image of Neuroimaging
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The central nervous system (CNS) is encased in the bones of the skull and the spine. Consequently CNS disease can result both from disorders of the nervous system itself and from disorders of the bones and soft tissues that encase and protect the nervous system. Therefore, when imaging the nervous system, the ability of the modality to depict lesions in bone and/or soft tissue must be appreciated. This chapter deals with radiography, advanced imaging.

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Image of 5.1
5.1 Correct positioning to obtain spinal radiographs. The white lines indicate the level at which the beam should be centred. The correct positioning for cervical radiography. Note that there are foam pads placed under the nose and neck of the animal (arrowed) to ensure that a true lateral view is obtained. The correct positioning for thoracolumbar radiography. Note that here the foam pads have been placed between the limbs to ensure that the thoracolumbar spine is lateral.
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5.2 Anatomy of a vertebra.
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5.3 Lateral and VD view of the normal adult atlantoaxial junction. The dens is visible in (b) (arrowed).
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5.4 Lateral view of the atlantoaxial junction in a normal 6-week-old Boston Terrier. The apparently separate fragment of bone (arrowed) ventral to the atlas is part of the developing body of the vertebra.
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5.5 VD view of the thoracolumbar junction in a Cocker Spaniel. Note that the 13th vertebra (*) only has one rib.
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5.6 Lateral and VD views showing a block vertebra at C2–C3 and complete absence of the dens in a 10-year-old Poodle. The point at which the two vertebrae are fused is visible (arrowed).
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5.7 Lateral radiographs of the thoracic spine of two dogs with hemivertebrae. The hemivertebra (arrowed) is not causing clinical problems. The vertebral anomalies are causing severe kyphosis and the dog was paraplegic. Note the abnormal shape of the spinous processes of the affected vertebrae.
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5.8 VD radiograph of the cranial thoracic spine. There is spina bifida affecting the first thoracic vertebra. Note the duplication of the spinous process (arrowed).
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5.9 Lateral radiographs of the lumbar spine and lumbosacral junction in two dogs with discospondylitis. In both dogs there is obvious destruction of the endplates of the affected vertebrae. Sclerosis, ventral spondylosis and degenerative changes of the articular processes are also present. Mild ventral subluxation of the sacrum and ventral spondylosis are visible.
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5.10 Lateral radiographs showing vertebral neoplasia. There is almost total destruction of the spinous process of T2 by a poorly differentiated sarcoma. The vertebral canal and intervertebral foramen at L6–L7 are expanded and there is new bone ventral to the body of L6 (arrowed). The cause was a poorly differentiated sarcoma.
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5.11 Lateral and VD view of the caudal thoracic spine in a dog that had been hit by a car. (a) The body of T11 appears shorter than usual and a fracture line is faintly visible (arrowed). (b) A dramatic fracture of T11 with craniolateral displacement of the caudal fragment is evident, emphasizing the importance of obtaining orthogonal views. Lateral view of the lumbar spine of a dog that had fallen from a height. There are fractures of the lateral pedicle (white arrow) and cranial endplate of the caudal vertebra (black arrow). This is an unusual fracture that is stable. Lateral view of the cervical spine of a Greyhound that had run into a tree. There is collapse of the C3–C4 intervertebral disc space and cranial displacement of the fractured caudoventral body of C3. Common fractures and luxations of the lumbosacral articulation and cranial lumbar spine. Flexion of the spine combined with caudal impact results in fractures of the caudoventral aspect of the cranial vertebral body and malalignment in the region of the lumbosacral and thoracolumbar junctions (arrowed).
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5.12 Lateral views of the cervical and lumbar spine in two dogs with acute intervertebral disc herniations. (a) There is obvious narrowing of the C3–C4 disc space. Although there is no radiographic evidence of mineralized disc material at this site, a large amount was visible in the canal on CT images. (b) Mineralized disc material is present within the L2–L3 disc space, projecting into the vertebral canal and causing opacification of the intervertebral foramen (arrowed).
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5.13 Degenerative changes commonly identified on spinal radiographs. These changes are often of no clinical significance. Ventral spondylosis and sclerosis of the endplates in the thoracolumbar spine of an 8-year-old German Shepherd Dog. Marked ventral spondylosis and endplate sclerosis in an old Boxer. Degenerative joint disease of the articular processes in the lumbar spine of a 4-year-old Rhodesian Ridgeback (arrowed).
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5.14 Multiple cartilaginous exostoses in a 4-month-old Golden Retriever. The exostoses are present on the ribs and the bodies and spinous processes of the thoracic vertebrae (arrowed).
