Radiographic evaluation in clinical practice of the types and stage of incisor tooth resorption and hypercementosis in horses.

BACKGROUND: There are several reports of incisor tooth resorption and hypercementosis in horses but, to date, studies have been limited in case numbers and to advanced lesions. Tooth resorption in other species is a radiographic diagnosis of types of resorption that are often identified before clinical signs. Our goal was to evaluate radiographically incisor tooth resorption in a large population of horses, utilising interpretation criteria from canine and human dentistry. OBJECTIVE: To document and classify incisor tooth resorption and hypercementosis. STUDY DESIGN: Retrospective descriptive case series. METHODS: Horses presented for routine dental care >5 years old were included only if owners were unaware of incisor pathology. Radiographs (three views) were obtained of the incisor teeth and incisor teeth resorption was classified according to the radiographic criteria described for man and dogs. Hypercementosis and its location were recorded. RESULTS: Tooth resorption was detected in 149 of 169 (88.2%) horses and 951 of 1952 (48.7%) of incisor teeth. The classification system used was applicable in 926 (97.2%) of 951 affected teeth. Hypercementosis was detected in 34 (20.1%) horses and 148 (7.6%) teeth. As horses increased in age, resorption and hypercementosis was more frequent; no significant differences were found among sex or breed categories. All horses with hypercementosis had resorption, but only 23.4% of horses with resorption had hypercementosis. Advanced (stage ≥3) resorption was detected in 159 (8.1%) teeth and 54 (32.0%) horses in an otherwise clinically healthy population. MAIN LIMITATIONS: Certain horses' anatomy precluded isolation of the mandibular third incisor teeth from the canine teeth due to superimposition. CONCLUSIONS: Incisor tooth resorption, in particular external replacement resorption and external inflammatory resorption, is common in horses. Hypercementosis is consistently associated with resorption, but the inverse association is inconsistent.

Contrast-enhanced computed tomographic evaluation of the deep digital flexor tendon in the equine foot compared to macroscopic and histological findings in 23 limbs.

REASONS FOR PERFORMING THE STUDY: Distal deep digital flexor tendinopathy is an important cause of foot lameness in horses that is difficult to diagnose with radiography and ultrasonography. Magnetic resonance imaging is a well-accepted and validated technique for the identification of deep digital flexor tendon (DDFT) lesions, but has some practical and financial drawbacks. Contrast-enhanced computed tomography (CECT) has been proposed as a suitable alternative, but validation studies are currently lacking. OBJECTIVE: To assess the accuracy of CECT for the identification and characterisation of deep digital flexor tendinopathy. STUDY DESIGN: Descriptive study of CT, macroscopic and histological findings of the DDFT. METHODS: Plain and CECT scans were acquired of 23 limbs of 16 horses with clinical lameness localised to the foot. All horses had lesions of the DDFT that were identified and characterised with CT and CECT with respect to their anatomic location and extent. All horses underwent post mortem examination and gross abnormalities were described. Samples of the DDFT were taken at specific sites (lesion and nonlesion) for histological evaluation. Macroscopic and histological outcomes were compared with CECT findings. RESULTS: Of 67 sites in 23 DDFTs that were evaluated, 42 sites in 18 tendons had lesions on CECT images. These 42 sites also had lesions on macroscopic evaluation. There were 3 false negative and 3 false positive results identified on CECT. The sensitivity of CECT for diagnosing lesions of the DDFT in the equine foot was 93%. CONCLUSION: CECT is an effective adjunct to the more commonly used diagnostic techniques in equine foot pain.

Clinical, radiographic, ultrasonographic and computed tomographic features of nonseptic osteitis of the axial border of the proximal sesamoid bones.

