Use of standing low‐field magnetic resonance imaging to diagnose middle phalanx bone marrow lesions in horses

Bone marrow lesions (BMLs) (also known as ‘bone bruises’, ‘bone oedema’, ‘bone contusions’ and ‘occult fractures’) within the middle phalanx were diagnosed by standing low field magnetic resonance imaging (MRI) in 7 horses. The lesions were characterised by low signal intensity on T1‐ and T2*‐weighted gradient echo sequences, mildly increased signal intensity on T2 fast spin echo sequences, and high signal intensity on short tau inversion recovery (STIR) sequences. Four distinct patterns of abnormal signal were identified: BML associated with osteoarthritis of either the proximal or distal interphalangeal joints; BML associated with soft tissue injury; BML associated with acute trauma; and BML unassociated with any other injury or lameness (assumed to represent bone response to biomechanical stress). Repeat MRI was undertaken in 4 cases. In most cases the BML resolved with rest and time, although lameness was persistent in 2 horses (one of which had an associated osteoarthritis of the proximal interphalangeal joint).     

Reliability of high‐ and low‐field magnetic resonance imaging systems for detection of cartilage and bone lesions in the equine cadaver fetlock

Reasons for performing study: To determine the reliability of 2 magnetic resonance imaging (MRI) systems for detection of cartilage and bone lesions of the equine fetlock. Objectives: To test the hypotheses that lesions in cartilage, subchondral and trabecular bone of the equine fetlock verified using histopathology can be detected on high‐ and low‐field MR images with a low incidence of false positive or negative results; that low‐field images are less reliable than high‐field images for detection of cartilage lesions; and that combining results of interpretation from different pulse sequences increases detection of cartilage lesions. Methods: High‐ and low‐field MRI was performed on 19 limbs from horses identified with fetlock lameness prior to euthanasia. Grading systems were used to score cartilage, subchondral and trabecular bone on MR images and histopathology. Sensitivity and specificity were calculated for images. Results: High‐field T2*‐weighted gradient echo (T2*W‐GRE) and low‐field T2‐weighted fast spin echo (T2W‐FSE) images had high sensitivity but low specificity for detection of cartilage lesions. All pulse sequences had high sensitivity and low–moderate specificity for detection of subchondral bone lesions and moderate sensitivity and moderate–high specificity for detection of trabecular bone lesions (histopathology as gold standard). For detection of lesions of trabecular bone low‐field T2*W‐GRE images had higher sensitivity and specificity than T2W‐FSE images. Conclusions: There is high likelihood of false positive results using high‐ or low‐field MRI for detection of cartilage lesions and moderate–high likelihood of false positive results for detection of subchondral bone lesions compared with histopathology. Combining results of interpretation from different pulse sequences did not increase detection of cartilage lesions. MRI interpretation of trabecular bone was more reliable than cartilage or subchondral bone in both MR systems. Potential relevance: Independent interpretation of a variety of pulse sequences may maximise detection of cartilage and bone lesions in the fetlock. Clinicians should be aware of potential false positive and negative results.     

Magnetic resonance imaging findings in the carpus and proximal metacarpal region of 50 lame horses

Reasons for performing study: There is limited information on magnetic resonance imaging (MRI) findings in the carpus and proximal metacarpal region of lame horses. Objectives: To document MRI findings in horses with lameness localised to the carpus and/or proximal metacarpal region. Methods: Clinical records of horses that underwent MRI of the carpus and/or proximal metacarpal region at the Animal Health Trust between January 2003 and September 2010 were reviewed. Magnetic resonance images of all horses and available radiographs, ultrasonographic and scintigraphic images were assessed. When possible, MRI findings were related to the results of other diagnostic imaging techniques. Results: Seventy‐two MR studies of 58 lame limbs in 50 horses from a broad range of work disciplines and ages were reviewed. The most commonly detected primary abnormality was decreased signal intensity in T1‐ and T2‐weighted images in the medial aspect of the carpal bones and/or the proximomedial aspect of the metacarpal bones (n = 29). Nine horses had syndesmopathy between the second and third metacarpal bones. In 6 horses the primary abnormalities were identified in the palmar cortex of the third metacarpal bone (McIII). Significant abnormalities of the suspensory ligament (SL) with associated lesions in the adjacent palmar cortex of the McIII were seen in 4 limbs. Ligament and associated osseous abnormalities between the second and third carpal bones and second and third metacarpal bones were detected in 4 limbs. Conclusions and potential relevance: Magnetic resonance imaging enabled diagnosis of a variety of lesions not detected by conventional imaging in horses from a wide range of work disciplines. The distribution of injury types differed considerably from previous studies.     

