MAGNETIC RESONANCE IMAGING OF THE EQUINE DIGIT WITH CHRONIC LAMINITIS

Chronic laminitis is a severe disease affecting the equine digit. It was hypothesized that magnetic resonance (MR) imaging would improve visualization of structures within the foot and pathology associated with chronic laminitis. This study aimed to describe the MR imaging findings in chronic laminitis, compare different pulse sequences for visualization of pathology, and to compare MR imaging with standard radiography. Twenty (10 forelimb, 10 hindlimb) cadaver limbs from 10 horses clinically diagnosed with chronic laminitis (group L) and 10 limbs without laminitis (group N) were used. Lateromedial radiographs and sagittal and transverse MR images of the foot were obtained. Radiographs and MR images were evaluated for anatomic definition and evidence of pathology. Dorsal hoof wall thickness and angle of rotation and displacement distance of the distal phalanx were measured. Comparisons were made between group L and N, forelimb and hindlimb within each horse, and MR imaging and radiography. Features consistently noted with MR images in group L, but not detected using radiography, included laminar disruption, circumscribed areas of laminar gas, laminar fluid, and bone medullary fluid. Other findings seen only on MR images included increased size and number of vascular channels, alterations in the corium coronae, and distal interphalangeal joint distension. Magnetic resonance imaging allowed better definition of laminar gas lines and P3 surface irregularity observed on radiographs. Based on measurements, group L had a greater angle of rotation, distal displacement, and dorsal hoof wall thickness than group N; forelimb hoof wall thickness was greater than hindlimb; and distal displacement and hoof wall thickness measurements were smaller using MR imaging than radiography, but had a similar pattern. It is concluded that there are features of chronic laminitis consistently observed using MR imaging and that these may be additional to features observed radiographically.     

MAGNETIC RESONANCE IMAGING OF THE INITIAL ACTIVE STAGE OF EQUINE LAMINITIS AT 4.7 T

Equine laminitis is a severely debilitating disease. There is a poor understanding of the underlying pathophysiology, and traditional imaging modalities have limited diagnostic capacity. High field strength magnetic resonance (MR) imaging allows direct visualization of the laminae, which other modalities do not. This would prove useful both in assessment of clinical patients and in further investigation into the pathophysiology of the disease. The objective of this study was to characterize the anatomic changes within the equine foot associated with the initial active stage of laminitis. Images obtained using a 4.7 T magnet were compared with digital radiographs using histologic diagnosis as the reference standard. Objective measurements and subjective evaluation for both modalities were evaluated for the ability to predict the histologic diagnosis in horses with clinical signs of laminitis as well as in clinically normal horses and horses that were in a population at risk for developing laminitis. Signal intensity and architectural changes within the corium and laminae were readily seen at 4.7 T, and there was a strong association with the histologic diagnosis of active laminitis. Measurements obtained with MR imaging were more sensitive and specific predictors of laminitis than those obtained radiographically. Subjective evaluation with MR imaging was more sensitive than with radiography and should become more specific with greater understanding of normal anatomy.     

LOW FIELD MAGNETIC RESONANCE IMAGING CHARACTERISTICS OF CRANIAL VAULT MENINGIOMAS IN 13 DOGS

Meningiomas are common intracranial masses in the dog, and surgical or radiation treatment of meningiomas depends on accurate identification and location. In this review of 13 patients with confirmed meningioma, low field magnetic resonance imaging characteristics of cranial vault meningiomas included increased signal intensity on T2-weighted images, decreased signal intensity on T1-weighted images, and marked contrast enhancement that was usually nonhomogeneous and well-defined. Mass effect and edema were usually present. Cyst formation and meningeal enhancement were also found in some patients. Low field magnetic resonance imaging characteristics of the meningiomas in these patients were similar to those magnetic resonance imaging findings reported in humans and the few reports pertaining to animals.     