REASONS FOR PERFORMING STUDY: Lysis of the axial aspect of equine proximal sesamoid bones (PSBs) is a rare condition reported to have septic or traumatic origins. Limited information exists regarding imaging of nonseptic axial osteitis of a PSB. OBJECTIVES: To report the clinical, radiographic, ultrasonographic, computed tomographic and intra-arterial contrast-enhanced computed tomographic abnormalities in horses with axial nonseptic osteitis of a PSB. STUDY DESIGN: Retrospective clinical study. METHODS: Eighteen horses diagnosed with nonseptic osteitis of the axial border of a PSB between 2007 and 2012 were reviewed retrospectively. Case details, clinical examination, radiographic, ultrasonographic, computed tomographic and intra-arterial/intra-articular contrast-enhanced computed tomographic features were recorded, when available. Radiographic, ultrasonographic and computed tomographic evaluations of the fetlock region had been performed on 18, 15 and 9 horses, respectively. The effect of the degree of lysis on the grade and duration of lameness was determined. RESULTS: All horses had chronic unilateral lameness, 4 with forelimb and 14 with hindlimb signs. On radiographs, lysis was identified in both PSBs in 14 horses, one PSB in 3 horses and in one horse no lysis was identified. The degree of osteolysis was variable. Ultrasonography identified variably sized irregularities of the bone surface and alteration in echogenicity of the palmar/plantar ligament (PL). All horses undergoing computed tomographic examination (n = 9) had biaxial lysis. The lesions were significantly longer and deeper on computed tomographic images compared with radiographic images. Intra-arterial contrast-enhanced computed tomography may reveal moderate to marked contrast enhancement of the PL. There was no significant effect of the degree of lysis on the grade and duration of lameness. CONCLUSIONS: Lesions of nonseptic axial osteitis of a PSB can be identified using a combination of radiography and ultrasonography. Computed tomography provides additional information regarding the extent of the pathology.

Humeral stress remodelling locations differ in Thoroughbred racehorses training and racing on dirt compared to synthetic racetrack surfaces.

REASONS FOR PERFORMING STUDY: Veterinarians have observed a putative change in the location of humeral stress remodelling in Thoroughbred racehorses with change from dirt to synthetic racetrack surfaces. OBJECTIVES: To determine whether the location and severity of humeral stress remodelling differs between Thoroughbred racehorses exercising on dirt and synthetic racetrack surfaces, the potential significance of different locations of stress remodelling, and the potential usefulness of scintigraphy for prevention of complete humeral fracture. METHODS: Scintigraphic images of humeri from 841 Thoroughbred racehorses at 3 racetracks during 2 years before and after conversion from dirt to synthetic surfaces were evaluated for location and severity of lesions. The effects of surface on lesion distributions were examined using Chi-square or Fisher's exact tests. Archived fractured humeri were examined to determine the location and severity of stress remodelling associated with complete fracture. Databases were queried to determine whether racehorses with scintigraphic lesions suffered humeral fracture and whether racehorses with a complete humeral fracture had had a scintigraphic examination. RESULTS: Horses at synthetic racetracks had a greater proportion of distal humeral lesions, whereas horses at dirt racetracks had a greater proportion of caudoproximal lesions (P<0.001). Proximal lesions were more likely to be severe than distal lesions (P<0.001). Most complete fractures were associated with caudoproximal lesions, which were more often severe than distal lesions (P = 0.002). None of the horses with a scintigraphic lesion had a complete humeral fracture. None of the horses with a complete humeral fracture underwent scintigraphic examination. CONCLUSIONS: Race surface affected humeral scintigraphic lesion location and hence the location of stress remodelling. Lesion severity was associated with lesion location. Complete humeral fracture was associated with caudoproximal stress remodelling and lack of scintigraphic examination. POTENTIAL RELEVANCE: Risk for complete humeral fracture may be lower on synthetic surfaces than on dirt surfaces, and, by inference, for horses examined using scintigraphy.

Comparisons of computed tomography, contrast-enhanced computed tomography and standing low-field magnetic resonance imaging in horses with lameness localised to the foot. Part 2: Lesion identification.

