I. General considerations
A necropsy can be defined as the orderly, systematic dissection of a cadaver. It should have as its objective to determine the cause of death or nature of a disease process. A necropsy always should be thorough and complete to obtain the best possible answer to the cause of disease or death. A partial necropsy yields only partial answers. Gross examination alone frequently provides an incomplete diagnosis. Additional microscopic, toxicologic, parasitologic, bacteriologic, virology, or molecular biologic assays are ancillary tests to obtain the most accurate final diagnosis. There are many methods to perform a complete necropsy. Regardless of the choice, to generate the most accurate outcome, the approach should always be the same so that no organs or tissues are overlooked.
Equine necropsies can be divided into three types: the disease-oriented necropsy, the insurance necropsy, and the medicolegal necropsy, each of them requiring a modified approach. The events of a necropsy should be documented by records of the physical findings and by photography, radiographs, collected specimens, and laboratory findings. Protective attire and the right set of instruments are important prerequisites for the adequate performance of a necropsy, so is the optimal environment under field conditions. The necropsy should be conducted within a reasonable time frame after death to avoid tissue decomposition. If euthanasia is performed, the animal should be bled out before the postmortem examination is begun to avoid spilling of blood into organs to be examined.
At the end of the necropsy, all observations should be written down or recorded. All findings should be documented objectively because the signed necropsy record becomes a legal document. The results of all ancillary tests including histopathology should be accompanied by a narrative and interpretation of the findings.
The necropsy procedure described in this chapter is taught at the University of Florida. Other methods are described elsewhere.
II. Techniques
1. Positioning, examining, and opening of the carcass
After the body weight is determined or estimated, the animal is positioned in left lateral recumbency. For identification purposes, a whole-body photograph is taken. If there is a tattoo or brand, these are recorded. The external examination involves all body orifices, mucous membranes including the lining, ocular sclera, the hooves, ears, eyes, and the condition of the hair coat. Valuable information concerning disease of internal organs can be obtained by observing color changes of visible mucous membranes. The gross examination should also include the nutritional status of the animal.
A ventral midline incision extending from the pelvis to the head facilitates the subsequent skinning of the carcass and reflection of the right front leg and hind leg. In the male horse the prepuce is reflected and testes removed from the scrotal sac. This is followed by opening of the abdominal cavity by incision through the abdominal wall.
2. Evisceration of the abdominal, pelvic, and thoracic organs
The abdominal viscera, in particular the intestinal tract, are checked for expected anatomic position. The amount and character of the peritoneal fluid (100–200 mL normal, clear, and straw colored) is assessed. After examination of the cranial mesenteric root, the entire gastrointestinal tract is removed to inspect and remove the remaining organs from the abdominal cavity. Individual organs are assessed for color, consistency, symmetry, and, where appropriate, aspect of the cut surface. Individual organs can be weighed and measured under certain circumstances.
Figure 1.1. Horse. Gastrointestinal Tract. The length of the gastrointestinal tract requires separation into four segments: stomach, small intestinal loops, large colon, cecum, and transverse small colon. (Reprinted with permission from Equine Medicine and Surgery, Colahan et al., Figure 3-55, Page 122, Copyright Elsevier, 1999.)
The bones of the pelvic cavity are cut with a handsaw for removal of the organs of the pelvic cavity including the urinary bladder, rectum, and genital tract.
The right rib cage is removed from the chest using strong rib cutters. The entire pluck is removed en bloc, starting with loosening of the tongue from the oral cavity. The tongue is left attached to the esophagus, which is cut at the diaphragmatic hiatus and removed from the opened thorax together with trachea, lungs, and the heart. Trachea, lungs, and heart are separately examined.
Figure 1.2. Horse. Normal Heart. There are several methods of orderly dissection of the heart. Care should be taken not to mutilate major anatomic structures and pathologic alterations of the heart. The left and right heart sides should be identified before the atria and ventricles are opened. The pointed apex is entirely formed by the left ventricle.
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