Diagnostic accuracy of magnetic resonance imaging for meniscal tears in dogs affected with naturally occuring cranial cruciate ligament rupture

A stifle magnetic resonance (MR) imaging protocol was developed based on the appearance of the cruciate ligaments and menisci in normal dogs. Proton density images were subjectively considered to have the highest likelihood of detecting a meniscal lesion. Following this initial evaluation, the accuracy of high-field MR imaging to detect meniscal tears in dogs was evaluated in 11 dogs suffering from naturally occurring cranial cruciate ligament rupture. Dogs underwent MR imaging of the affected stifle before surgery. MR imaging and surgical findings were assessed independently, and then compared. Five tears of the medial meniscus were correctly diagnosed with MR imaging and 19 normal menisci were accurately characterized as such, based on MR images. In one medial meniscus, changes consistent with meniscal degeneration were seen on MR images but this was not seen at surgery. With regard to the lateral meniscus, one false positive diagnosis of a tear was made and this likely represented a normal variation. One other lateral meniscus had changes consistent with meniscal degeneration but, as with the similar lesion seen in the medial meniscus, this was not confirmed surgically. The global sensitivity of MR imaging for the diagnosis of a meniscal tear was 100% and the specificity was 94%. High-field MR imaging is a reliable method to diagnose meniscal tears preoperatively and this may be useful in selecting the surgical approach to clinically abnormal joints and may decrease the need for arthrotomy.     

STAGING OF LUMBAR INTER VERTEBRAL DISC DEGENERATION IN NONCHONDRODYSTROPHIC DOGS USING LOW-FIELD MAGNETIC RESONANCE IMAGING

Recognition of disc degeneration in vivo is important in the investigation of the pathophysiology of intervertebral disc disease as well as the assessment of patients. The purpose of this study was to compare low-field magnetic resonance imaging and histopathologic findings of disc degeneration in the canine caudal lumbar spine. A simple four-stage classification system for disc degeneration is proposed. Most common signs of disc degeneration in magnetic resonance imaging included nuclear clefts, decreased signal intensity of the nucleus pulposus and tears of the annulus fibrosus, or disc herniations. The association between magnetic resonance images and histopathologic findings was highly significant. A sensitivity of 100% and specificity of 79% for magnetic resonance imaging was calculated using histopathology as the gold standard.     

Ischaemic and haemorrhagic stroke in the dog

Cerebrovascular disease results from any pathological process of the blood vessels supplying the brain. Stroke, characterised by its abrupt onset, is the third leading cause of death in humans. This rare condition in dogs is increasingly being recognised with the advent of advanced diagnostic imaging. Magnetic resonance imaging (MRI) is the first choice diagnostic tool for stroke, particularly using diffusion-weighted images and magnetic resonance angiography for ischaemic stroke and gradient echo sequences for haemorrhagic stroke. An underlying cause is not always identified in either humans or dogs. Underlying conditions that may be associated with canine stroke include hypothyroidism, neoplasia, sepsis, hypertension, parasites, vascular malformation and coagulopathy. Treatment is mainly supportive and recovery often occurs within a few weeks. The prognosis is usually good if no underlying disease is found.     

MAGNETIC RESONANCE IMAGING OF THE EQUINE FOOT

The purpose of this study was to assess the ability of magnetic resonance imaging to depict abnormalities of the equine foot. MRI was performed on isolated limbs which had lesions of the foot. These images were made in 3 perpendicular planes (sagittal, transverse and frontal) using a T1 weighted sequence and were 5mm thick. Images accurately depicted normal and pathologic structures in the foot and proved to be very precise for documenting degenerative joint disease, navicular disease and laminitis lesions. This preliminary study demonstrates the considerable potential of MRI in the diagnosis of locomotor problems in the horse.     

Diagnostic Features of Clinical Neurologic Feline Infectious Peritonitis

Feline infectious peritonitis (FIP) is a fatal Arthus-type immune response of cats to infection with FIP virus, a mutant of the ubiquitous feline enteric coronavirus (FECV). The disease may occur systemically or in any single organ system, and primary neurologic disease is a common subset of such manifestations. We examined 16 domestic cats with clinical neurologic FIP and 8 control cats with nonneurologic FIP, with the intention of identifying the ante-and postmortem diagnostic tests that most contribute to accurate diagnosis. Of the 16 cats with neurologic FIP, 15 were less than 2 years of age and all 16 originated from large multiplecat households. The most useful antemortem indicators of disease were positive anti-coronavirus IgG titer in cerebrospinal fluid, high serum total protein concentration, and findings on magnetic resonance imaging suggesting periventricular contrast enhancement, ventricular dilatation, and hydrocephalus. Postmortem diagnosis was facilitated by FIP monoclonal antibody staining of affected tissue and coronavirus-specific polymerase chain reaction. Most cats with neurologic and ocular forms of FIP had patchy, focal lesions, suggesting that recently developed technologies described in this report may be useful for evaluation of cats with suspected FIP.     