REASONS FOR PERFORMING STUDY: No previous study compares computed tomography (CT), contrast-enhanced computed tomography (CECT) and standing low-field magnetic resonance imaging (LFMRI) to detect lesions in horses with lameness localised to the foot. This study will help clinicians understand the limitations of these techniques. OBJECTIVES: To determine if CT, CECT and LFMRI would identify lesions within the distal limb and document discrepancies with lesion distribution and lesion classification. METHODS: Lesions in specific structures identified on CT and MR images of feet (31 limbs) from the same horse were reviewed and compared. Distributions of lesions were compared using a Chi-squared test and techniques analysed using the paired marginal homogeneity test for concordance. RESULTS: Lesions of the deep digital flexor tendon (DDFT) were most common and CT/CECT identified more lesions than LFMRI. Deep digital flexor tendon lesions seen on LFMRI only were frequently distal to the proximal extent of the distal sesamoid and DDFT lesions seen on CT/CECT only were frequently proximal to the distal sesamoid. Lesions identified on LFMRI only were core (23.3%) or splits (43.3%), whereas lesions identified only on CT were abrasions (29.8%), core (15.8%), enlargement (15.8%) or mineralisation (12.3%). Contrast-enhanced CT improved lesion identification at the DDFT insertion compared to CT and resulted in distal sesamoidean impar ligament and collateral sesamoidean ligament vascular enhancement in 75% of cases. Low-field MRI and CT/CECT failed to identify soft tissue mineralisation and bone oedema, respectively. CONCLUSIONS AND POTENTIAL RELEVANCE: Multiple lesions are detected with CT, CECT and LFMRI but there is variability in lesion detection and classification. LFMRI centred only on the podotrochlear apparatus may fail to identify lesions of the pastern or soft tissue mineralisation. Computed tomography may fail to identify DDFT lesions distal to the proximal border of the distal sesamoid.

Comparisons of computed tomography, contrast enhanced computed tomography and standing low-field magnetic resonance imaging in horses with lameness localised to the foot. Part 1: anatomic visualisation scores.

REASONS FOR PERFORMING STUDY: To date, few reports exist comparing magnetic resonance imaging (MRI) and computed tomography (CT) for imaging of the equine distal limb, yet clinicians are required to decide which modality to use regularly. OBJECTIVES: To report and compare anatomic visualisation scores obtained for CT, contrast enhanced CT (CECT) and standing low-field MRI (LFMRI) in the equine foot. HYPOTHESIS: Anatomic visualisation score discrepancies would exist between CT, CECT and LFMRI. METHODS: Images of 22 lame horses (31 limbs) undergoing both CT and LFMRI of the foot were reviewed. When available, CECT images were reviewed. The deep digital flexor tendon (DDFT) was categorised into proximal to distal levels (A-D), structures were assigned visualisation scores (Grades 0-3) and technique comparisons were made using the paired marginal homogeneity test. RESULTS: Computed tomography and LFMRI had similar visibility scores for the navicular bone, middle phalanx, DDFT-B, collateral ligaments of the distal interphalangeal joint and collateral sesamoidean ligament of the navicular bone. The proximal and distal phalanx had lower visibility scores with LFMRI. The distal DDFT (C-D), distal sesamoidean impar ligament and synovial structures had higher scores with LFMRI. Contrast enhanced CT lowered DDFT and collateral sesamoidean ligament scores and raised distal interphalangeal synovium CT visualisation scores. CONCLUSIONS AND POTENTIAL RELEVANCE: Visualisation scores differ depending on imaging technique and anatomic structure of interest. This information increases our understanding of the limitations of CT, CECT and LFMRI to visualise anatomy in clinical cases.

Magnetic resonance and radiographic diagnosis of osseous resorption of the flexor surface of the distal phalanx in the horse.

