COMPUTED TOMOGRAPHY OF THE NORMAL CANINE LUMBOSACRAL SPINE: A MORPHOLOGIC PERSPECTIVE

The lumbosacral spine of six normal dogs weighing 4.5 to 24.5kg was imaged by computed tomography in 5.0 mm & 10.0 mm transverse planes. The vertebral canal and thecal sac (including emerging nerve roots not distinguished as separate structures from the spinal cord) were measured along dorsoventral and transverse dimensions at cranial, middle and caudal levels within each vertebra from transverse tomographic images. Linear measurements were standardized to the dorsoventral dimension of the L₆ vertebral midbody to permit comparison and averaging of the vertebral and thecal sac dimensions among different sized dogs. The dorsoventral and transverse vertebral canal size progressively increased from cranial to caudal within each vertebra from L₁?L₆ (p ≤ 0.05). The transverse dimension of the thecal sac image increased caudally within each vertebra from L₁?L₄ (p ≤ 0.05). The vertebral canal dorsoventral and transverse dimensions were largest in the midlumbar area (p ≤ 0.05). The transverse, but not the dorsoventral, imaged dimension of the thecal sac peaked in the L₄ vertebra (p ≤ 0.05). The dorsoventral thecal sac image was observed to fill the vertebral canal in the cranial and middle vertebral levels in vertebrae L₁ through L₅ in over 60% of these normal dogs. However, epidural fat could almost always be seen lateral to the thecal sac regardless of what lumbar vertebra or vertebral level was imaged. Cranial to the lumbosacral junction, the dorsal intervertebral disk margin was almost always concave relative to the thecal sac. However, at the L₇-S₁ junction, some dogs had flat or even slightly convex dorsal intervertebral disk margins. The dorsal and ventral longitudinal ligaments and the ligamentum flavum could not be identified as distinct structures on the 5.0 mm transverse tomographic images.     

USE OF CONTRAST‐ENHANCED COMPUTED TOMOGRAPHY TO STUDY THE CRANIAL MIGRATION OF A LUMBOSACRAL INJECTATE IN CADAVER DOGS

Volumes used in lumbosacral epidural injections for anesthesia have remained unchanged since the 1960s. The goals of this cross‐sectional observational study were to characterize the three‐dimensional spread of a lumbosacral epidural injection, as well as confirm that the commonly used volume of 0.2 ml/kg injected into the lumbosacral epidural space reaches the thoracolumbar (TL) junction in the majority (≥80%) of dogs. Ten clinically normal, adult, nonpregnant, mixed‐breed dogs were obtained within five minutes of euthanasia and 0.2 ml/kg of radiopaque contrast medium was injected into the lumbosacral epidural space. A computed tomography scan of the TL spine was performed immediately following the injection. Migration of contrast reached the TL junction in 8 of 10 (80%) dogs. Contrast was well visualized in all epidural planes with contrast travelling predominantly in the dorsal epidural space in 7 of 10 (70%) dogs. There was no significant difference in the weight of dogs where the epidural injectate reached the TL junction and those where it did not (P = 0.16), or in the weight of dogs where the cranial‐most point of the contrast column was in the dorsal versus the ventral epidural space (P = 0.32). This preliminary study supports the use of computed tomography to characterize injectate distribution in the canine thoracolumbar epidural space and provides evidence that a 0.2‐ml/kg volume is likely to reache the TL junction in most dogs. Further studies are needed in live dogs to determine if variables affecting human epidural injectate doses have similar effects in the dog.     

A REVIEW OF HIGH RESOLUTION COMPUTED TOMOGRAPHY AND A PROPOSED TECHNIQUE FOR REGIONAL EXAMINATION OF THE CANINE LUMBOSACRAL SPINE

High resolution computed tomography (CT) is a noninvasive imaging modality that has been used extensively in evaluating diseases of the human lumbosacral spine. Excellent spatial and contrast resolution, combined with multiplanar reformatting capability make high resolution CT scanners well-suited for similar applications in dogs. Consistently good quality images can be obtained when careful attention is given to factors affecting resolution. This paper reviews and illustrates some principles of high resolution CT, and proposes a technique for regional CT examination of the canine lumbosacral spine.     

