Degenerative Spinal Diseases PDF

CHAPTER 7.11 DEGENERATIVE SPINAL DISEASES 618 Wilfried Mai CONTENTS Spond...

CHAPTER 7.11 DEGENERATIVE SPINAL DISEASES 618 Wilfried Mai CONTENTS Spondylosis deformans........................................................................................................................................................................................ 618 Diffuse idiopathic skeletal hyperostosis................................................................................................................................................................ 619 Degenerative myelopathy...................................................................................................................................................................................... 619 Leukoencephalomyelopathy.................................................................................................................................................................................. 619 References.............................................................................................................................................................................................................621 Degenerative spinal disease can affect various portions of laterally) of the endplates of the vertebral bodies, and the spine, including the intervertebral discs, the vertebrae, which attempt to bridge the intervertebral disc spaces. and the spinal cord. Degenerative intervertebral disc disease The ventral and lateral cortex of the body of affected ver- is covered in Chapter 7.1. Degenerative conditions particu- tebrae is preserved. Sclerosis of the adjacent endplates is lar to the lumbosacral junction are covered in Chapter 7.3. common.1 Degenerative conditions involving the articular process It is commonly (but not systematically) associated with joints, such as osteoproliferative or cystic changes, are cov- degenerative intervertebral disc disease. ered in Chapters 7.2 and 7.8. There are a number of often The condition itself is typically considered incidental breed-specific neurodegenerative diseases that commonly and of no clinical significance, although spinal stiffness, affect the brain, with occasional involvement of the spinal lameness, gait abnormalities, and back pain can be seen, cord; these are described in Chapter 5.2. The conditions possibly associated with concurrent intervertebral disc described in this chapter are degenerative spinal conditions disease. for which specific MRI descriptions have been reported in MRI features associated with spondylosis deformans the veterinary literature. include (Figs. 7.11.1, 7.11.2):1 Ventral, markedly hypointense, smoothly margin- SPONDYLOSIS DEFORMANS ated new bone formation arising from the periphery of adjacent endplates and tending to bridge over the Spondylosis deformans is characterized by focal or mul- space. tifocal osteophytes or larger bone spurs that appear The signal from the new bone is hypointense on all pulse along the periphery (most commonly ventrally but also sequences compared with the vertebral bone marrow. Fig. 7.11.1 Sagittal T2W image of the thoracolumbar spine in a 7-year- old Shiba Inu dog with multiple sites of disc herniation including L1-L2, L2-L3, and L3-L4 (arrowheads). There is multifocal ventral spondylosis deformans forming smoothly marginated markedly hypointense new bone arising from the margins of the endplates and bridging the spaces ventrally (arrows). (1.5T MRI system)  D e ge n e r at i v e Spi n a l D is e a s e s 619 Moderate to marked degenerative changes of the Welsh Corgi, Chesapeake Bay Retriever, Rhodesian associated intervertebral discs are common. Disc pro- Ridgeback, Bernese Mountain Dog, Standard Poodle, trusion or extrusion may be present, with or without Kerry Blue Terrier, Cardigan Welsh Corgi, Golden associated spinal cord compression. Retriever, Wire Fox Terrier, American Eskimo Dog, Soft-coated Wheaten Terrier, and Pug.2 Cats have also DIFFUSE IDIOPATHIC SKELETAL rarely been affected by the condition.3 HYPEROSTOSIS Age at onset is typically 5 years and older.2 Clinically, the condition is characterized by progressive Diffuse idiopathic skeletal hyperostosis (DISH) is a sys- ataxia of the pelvic limbs, beginning with loss of pro- temic non-inflammatory disorder manifesting by ossifi- prioception and absence of paraspinal hyperesthesia.2 cation of soft tissues such as ligaments and attachments Typically, upper motor neuron signs of the pelvic limbs of tendons and joint capsules to bone.1 are seen on presentation, although less commonly, lower Although the condition can affect other parts of the skel- motor neuron signs may be present; later in the course eton, the spine is commonly affected. In