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5.15 Lateral view of the lumbar spine of a Boxer with disseminated idiopathic skeletal hyperostosis (DISH). Note the nearly continuous new bone along the ventral margin of the visible vertebrae. This new bone continued cranially throughout the thoracic spine.
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5.16 Equipment required for myelography. A syringe is attached to an extension set and filled with contrast medium. The entire field should be kept sterile. The contrast medium was passed through a 0.22 µm filter when drawn up from the bottle (note the syringe with filter attachment in the foreground).
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5.17 Normal myelographic appearance of the canine spinal cord with the contrast medium injection made at L5–L6. The normal appearance of the cranial cervical spinal cord. The normal appearance of the caudal cervical spinal cord. The cranial thoracic spine never fills well when the injection is first made, giving the appearance of thinning or even loss of the contrast medium column. The small circular filling defect over the caudal aspect of L4 is most likely an air bubble accidently introduced with the contrast medium. The spinal cord tapers in the caudal lumbar spine: the level depends on species and breed, but in general the spinal cord terminates more cranially in larger dogs. Therefore, myelography is not useful for delineating the contents of the vertebral column at the lumbosacral junction in dogs.
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5.18 Extradural, intradural/extramedullary and intramedullary myelographic patterns. (a) Lateral view of a 1-year-old cat with lymphosarcoma. The dorsal aspect of the contrast medium column is clearly deviated ventrally by an extradural mass. (b) VD view of the cat in (a). Note that the left lateral aspect of the contrast medium column is deviated to the right (arrowed). (c) Lateral and (d) VD views of the lumbar spine of a Labrador with a meningioma. On the lateral view, both the dorsal and ventral aspects of the contrast medium column are thinned and deviate abaxially over the caudal aspect of the third lumbar vertebra as if around an intramedullary lesion. However, there is an accumulation of contrast medium in the subarachnoid space delineating an oval filling defect (the classic golf tee sign) just dorsal to the caudal L3 endplate (arrowed). This appearance is most consistent with an intradural/extramedullary lesion. The deviation and splitting of the contrast medium on the right are clearly evident on the VD view. (e) Lateral and (f) VD view of a 1-year-old Yorkshire Terrier that had suffered a fibrocartilaginous embolism. There is expansion of the spinal cord in the caudal cervical region causing thinning and abaxial deviation of both lateral aspects of the contrast medium column. The endotracheal tube (arrowed) is visible on the VD view. If the tube prevents interpretation of the image it should be repositioned or even briefly removed to obtain a diagnostic view.
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5.19 Myelographic artefacts. An L5–L6 injection in which the contrast medium has entered the subdural space, causing a characteristic spindle-shaped end to the contrast medium column caudally (arrowed). The contrast medium has been injected into the epidural space, causing opacification of the intervertebral foramina (short arrow) and an undulating appearance to the contrast column due to opacification of the venous sinuses (long arrow).
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5.20 Lateral myelogram of a dog with ascending myelomalacia precipitated by an intervertebral disc herniation (arrowed). There is contrast medium within the subarachnoid space and spinal cord parenchyma.
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5.21 3D CT surface renderings of a dog with atlantoaxial subluxation. The axis is angled slightly with respect to the atlas. Approximately 50% of the anatomical structures on the left have been removed. The malalignment of the axis is now more obvious as is the dorsal displacement of the cranial aspect of the axis and the absence of the dens. Ventral aspect of the atlantoaxial junction. The anatomical relationships can be evaluated for planning the surgical stabilization. 3D renderings can be very useful for assessing complex anomalies and fractures.
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5.23 Transverse CT images of a lumbar vertebra in a Dachshund. The image is being viewed in a soft tissue window (high contrast) and the presence of mineralized disc material in the vertebral canal is obvious. The same image being viewed in a bone window (low contrast). Note that the herniated disc material is more difficult to identify.
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5.24 Non-contrast and contrast-enhanced transverse CT images of the brain of a 2-year-old Boxer. On the non-contrast image there is clear loss of symmetry in the brain, with dorsal deviation of the right lateral ventricle and expansion of the sutures in the skull, suggesting a pressure effect. A broad-based mass can just be identified on the floor of the skull (*) to the right of the clinoid process. This mass strongly enhances following intravenous administration of contrast medium. The blood vessels on the midline also enhance (arrowed), clearly showing the mass effect. The location of the mass to the periphery of the brain (i.e. extra-axial) and the strong contrast enhancement make a meningioma the most likely diagnosis, and this was confirmed at necropsy. The skull sutures probably opened as a result of increased intracranial pressure in this young dog.
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5.25 Non-contrast and contrast-enhanced CT images of an 8-year-old cat with paradoxical vestibular signs. The non-contrast image is unremarkable, but on the image obtained post-contrast medium administration there is a region of marked contrast enhancement (*) within the cerebellum. This intra-axial lesion was caused by fungal encephalitis. Note the (normal) enhancement of the choroid plexus (arrowed).
