COMPARISON BETWEEN 2‐18F‐FLUORO‐2‐DEOXY‐D‐GLUCOSE POSITRON EMISSION TOMOGRAPHY AND CONTRAST‐ENHANCED COMPUTED TOMOGRAPHY FOR MEASURING GROSS TUMOR VOLUME IN CATS WITH ORAL SQUAMOUS CELL CARCINOMA

Feline oral squamous cell carcinoma is one of the most refractory feline malignancies. Most patients succumb due to failure in local tumor control. 2‐¹⁸F‐fluoro‐2‐deoxy‐D‐glucose positron emission tomography (¹⁸F‐FDG PET) is increasingly being used for veterinary oncology staging as it highlights areas with higher glucose metabolism. The goal of the current prospective study was to compare gross tumor volume measurements using ¹⁸F‐FDG PET vs. those using computed tomography (CT) for stereotactic radiation therapy planning in cats with oral squamous cell carcinoma. Twelve cats with confirmed oral squamous cell carcinoma underwent pretreatment ¹⁸F‐FDG PET/CT. Gross tumor volumes based on contrast‐enhanced CT and ¹⁸F‐FDG PET were measured and compared among cats. Mean PET gross tumor volume was significantly smaller than mean CT gross tumor volume in the mandibular/maxillary squamous cell carcinoma group (n = 8, P = 0.002) and for the total number of patients (n = 12, P = 0.006), but not in the lingual/laryngeal group (n = 4, P = 0.57). Mismatch fraction analysis revealed that most of the lingual/laryngeal patients had a large region of high‐¹⁸F‐FDG activity outside of the CT gross tumor volume. This mismatch fraction was significantly greater in the lingual/laryngeal group than the mandibular/maxillary group (P = 0.028). The effect of poor spatial resolution of PET imaging was greater when the absolute tumor volume was small. Findings from this study indicated that ¹⁸F‐FDG PET warrants further investigation as a supplemental imaging modality in cats with oral squamous cell carcinoma because it detected regions of possible primary tumor that were not detected on CT images.     

ELASTOGRAPHIC EVALUATION OF NATURALLY OCCURING TENDON AND LIGAMENT INJURIES OF THE EQUINE DISTAL LIMB

Compression elastography is an ultrasonographic technique that estimates tissue strain and may have utility in diagnosing and monitoring soft tissue injuries in the equine athlete. Recently, elastography has been proven to be a feasible and repeatable imaging modality for evaluating normal tendons and ligaments of the equine distal forelimb. The purposes of this prospective study were to investigate the ability of elastography to detect spontaneously occurring lesions of equine tendons and ligaments diagnosed with magnetic resonance imaging (MRI) and gray‐scale ultrasound (US) and to characterize the differences in the elastographic appearance of acute vs. chronic injuries. Fifty seven horses with a total of 65 lesions were evaluated. Images were assessed quantitatively and qualitatively. Acute lesions were found to be significantly softer (P < 0.0001) than chronic lesions (P < 0.0001) and the stiffness of lesions increased with progression of healing (P = 0.0138). A negative correlation between lesion hypoechogenicity and softness was appreciated with more hypoechoic lesions appearing softer (P = 0.0087) and more hyperechoic regions harder (P = 0.0002). A similar finding occurred with increased signal intensity on short tau inversion recovery (STIR) and proton density (PD) MRI sequences correlating with increased softness on elastography (P = 0.0164). Using US and MRI as references, commonly encountered soft tissue injuries of the equine distal limb could be detected with elastography. However, elastography was limited for detecting small, proximal injuries of the hindlimb proximal suspensory ligament. Elastographic evaluation of equine tendons and ligaments may allow better characterization of lesion chronicity and severity, and sequential examinations may optimize lesion management, rehabilitation, and return to training.     