that location, of the disease (several months), the thoracic limbs may DISH appears radiographically as flowing ossification become affected.3 with a trabecular pattern along the lateral and ventral Histopathologically, there is progressive, non-inflamma- aspects of the vertebral column, extending over consecu- tory, segmental axonal degeneration and associated loss tive (at least three or four) vertebrae. The intervertebral of myelin.2 disc width is typically preserved. Antemortem diagnosis of degenerative myelopathy The etiology of DISH is unclear, although a hereditary relies on recognition of the clinical pattern followed basis has been suggested in some breeds such as the by completion of a series of diagnostic steps to rule out Boxer, as they appear predisposed; hypothyroidism and other disorders that could have a similar presentation hypercalcitonism have also been proposed as etiopatho- (CSF analysis, electrodiagnostic testing, spinal cord logic factors.1 imaging such as myelography, CT, or MRI). A presump- Clinical significance is variable, and the condition can tive diagnosis of degenerative myelopathy is usually be clinically silent or cause spinal pain and dysfunction. made based on absence of clinically significant myelopa- MRI features of DISH are best appreciated on sagittal thy on the basis of imaging; MRI is preferred, as it allows images and include (Fig. 7.11.2):1 exclusion of both extradural compressive lesions such Smoothly marginated new bone formation over as intervertebral disc herniation, and intramedullary or several consecutive vertebral segments, spanning intradural lesions that may be overlooked with myelog- the bodies and intervertebral spaces in a continuous raphy or CT. DNA testing is now also available that can manner. support an antemortem diagnosis of the condition. The new bone has signal intensity similar to the Although rare studies using CT-myelography have bone marrow of the vertebrae. This is attributed to reported morphologic changes in dogs with degenerative the presence of fat, a characteristic of bone marrow, as myelopathy (such as a smaller than normal spinal cord the new bone in DISH is made of normal trabecular with associated widening of the subarachnoid space or bone. change in shape of the spinal cord, becoming triangular The high signal within DISH lesions typically is sup- instead of rounded/oval-shaped on transverse images4), pressed on fat-suppressed pulse sequences such as no such morphologic changes have been reported to date STIR. with MRI. The intervertebral discs in the affected segments MRI is reportedly normal in dogs with confirmed degen- have normal appearance or only mild degenerative erative myelopathy.2,3,5 changes, with a preserved high T2 signal of their Sensitive imaging techniques such as MRI may reveal nuclei pulposi. areas of disc protrusions causing variable degrees of spi- Disc herniation at sites immediately adjacent to seg- nal cord compression, which may confound the diagno- ments affected by DISH may be observed. sis of degenerative myelopathy, and the clinician must in these cases be guided by clinical experience and take into DEGENERATIVE MYELOPATHY account rapidity of disease progression, presence of para- spinal hyperesthesia, and amount of spinal cord com- Degenerative myelopathy is a chronic progressive pression to account for the severity of the myelopathy. degenerative spinal cord disease that frequently occurs in large-breed dogs. Some breeds, such as German LEUKOENCEPHALOMYELOPATHY Shepherd Dogs, are predisposed. Mixed breed dogs can also be affected, as well as many other breeds including Leukoencephalomyelopathy is a rare degenerative disor- Siberian Husky, Miniature Poodle, Boxer, Pembroke der of unknown etiology recognized in the Rottweiler.6  D e ge n e r at i v e Spi n a l D is e a s e s 621 A similar condition has also been reported in Leonberger dogs are typically euthanized due to progressive disease dogs.7 In Rottweilers, a genetic basis for the disorder within 1 year of diagnosis.6 has been suggested because of the familial relationship Histopathologically, the white matter is affected, espe- among the dogs, but the mode of inheritance could not cially in the dorsal aspect of the lateral funiculi of the be elucidated. cervical spinal cord and pyramidal tracts of the medulla In Rottweilers, it is clinically characterized by a long- oblongata; there is primarily myelin loss with much less strided gait with the appearance of stiffness and over- pronounced involvement of the axons, and concurrent reaching as the limbs are advanced when walking, astrogliosis and astrocytosis.6 consistent with general proprioceptive ataxia and upper MRI features were reported in a Rottweiler and included:6 motor neuron tetraparesis.6 