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5.26 CT images of a normal and an abnormal lumbosacral junction in a dog. The images were taken with the animal in dorsal recumbency. (a) and (c) are transverse images and (b) and (d) are sagittal reconstructions. (a–b) The epidural fat (black) surrounds the cauda equina. (c–d) There is a lumbosacral malformation with a transitional lumbar vertebra. The intervertebral disc has protruded dorsally, obliterating the vertebral canal and displacing the epidural fat, making it impossible to see the cauda equina on the transverse image. The protruding disc material is clearly evident on the sagittal reconstruction (arrowed).
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5.27 Contrast-enhanced image of the brain at the level of the cerebellum demonstrating a beam-hardening artefact (arrowed). Note also the large contrast-enhancing mass at the right cerebellopontine angle (*).
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5.29 T2-weighed spin-echo brain image. Substances with a long T2 relaxation time (such as pure fluids) have a high signal in this image sequence. Note the high signal of the CSF within the lateral ventricles (arrowed). In modern spin-echo sequences, fat will also have a high signal. Note the high signal of the marrow fat in the bones at the base of the skull (arrowhead). T1-weighted spin-echo brain image. Substances with a short T1 relaxation time (such as fat) have a high signal in this image sequence. Note the high signal of the marrow fat in the bones at the base of the skull. Fluid has a long T1 relaxation time and, therefore, a low signal in this image sequence. Note the black signal from the lateral ventricles, which relates to the location of the fluid. Proton density-weighted spin-echo brain image. In this sequence, tissue signal is primarily dependent upon the spatial distribution of protons, or the absolute proton density per unit area. Note the lower signal of white versus grey matter due to the differences in proton density. The proton density sequence is the preferred sequence to assess white and grey matter distribution. T2-weighted fluid attenuated inversion recovery (FLAIR) brain image. This is a special sequence used to null the signal from free fluid and is useful for detecting hydrated lesions that would otherwise be obscured by the signal from normal fluid. Note the lack of signal from the CSF in the lateral ventricles, which has been nullified in this special sequence. This image is of a normal brain.
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5.30 T2-weighted spin-echo image of a cat with cerebellar infarction (black arrow). The cytotoxic oedema has led to an increase in water concentration in the lesion, which creates a region of high signal on T2-weighted images. There is exudate in the left tympanic bulla (white arrow). T1-weighted spin-echo image of the cat in (a). As fluid has a low signal in T1-weighted images, the cerebellar lesion is not conspicuous. However, the exudate in the left tympanic bulla (arrowed) can be seen. Some proteinaceous fluids have a shorter T1 relaxation time than more pure fluids and thus become visible on T1-weighted images.
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5.31 Pre-contrast and post-contrast T1-weighted spin-echo brain images of a dog with a pituitary macroadenoma. (a) There is a peripheral rim of high signal due to chronic haemorrhage. The magnetic effects of this chronic haemorrhage, which likely contains methaemoglobin, leads to a shortening of the T1 relaxation time and a high signal. (b) The contrast medium has leaked into the tumour, causing shortening of the T1 relaxation time and a high signal. Without obtaining the pre-contrast image, the peripheral haemorrhage would not have been detected.
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5.32 Sagittal T2-weighted spin-echo image of the thoracic spine. The bodies of vertebrae T7–T10 have an increased signal, as may been seen with an infiltrative tumour or infection. Sagittal STIR image of the same region. The signal from the fat is reduced, revealing that the signal from vertebrae T7–T10 is no different to any other vertebra. This indicates that the high signal seen in (a) was due to fat in the medullary cavity and not an infiltrative disease.
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5.33 T2-weighted spin-echo brain image. It is difficult to know whether the increased signal at the ventral aspect of the left lateral ventricle (arrowed) is due to CSF in the ventricle or to a lesion of the neuropil. T2-weighted FLAIR image of the same area. The signal from the free fluid (such as CSF) has been nullified in this sequence. The presence and extent of the lesion in the left piriform lobe is much more obvious without the superimposed signal from the CSF in the ventricle.
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5.34 Transverse images of the brain at the level of the thalamus using T1-weighted, T2-weighted and gradient-echo sequences. The arrows in (a) and (b) indicate a small, hypointense vascular lesion, which is difficult to detect. The same lesion is apparent on the gradient-echo image as a region of signal void due to the paramagnetic effects of haemoglobin.
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5.36 Transverse ultrasonogram of the brain via the bregmatic fontanelle at the level of the interthalamic adhesion. The lateral ventricles (*) and the thalamus (T) can be seen.
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