length, 88 to 99%; width, 81 to 92%; height, 58 to 71%; and volume, 43 to 55%.

CONCLUSIONS AND CLINICAL RELEVANCE

Accuracy of estimates of pituitary gland dimension in horses varied with CT scanning technique; via CT estimates of length and width of glands were more accurate than estimates of height or volume.

Diseases of the guttural pouches

Guttural pouches are unique anatomic structures in Equidae. Conditions affecting the guttural pouches present with clinical signs that are not observed in other domestic species, and treatment of some of these conditions can be challenging. This article describes the anatomy and examination of the guttural pouches and reviews the presenting signs and treatment of the more common conditions affecting them, including empyema, tympany, mycosis, and stylohyoid arthropathy.

Tools for the diagnosis of equine respiratory disorders

Respiratory disorders are among the most common problems leading horse owners to seek veterinary attention. Accurate diagnosis of these conditions allows for proper treatment to be instituted, much to the benefit of the patient and satisfaction of the client. As an introduction to this issue on equine respiratory disorders, we review some of the tools that are available to equine veterinarians for the diagnosis of respiratory disorders. Physical and endoscopic examination, radiology, diagnostic ultrasound, techniques for sampling the respiratory tract, hematology, blood gas analysis, respiratory mechanics, and some modern diagnostic tools are briefly covered.