DEVELOPING A TECHNIQUE FOR ULTRASOUND‐GUIDED INJECTION OF THE ADULT CANINE HIP

An accurate method for guiding injections into the canine hip would facilitate diagnostic localization of lameness and targeted treatments. Ultrasound‐guided hip injections are commonly used in humans and large animals. Aims of this prospective study were to describe ultrasound (US) anatomy of the adult canine hip and determine the feasibility and accuracy of intra‐articular placement of injectate using US‐guidance. Seven adult dogs were used to describe US anatomy, five dog cadavers were used to assess the feasibility of the injection technique and 11 dog cadavers were used to assess accuracy of injections. For the accuracy test, 22 joints were injected with iodinated contrast medium by three operators with different experience. With dogs in lateral recumbency, the hyperechoic femoral head surface was identified by following the femoral neck from the greater trochanter or the acetabular rim was localized by following caudally the ilium from the iliac wing.  An anechoic gap between the femoral head and acetabular surface represented the joint. The capsule was visible as a triangular echoic structure and the femoral head articular cartilage appeared as an anechoic band. The needle was inserted axial to the greater trochanter and directed in a dorsolateral–ventromedial direction toward the joint space and then pushed through the capsule. Based on postinjection radiography, accuracy was 81.8% at first attempt and 100% at second attempt. This study indicated that US‐guided injection is a feasible and accurate technique for injecting the adult canine hip. Future studies in live dogs are needed to assess safety and efficacy.     

VACUUM PHENOMENON OF THE CANINE SPINE: CT FINDINGS IN 3 PATIENTS

The vacuum phenomenon was identified in the spine of 3 dogs by computed tomography. Gas from the vacuum phenomenon was clearly present in the disc space in 2 dogs. In the other the disc space was collapsed, and the gas was in the caudal vertebral endplate. In humans, gas accumulation in the intervertebral disc caused by the vacuum phenomenon seen on computed tomography spinal images is a sign of degenerative disc disease rather than infection. It may also be seen in the apophyseal joints and in the vertebral canal associated with the vacuum phenomenon in the disc or apophyseal joints. The recognition of the vacuum phenomenon in the spine in veterinary patients will likely become more important as computed tomography imaging becomes more common with the increased availability of this imaging procedure.     

ULTRASONOGRAPHIC PERCUTANEOUS ANATOMY OF THE CAUDAL LUMBAR REGION AND ULTRASOUND‐GUIDED LUMBAR PUNCTURE IN THE DOG

Subarachnoid lumbar puncture is used commonly in the dog for cerebrospinal fluid collection and/or myelography. Here in we describe the percutaneous ultrasound anatomy of the lumbar region in the dog and a technique for ultrasound‐guided lumbar puncture. Ultrasound images obtained ex vivo and in vivo were compared with anatomic sections and used to identify the landmarks for ultrasound‐guided lumbar puncture. The ultrasound‐guided procedure was established in cadavers and then applied in vivo in eight dogs. The anatomic landmarks for the ultrasound‐guided puncture, which should be identified on the parasagittal oblique ultrasound image are the articular processes of the fifth and sixth lumbar vertebrae and the interarcuate space. The spinal needle is directed under ultrasound‐guidance toward the triangular space located between the contiguous articular processes of the fifth and sixth lumbar vertebrae and then advanced to enter the vertebral canal. Using these precise ultrasound anatomic landmarks, an ultrasound‐guided technique for lumbar puncture is applicable in the dog.     

COMPARISON OF THREE RADIOGRAPHIC CONTRAST PROCEDURES IN THE EVALUATION OF THE CANINE LUMBOSACRAL SPINAL CANAL

Lumbar myelography, intraosseous caudal vertebral venography, and epidurography were performed in 12 normal, mature mixed-breed dogs. The radiographic appearance of the lumbosacral region was evaluated in both the lateral and ventrodorsal projections. These three radiographic contrast procedures were repeated in the same dogs after the introduction of a silicone mass into the spinal canal at the lumbosacral junction. The radiographic findings were compared with postmortem findings to determine which contrast procedure was most useful in detecting the mass in the lumbosacral spine. None of the procedures evaluated consistently produced good-quality studies in the normal dogs. After introduction of the silicone mass, lumbosacral epidurography yielded the largest number of positive correlations. However, the sensitivity of lumbosacral epidurography was less than 50% in the lateral projection and less than 20% in the ventrodorsal projection. Though none of the procedures were consistently helpful in the diagnosis of the lumbosacral masses, lumbosacral epidurography has the most potential to give consistently good-quality studies and thereby a greater probability of detecting an abnormality.     