In Leonbergers, ataxia, dys- Bilateral and symmetric lesions in the white matter of metria, and stumbling are reported.7 the dorsolateral funiculi in the cervical spinal cord. Age at onset is between 1.5 and 3.5 years. The thoracic Concurrent lesions in the brain, affecting the pyra- limbs are typically affected first, and the pelvic limbs are mids of the medulla oblongata, and ventral aspect of affected later, usually less severely. Prognosis is poor, and the crus cerebri. Lesions were hyperintense on T2W, T2*W, and T2-FLAIR images, isointense on T1W images, with no contrast enhancement after gadolinium adminis- tration. MRI changes were also reported in two Leonberger dogs (Fig. 7.11.3) and included similar but more focal changes, with bilateral, symmetric T2W, and T2-FLAIR hyper- intensity within the dorsolateral funiculi of the cervical spinal cord from C1 to C4 in one dog and only over C2 in the other. In these dogs, lesions were also found in the brain histopathologically, but were not visible on MRI. The lesions were isointense on T1W images and non-enhancing.7 REFERENCES 1. Togni A, Kranenburg HJ, Morgan JP et al. (2014). Radiographic and MRI characteristics of lumbar disseminated idiopathic spinal hyperostosis and spondylosis deformans in dogs. J Small Anim Pract 55(7):343–9. 2. Coates JR, Wininger FA (2010). Canine degenerative myelopathy. Vet Clin North Am Small Anim Pract 40(5): 929–50. Fig. 7.11.3 Transverse T2W image in a 2.5-year-old 3. Okada M, Kitagawa M, Kanayama K et al. (2009). Negative female Leonberger dog presented with a 1-year history of MRI findings in a case of degenerative myelopathy in a dog. intermittent knuckling in the thoracic limbs. Both lateral J S Afr Vet Assoc 80(4):254–6. funiculi of the spinal cord show increased signal intensity 4. Jones JC, Inzana KD, Rossmeisl JH et al. (2005). CT (arrows). At necropsy, lesions were most prominent in the myelography of the thoraco-lumbar spine in 8 dogs with lateral corticospinal tract, but encroached on the dorsal degenerative myelopathy. J Vet Sci 6(4):341–8. spinocerebellar, rubrospinal, and lateral spinothalamic 5. Coates JR, March PA, Oglesbee M et al. (2007). Clinical tracts. Histopathologically, severe myelin breakdown was the characterization of a familial degenerative myelopathy in Pembroke Welsh Corgi dogs. J Vet Intern Med 21(6):1323–31. most prominent change, and axons were largely preserved, 6. Eagleson JS, Kent M, Platt SR et al. (2013). MRI findings in consistent with a primary degenerative myelinolytic a rottweiler with leukoencephalomyelopathy. J Am Anim Hosp leukoencephalomyelopathy. (Reproduced, with permission, Assoc 49(4):255–61. from Oevermann A, Bley T, Konar M et al. (2008). A novel 7. Oevermann A, Bley T, Konar M et al. (2008). A novel leukoencephalomyelopathy of Leonberger dogs. J Vet Intern leukoencephalomyelopathy of Leonberger dogs. J Vet Intern Med 22(2):467–71.) Med 22(2):467–71.  CHAPTER 7.12 MRI OF SPINAL TRAUMA 622 Wilfried Mai CONTENTS Vertebral bony and ligamentous traumatic injuries................................................................................................................................................622 Traumatic disc herniation......................................................................................................................................................................................623 Hemorrhage..........................................................................................................................................................................................................625 Spinal cord parenchymal lesions..........................................................................................................................................................................626 Traumatic dural tears.............................................................................................................................................................................................628 References.............................................................................................................................................................................................................629 Acute spinal trauma can cause instability, which can result strapped to a spinal board, thus protecting against fur- in failure of the vertebral column to protect the spinal cord ther damage.3 and nerve roots from severe damage, resulting in myelora- In people, MRI is more sensitive for assessing spinal cord diculopathy with associated temporary or permanent pare- and supporting soft tissue injuries secondary to spinal sis/paralysis. Adequate treatment planning and informed trauma. However, spinal fractures may be missed with