FDG PET/CT IMAGING IN CANINE CANCER PATIENTS

2‐Deoxy‐2‐[¹⁸F]fluoro‐d ‐glucose positron emission tomography/computed tomography (FDG PET/CT) is becoming increasingly available as an imaging modality in veterinary medicine. The purpose of this study was to report semiquantitative standard uptake values (SUV) of malignant and nonmalignant tissues and organs in canine cancer patients. FDG PET/CT was performed in 14 dogs including, nine mesenchymal tumors, four carcinomas, and one incompletely excised mast cell tumor. A generally higher FDG uptake was observed in carcinomas relative to sarcomas. Maximum SUV of carcinomas ranged from 7.6 to 27.0, and for sarcomas from 2.0 to 10.6. The FDG SUV of several organs and tissues, including regional brain uptake is reported, to serve as a reference for future FDG PET studies in canine cancer patients. Several potential pitfalls have been recognized in interpretation of FDG PET images of human patients, a number of these were also observed in this study.     

Pilot study utilizing Fluorine‐18 fluorodeoxyglucose‐positron emission tomography/computed tomography for glycolytic phenotyping of canine mast cell tumors

The goal of this prospective pilot study was to use naturally occurring canine mast cell tumors of various grades and stages as a model for attempting to determine how glucose uptake and markers of biologic behavior are correlated. It was hypothesized that enhanced glucose uptake, as measured by 2‐[fluorine‐18]fluoro‐d ‐glucose‐positron emission tomography/computed tomography (F18 FDG PET‐CT), would correlate with histologic grade. Dogs were recruited for this study from a population referred for treatment of cytologically or histologically confirmed mast cell tumors. Patients were staged utilizing standard of care methods (abdominal ultrasound and three view thoracic radiographs), followed by a whole body F18 FDG PET‐CT. Results of the F18 FDG PET‐CT were analyzed for possible metastasis and standard uptake value maximum (SUV_max) of identified lesions. Incisional or excisional biopsies of the accessible mast cell tumors were obtained and histology performed. Results were then analyzed to look for a possible correlation between the grade of mast cell tumors and SUV_max. A total of nine animals were included in the sample. Findings indicated that there was a correlation between grade of mast cell tumors and SUV_max as determined by F18 FDG PET‐CT (p‐value = 0.073, significance ≤ 0.1). Based on the limited power of this study, it is felt that further research to examine the relationship between glucose utilization and biologic aggressiveness in canine mast cell tumors is warranted. This study was unable to show that F18 FDG PET‐CT was a better staging tool than standard of care methods.     

CHARACTERIZATION OF PHYSIOLOGIC 18F‐FDG UPTAKE WITH PET‐CT IN DOGS

We evaluated the whole body distribution of 2‐deoxy‐2‐[18F]fluoro‐d ‐glucose (¹⁸F‐FDG) in seven beagle dogs using positron emission tomography/computed tomography. The mean and maximum standard uptake values (SUV) for various tissues were computed. The SUV of the aortic blood pool was 0.65±0.19. Moderate uptake was present in brain (3.40±1.01). Mild uptake was present in orbital muscles, soft palate, laryngeal and pharyngeal region, mandibular salivary gland, myocardium, liver, pancreas, kidney, and intestine. ¹⁸F‐FDG uptake would be normally higher in these tissues because of normal physiologic activity. Mean and maximum SUV values of the eye, skeletal muscle, bone tissue, spleen, adrenal gland, stomach, tongue, gall bladder, and lung were similar to or lower than that of the aortic blood pool. These data provide a normal baseline for comparing pathologic ¹⁸F‐FDG uptake.     

Effect of Harderian adenectomy on the statistical analyses of mouse brain imaging using positron emission tomography

Positron emission tomography (PET) using 2-deoxy-2-[¹⁸F] fluoro-D-glucose (FDG) as a radioactive tracer is a useful technique for in vivo brain imaging. However, the anatomical and physiological features of the Harderian gland limit the use of FDG-PET imaging in the mouse brain. The gland shows strong FDG uptake, which in turn results in distorted PET images of the frontal brain region. The purpose of this study was to determine if a simple surgical procedure to remove the Harderian gland prior to PET imaging of mouse brains could reduce or eliminate FDG uptake. Measurement of FDG uptake in unilaterally adenectomized mice showed that the radioactive signal emitted from the intact Harderian gland distorts frontal brain region images. Spatial parametric measurement analysis demonstrated that the presence of the Harderian gland could prevent accurate assessment of brain PET imaging. Bilateral Harderian adenectomy efficiently eliminated unwanted radioactive signal spillover into the frontal brain region beginning on postoperative Day 10. Harderian adenectomy did not cause any post-operative complications during the experimental period. These findings demonstrate the benefits of performing a Harderian adenectomy prior to PET imaging of mouse brains.     