MAGNETIC RESONANCE IMAGING OF THE CAUDAL LUMBAR AND LUMBOSACRAL SPINE IN 13 DOGS (1990–1993)

The caudal lumbar and lumbosacral spine of 13 dogs with pain or neurologic deficits were evaluated using magnetic resonance imaging (MRI). Spin echo T1, proton density, and T2 weighted and gradient echo T2* imaging sequences were utilized. MRI permitted direct, multiplanar, tomographic visualization of the spine facilitating evaluation of all components of degenerative caudal lumbar and lumbosacral stenosis. Abnormalities detected included intervertebral disc degeneration, intervertebral disc protrusion involving both the vertebral canal and intervertebral foramina, articular process osteophytosis, articular process fracture, nerve root impingement by spondylosis deformans, and the presence of low signal material within the vertebral canal of 2 dogs with recurrent pain following previous spinal surgery. In all 7 dogs treated surgically, MRI findings were consistent with surgical findings.     

COMPARISON OF NONCONTRAST COMPUTED TOMOGRAPHY AND HIGH‐FIELD MAGNETIC RESONANCE IMAGING IN THE EVALUATION OF GREAT DANES WITH CERVICAL SPONDYLOMYELOPATHY

Computed tomography (CT) provides excellent bony detail, whereas magnetic resonance (MR) imaging is superior in evaluating the neural structures. The purpose of this prospective study was to assess interobserver and intermethod agreement in the evaluation of cervical vertebral column morphology and lesion severity in Great Danes with cervical spondylomyelopathy by use of noncontrast CT and high‐field MR imaging. Fifteen client‐owned affected Great Danes were enrolled. All dogs underwent noncontrast CT under sedation and MR imaging under general anesthesia of the cervical vertebral column. Three observers independently evaluated the images to determine the main site of spinal cord compression, direction and cause of the compression, articular process joint characteristics, and presence of foraminal stenosis. Overall intermethod agreement, intermethod agreement for each observer, overall interobserver agreement, and interobserver agreement between pairs of observers were calculated by use of kappa (κ) statistics. The highest overall intermethod agreements were obtained for the main site of compression and direction of compression with substantial agreements (κ = 0.65 and 0.62, respectively), whereas the lowest was obtained for right‐sided foraminal stenosis (κ = 0.39, fair agreement). For both imaging techniques, the highest and lowest interobserver agreements were recorded for the main site of compression and degree of articular joint proliferation, respectively. While different observers frequently agree on the main site of compression using both imaging techniques, there is considerable variation between modalities and among observers when assessing articular process characteristics and foraminal stenosis. Caution should be exerted when comparing image interpretations from multiple observers.     