A Fresh Look at the Process of Arriving at a Clinical Prognosis Part 1: Laminitis

Laminitis is a disease that represents a loss of the normal homeostatic mechanisms that control the day-to-day function of the distal phalanx. The degree or severity to which homeostasis is affected is directly related to the severity and the final outcome for the equine patient. A systematic approach including the physical examination, digital radiography, venography, and newer techniques such as computer tomography and magnetic resonance imaging can assist the clinician in developing a prognosis for the acute and chronic laminitis case. How quickly we are able to return the foot back to a normal state of homeostasis or the response to treatment is important as a predictive value for outcome.     

Magnetic resonance imaging appearance of hypertensive encephalopathy in a dog

A 16-year-old female spayed English Staffordshire terrier was presented for evaluation of a 10-month history of intermittent myoclonic episodes, and a one weeks history of short episodes of altered mentation, ataxia and collapse. Magnetic resonance imaging identified subcortical oedema, predominately in the parietal and temporal lobes and multiple cerebral microbleeds.Serum biochemistry, indirect blood pressure measurements and magnetic resonance imaging abnormalities were consistent with hypertensive encephalopathy secondary to chronic kidney disease.     

USE OF RADIOGRAPHY, COMPUTED TOMOGRAPHY AND MAGNETIC RESONANCE IMAGING FOR EVALUATION OF NAVICULAR SYNDROME IN THE HORSE

Radiographic evaluation of navicular syndrome is problematic because of its inconsistent correlation with clinical signs. Scintigraphy often yields false positive and false negative results and diagnostic ultrasound is of limited value. Therefore, we assessed the use of computed tomography and magnetic resonance imaging in a horse with clinical and radiographic signs of navicular syndrome. Cadaver specimens were examined with spiral computed tomographic and high-field magnetic resonance scanners and images were correlated with pathologic findings. Radiographic changes consisted of bony remodeling, which included altered synovial fossae, increased medullary opacity, cyst formation and shape change. These osseous changes were more striking and more numerous on computed tomographic and magnetic resonance images. They were most clearly defined with computed tomography. Many osseous changes seen with computed tomography and magnetic resonance imaging were not radiographically evident. Histologically confirmed soft tissue alterations of the deep digital flexor tendon, impar ligament and marrow were identified with magnetic resonance imaging, but not with conventional radiography. Because of their multiplanar capability and tomographic nature, computed tomography and magnetic resonance imaging surpass conventional radiography for navicular imaging, facilitating earlier, more accurate diagnosis. Current advances in imaging technology should make these imaging modalities available to equine practitioners in the future.     

COMPUTED TOMOGRAPHY AND MAGNETIC RESONANCE IMAGING OF CAVERNOUS SINUS ENLARGEMENT IN A DOG WITH UNILATERAL EXOPHTHALMOS

Computed tomography (CT), magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) were performed on a dog with a two year history of unilateral exophthalmos occurring two years following head trauma. On CT images, an expansile enhancing mass was present along the right intracranial cavernous sinus and extended through the orbital fissure into the retrobulbar space. With MRI, the structure appeared as a signal void due to the presence of rapidly flowing blood. Gadolinium enhancement of the adjacent brain was not present. A vascular origin of the lesion was confirmed with MRA. Based on the CT and MRI findings, the enlarged cavernous sinus and associated ophthalmic plexus were believed to represent an arterialized aneurysm, most likely the result of traumatic arteriovenous fistulization. Treatment consisted of surgical enucleation. At the time of this report, 29 mouths later, the dog remains free of clinical signs.     