18F‐FDG‐PET/CT as adjunctive diagnostic modalities in canine fever of unknown origin

Fever of unknown origin (FUO) is a persistent or recurrent fever for which the underlying source has not been identified despite diagnostic investigation. In people, ¹⁸F‐fluoro‐2‐deoxyglucose positron emission tomography (¹⁸F‐FDG‐PET) alone or in combination with computed tomography (CT) is often beneficial in detecting the source of fever when other diagnostics have failed. Veterinary reports describing use of these modalities in animals with fever of unknown origin are currently lacking. Aims of this retrospective case series were to describe ¹⁸F‐FDG‐PET or ¹⁸F‐FDG‐PET/CT findings in a group of dogs with fever of unknown origin. Dogs presenting to a single center between April 2012 and August 2015 were included. A total of four dogs met inclusion criteria and underwent either positron emission tomography (n = 2) or positron emission tomography/CT (n = 2) as a part of their diagnostic investigation. All subjects underwent extensive diagnostic testing prior to ¹⁸F‐FDG‐PET/CT. Initial diagnostic evaluation failed to identify either a cause of fever or an anatomic location of disease in these four dogs. In each dog, positron emission tomography or positron emission tomography/CT was either able to localize or rule out the presence of focal lesion thereby allowing for directed sampling and/or informed disease treatment. Follow up ¹⁸F‐FDG‐PET/CT scans performed in two patients showed improvement of observed abnormalities (n = 1) or detected recurrence of disease allowing for repeated treatment before clinical signs recurred (n = 1). Fever resolved after specific treatment in each dog. Findings from the current study supported the use of positron emission tomography or positron emission tomography/CT as adjunctive imaging modalities for diagnosis and gauging response to therapy in dogs with fever of unknown origin.     

STATIC AND DYNAMIC 18FDG‐PET IN NORMAL HISPANIOLAN AMAZON PARROTS (AMAZONA VENTRALIS)

Positron emission tomography (PET) is often used to stage and monitor human cancer and has recently been used in a similar fashion in veterinary medicine. The most commonly used radiopharmaceutical is 2‐Deoxy‐2‐[¹⁸F]‐Fluoro‐d ‐glucose (¹⁸F‐FDG), which is concentrated and trapped within cells that use glucose as their energy substrate. We characterized the normal distribution of ¹⁸F‐FDG in 10 healthy Hispaniolan Amazon parrots (Amazona ventralis) by performing whole body PET scans at steady state, 60 min after injection. Significant variability was found in the intestinal activity. Avian species are known to reflux fluid and electrolytes from their cloaca into their colon. To evaluate reflux as the cause of variability in intestinal distribution of ¹⁸F‐FDG, dynamic PET scans were performed on the coelomic cavity of six Hispaniolan Amazon parrots from time 0 to 60 min postinjection of radiotracer. Reflux of radioactive material from the cloaca into the colon occurred in all birds to varying degrees and occurred before 60 min. To evaluate the intestinal tract of clinical avian patients, dynamic scans must be performed starting immediately after injection so that increased radioactivity due to metabolism or hypermetabolic lesions such as cancer can be differentiated from increased radioactivity due to reflux of fluid from the cloaca.     