SUSCEPTIBILITY ARTIFACTS ON T2*‐WEIGHTED MAGNETIC RESONANCE IMAGING OF THE CANINE AND FELINE SPINE

The T2*‐weighted gradient recalled echo sequence is a sensitive means to detect blood degradation products. While not a routine sequence in magnetic resonance imaging of the spine in small animals, it can provide additional valuable information in select cases. The goal of this retrospective, cross‐sectional study was to describe findings when acquiring this sequence during magnetic resonance imaging examination of the spine in small animals. The University of Tennessee's veterinary radiology database was searched for dogs and cats that underwent magnetic resonance imaging for suspect spinal disease in which a T2*‐weighted gradient recalled echo sequence was acquired and susceptibility artifact was identified. The following information was recorded: signalment, clinical signs, location and appearance of susceptibility artifact, and final diagnosis. Thirty‐nine cases were included in the study. Extradural susceptibility artifacts were observed in cases of intervertebral disc herniation with or without associated hemorrhage (n = 28), extradural hemorrhage associated with spinal trauma (n = 2), hemophilia (n = 1), and in a cystic extradural mass (n = 1). Remaining lesions displaying susceptibility artifact were intramedullary and included presumptive acute noncompressive nucleus pulposus extrusion (n = 2), hematoma (n = 1), hemangiosarcoma metastasis (n = 1), intramedullary disc extrusion (n = 1), presumptive meningomyelitis (n = 1), and a mass of undetermined etiology (n = 1). Inclusion of a T2*‐weighted gradient recalled echo sequence may be helpful in spinal magnetic resonance imaging when standard imaging sequences are ambiguous or intramedullary lesions are observed.     

COMPARISON OF ULTRASOUND‐GUIDED VS. STANDARD LANDMARK TECHNIQUES FOR TRAINING NOVICE OPERATORS IN PLACING NEEDLES INTO THE LUMBAR SUBARACHNOID SPACE OF CANINE CADAVERS

The standard technique for placing a needle into the canine lumbar subarachnoid space is primarily based on palpation of anatomic landmarks and use of probing movements of the needle, however, this technique can be challenging for novice operators. The aim of the current observational, prospective, ex vivo, feasibility study was to compare ultrasound‐guided vs. standard anatomic landmark approaches for novices performing needle placement into the lumbar subarachnoid space using dog cadavers. Eight experienced operators validated the canine cadaver model as usable for training landmark and ultrasound‐guided needle placement into the lumbar subarachnoid space based on realistic anatomy and tissue consistency. With informed consent, 67 final year veterinary students were prospectively enrolled in the study. Students had no prior experience in needle placement into the lumbar subarachnoid space or use of ultrasound. Each student received a short theoretical training about each technique before the trial and then attempted blind landmark‐guided and ultrasound‐guided techniques on randomized canine cadavers. After having performed both procedures, the operators completed a self‐evaluation questionnaire about their performance and self‐confidence. Total success rates for students were 48% and 77% for the landmark‐ and ultrasound‐guided techniques, respectively. Ultrasound guidance significantly increased total success rate when compared to the landmark‐guided technique and significantly reduced the number of attempts. With ultrasound guidance self‐confidence was improved, without bringing any significant change in duration of the needle placement procedure. Findings indicated that use of ultrasound guidance and cadavers are feasible methods for training novice operators in needle placement into the canine lumbar subarachnoid space.     

THE EFFECT OF A TECHNICAL QUALITY ASSESSMENT OF HIP‐EXTENDED RADIOGRAPHS ON INTEROBSERVER AGREEMENT IN THE DIAGNOSIS OF CANINE HIP DYSPLASIA

Experienced and inexperienced observers evaluated the assessability of 50 radiographs (25 dogs) and determined the hip status (dysplasia/nondysplasia and final scoring according Fédération Cynologique Internationale [FCI]‐criteria) individually. A radiographic technical quality assessment was performed in a separate reading session. Interobserver agreement in determining dysplasia/nondysplasia and FCI‐scoring did not significantly increase with the increasing quality of a radiograph, irrespective whether these observers are experienced or not. There was a significant agreement between the technical quality assessment and assessability (P<0.0005). Despite the effort to objectify radiographic quality and to present high‐quality radiographs to observers, interobserver agreement on dysplasia/nondysplasia and final scoring, remains low, even in the experienced group. Although increased radiographic quality narrows the range of scoring, the range remains unacceptably high.     

