5.4.2.3 Necropsy Analysis and Sampling, a Beginning
1 Place the carcass on its left side.
2 Assess the general condition.Determine the nutritional state of the animal. This can be done using a body condition scoring system but should also include looking for external (subcutaneous) and internal fat stores. In most animals, stores of fat surrounding the kidney and the heart are the longest retained, so these should be specifically examined if emaciation is suspected. Note the muscle mass of the animal.
3 Oral examNote the condition of the teeth, look for masses or ulcers on the lingual, buccal and/or gingival mucosa.
4 Cut the skin along the ventral midline from the chin to the tail.
5 Reflect the right limbs by cutting through the muscles to the hip and shoulder joints.Reflect the skin to the level of the backbone (See Figure 5.3).
6 Open the two body cavities (abdomen, chest):Open the abdominal cavity by cutting through the body wall musculature along the caudal border of the ribcage and extend the cut to the pelvic region. Open the right side of the chest cavity by cutting the ribs along the sternum and adjacent to the backbone (see Figure 5.3).Record any abnormal locations or sizes of organs.Figure 5.3 Prepare to open the animal by reflecting the skin. A cut along the thin, black solid line will reveal the abdominal cavity; continue the incision across the pelvic region and along the ventral midline. Open the thoracic cavity by cutting the ribs along the dotted line to the thoracic inlet and finish the opening by cutting each rib just dorsal to the vertebrae.Record the quantity, color, and contents of any fluids in the body cavities.Note the amount and quality of food in the digestive tract.If samples of organs are to be taken for culture or microbe analysis of any type, do so early, before they have been removed and handled. A description of the best samples to take for common shelter problems is provided in the next section.
7 The organ systems should be examined in a methodical manner, which can be guided by any of the resource sites listed in the previous section. A tissue checklist should be on hand. For samples destined for histopathology, a sharp knife or scalpel should be used, the tissues held at the edges only and quickly placed in formalin. If a complete necropsy is desired (e.g. if there is a sudden death) samples should be taken from all listed organs (refer to the tissue checklist), including normal and abnormal regions. Samples that include both abnormal areas and surrounding normal areas are best. Do not scrape surfaces of tissues. Histopathology samples from any organ should be no thicker than 1 cm so that formalin penetration of the tissue is adequate, but multiple samples should be taken so that they represent the range of lesions (See Figure 5.4)Figure 5.4 A properly opened body ready for diagnostic sampling.
8 Specific tissues to sample in the case of gastrointestinal or respiratory disease are listed separately later in the chapter. For shipping, if the appropriate ratio for fixation has been used (10 formalin:1 tissue), and there has been an appropriate time of fixation, most of the formalin can be removed once the specimen is fixed. It is important to leave just enough formalin so the sample does not dry during shipment. Proper fixation depends on the sample size and the density of the tissue. For properly cut samples of most visceral organs, 24 hours is usually sufficient. Waste formalin is considered hazardous waste and must be handled following current state and federal regulations, as well as U.S. Environmental Protection Agency guidelines. Similarly, the size and quantity of formalin containers that can be shipped may be limited, which may be of particular importance when multiple samples are collected.
For shipping samples, four layers of packaging are generally required to include a primary watertight inner receptacle, absorbent material, a secondary watertight inner receptacle, and sturdy outer packaging. The second receptacle should contain any required clinical history and request forms. Both the shipping company and the receiving laboratory should be consulted to ensure proper packaging prior to sample submission. Remaining samples can be placed and stored in a large plastic container of formalin in case additional samples are needed.
5.4.2.4 Tissue Checklist for Necropsy
The following tissues should be preserved in 10% buffered formalin at a ratio of 1 part tissue to 10 parts formalin. Tissues should be no thicker than 1 cm.
1 Liver – sections from each lobe, including gall bladder
2 Kidney – sections should extend from cortex to medulla and be collected from each kidney (see Figure 5.5)
3 Stomach – sections from fundus (body) and pylorusFigure 5.5 Sections to be submitted for histological analysis need to be thin enough to properly fix in formalin. In this example, the (a) kidney has been cut along a (b) mid‐sagittal plane. (c) A properly cut section for fixation in 10% buffered formalin is pictured.
4 Gastrointestinal (GI) TractOral/pharyngeal mucosa and tonsil – plus any areas with erosions or ulcerationsTongue – cross section near tip including both mucosal surfaces Segmental (up to 5 cm long) sections of:EsophagusSmall intestines – duodenum, jejunum, ileumLarge intestines – cecum, colon
5 Spleen
6 Pancreas
7 Adrenal gland
8 Heart – longitudinal sections including atrium, ventricle and valves from both left and right sides
9 Lung – regional samples including cranioventral, caudodorsal, and hilar with major bronchus included
10 Lymph nodes – possibilities include iliac, mesenteric, hilar, mandibular, retropharyngeal
11 Thymus (if young animal)
Other possible tissue sections to consider (case dependent):
1 Skin – any affected regions
2 Brain – if there are neurologic signs, the entire brain should be submitted, cut longitudinally along the midline
3 Reproductive tract – entire uterus and ovaries with longitudinal cuts into the lumen of uterine horns,