PHYSIOLOGIC VARIANTS,BENIGN PROCESSES,AND ARTIFACTS FROM 106 CANINE AND FELINE FDG‐PET/COMPUTED TOMOGRAPHY SCANS

18F‐Fluoro‐deoxyglucose positron emission computed tomography (FDG‐PET/CT) is an emerging diagnostic imaging modality in veterinary medicine; however, little published information is available on physiologic variants, benign processes, and artifacts. The purpose of this retrospective study was to describe the number of occurrences of non‐neoplastic disease‐related FDG‐PET/CT lesions in a group of dogs and cats. Archived FDG‐PET/CT scans were retrieved and interpreted based on a consensus opinion of two board‐certified veterinary radiologists. Non‐neoplastic disease‐related lesions were categorized as physiologic variant, benign activity, or equipment/technology related artifact. If the exact cause of hypermetabolic areas could not be determined, lesions were put into an indeterminate category. A total of 106 canine and feline FDG‐PET/CT scans were included in the study. In 104 of the 106 scans, a total of 718 occurrences of physiologic variant, areas of incidental benign activity, and artifacts were identified. Twenty‐two of 23 feline scans and 82 of 83 canine scans had at least one artifact. Previously unreported areas of increased radiopharmaceutical uptake included foci associated with the canine gall bladder, linear uptake along the canine mandible, and focal uptake in the gastrointestinal tract. Benign activity was often seen and related to healing, inflammation, and indwelling implants. Artifacts were most often related to injection or misregistration. Further experience in recognizing the common veterinary FDG physiologic variation, incidental radiopharmaceutical uptake, and artifacts is important to avoid misinterpretation and false‐positive diagnoses.     

FDG‐PET IN HEALTHY AND EPILEPTIC LAGOTTO ROMAGNOLO DOGS AND CHANGES IN BRAIN GLUCOSE UPTAKE WITH AGE

Regional cerebral metabolism and blood flow can be measured noninvasively with positron emission tomography (PET). 2‐[¹⁸F]fluoro‐2‐deoxy‐D‐glucose (FDG) widely serves as a PET tracer in human patients with epilepsy to identify the seizure focus. The goal of this prospective study was to determine whether juvenile or adult dogs with focal‐onset epilepsy exhibit abnormal cerebral glucose uptake interictally and whether glucose uptake changes with age. We used FDG‐PET to examine six Lagotto Romagnolo dogs with juvenile epilepsy, two dogs with adult‐onset epilepsy, and five control dogs of the same breed at different ages. Three researchers unaware of dog clinical status visually analyzed co‐registered PET and magnetic resonance imaging (MRI) images. Results of the visual PET analyses were compared with electroencephalography (EEG) results. In semiquantitative analysis, relative standard uptake values (SUV) of regions of interest (ROI) drawn to different brain regions were compared between epileptic and control dogs. Visual analysis revealed areas of hypometabolism interictally in five out of six dogs with juvenile epilepsy in the occipital, temporal, and parietal cortex. Changes in EEG occurred in three of these dogs in the same areas where PET showed cortical hypometabolism. Visual analysis showed no abnormalities in cerebral glucose uptake in dogs with adult‐onset epilepsy. Semiquantitative analysis detected no differences between epileptic and control dogs. This result emphasizes the importance of visual analysis in FDG‐PET studies of epileptic dogs. A change in glucose uptake was also detected with age. Glucose uptake values increased between dog ages of 8 and 28 weeks and then remained constant.     

PET/CT today and tomorrow in veterinary cancer diagnosis and monitoring: fundamentals,early results and future perspectives

Functional imaging using positron emission tomography (PET) plays an important role in the diagnosis, staging, image‐guided treatment planning and monitoring of malignant diseases. PET imaging complements conventional anatomical imaging such as computed tomography (CT) and magnetic resonance imaging (MRI). The strength of CT scanning lies in its high spatial resolution, allowing for anatomical characterization of disease. PET imaging, however, moves beyond anatomy and characterizes tissue based on functions such as metabolic rate. Combined PET/CT scanners were introduced commercially in 2001 and a number of technological advancements have since occurred. Radiolabelled tracers such as ¹⁸F‐fluorodeoxyglucose (FDG) and ¹⁸F‐fluorothymidine (FLT) allow visualization of various metabolic processes within cancer cells. Many studies in human oncology evaluating the utility of PET/CT have demonstrated clinical benefits. Few veterinary studies have been performed, but initial studies show promise for improved detection of malignancy, more thorough staging of canine cancer and determination of early response and disease recrudescence.     