Magnetic resonance features of closed head trauma in two foals

Two foals were admitted for neurological signs after trauma. Clinical and diagnostic investigations were performed that were suggestive of closed head trauma characterised by right parietal bone deviation (ping‐pong fracture), cerebral contusion, haematoma and cerebellar contusion. The histopathological findings were consistent with areas of abnormal signal found on magnetic resonance investigations.     

Radiographic, scintigraphic and magnetic resonance imaging findings in the palmar processes of the distal phalanx

REASON FOR PERFORMING STUDY: Increased radiopharmaceutical uptake (IRU) in the palmar processes of the distal phalanx is recognised but its clinical significance has not been established. OBJECTIVES: To investigate the relationship between radiographic, scintigraphic and MRI findings in the palmar processes of the distal phalanx. HYPOTHESES: Increased radiopharmaceutical uptake in the palmar processes of the distal phalanx is associated with MRI abnormalities; IRU and MRI abnormalities are over-represented in lame limbs. METHODS: Clinical data, radiographic, scintigraphic and MRI findings of 258 horses with unilateral or bilateral foot pain were recorded. Scintigraphic images were assessed subjectively and using region of interest and profile analysis, and intensity of IRU graded. Alteration in signal intensity in T1 and T2 weighted and short tau inversion recovery (STIR) MR images was documented, and MRI abnormalities graded. Relationships between scintigraphic, MRI, radiographic and clinical findings were assessed. RESULTS: Focal IRU was over-represented in palmar processes with most MRI abnormalities. There was a significant correlation between IRU and MRI grades and IRU was over-represented in palmar processes with MRI Grades 2 and 3. Both IRU and MRI abnormalities occurred most frequently in the medial palmar process. MRI abnormalities were generally over-represented in lame limbs. The most common MRI abnormality was mild diffuse decreased signal intensity in T1 and T2 weighted images, which was associated with mild generalised IRU. CONCLUSIONS: There was considerable variation in the radiographic, scintigraphic and MRI appearance of palmar processes of the distal phalanx. Focal IRU in a palmar process was seen in association with MRI abnormalities and lameness or as an incidental finding. Magnetic resonance imaging abnormalities occurred more frequently in lame limbs, either contributing to lameness or as a consequence of lameness. POTENTIAL RELEVANCE: Further investigation is needed to establish the clinical significance of MRI abnormalities in the palmar processes of the distal phalanx and their relationship with lesions in adjacent structures.     

Magic angle magnetic resonance imaging of diode laser induced and naturally occurring lesions in equine tendons

Magic angle magnetic resonance (MR) imaging consists of imaging tendons at 55° to the magnetic field. In people, magic angle MR imaging is valuable for detection of chronic tendon lesions and allows calculation of tendon T1 values. Increased T1 values occur in people with chronic tendinopathy. The T1 values of normal equine tendons have been reported but there are no available data for abnormal equine tendons. Twelve limbs were studied. Two limbs had diode laser tendon lesions induced postmortem, four limbs had diode laser tendon lesions induced in vivo and six limbs had naturally occurring tendon lesions. The limbs were imaged at 1.5 T using both conventional MR imaging and magic angle MR imaging. The post-mortem laser induced lesions were identified only with magic angle MR imaging. The in vivo induced lesions and naturally occurring lesions were identified with both techniques but had a different appearance with the two imaging techniques. Magic angle imaging was helpful at identifying lesions that were hypointense on conventional imaging. Increased T1 values were observed in all abnormal tendons and in several tendons with a subjectively normal MR appearance. The increased T1 value may reflect diffuse changes in the biochemical composition of tendons. Magic angle imaging has potential as a useful noninvasive tool to assess the changes of the extracellular tendon matrix using T1 values.     