prognosis are highly dependent on a rapid and accurate MRI,2 and this is likely the case in dogs and cats as well. evaluation of the vertebral column and status of the spinal Combined MRI and CT imaging of the trauma patient cord. There is little documentation about the utility of MRI is therefore recommended when possible, as it provides in the evaluation of spinal trauma in dogs and cats, but it is the most complete assessment of extent, location, and a valuable tool, especially to evaluate the soft tissue compo- anatomy of both bone and soft tissue damage.5 However, nents and secondary spinal cord injury.1,2 this approach depends on imaging availability, inter- pretative expertise, rapidity of imaging in the presence VERTEBRAL BONY AND LIGAMENTOUS of challenging clinical scenarios, and, of course, cost TRAUMATIC INJURIES consideration. Despite its limitations, MRI is still capable of identify- Radiography is insensitive for diagnosis of vertebral frac- ing traumatic spinal injuries such as fractures. In people, tures and subluxations in the acute canine spinal trauma like CT, MRI is more sensitive than plain radiographs in patient, and is a poor diagnostic tool to assess the stabil- the identification and classification of vertebral traumatic ity of spinal fractures. Plain radiographs are also not use- injuries.5 Studies in people have even shown a slight ful to detect compressive spinal cord lesions. superiority in accuracy of MRI versus CT for identifica- CT, where available, is therefore recommended in tion and correct classification of some types of thoraco- patients with a high clinical suspicion of such injury, and lumbar spinal injuries.5 has been reported to be superior to radiography in the In people, the sensitivity and specificity of MRI for diag- canine spinal trauma patient.3 Multidetector CT scan- nosing vertebral traumatic injuries is quite variable: ners now provide the ability to obtain submillimeter For vertebral fractures: CT slices in a bone kernel in a short time, and CT has – Sensitivity of 37%–100%, specificity of 98%–100% become the standard of care for the spinal trauma patient for the vertebral body. at many referral and university hospitals. High-quality – Sensitivity of 12%–45%, specificity of 90%–97% multiplanar reformatted images, as well as surface and for the posterior vertebral elements (pedicles, volume rendering, are very useful for surgical planning arch, spinous processes). and can be obtained with CT.4 With multidetector CT – For acute vertebral subluxation and acute verte- units, short acquisition times make it possible to per- bral articular process joint subluxation, sensitivity form a study with the anesthetized or sedated patient is about 45% and 59%, respectively.  M R I of Spi n a l Tr au m a 623 Overall sensitivity of MRI to detect spinal soft tissue Vertebral subluxation or luxation can be spotted on MR injuries (e.g., longitudinal ligaments, ligamentum images in various planes, depending on the location of flavum, or interspinous ligaments) varies between the injury and direction of the subluxation/luxation 46% and 71%.6 (Figs. 7.12.5, 7.12.6). Combined assessment of multipla- To date, there is no report on the sensitivity and specific- nar images, especially in the sagittal and dorsal planes, is ity of MRI in the diagnosis of traumatic spinal injuries recommended to better evaluate for subtle intervertebral in dogs and cats. subluxation, paying particular attention to the alignment Determining the location and severity of soft tissue/ and congruence of the articular process joints and adja- bony trauma and resulting spinal instability is impor- cent vertebral bodies (see Fig. 4.2.11). tant for surgical planning. Similar to people, a three- Injuries to the supporting soft tissue structures of the compartment model has been developed in canine and spine are best identified on T2W images, preferably with feline patients that divides the vertebral column into fat saturation.7 These ligamentous structures normally dorsal, middle, and ventral compartments. When there appear as thin hypointense bands on all pulse sequences.7 is involvement of two or three compartments, a trau- MRI features of injuries to these structures include matic injury is considered unstable:2 (Figs. 7.12.4, 7.12.6, 7.12.7):2 The dorsal compartment comprises the vertebral Increased T2W intensity and changes in appearance arch, which is made up of the spinous process, artic- (fuzziness, irregular/interrupted margins, or com- ular processes, lamina, and pedicles and also includes plete lack of identification) of the interspinous, inter- the soft tissue structures of the ‘dorsal ligamentous arcuate, dorsal, and ventral longitudinal ligaments. complex’ (articular process joint capsules, interarcu- Poor