Findings on low-field cranial MR images in epileptic dogs that lack interictal neurological deficits

Recurrent seizuring is a common neurological problem in dogs and can present diagnostic difficulties for the attending clinician. Associated interictal neurological deficits strongly suggest brain disease but the frequency of structural abnormalities in patients without such deficits is unknown. In this study the prevalence of clinically significant magnetic resonance imaging (MRI) abnormalities was determined in two groups of interictally normal dogs, those younger than 6 years and those older than 6 years of age. In the former group, only 1/46 dogs (2.2%) had significant MRI abnormalities, whereas in the latter group, 8/30 (26.7%) were abnormal. None of the dogs had an identifiable metabolic cause for the seizures. These findings suggest that the diagnostic yield of advanced neuroimaging techniques in young seizuring dogs without interictal neurological deficits is low, but reaffirms their value in similar older individuals.     

MAGNETIC RESONANCE IMAGING FEATURES OF PARASPINAL INFECTION IN THE DOG AND CAT

The magnetic resonance (MR) imaging findings in 22 dogs and two cats with confirmed paraspinal infection of the thoracolumbar spine were characterized. These findings included extensive T2-hyperintense areas (24/24), abscessation (20/24), mild inherent T1-hyperintensity of muscle and abscesses (18/24), and postcontrast enhancement (24/24). Changes involved the vertebral canal in four patients. The longus coli muscles were affected in one cat. Thoracolumbar changes in the remaining 23 patients involved the iliopsoas and epaxial muscles in 23/23 and 19/23 patients, respectively. Iliopsoas muscle abscessation was unilateral in 12/23, and bilateral in 6/24 patients. Abscessation involved both epaxial and iliopsoas muscles in 2/23 patients and the epaxial muscles alone in one patient. A contrast-enhancing sinus tract within the deep thoracolumbar fascia was present in 10/23 patients. Lumbar vertebrae periosteal reactions were identified in 19/23 patients on MR images compared with 15/17 patients with radiography. A focal area of signal void suspected to represent foreign material was seen in 5/23 patients but foreign material was actually found in only two of these five. There was no recurrence of clinical signs following MR imaging and revision surgery. MR imaging permits the severity and extent of changes associated with paraspinal infection to be characterized and allows the location, number and any communication of sinus tracts to be documented.     

MR, CT AND CLINICAL FEATURES FROM FOUR DOGS WITH NASAL TUMORS INVOLVING THE ROSTRAL CEREBRUM

The clinical findings and computed tomographic and magnetic resonance images from four dogs with nasal tumors that invaded the central nervous system were revlewed. There were minimal or no clinical signs related to nasal disease. Brain imaging with magnetic resonance or computed tomography demonstrated antemortem involvement of brain and nasal structures. Magnetic resonance imaging was optimal for demonstrating this involvement and showed more detailed anatomic features of the mass and secondary pathologies attributed to the mass.     

The use of magnetic resonance imaging in the management of pharyngeal penetration injuries in dogs

Objectives: To investigate the correlation between the magnetic resonance imaging findings and subsequent surgical findings for a series of dogs presenting with suspected pharyngeal stick injuries to the Animal Health Trust, Newmarket, between 1995 and 2004. Methods: Magnetic resonance imaging findings were reviewed for patients undergoing a scan of the pharyngeal or cervical area for suspected foreign bodies during the years 1995 to 2004. Results: Case signalment, history and clinical signs were similar to those reported in previous studies. Magnetic resonance imaging demonstrated foreign material in six of seven cases where this was present. There was good correlation between diagnosis of a foreign body at magnetic resonance imaging and subsequent surgical identification. Clinical Significance: Compared with other imaging modalities, magnetic resonance imaging is very helpful for this type of injury, especially in chronic cases where radiographic evidence of a foreign body is unlikely. It is a valuable aid in the diagnosis of pharyngeal penetration injury and in surgical planning.     

High-resolution fluorodeoxyglucose positron emission tomography and magnetic resonance imaging findings of a pituitary microtumor in a dog

A 16-year-old, castrated, male English cocker spaniel dog was presented due to generalized alopecia. Routine clinical pathology, endocrine and abdominal ultrasonography results were consistent with a diagnosis of pituitary-dependent hyperadrenocorticism. The adenohypophyseal lesion was clearly visualized on both 3 T and 7 T magnetic resonance imaging (MRI) of the pituitary gland. Although biochemical and MRI findings were consistent with a functional pituitary microtumor, a pituitary lesion was not detected using ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET). This report firstly describes the application of high-resolution FDG-PET to a spontaneous pituitary microtumor in a dog.     