IMPROVING CONSPICUITY OF THE CANINE GASTROINTESTINAL WALL USING DUAL PHASE CONTRAST‐ENHANCED COMPUTED TOMOGRAPHY: A RETROSPECTIVE CROSS‐SECTIONAL STUDY

Gastrointestinal (GI) disease is a common clinical complaint in small animal patients; computed tomography (CT) examinations enable a global overview of the GI tract and associated structures. Previously, the GI wall has been reportedly identified from serosa to mucosa in 77% of standard postcontrast CT studies and wall layers seen in ultrasound have not been distinguished. Inconsistent strong contrast enhancement of the inner layer of the GI mucosal surface was noted on dual phase CT studies acquired in our institution, which increased the visibility of the GI tract and disease processes. The aim of this retrospective, observational, cross‐sectional study was to determine the optimal portal vein attenuation for maximizing GI wall conspicuity using dual phase contrast‐enhanced CT. Patients with abdominal CT for a non‐GI related disease were included. In a pilot study, 175 GI segments from 35 CT studies were graded for presence of mucosal surface enhancement (MSE). The strongest mucosal surface enhancement grade correlated with portal vein attenuation of 43–150 HU; this value was used as inclusion criterion in the main study. A total of 441 GI segments were evaluated in 42 CT studies postcontrast for GI wall conspicuity. The GI wall was conspicuous in 56.7% precontrast, 84.5% at 30s, and 77.3% late postcontrast; 4.7% of segments were removed due to motion blur. At 30 s distinct mucosal surface enhancement was seen in the small intestine and gastric mucosal surface enhancement was poor. Findings supported the use of dual phase contrast‐enhanced CT for improving conspicuity of the GI wall.     

THORACOLUMBAR INTRADURAL DISC HERNIATION IN EIGHT DOGS: CLINICAL,LOW‐FIELD MAGNETIC RESONANCE IMAGING,AND COMPUTED TOMOGRAPHIC MYELOGRAPHY FINDINGS

Intradural disc herniation is a rarely reported cause of neurologic deficits in dogs and few published studies have described comparative imaging characteristics. The purpose of this retrospective cross sectional study was to describe clinical and imaging findings in a group of dogs with confirmed thoracolumbar intradural disc herniation. Included dogs were referred to one of four clinics, had acute mono/paraparesis or paraplegia, had low field magnetic resonance imaging (MRI) and/or computed tomographic myelography, and were diagnosed with thoracolumbar intradural disc herniation during surgery. Eight dogs met inclusion criteria. The prevalence of thoracolumbar intradural disc herniation amongst the total population of dogs that developed a thoracolumbar intervertebral disc herniation and that were treated with a surgical procedure was 0.5%. Five dogs were examined using low‐field MRI. Lesions that were suspected to be intervertebral disc herniations were observed; however, there were no specific findings indicating that the nucleus pulposus had penetrated into the subarachnoid space or into the spinal cord parenchyma. Thus, the dogs were misdiagnosed as having a conventional intervertebral disc herniation. An intradural extramedullary disc herniation (three cases) or intramedullary disc herniation (two cases) was confirmed during surgery. By using computed tomographic myelography (CTM) for the remaining three dogs, an intradural extramedullary mass surrounded by an accumulation of contrast medium was observed and confirmed during surgery. Findings from this small sample of eight dogs indicated that CTM may be more sensitive for diagnosing canine thoracolumbar intradural disc herniation than low‐field MRI.     

A NOVEL,REMOVABLE, CERROBEND,BEAM‐BLOCKING DEVICE FOR RADIATION THERAPY OF THE CANINE HEAD AND NECK: PILOT STUDY

Radiation therapy of the head and neck can result in mucositis and other acute affects in the oral cavity. This prospective pilot study evaluated a novel, intraoral, beam‐blocking device for use during imaging and therapeutic procedures. The beam‐blocking device was made from a metal alloy inserted into a coated frozen dessert mold (Popsicle® Mold, Cost Plus World Market, Oakland, CA). The device was designed so that it could be inserted into an outer shell, which in turn allowed it to be placed or removed depending on the need due to beam configuration. A Farmer type ionization chamber and virtual water phantom were used to assess effects of field size on transmission. Six large breed cadaver dogs, donated by the owner after death, were recruited for the study. Delivered dose at the dorsal and ventral surfaces of the device, with and without the alloy block in place, were measured using radiochromic film. It was determined that transmission was field size dependent with larger field sizes leading to decreased attenuation of the beam, likely secondary to scatter. The mean and median transmission on the ventral surface without the beam‐blocking device was 0.94 [range 0.94–0.96]. The mean and median transmission with the beam‐blocking device was 0.52 [range 0.50–0.57]. The mean and median increase in dose due to backscatter on the dorsal surface of the beam‐blocking device was 0.04 [range 0.02–0.04]. Findings indicated that this novel device can help attenuate radiation dose ventral to the block in dogs, with minimal backscatter.     