Magnetic resonance imaging of navicular bursa adhesions

Adhesions occur in the navicular bursa between the deep digital flexor tendon (DDFT) and other structures. Our objectives were to describe the appearance of navicular bursa adhesions on high-field magnetic resonance (MR) images, to compare these findings to findings at navicular bursoscopy, and to determine the prevalence of lesions in the remainder of the podotrochlear apparatus. Sixteen forelimbs from 14 horses that underwent MR imaging and navicular bursoscopy were evaluated. Adhesions were considered type 1 when characterized by a discontinuity in the navicular bursa fluid signal between two structures, type 2 when the navicular bursa fluid signal was disrupted and ill-defined tissue was present between two structures, and type 3 when the fluid signal was disrupted and well-defined tissue was present between two structures. Twenty-six adhesions were suspected on MR images and nineteen were visualized at surgery. The positive predictive value was 50% for type 1 adhesions, 67% for type 2 adhesions, and 100% for type 3 adhesions. Additional lesions were detected in the navicular bursa in 15 limbs, the DDFT in 13, the navicular bone in 15, the collateral sesamoidean ligaments in 9, and the distal sesamoidean impar ligament in 8. A discontinuity in the navicular bursa fluid signal with well-defined tissue between two structures detected on high-field MR images is diagnostic for a navicular bursa adhesion. Additional lesions in the podotrochlear apparatus are common in horses with navicular bursa adhesions.     

High field magnetic resonance imaging contributes to diagnosis of equine distal tarsus and proximal metatarsus lesions: 103 horses

Injury of the distal tarsus and proximal metatarsus commonly causes lameness. Magnetic resonance imaging (MRI) allows concurrent assessment of both the distal tarsal joints and suspensory ligament origin, and aids identification of lesions that may otherwise go undetected by other modalities. In this retrospective observational study, the medical records of a veterinary imaging center were searched for MRI exams of the distal tarsus and proximal metatarsus for the years 2012 through 2014. Studies for 125 limbs of 103 horses were identified and retrospectively evaluated by two board‐certified veterinary radiologists. Soft tissue and osseous changes were characterized and graded by degree of severity. The patients’ signalment, lameness severity, and results of diagnostic analgesia were recorded. Osteoarthritic changes of the distal intertarsal and tarsometatarsal joints were the most common findings. Other findings included bone marrow lesions, degenerative changes of the small cuboidal bones, subchondral cystic lesions, and intertarsal desmopathy. Suspensory ligament desmopathy was found in 53% of limbs. Fourty‐seven percent of limbs that responded to analgesia of the proximal suspensory ligament had more severe lesions in the distal tarsus. Bone marrow lesions of the third tarsal bone were the only MRI finding that correlated with grade of lameness in patients for which lameness grade was reported. The grade of lameness has a poor correlation with the severity of lesions found on MRI. The findings support the use of MRI for simultaneous evaluation of the proximal metatarsus and distal tarsus, particularly given the difficulty of lesion localization with diagnostic analgesia.     

