Blood and Urine tests. The main role of these tests is to be sure that an animal’s liver, kidneys and other organs are functioning normally. Occasionally these tests can also provide specific insight into the neurological problem itself. For example, the crystals shown below may be formed in animals with a type of liver disease known as hepatic encephalopathy (Figure 4A).
Figure 4A: Biurate crystals in the urine of a dog with hepatic encephalopathy.
Chest X-rays are performed in order to be sure that there is no sign of heart enlargement and no tumors in the lungs (Figure 4B) or surrounding tissues. Chest X-rays can also provide other information such as the identification of esophageal muscle weakness (called megaesophagus) that occurs in some diseases of the neuromuscular system (for example myasthenia gravis). Some animals require mild sedation in order to stay still enough for X-rays to be taken.
Figure 4B: Chest X-ray showing tumors that have spread into the lungs of a dog (arrows).
Abdominal Ultrasound is an easy and accurate way of assessing the abdominal organs of animals (Figure 4C). It does not require the animal to be anesthetized, although some will require light sedation. An ultrasound is complimentary to an X-ray and ultrasound also permits a small needle to be guided into abnormal areas in order to obtain a sample of cells to look at under the microscope. Ultrasound can also be used to examine the inner workings of the heart and to diagnose hydrocephalus, a condition where fluid accumulates within the brain.
Figure 4C: Ultrasound of a dog’s bladder showing the dark shape of the urine-filled bladder clearly (white arrowheads) as well as the tumor growing within it (*).
CSF analysis (also known as a Spinal Tap) is the technique used to obtain a sample of the fluid that surrounds and bathes the brain and spinal cord (Figure 4D). This spinal fluid normally contains very few cells and minimal amounts of protein. Nervous system inflammation or tumors cause increased amounts of cells or protein to enter the CSF. CSF analysis may therefore provide crucial information to identify certain tumor types (such as lymphoma). CSF analysis can also indicate the presence of encephalitis & meningitis (inflammation of the brain and its protective covering).
Figure 4D: CSF from a dog with meningitis and encephalitis showing a markedly increased number of both red blood cells (white arrow) and white blood cells (black arrows).
Spinal X-rays remain an important diagnostic tool in veterinary neurology (Figure 4E). Their main value is to identify fractures of the spine as well as tumors and infections that destroy bone. They are not very useful for identifying disc herniations as it is often very hard to see the exact position of disc material clearly.
Figure 4E: X-ray of a dog with a bacterial infection of the disc space at the lumbosacral junction called discospondylitis. There has been marked destruction of bone (black arrows) and the normal plate of bone adjacent to the disc has been destroyed (white arrow).
Myelography is a technique where an X-ray is taken after a contrast agent (a type of dye with similar properties to barium) is injected into the fluid (known as CSF) that surrounds the spinal cord. Myelograms are shown in images 4F and 4G below, under Neuroimaging and also in Wobbler Syndrome
Figure 4F: The dye is introduced using a needle as shown above. The dye then outlines the spinal cord and identifies any structure deforming it, such as a disc herniation (see Figure 4G).
Figure 4G: Myelogram in a dog with a large disc herniation in the neck (white arrow). The mass of disc material is pushing the myelographic contrast agent (black arrowheads) and the spinal cord upwards and will cause severe pain and weakness.
CT scan is an X-ray technique where a computer is used to reconstruct cross-sectional images of the animal in the scanner (Figure 4H). CT provides invaluable information for surgical planning of many spinal cord disorders. We now use CT almost exclusively for the diagnosis of disc disease in dogs and cats because it is fast and accurate. In contrast to myelography, CT scanning is also a non-invasive technique. Extruded disc material can usually be seen without the need for a contrast agent. Examples of CT scans are also shown below and under Seizures, Vestibular Disease , Lumbosacral Disease , Nervous System Tumors and Meningitis, Encephalitis, Myelitis. Cross-sectional imaging such as CT and MRI also permit the brain to be examined in detail.
Figure 4H: CT scan of a dog’s head showing the skull (white arrow) and a large tumor near to the center of the brain (black arrow). The tumor has a rim of bright, contrast enhancement along with a darker center that probably represents poor blood flow.
MRI is an extremely useful technique that employs a powerful magnetic field instead of X-rays to produce an image (Figure 4I). It is the gold standard imaging technique for many brain disorders as it depicts anatomy in exquisite detail. In contrast to CT scanning, MRI can be used to image an animal in either a longitudinal or lengthwise manner (sagittal plane) as well as in a cross-sectional manner (transverse plane). MRI can also be very useful for certain spinal cord disorders although it may not always give the resolution of CT, particularly for smaller animals. Like CT, MRI is also non-invasive. We are fortunate to be able to use the state of the art scanner at MRI Vancouver. Examples of MRIs are shown below as well as under Disc Disease, Seizures, Lumbosacral Disease, Fibrocartilaginous Embolism, Nervous System Tumors and Further Resources on Magnetic Resonance Imaging.
Figure 4I: MRI of a dog’s head showing the skull (white arrow) and a tumor at the base of the brain (black arrow). The tumor has enhanced (been made brighter) with the contrast agent and so it appears light grey compared to the surrounding, normal brain tissue.
Biopsy is an important tool to identify the exact type of cells within a structure or organ. For example an MRI of the brain might identify a mass within the brain but it does not provide definitive information on the origin of that mass. In many cases the mass will be a tumor but in a significant proportion of cases the mass may be something other than a tumor, such as an infection or a blood clot. A biopsy is either done indirectly using CT- or ultrasound-guidance, or directly by a surgeon approaching the mass surgically. By helping to make an accurate diagnosis, a biopsy usually provides the most useful means to obtain an exact prognosis.
Figure 4J: Cells taken from the spine of a dog with a plasma cell tumor (same dog as shown in Nervous System Tumors, Figure 13-2). The cells are cancerous; two of the cells have double nuclei, which is one feature of malignancy.
