Large Animal Neurology. Joe Mayhew

characterizing the cricoarytenoideus dorsalis muscle in horses. J Equine Vet Sci 2019; 77: 121–124.

      206 206 Gosselin VB, Babkine M and Francoz D. Ultrasonography of the Tympanic Bullae and Larynx in Cattle. Vet Clin North Am: Food Anim Pract 2016; 32(1): 119–131.

      207 207 Boado A, Nagy A and Dyson S. Ultrasonographic features associated with the lumbosacral or lumbar 5–6 symphyses in 64 horses with lumbosacral‐sacroiliac joint region pain (2012–2018). Equine Vet Educ 2020; 32(S10): 136–143.

      208 208 Espinosa P, Benoit P, Salazar I, de la Fuente J and Heiles P. Transrectal ultrasonography of equine lumbosacral nerves: pilot study in 28 healthy warmblood horses. Vet Radiol Ultrasound 2017; 58(2): 228–236.

      209 209 Cousty M, Firidolfi C, Geffroy O and David F. Comparison of medial and lateral ultrasound‐guided approaches for periarticular injection of the thoracolumbar intervertebral facet joints in horses. Vet Surg 2011; 40(4): 494–499.

      210 210 Levy M, Gaschen L, Rademacher N and Bragulla H. Technique for ultrasound‐guided intraarticular cervical articular process injection in the dog. Vet Radiol Ultrasound 2014; 55(4): 435–440.

      211 211 Purefoy Johnson J, Stack JD, Rowan C, Handel I and O'Leary JM. Ultrasound‐guided approach to the cervical articular process joints in horses: a validation of the technique in cadavers. Vet Comp Orthop Traumatol 2017; 30(3): 165–171.

      212 212 Berg LC, Nielsen JV, Thoefner MB and Thomsen PD. Ultrasonography of the equine cervical region: a descriptive study in eight horses. Equine Vet J 2003; 35(7): 647–655.

      213 213. Mattoon JS, Drost WT, Grguric MR, Auld DM and Reed SM. Technique for equine cervical articular process joint injection. Vet Radiol Ultrasound 2004; 45(3): 238–240.

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      216 216 Prange T, Derksen FJ, Stick JA, Garcia‐Pereira FL and Carr EA. Cervical vertebral canal endoscopy in the horse: intra‐ and post operative observations. Equine Vet J 2011; 43(4): 404–411.

      217 217 Arishima H, Higashino Y, Yamada S, et al. Spinal endoscopy combined with selective CT myelography for dural closure of the spinal dural defect with superficial siderosis: technical note. J Neurosurg Spine 2018; 28(1): 96–102.

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4 Pathologic responses of the nervous system

      Disease

        Gross changes

        Histologic reactions

        Mechanisms of disease

        References

This chapter reviews the gross and cellular reactions of nervous tissue in disease states and covers the general clinicopathologic characteristics of the mechanisms of neurologic disease. The aim is not to review veterinary neuropathology, but to provide a basic understanding of clinically important, neuropathologic principles. The reader is referred to pathology references for a more detailed coverage of most of these aspects of neuropathology.^1–6

      General reactions seen in tissues in response to pathologic insults and the associated terminology should be understood. We must be able to communicate with each other about neurologic diseases and understand the pathogenesis of these diseases. Importantly, such an understanding allows us to sensibly investigate a neurologic disorder of unknown cause and to understand, evaluate, and clinically interpret pathology reports on animals dying of neurologic diseases. This becomes economically significant when dealing with an outbreak of a neurologic disorder.

Gross changes visible in nervous tissues

       Finding the lesion

      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 (