REASONS FOR PERFORMING STUDY: Osseous resorption of the flexor surface of the distal phalanx of the horse has been identified previously using magnetic resonance (MR) imaging; however, little is known about the prevalence and characteristics of this lesion. OBJECTIVES: To establish the MR prevalence of resorptive lesions in the flexor surface of the distal phalanx and identify concurrent lesions associated with this finding and associations between the MR and radiographic findings. METHODS: Horses with distal extremity MR and radiographs performed within 2 weeks of each other were included in the study. The flexor surface of the distal phalanx was graded independently on both modalities for the presence of osseous resorption. The sensitivity and specificity of radiography for identifying osseous resorption was calculated using MR as the gold standard. RESULTS: Eighty-two MR studies met the inclusion criteria, 8 of which included osseous resorption of the flexor surface of the distal phalanx. Concurrent injury to the deep digital flexor tendon and the navicular bone was a common finding. An association between MR and radiographic grades was identified. Radiography had a high specificity (0.96) but lower sensitivity (0.45-0.55) for detecting osseous resorption. CONCLUSIONS: Osseous resorption of the flexor surface of the distal phalanx can be observed both on MR and radiographic examinations of horses with lameness localised to the foot. This lesion is most often associated with other pathological changes in the podotrochlear apparatus. POTENTIAL RELEVANCE: Focal radiolucency of the flexor surface of the distal phalanx is a newly recognised radiographic sign associated with pathological changes of the podotrochlear apparatus.

Osteoporosis associated with pulmonary silicosis in an equine bone fragility syndrome.

California horses incur a bone fragility syndrome manifested by pathologic fractures. This study investigated gross, radiographic, and histologic features of the disorder as well as relationships with silicosis and levels of heavy metals and trace minerals through a postmortem study of 9 affected and 3 unaffected horses. Bones and soft tissues were evaluated grossly and histologically. Bones, lymph nodes, and lung tissue were evaluated radiographically. Tissues were evaluated for silicon levels, intracytoplasmic crystals, heavy metals, and trace minerals. All 9 affected horses had osteoporosis and clinical or subclinical pulmonary disease due to silicosis (8/9) or pneumoconiosis (1/9). All affected horses had radiographic findings consistent with osteopenia and histologic evidence of osteoporosis characterized by osteopenia, numerous resorption cavities, cement lines, and a mosaic lamellar pattern indicative of multiple remodeling events. Silicosis was characterized by widespread pulmonary granuloma formation with fibrosis; variable tracheobronchiolar and mediastinal granulomatous lymphadenitis; intracellular crystals within lung and lymph node macrophages; and pronounced lymph node fibrosis, focal necrosis, and dystrophic calcification. Crystals in lung (6/9) and lymph node (8/9) tissues were identified as cytotoxic silica dioxide polymorphs. Lung and liver tissue from affected horses had elevated levels of elemental silicon. Osteoporosis was highly correlated (r = 0.8, P < .01) with silicosis. No abnormalities in heavy metal or trace minerals were detected. This evaluation indicated that horses with bone fragility disorder have systemic osteoporosis associated with fibrosing pulmonary silicosis. The etiopathogenesis of the bone fragility syndrome is unknown; however, this study provides circumstantial evidence for a silicate associated osteoporosis.

Brainstem auditory-evoked responses in horses with temporohyoid osteoarthropathy.

BACKGROUND: Facial and vestibulocochlear nerve dysfunction occurs commonly in horses with temporohyoid osteoarthropathy (THO); however, auditory dysfunction has not been thoroughly assessed. OBJECTIVE: To determine if auditory abnormalities occur in horses with THO. ANIMALS: Eleven diseased and 8 control horses. METHODS: This is a prospective study in which brainstem auditory-evoked responses (BAER) were recorded in 11 horses diagnosed with THO through neurologic, endoscopic, radiographic, or computed tomographic examinations. BAER findings were compared with those recorded from 8 adult control horses. RESULTS: All horses with THO were found to have BAER abnormalities that included complete unilateral BAER loss (82%, n=9/11), partial unilateral BAER loss (18%, n=2/11) on the most affected side, and contralateral partial BAER loss (46%, n=5/11). Nine horses had bilateral THO based on diagnostic imaging findings; of these, 5 (56%) horses also had bilateral BAER abnormalities. The complete absence of BAER in affected horses was most consistent with peripheral sensorineural hearing loss. There was a significant association between complete BAER loss and neurologic and diagnostic abnormalities. CONCLUSIONS AND CLINICAL IMPORTANCE: Auditory abnormalities such as complete or partial BAER loss are common in horses with THO. The BAER test is an objective diagnostic tool that can aid along with other diagnostic modalities in the assessment, management, and follow-up of horses with THO. Furthermore, BAER studies may help to elucidate the pathophysiology of THO in horses.