CEREBRAL GLUCOSE UTILIZATION MEASURED WITH HIGH RESOLUTION POSITRON EMISSION TOMOGRAPHY IN EPILEPTIC FINNISH SPITZ DOGS AND HEALTHY DOGS

In human epileptic patients, changes in cerebral glucose utilization can be detected 2‐deoxy‐2‐[¹⁸F] fluoro‐d ‐glucose positron emission tomography (FDG‐PET). The purpose of this prospective study was to determine whether epileptic dogs might show similar findings. Eleven Finnish Spitz dogs with focal idiopathic epilepsy and six healthy dogs were included. Dogs were examined using electroencephalography (EEG) and FDG‐PET, with epileptic dogs being evaluated during the interictal period. Visual and semi‐quantitative assessment methods of FDG‐PET were compared and contrasted with EEG findings. Three independent observers, unaware of dog clinical status, detected FDG‐PET uptake abnormalities in 9/11 epileptic (82%), and 4/8 healthy dogs (50%). Occipital cortex findings were significantly associated with epileptic status (P = 0.013). Epileptic dogs had significantly lower standardized uptake values (SUVs) in numerous cortical regions, the cerebellum, and the hippocampus compared to the control dogs. The lowest SUVs were found in the occipital lobe. White matter normalized and left‐right asymmetry index values for all pairs of homologous regions did not differ between groups. Visual evaluation of the EEGs was less sensitive (36%) than FDG‐PET. Both diagnostic tests were consensual and specific (100%) for occipital findings, but EEG had a lower sensitivity for detecting lateralized foci than FDG‐PET. Findings supported the use of FDG‐PET as a diagnostic test for dogs with suspected idiopathic epilepsy. Visual and semiquantitative analyses of FDG‐PET scans provided complementary information. Findings also supported the theory that epileptogenesis may occur in multiple brain regions in Finnish Spitz dogs with idiopathic epilepsy.     

Evaluation of 18F‐FDG PET/CT as a diagnostic imaging and staging tool for feline oral squamous cell carcinoma

18F‐fluorodeoxyglucose positron emission tomography combined with computed tomography (18FDG‐PET/CT) has been shown to be effective for staging human oral squamous cell carcinoma (SCC) but its application for cats with oral SCC is unknown. Twelve cats with biopsy‐proven oral SCC were imaged with whole body 18FDG‐PET/CT to determine its value as a diagnostic imaging and staging tool and fine needle aspirates were obtained of accessible regional lymph nodes. All tumors were FDG avid and conspicuous on 18FDG‐PET/CT images, with an average of the maximum standardized uptake value 9.88 ± 5.33 SD (range 2.9–24.9). Soft tissue infiltrative tumors that were subtle and ill defined on CT were highly visible and more extensive on FDG‐PET/CT. Tumors invading the osseous structures were more similar in extent on 18FDG‐PET/CT and CT although they were more conspicuous on PET images. Three cytologically confirmed metastases were hypermetabolic on PET, while two of those metastases were equivocal on CT.     

