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A complete necropsy, including the removal of the entire brain and spinal cord from a large animal, is an arduous task. Nervous tissue shows the effects of autolysis rapidly and is extremely susceptible to distortion before it is well fixed. There is nothing more frustrating for a pathologist than scanning numerous histologic sections of tissue soup because of careless and rushed processing of samples of neural tissue. However, because of these facts and because so much vital information can be gained by a thorough neurologic necropsy, it is worth doing if it is performed well. Failing this, a compromised or no pathologic diagnosis can be expected. With the submission of inadequately prepared specimens for study, cases such as harvesting only the cervical spinal cord from a wobbler horse with a thoracic lesion, or only the brain from a lamb with tetraplegia, or no peripheral nerves and muscles from a calf with monoplegia all can be expected to frustrate both clinician and pathologist. Sometimes an abbreviated necropsy will suffice in obtaining a diagnosis. Thus, there is no need to remove the petrosal bones and vestibular nerves from a cow with only tail paralysis, although this does presuppose that an accurate neuroanatomic diagnosis has been made!

A practical approach to the postmortem examination of a large animal with neurologic disease is to begin at the site suspected of having a lesion such as the temporohyoid region or the cervical vertebrae—cranial base to T1‐and continue to harvest further tissues if no gross explanation for the signs becomes evident. Histopathologically, most compressive lesions of the spinal cord, whether they are caused by previous external injury, a stenotic vertebral canal, osteomyelitis, or a tumor, are the result of trauma. Thus, the burden is often on the prosector to supply such pertinent etiologic information.

A technique for a full postmortem examination including removal of the brain and spinal cord from the adult horse can be consulted.^7,8 In lieu of the technique outlined which requires facilities and time, there are other suitable techniques for brain removal. A midline saw or hatchet cut allows for the removal of the brain halves. It is probably better to make two transverse saw cuts through the calvarium, one at the level of the external auditory meatus (except for vestibular syndromes) and the other at a level halfway between the caudal aspect of the bony orbit and the external auditory meatus. This preserves most midline structures and allows for removal of four sections of brain after the cerebellar peduncles are cut to separate the cerebellum. For all cases, particularly for smaller heads, the dorsal neurocranium can be removed piecemeal starting at the foramen magnum using bone cutters, thus allowing the whole brain to be lifted out from the olfactory lobes and progressing caudaly cutting cranial nerves as they exit the brain cavity (Figure 4.1). The spinal cord can be harvested by preparing cervical, thoracic, and thoracolumbosacral vertebral column sections. Then, a dorsal laminectomy is performed using bone cutters for smaller samples allowing for removal of the spinal cord sections using traction applied to the dura mater and careful sharp sectioning of neural and vascular attachments. Alternatively, the spinal cord sections can be exposed by making a sagittal saw cut along the vertebrae exposing the vertebral canal and lateral spinal cord and removing and labeling each section of cord for orientation. A spinal cord removal instrument⁹ can be useful in removing long sections of spinal cord from trimmed blocks of vertebral column in large animals (Figure 4.2). The dura mater should be carefully split along the dorsal surface and almost complete transverse sections made with a new razor blade through the cord at least at every segment. Alternatively, in wobblers, the cervical vertebrae may be disarticulated and each segment of spinal cord labeled and oriented as to cranial versus caudal. If there is good evidence from clinical and imaging studies of the site of a focal spinal cord lesion, then the preparation of the site of interest can be more focused and carefully performed. As a rule, there will be no epidural fat evident on opening each dorsal intervertebral space at sites of spinal cord compression. This then becomes a signal of a likely compressive lesion, warranting care when that segment of cord is harvested. If in large wobbler cadavers the site of a suspected compressive lesion(s) is not known, the cervical vertebral column can be sectioned transversely through the middle of each vertebral body so that each segment of spinal cord can be removed after cutting the spinal nerve roots. After spinal cord removal, each block of vertebral sections or adjacent halves of two vertebrae can be cut on the median plane to expose all intervertebral sites where most compressions occur in the neck of large animals.

Figure 4.1 To remove the brain intact, a craniectomy can be performed as depicted here. Two saw cuts through the bones of the cranium are made (between arrows 1 and between arrows 2) on each side and then a transverse cut is made over the rostral frontal region just caudal to the level of the caudal extent of the bony orbits (arrows at 3). With further careful sawing and leverage (arrowhead) with a hand wedge (4), the cranial roof can be removed. The brain is then removed by tilting the nasal region up and over while cutting the exposed cranial nerves as they exit the calvarium.

Because the removal of the entire spinal cord from an adult large animal is particularly difficult, the procedure of sectioning the entire or appropriate parts of the vertebral column with enclosed spinal cord, trimming off excess soft tissues, and immersing the sections of vertebral column in large volumes of 10% formalin is an appropriate alternative means of preservation for shipment to a pathology laboratory. A band saw may not be available to perform a laminectomy or sagittal vertebral cut to remove the spinal cord, and it may be unpractical to preserve large sections of vertebral column for the pathologist. A hatchet may then be used to remove the vertebral bodies from the vertebral arches using a ventral approach. The cuts are made in a slightly medial direction, from the angle between the vertebral bodies and the transverse processes in the cervical and lumbar regions, or from the rib remnants in the thoracic region. Alternatively, a spinal cord removal tool⁹ may be used (Figure 4.2).