Magnetic resonance imaging of bone marrow in the pelvis and femur of young dogs

The purpose of this study was to determine the magnetic resonance (MR) imaging characteristics of bone marrow in the pelvis and femur of normal, young dogs. Six greyhounds were imaged at 4, 8, 12, and 16 months of age. Sagittal images of the femur and dorsal images of the pelvis were obtained with T1-weighted, fast spin echo (FSE) T2-weighted, and short tau (T1) inversion recovery (STIR) sequences. On T1-weighted images areas with high signal intensity, similar to fat, included the femoral heads, mid-diaphysis of the femur, femoral condyles, and the body of the ilium. T2-weighted images were characterized by uniform intermediate signal intensity (less than fat, but greater than muscle) in the femoral head, high signal intensity, similar to fat, in the mid-diaphysis of the femur and ilial body, and intermediate to high signal intensity in the femoral condyle. By 16 months high signal intensity was seen in the diaphysis and distal metaphysis on both T1- and T2-weighted images. On STIR images the femoral head had intermediate to low signal intensity, compared with muscle. The mid-diaphysis of the femur was of low signal intensity, similar to fat, and the body of the ilium had mixed signal intensity at all ages. The femoral condyle had inhomogenous, intermediate to low signal intensity at 4 months, but was of uniform low signal intensity at 8-16 months.     

Magnetic resonance imaging and histological findings in the proximal aspect of the suspensory ligament of forelimbs in nonlame horses

Reasons for performing study: Detailed magnetic resonance imaging (MRI) and histological appearances of the proximal aspect of the suspensory ligament (PSL) in the forelimb of nonlame horses have not been previously documented. Objectives: 1) to describe detailed anatomy of the PSL, 2) describe high‐ and low‐field MRI and histological appearances of the PSL and surrounding structures in the forelimb of horses with no carpal or proximal metacarpal pain, 3) assess the relationship between age, breed, gender, height, bodyweight and MRI findings and 4) describe the histological appearance of the PSL and compare this with MRI findings. Methods: High‐ and low‐field MR images of the PSL and related structures from 30 cadaver limbs of nonlame horses were analysed subjectively and objectively. Univariable and multivariable linear regression analyses were used to assess the association of age, breed, gender, height and bodyweight with MRI findings. Histological and MRI findings of the PSL of 9 limbs were compared subjectively. Results: The collagenous tissue of the PSL had low to intermediate signal intensity depending on the pulse sequence. There was a large variation among horses in the amount, shape and signal intensity of the muscle and adipose tissue within the PSL. Comparison of MR images with histological slides revealed that the high signal intensity areas corresponded to adipose tissue and intermediate signal intensity areas to muscle tissue. The medial lobe of the PSL had a smaller cross sectional area (CSA) than the lateral lobe; there was a positive association between CSA of the PSL and both horse height and bodyweight (P<0.001). Conclusions and potential relevance: The large variability in the MRI appearance of the PSL in nonlame horses should be borne in mind when interpreting MR images of lame horses.     

Magnetic resonance imaging‐detected adaptation and pathology in the distal condyles of the third metacarpus,associated with lateral condylar fracture in Thoroughbred racehorses

Reasons for performing the study: Lateral condylar (LC) fractures of the third metacarpus (McIII) are a common reason for euthanasia in racehorses, and may be the result of repetitive overloading or cumulative pathological change. Magnetic resonance imaging (MRI) allows monitoring of bone and cartilage to detect pathological and adaptive changes that may be precursors of fracture. Objectives: To describe bone and cartilage MRI features in the distal condyles of McIII of Thoroughbred racehorses, with and without condylar fracture. Hypotheses: 1) A greater degree of bone and cartilage adaptation or pathology will be seen in fractured McIIIs compared with their respective contralateral McIIIs. 2) Contralateral McIIIs will have a greater degree of bone and cartilage adaptation or pathology than McIIIs from control horses that did not sustain a LC fracture. Methods: The McIIIs from 96 horses subjected to euthanasia at racecourses were divided into 3 groups: Group 1: nonfractured bones from horses without LC fracture; Group 2: nonfractured bones from horses with unilateral LC fracture; and Group 3: fractured bones from horses with unilateral LC fracture. The MR images were examined and graded for bone and cartilage changes. Results: Nine percent of Group 1 (n = 9) and 11% of Group 2 bones (n = 5) had incomplete LC fractures. Focal palmar necrosis was most frequently detected in bones from Group 1 (12%) compared with Groups 2 (9%) and 3 (4%). The prevalence of bone and/or cartilage abnormalities tended to increase from Group 1 to Group 2 to Group 3. Conclusions: Magnetic resonance imaging is able to detect cartilage and bone changes that may be associated with LC fracture. There was no significant difference in bone/cartilage changes between bones from Groups 1 and 2, despite increased pathology in Group 2 bones. Potential relevance: Periodic monitoring of bone and/or cartilage changes in distal McIII of Thoroughbred racehorses may help to prevent catastrophic LC fractures.     