WHOLE‐BODY BIODISTRIBUTION OF 3′‐DEOXY‐3′‐[18F]FLUOROTHYMIDINE (18FLT) IN HEALTHY ADULT CATS

Positron emission tomography/computed tomography (PET/CT) utilizing 3′‐deoxy‐3′‐[¹⁸F]fluorothymidine (¹⁸FLT), a proliferation tracer, has been found to be a useful tool for characterizing neoplastic diseases and bone marrow function in humans. As PET and PET/CT imaging become increasingly available in veterinary medicine, knowledge of radiopharmaceutical biodistribution in veterinary species is needed for lesion interpretation in the clinical setting. The purpose of this study was to describe the normal biodistribution of ¹⁸FLT in adult domestic cats. Imaging of six healthy young adult castrated male cats was performed using a commercially available PET/CT scanner consisting of a 64‐slice helical CT scanner with an integrated whole‐body, high‐resolution lutetium oxy‐orthosilicate (LSO) PET scanner. Cats were sedated and injected intravenously with 108.60 ± 2.09 (mean ± SD) MBq of ¹⁸FLT (greater than 99% radiochemical purity by high‐performance liquid chromatography). Imaging was performed in sternal recumbency under general anesthesia. Static images utilizing multiple bed positions were acquired 80.83 ± 7.52 (mean ± SD) minutes post‐injection. Regions of interest were manually drawn over major parenchymal organs and selected areas of bone marrow and increased tracer uptake. Standardized uptake values were calculated. Notable areas of uptake included hematopoietic bone marrow, intestinal tract, and the urinary and hepatobiliary systems. No appreciable uptake was observed within brain, lung, myocardium, spleen, or skeletal muscle. Findings from this study can be used as baseline data for future studies of diseases in cats.     

ELASTOGRAPHIC CHARACTERISTICS OF THE METACARPAL TENDONS IN HORSES WITHOUT CLINICAL EVIDENCE OF TENDON INJURY

Tendon and ligament injuries are common causes of impaired performance in equine athletes. Gray‐scale ultrasonography is the current standard method for diagnosing and monitoring these injuries, however this modality only provides morphologic information. Elastography is an ultrasound technique that allows detection and measurement of tissue strain, and may provide valuable mechanical information about equine tendon and ligament injuries. The purpose of this study was to determine the feasibility, reproducibility, and repeatability of elastography; and to describe elastographic characteristics of metacarpal tendons in sound horses. Nineteen legs for 17 clinically sound horses without evidence of musculoskeletal pathology were included. Elastographic images of the superficial and deep digital flexor tendons and the branches of the suspensory ligament (tendon of the interosseous muscle) were described quantitatively and qualitatively. There was no statistically significant difference between operators (P = 0.86) nor within operators (P = 0.93). For qualitative assessments, reproducibility (0.46) was moderate and repeatability (0.78) was good. Similar to human Achilles tendons, equine tendons were classified as predominantly hard using elastography. There was no statistically significant difference in stiffness of the flexor tendons (P = 0.96). No significant difference in stiffness was found with altered leg position during standing (P = 0.84) and while nonweight bearing (P = 0.61). The flexor tendons were softer when imaged in longitudinal versus transverse planes (P < 0.01) however, the suspensory branches were not (P = 0.67). Findings supported future clinical application of elastography as a noninvasive “stall‐side” imaging modality for evaluation of the tendons and ligaments of the distal forelimb in horses.     

ULTRASONIC ANATOMY OF THE TENDONS AND LIGAMENTS IN THE DISTAL METACARPAL-METATARSAL REGION OF THE EQUINE LIMB

In a two-phase study, ultrasound was used to delineate the normal sonographic anatomy of soft tissues of the equine distal limb. The study was limited to the soft tissues of the palmar surface of the limb just proximal to the fetlock joint. In the first phase, cadavers were evaluated with a B-mode ultrasound machine, † Then the limbs were radiographed and dissected to compare their gross, radiographic, and ultrasonographic appearances. In the second phase, nine normal adult horses were ultrasonographically scanned. The sonographic appearance of the normal animals was compared with that of the cadavers. Front and rear limbs of all horses had similar ultrasonographic appearances. Flexor tendons and the suspensory ligament were easily identified as having linear, uniformly intense ecogenicity. The borders of the digital sheath and of the proximal palmar pouch of the fetlock joint had a less organized and less intense ecogenic appearance than the flexor tendons and suspensory ligament, and they were poorly delineated unless distended with fluid. Ultrasonography was used in three lame horses and aided the diagnoses of synovial proliferation in the fetlock joint, tendosynovitis, and bowed tendon. Diagnostic ultrasonography was effective in identifying and characterizing soft-tissue structures of the distal equine limb. It is a valuable, noninvasive diagnostic aid.     