definition, increased T2 signal, interruption, or ate ligaments, interspinous ligaments, supraspinous complete lack of identification of the normally hypoin- and intertransverse ligaments). tense dorsal and ventral portions of the annulus fibro- The middle compartment includes the dorsal longitu- sus. dinal ligament, dorsal aspect of the annulus fibrosus, Distortion of the intervertebral disc with increased/ and dorsal margin of the vertebral body. heterogeneous signal extending in the area of the The ventral compartment includes the remainder of annulus fibrosus on T2W images, with widening or the vertebral body, lateral and ventral aspects of the narrowing of the corresponding intervertebral disc annulus fibrosus, nucleus pulposus, and ventral longi- space. Concurrent disc herniation in various direc- tudinal ligament. tions may be present (see below). General MRI assessment of the spine in the trauma MRI evidence of rupture of both the ventral and patient should start with careful assessment of large field dorsal disc annulus and associated ventral and dorsal of view sagittal and dorsal plane images, scrutinizing the longitudinal ligaments may indicate spinal instability paravertebral soft tissue, looking for focal areas of hyper- even in the absence of concurrent fracture/sublux- intense signal on fat-suppressed images such as STIR ation, and may warrant further investigation with series, which would pinpoint areas of traumatic injury.2 stress radiographs and surgical stabilization.2 Vertebral fractures may be recognized on MRI due to the focal interruption of the normal hypointense vertebral TRAUMATIC DISC HERNIATION cortex, together with changes in contour and changes in signal intensity of the vertebral body due to hemor- The MRI appearance of intervertebral disc herniation rhage and edema.2,7 T1W and proton density images are is covered extensively in Chapter 7.1, and the reader is particularly useful for this specific assessment. Variable referred to that specific chapter for more information. degrees of relative displacement of the fractured frag- Disc extrusion secondary to trauma is relatively common ments may be identified (Figs. 7.12.1–7.12.4). The frac- in dogs, even in the absence of concurrent vertebral frac- ture line itself may appear as a hypointense line on T2W ture and/or subluxation/luxation.8 or T2*W images due to the focal hemorrhage along the In most cases, traumatic disc extrusion is non-compres- margins of the fracture. Minimally or non-displaced fac- sive,8 and spinal cord trauma is due to contusion or intra- tures can be spotted on MRI as focal, somewhat linear medullary disc herniation, as typically seen with acute areas of T2W hyperintense signal due to bone marrow non-compressive hydrated nucleus pulposus extrusion, edema (Fig. 7.12.1). In people, sensitivity of MRI for covered in Chapter 7.1 (Fig. 7.12.1). detection of non- or minimally displaced fractures pos- Pre-existing degenerative intervertebral disc disease terior to the vertebral body (pedicles, lamina, arch, and may be a predisposing factor for spinal cord compres- spinous process) is less than for the vertebral body, due sion after traumatic extrusion;8 as a result, older dogs and to the lesser amount of cancellous bone in these verte- chondrodystrophic breeds are more likely to have spinal bral segments.6 CT is reportedly far superior to MRI for cord compression following traumatic intervertebral disc diagnosis of fractures of the neural arch in people.7 herniation. 624 CHAPTER 7.12 (a) (b) (c) (d) Fig. 7.12.1 Sagittal T2W image of the cervical spine (a), transverse T2W (b) and T2*W gradient echo (c) images at the level of caudal C3, and transverse T2*W gradient echo image (d) at the level of cranial C4 in a 5-year-old Labrador Retriever after a collision with another dog. A wedge fracture of the caudoventral body of C3 is visible (solid arrows, a–c). There are ill-defined hyperintense areas in the hypaxial muscles ventral to C3 and C4 (dashed arrows, a–c). The C3-C4 intervertebral disc space is collapsed and the signal from the disc is absent (dotted arrow, a), consistent with concurrent acute traumatic disc herniation of hydrated disc material. There are intramedullary hyperintense areas (arrowhead, a), consistent with contusion/edema secondary to the traumatic event. On the T2*W gradient echo transverse image at the level of cranial C4 (d), a curvilinear hypointense area is seen in the left epidural region conforming to the left lateral border of the spinal cord, consistent with susceptibility artifact from epidural hemorrhage (open arrow). (1.5T MRI system)  M R I of Spi n a l Tr au m a 625 (a) (b) (c) Fig. 7.12.2 Dorsal T1W (a) and T2W (b) images at the level of C1-C2 and ventrodorsal radiograph of the cervical