Magnetic resonance imaging findings in histologically confirmed Pug dog encephalitis

The purpose of the study was to describe magnetic resonance (MR) imaging features of histologically confirmed necrotizing encephalitis in four Pugs and to compare those findings with MR imaging characteristics of necrotizing encephalitis in other breeds. All dogs had the following common findings: lesions restricted to the forebrain, both cerebral hemispheres diffusely but asymmetrically affected, lesions affected gray and white matter resulting in loss of distinction between both, most severe lesions in occipital and parietal lobes, lesions were irregularly T2-hyperintense and T1-isointense to slightly T1-hypointense, and no cavitation. There were various degrees of contrast enhancement of brain and leptomeninges. Asymmetry of lateral ventricles and midline shift was seen in one dog each. Two dogs had brain herniation, which may have contributed to the progression of neurologic signs. Hyperintensity on T2-weighted and fluid attenuated inversion recovery images in the hippocampus and piriform lobe was consistent with excitotoxic edema, whereas similar imaging features in other forebrain areas corresponded to areas of inflammation or liquefaction on histopathology. In comparison with necrotizing encephalitis in other canine breeds, Pug dog encephalitis has some unique MR imaging features. Therefore, these characteristics cannot be applied to other breeds, nor should imaging features of necrotizing encephalitis of other canine breeds be used for interpretation of MR images in Pug dogs.     

A COMPARISON OF RADIOGRAPHY, COMPUTED TOMOGRAPHY, AND MAGNETIC RESONANCE IMAGING FOR THE DIAGNOSIS OF PALMAR PROCESS FRACTURES IN FOALS

The relative sensitivity of radiography, computed tomography, and magnetic resonance imaging for detecting palmar process fractures of the distal phalanx in foals was determined and the imaging findings were compared with histomorphologic evaluations of the palmar processes. Compared to radiography, computed tomography and magnetic resonance imaging did not improve the sensitivity for detection of palmar process fractures. Statistical agreement for palmar process fracture diagnosis was excellent among the three imaging modalities. Histomorphologic evaluations were more sensitive for diagnosis of palmar process fracture than any of the imaging modalities. Three-dimensional image reconstructions and volume measurements of distal phalanges and palmar process fracture fragments from computed tomography studies provided more complete anatomical information than radiography. Magnetic resonance imaging confirmed that the deep digital flexor tendon insertion on the distal phalanx is immediately axial to the site where palmar process fractures occur, and differentiated cartilage, bone, and soft tissue structures of the hoof.     

Magnetic resonance imaging findings and clinical associations in 52 dogs with suspected ischemic myelopathy

BACKGROUND: The magnetic resonance imaging (MRI) features of ischemic myelopathy have been described in the human literature and in a small number of cases in the veterinary literature. HYPOTHESIS: The aims of this study were to identify associations among MRI findings, timing of imaging, and presenting neurologic deficits in a large series of dogs with a presumptive diagnosis of ischemic myelopathy. ANIMALS AND METHODS: The medical records and MR images of dogs with a presumptive diagnosis of ischemic myelopathy (2000-2006) were reviewed retrospectively. Inclusion criteria were acute onset of nonprogressive and nonpainful myelopathy, 1.5-tesla MRI of the spine performed within 7 days of onset, and complete medical records and follow-up information. Presumptive diagnosis was based on history, as well as clinical, MRI, and cerebrospinal fluid (CSF) findings. The extent of the lesion on MRI was assessed as the following: (1) the ratio between the length of the hyperintense area on sagittal T2-weighted images and the length of C6 or L2 vertebral body, and (2) the maximal cross-sectional area of the hyperintense area on transverse T2-weighted images as a percentage of cross-sectional area of the spinal cord. RESULTS: Fifty-two dogs met the inclusion criteria. MRI findings were abnormal in 41 dogs and normal in 11 dogs. The presence of MRI abnormalities was not significantly associated with the timing of imaging (P = .3) but was associated with ambulatory status on presentation (P = .04). Severity of signs on presentation was associated with extent of the lesion on MRI (P = .02). CONCLUSION AND CLINICAL IMPORTANCE: The severity of signs on presentation is associated with the presence and the extent of the lesion on MRI.