IMAGING DIAGNOSIS—MULTICENTRIC LYMPHOMA OF GRANULAR LYMPHOCYTES IMAGED WITH FDG PET/CT IN A DOG

A 5‐year‐old female spayed bulldog was referred for mild dyspnea, decreased activity and appetite, occasional nonproductive cough, polydipsia, and polyuria. A 2‐deoxy‐2‐[¹⁸F]fluoro‐D‐glucose (FDG) positron emission tomography/computed tomography (PET/CT) scan revealed unexpected activity in the heart, lungs, and mild generalized lymphadenopathy that led to the diagnosis of lymphoma of granular lymphocytes after nonspecific findings on imaging with standard modalities of echocardiography, thoracic radiography, and abdominal ultrasound. PET/CT scanning is a useful whole body imaging modality with high sensitivity for changes associated with canine lymphoma.     

Influence of the position of the foot on MRI signal in the deep digital flexor tendon and collateral ligaments of the distal interphalangeal joint in the standing horse

Reasons for performing study: Hyperintense signal is sometimes observed in ligaments and tendons of the equine foot on standing magnetic resonance examination without associated changes in size and shape. In such cases, the presence of a true lesion or an artifact should be considered. A change in position of a ligament or tendon relative to the magnetic field can induce increased signal intensity due to the magic angle effect. Objectives: To assess if positional rotation of the foot in the solar plane could be responsible for artifactual changes in signal intensity in the collateral ligaments of the distal interphalangeal joint and in the deep digital flexor tendon. Methods: Six isolated equine feet were imaged with a standing equine magnetic resonance system in 9 different positions with different degrees of rotation in the solar plane. Results: Rotation of the limb induced a linear hyperintense signal on all feet at the palmar aspect of one of the lobes of the deep digital flexor tendon and at the dorsal aspect of the other lobe. Changes in signal intensity in the collateral ligaments of the distal interphalangeal joint occurred with rotation of the limb only in those feet where mediolateral hoof imbalance was present. Conclusions: The position and conformation of the foot influence the signal intensity in the deep digital flexor tendon and in the collateral ligaments of the distal interphalangeal joint. Potential relevance: The significance of increased signal intensity in the deep digital flexor tendon and in the collateral ligaments of the distal interphalangeal joint should be interpreted with regard to the position and the conformation of the foot.     

MRI FINDINGS IN 232 HORSES WITH LAMENESS LOCALIZED TO THE METACARPO(TARSO)PHALANGEAL REGION AND WITHOUT A RADIOGRAPHIC DIAGNOSIS

Two hundred and thirty‐two horses with lameness localized to the metacarpo(tarso)phalangeal (MCP/MTP) region without a radiographic diagnosis were evaluated. All horses had high‐field magnetic resonance (MR) imaging of the MCP/MTP region performed for the lame limb and the contralateral limb for comparison. There were 46 horses that had bilateral abnormalities in the forelimbs; 27 of these horses were not lame in the contralateral limb at the time of examination. Bilateral hind limb abnormalities were observed in 37 horses; 22 horses were not lame in the contralateral limb. Soft tissue abnormalities alone were observed in 218 limbs (162 horses). Subchondral bone and articular cartilage abnormalities alone were observed in 43 limbs (34 horses). A combination of soft tissue, subchondral bone, and cartilage abnormalities were observed in 64 limbs (36 horses). The distribution of primary abnormalities was as follows; oblique distal sesamoidean ligament desmitis (73 limbs in 56 horses), straight distal sesamoidean ligament desmitis (44 limbs in 38 horses), chronic subchondral bone injuries (15 limbs in 12 horses), suspensory ligament branch desmitis (14 limbs in 12 horses), collateral ligament desmitis (12 limbs in 12 horses), tendonitis of the superficial and deep digital flexor tendons (10 limbs in 10 horses), osteochondral defects greater than 1 cm (nine limbs in six horses), osteochondral defects less than 1 cm (eight limbs in seven horses), bone marrow lesions (six limbs in five horses), intersesamoidean ligament desmitis (five limbs in four horses). MR imaging is useful in diagnosing bone and soft tissue injuries when radiographs and ultrasound fail to yield a diagnosis.