spine (c) in a 7-year-old Afghan Hound that was hit by a car. There is a chip fracture of the apex of the dens of the axis (arrows). (1.5T MRI system) (a) (b) Fig. 7.12.3 Sagittal T2W image (a) and corresponding sagittal reformatted CT image (b) of the thoracic spine in a 1-year-old mixed breed dog that was hit by a car. A comminuted compression fracture of the body of T11 (arrows) is visible, causing shortening, misshaping, and heterogeneous signal in the body of T11, with impingement into the vertebral canal causing ventral spinal cord compression. (1.5T MRI system) Compressive disc herniation secondary to trauma is hemoglobin by-products are typically seen, and improve more common in the cranial cervical, thoracolumbar, sensitivity of MRI in the identification of these specific and cranial lumbar segments.8 changes.9,10 Epidural hemorrhage in dogs with traumatic verte- HEMORRHAGE bral subluxation was reported to form areas of signal void partially surrounding and conforming to the out- Specific MRI features of spinal hemorrhage are covered line of the spinal cord on T2*W gradient echo images in Chapter 7.7. (Fig. 7.12.1); these areas are of variable signal on T1W Paravertebral, intraspinal extradural, or intramedullary and T2W spin echo images.10 Susceptibility artifacts can hemorrhage can occur secondary to traumatic spinal be observed in the paraspinal soft tissues adjacent to the injuries in dogs and cats. region of spinal trauma due to intramuscular hemor- Although no systematic study exists on specifically trau- rhage. Epidural space hemorrhage (hematomas) can also matic cases, T2*W gradient echo pulse sequences have cause focal epidural masses that are of variable signal, been reported to be useful in identification of extradural depending on the age of the lesion, and rarely contrast or intramedullary hemorrhagic changes in dogs. Signal enhance. T2*W imaging signal voids due to suscepti- voids due to susceptibility artifacts associated with bility artifacts were also reported.2,9 Variable degrees of 626 CHAPTER 7.12 (a) (b) Fig. 7.12.4 Transverse T2W image (a) and corresponding transverse CT image (b) at the level of C5-C6, and sagittal T2W image (c) of the cervical spine in a 7-year-old mixed breed dog that was attacked by a larger dog. On the transverse T2W image (a), there is subluxation of the left articular process joint (dashed arrow), with mild lateral displacement of the cranial articular process of C6 relative to the caudal articular process of C5. An ill-defined, irregular, hypointense fragment is seen immediately ventral to the joint (solid arrow, a), which on the CT image corresponds to a small irregular fracture fragment (solid arrow, b). There is discontinuity and hyperintense signal in the dorsal annulus fibrosus of the C5-C6 disc (dotted arrow, a) and on the sagittal image (dotted arrow, c), and interruption of the dorsal longitudinal ligament is noted; these changes are consistent with middle compartment ligament alteration and rupture. Patchy areas of hyperintensity within the spinal cord parenchyma are noted on the T2W (c) images (a, c), consistent with edema. (1.5T MRI system) spinal cord compression may be present secondary to (T2W hyperintensity), multilevel edema, and edema these epidural lesions. with concurrent hemorrhage (T2/T2*W hypointense Intramedullary hemorrhagic changes are also associated foci). The severity of the initial neurologic grade and the with susceptibility artifacts causing low-signal foci on degree of clinical improvement respectively increase and T2*W and, potentially, T2W images;2,10,11 they are typi- decrease when progressing from normal cord to single cally associated with a more severe neurologic grade at level edema, multilevel edema, and mixed edema and presentation and poorer prognosis (see below).6,11 hemorrhage. Sagittal T2W series are recommended in people for this prognostic evaluation.6 SPINAL CORD PARENCHYMAL LESIONS No systematic large scale study exists in veterinary medi- cine on the prevalence and prognostic values of such pat- Generally, in people, MR signal changes in the spi- terns, although MRI allows identification of spinal cord nal cord parenchyma following trauma are catego- changes such as presence/location/degree of spinal cord rized in four levels: normal spinal cord, focal edema compression and parenchymal signal intensity changes  M R I of Spi n a l Tr au m a 627 (a) (b) (c) (d) Fig. 7.12.5 Transverse T1W (a) and T2W (b) images at the level of C1, transverse CT image cranial to the apex of the dens (c), and left parasagittal T2*W gradient echo image (d) of the cervical spine in a 2-year-old Golden Retriever that was hit by a car. On the transverse images, there is subluxation of the dens of the axis to the right relative