IMAGING DIAGNOSIS—TRANSESOPHAGEAL ULTRASOUND‐GUIDED REMOVAL OF A MIGRATING GRASS AWN FOREIGN BODY IN A DOG

A 3‐year‐old English Setter dog was presented for an acute onset of coughing. Tracheobronchoscopic examination allowed localization and removal of one grass awn foreign body. A second migrated grass awn was suspected to be present in the left caudal lung lobe. Transesophageal ultrasound revealed an area of pulmonary consolidation in the dorsomedial portion of left caudal lobe and a linear hyperechoic structure consistent with a grass awn foreign body within the area of consolidation. Transesophageal ultrasonography was also used to provide anatomical landmarks that facilitated successful thoracoscopic removal of the foreign body.     

TRIPLE PHASE DYNAMIC COMPUTED TOMOGRAPHIC PERFUSION CHARACTERISTICS OF SPIROCERCOSIS INDUCED ESOPHAGEAL NODULES IN NON‐NEOPLASTIC VERSUS NEOPLASTIC CANINE CASES

Neoplastic transformation of Spirocerca lupi induced esophageal nodules carries a poor prognosis. Clinical, clinicopathological, endoscopic, and radiographic characteristics may be indicative of neoplastic transformation but variable sensitivity and specificity of these parameters makes their use questionable. We hypothesized that CT would be a better diagnostic modality to discriminate between non‐neoplastic and neoplastic nodules. In this prospective study of 38 dogs, the appearance and perfusion characteristics of confirmed spirocercosis‐induced neoplastic and non‐neoplastic esophageal nodules were described using survey CT and triple phase dynamic CT angiography (CTA). Pre‐ and post‐contrast early arterial, late arterial, and venous CTA images were evaluated. Non‐neoplastic nodules were smooth and nonmineralized with a higher proportion of hypoattenuating necropurulent cavities compared to neoplastic nodules that had a more irregular surface, with 93% having mineralized foci and rarely any hypoattenuating pockets. Non‐neoplastic nodules were significantly more perfused than neoplastic nodules with the difference being up to 23 Hounsfield units. The difference was most marked in the early and late arterial phases (P = 0.0005 and 0.00005, respectively). Ratios of the normal esophagus adjacent to the neoplastic and non‐neoplastic nodules did not differ significantly from each other. Perfusion findings demonstrated relative hypoperfusion of the esophageal sarcomas. Findings from the current study indicated that CT characteristics of relative postcontrast hypoperfusion, combined with nodule irregularity and mineralization warrant a high level of concern for neoplastic transformation in canine spirocercosis‐induced esophageal nodules.     

OPTIMIZING A PROTOCOL FOR 1H‐MAGNETIC RESONANCE SPECTROSCOPY OF THE CANINE BRAIN AT 3T

Intracranial diseases are common in dogs and improved noninvasive diagnostic tests are needed. Magnetic resonance (MR) spectroscopy is a technique used in conjunction with conventional MR imaging to characterize focal and diffuse pathology, especially in the brain. As with conventional MR imaging, there are numerous technical factors that must be considered to optimize image quality. This study was performed to develop an MR spectroscopy protocol for routine use in dogs undergoing MR imaging of the brain. Fifteen canine cadavers were used for protocol development. Technical factors evaluated included use of single‐voxel or multivoxel acquisitions, manual placement of saturation bands, echo time (TE), phase‐ and frequency‐encoding matrix size, radiofrequency coil, and placement of the volume of interest relative to the calvaria. Spectrum quality was found to be best when utilizing a multivoxel acquisition with the volume of interest placed entirely within the brain parenchyma without use of manually placed saturation bands, TE = 144 ms, and a quadrature extremity radiofrequency coil. An 18 × 18 phase‐ and frequency‐encoding matrix size also proved optimal for image quality, specificity of voxel placement, and imaging time.