Large Animal Neurology. Joe Mayhew
Чтение книги онлайн.

Читать онлайн книгу Large Animal Neurology - Joe Mayhew страница 53

Название: Large Animal Neurology

Автор: Joe Mayhew

Издательство: John Wiley & Sons Limited

Жанр: Биология

Серия:

isbn: 9781119477198

isbn:

СКАЧАТЬ 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.

Photo depicts removing the brain intact, a craniectomy.

      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).

       Gross artifacts

      Vertebral and cranial fractures and separations sometimes occur at the time of euthanasia and during any manipulation of the cadaver of both immature and heavy large animals. This may be the result of falling, electrocution, dragging, and slinging. Surprisingly, considerable hemorrhage may be present around such fracture sites, and the histologic appearance can be difficult to interpret. Irrespective of this, large, mainly subarachnoid, spinal and cranial hemorrhages also occur, especially if decapitation is performed immediately after death.

      Gross estimates of an excessive (or deficient) volume of CSF are almost impossible to make, and except for noting any other major malformation, the evaluation of an apparent slight increase in the size of ventricles should await measurements made after fixation.

Photo depicts the vertebral column cut into cervical, cranial thoracic, and thoracolumbosacral sections, a laminectomy may be performed to remove the spinal cord sections or a spinal cord removal instrument as shown can be used to gently cut the spinal nerves in the epidural space allowing withdrawal of the spinal cord segments.

      A common error in preserving large masses of neural tissue is underestimating the volume of aldehyde fixative to use resulting in autolysis of tissues and even bacterial growth in the cramped samples sitting in a small volume of fixative! A ratio of one‐part nervous tissue to ten parts fixative is ideal, and changing the fixative after 24 h is good practice and helps reduce any blood staining of the preserved specimens. Partial and differential fixation can produce localized changes in texture and color, so comment is best reserved until fixation is complete. This does not preclude initial sectioning of the brain and spinal cord, as this also aids in fixation.

       Gross lesions