to the mid-sagittal plane (solid arrows, a and b). There is irregular hypointense material in the left ventral aspect of the vertebral canal on the T2W image (dotted arrow, b), corresponding to irregular hypointense signal voids on the parasagittal T2*W gradient echo image (dotted arrow, d), consistent with hemorrhage. On the CT image (c), tiny mineral bodies are seen in the area of the alar ligaments, consistent with small avulsion fractures (dotted arrows). (1.5T MRI system) 628 CHAPTER 7.12 Fig. 7.12.6 Sagittal T2W image in a dog with a traumatic subluxation at L2-L3. The ventral displacement of the cranial endplate of L3 relative to the caudal endplate of L2 is visible (arrow). There is an irregular signal within the corresponding disc, with lack of differentiation between the nucleus pulposus and annulus fibrosus. There is an elongated area of hyperintensity in the spinal cord parenchyma dorsal to L2-L3, consistent with edema and contusion. (1.5T MRI system; reproduced, with permission, from Johnson P, Beltran E, Dennis R et al. (2012). Magnetic resonance imaging characteristics of suspected vertebral instability associated with fracture or subluxation in eleven dogs. Vet Radiol Ultrasound 53(5):552–9.) Fig. 7.12.7 Sagittal T2W image of the lumbar spine in a dog demonstrating MRI characteristics consistent with dorsal compartment ligament alteration and rupture. There is alteration of the interspinous ligament creating irregular hyperintense areas between the spinous processes (arrowheads). There is no widening of the interspinous space. There is rupture of the annulus fibrosus of the L2-L3 disc, both dorsally and ventrally, as well as heterogeneous hyperintense signal within the disc. (1.5T MRI system; reproduced, with permission, from Johnson P, Beltran E, Dennis R et al. (2012). Magnetic resonance imaging characteristics of suspected vertebral instability associated with fracture or subluxation in eleven dogs. Vet Radiol Ultrasound 53(5):552–9.) such as edema (bright on T2W and T2-FLAIR images) been described in a case report and a small case series. and hemorrhage (signal void due to susceptibility arti- It is, however, not currently approved worldwide for this facts on T2*W images).2 specific indication, and is off-label in the USA and many European countries.12,13 TRAUMATIC DURAL TEARS The technique reported includes the following steps, performed after standard MRI without contrast Dural tears secondary to trauma are potentially seri- administration: ous injuries that, if left unrepaired, may cause hernia- Atlantoaxial puncture with removal of 1 mL of CSF. tion of neural elements through the defect. These neural That CSF is then mixed with 0.2–0.5 mL of elements may become entrapped in scar tissue, causing Gd-DTPA and reinjected via the same atlantoaxial chronic pain and/or neurologic deficits. Continuous leak puncture site.12,13 of CSF through the tear can also lead to intracranial The animal is then positioned upright for 5–6 minutes hypotension syndrome. Dural tears can also increase the to allow for diffusion of contrast material along the risk for meningitis or focal infection.12,13 subarachnoid space and, after repositioning of Intrathecal administration of gadolinum-based contrast the patient, sagittal and transverse T1W images agent (Gd-DTPA) to diagnose traumatic dural tears has are obtained with fat saturation.  M R I of Spi n a l Tr au m a 629 Leakage of enhanced CSF is readily visible on T1W 5. Rajasekaran S, Vaccaro AR, Kanna RM et al. (2017). The value images with fat saturation, with various patterns identi- of CT and MRI in the classification and surgical decision- fied, including:12,13 making among spine surgeons in thoracolumbar spinal injuries. Eur Spine J 26(5):1463–9. Well-defined tracks of leakage following a linear or 6. Bozzo A, Marcoux J, Radhakrishna M et al. (2011). The role curvilinear path and pinpointing the area of dural of magnetic resonance imaging in the management of acute tear; this is commonly associated with less extensive spinal cord injury. J Neurotrauma 28(8):1401–11. traumatic lesions with nerve root or sleeve avulsion. 7. Saifuddin A (2001). MRI of acute spinal trauma. Skeletal Radiol Diffuse leakage, with dissemination into extensive 30(5):237–46. areas adjacent to the region of injury around the 8. Henke D, Gorgas D, Flegel T et al. (2013). Magnetic vertebral column, in cases of more extensive dural resonance imaging findings in dogs with traumatic lacerations. intervertebral disk extrusion with or without spinal cord Focal outpouching of enhanced CSF in cases of trau- compression: 31 cases (2006–2010). J Am Vet Med Assoc 242(2):217–22. matic meningocele. 9. Hague DW, Joslyn S, Bush WW et al. (2015). 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