Computed tomography of proximal metatarsal and concurrent third tarsal bone fractures in a Thoroughbred racehorse

A 2‐year‐old Thoroughbred filly presented to the William R. Pritchard Veterinary Medical Teaching Hospital at the University of California at Davis for whole body nuclear scintigraphic evaluation after an acute onset of nonweightbearing right hindlimb lameness post race. The use of computed tomography (CT) enabled visualisation of additional pathology that was not initially appreciable using combined imaging modalities of nuclear scintigraphy and digital radiography, which ultimately altered the selected course of treatment. Computed tomography in horses with fractures of the cuboidal bones of the hock can provide valuable additional information regarding fracture configuration and radiographically occult pathology, which may help to guide clinical decisions about treatment.     

Comparison between radiological and magnetic resonance imaging lesions in the distal border of the navicular bone with particular reference to distal border fragments and osseous cyst-like lesions

Reasons for performing study: There are no data concerning the accuracy of conventional and computed or digital radiography for evaluation of the equine foot. Objectives: To compare conventional film‐screen and computed radiography with magnetic resonance imaging (MRI) for detection of distal border fragments of the navicular bone; and to establish which type of fragment was more likely to be detected radiologically. Methods: Horses were included if forelimb lameness was localised to the foot and both radiography and high‐field MR images had been acquired. Horses were divided into 2 groups based on acquisition of conventional (Group A) or computed (Group B) radiographs. The presence of distal border fragments was recorded. From MR images, distal border fragments were graded based on their size and changes in signal intensity in the adjacent navicular bone. Sensitivity and specificity of conventional and computed radiography for detection of fragments were calculated using MRI as the gold standard. A Chi‐squared test was used to test for associations between specific radiological and MRI findings in the distal border of the navicular bone. Results: In Group A 46 and 18 fragments were identified on MR and radiographic images, respectively; in Group B 45 and 17 fragments were seen. There was no significant difference between computed and conventional radiography. Grades 4 and 5 fragments or large‐sized fragments were identified most frequently; low‐grade fragments were unlikely to be observed. There was a significant correlation between radiological and MRI abnormalities of the distal border of the navicular bone. Conclusions: Conventional and computed radiography had similar, rather low sensitivity for identification of distal border fragments of the navicular bone, but specificity was high. Large‐sized and high‐grade fragments were most likely to be identified radiologically. Potential relevance: Fragments observed radiologically are likely to be associated with other pathological abnormalities of the distal border of the navicular bone.     

Standing low‐field magnetic resonance imaging of a comminuted central tarsal bone fracture in a horse

This report describes the use of low‐field standing magnetic resonance imaging (MRI) in the diagnosis and clinical decision making process in a 14‐year‐old Dutch Warmblood mare with a comminuted central tarsal bone fracture. Magnetic resonance imaging in the standing horse was preferred over computed tomography examination under general anaesthesia because the animal had sustained the injury during a poor recovery from a previous general anaesthetic episode. Magnetic resonance imaging examination identified a comminuted central tarsal bone fracture with a configuration that was not identifiable with radiography. Due to extensive comminution of this fracture, conservative management was pursued. Standing low‐field MRI examination enabled safe examination of this animal and provided useful diagnostic information whilst facilitating the clinical decision making process.