Measuring and recording the body weight (Figure 3.1) is an important first step in a necropsy for several reasons. One of the most important is to provide a basis for determining the relative size of viscera. Particularly heart and brain weights are most useful when compared to the total body weight (see Appendix 1).

The external examination is very similar to the physical examination of a living animal. The purpose of the external examination is to establish or confirm the identifying features of the animal (species, breed, sex, coat color, identifying markings, and tattoo or microchip number; Figure 3.2), to document evidence of medical or surgical intervention, and to detect and describe any external lesions. This step includes visual examination of the eyes, ears, oral cavity, skin and hair coat, nails, external genitalia, and perineum and palpation of the skull, limbs, joints, ribs, vertebrae, and pelvis. Note any discharges from body orifices. If the birth date is unknown, tooth eruption and wear patterns can be used to estimate the age of the animal (see Chapter 16). The retina can be inspected by flattening the cornea with a glass microscope slide and shining a penlight through the pupil (see Chapter 12). Abdominal distention can be due to the accumulation of fat, distention of the gastrointestinal tract with food or gas, accumulation of hemorrhage or ascitic fluid, or advanced pregnancy in female dogs and cats. Depending on the degree of rigor mortis, it may not be possible to palpate internal organs. Assessment and documentation of body condition score and degree of postmortem change provide useful data in cases where little history is available, or the circumstances of the death are unknown. An overview photograph of the body as a whole (Figure 3.3) and photographs of all external lesions should be taken before making the first incision.

Place the body in left lateral recumbency and begin with a stab incision in the right axilla (Figure 3.4). This initial incision should be the only time the sharp edge of your knife contacts the haired side of the skin. To keep your knife sharp, additional skin incisions should be made by inserting the knife blade in the subcutis and cutting from the inside out. Extend the skin incision cranially along the midline to the mandibular symphysis (Figure 3.5) and caudally to the perineum, just dorsal to the external genitalia. If the animal is an intact male with scrotal testes, remove the testes at this point by incising the scrotal skin and transecting the spermatic cord. Either leave a longer segment of spermatic cord attached to the left testes or make a small transverse nick in the right testis to help distinguish left from right.

Cut the pectoral muscles and brachial plexus to reflect the right forelimb. Placing hemostats on the axillary artery and vein can help keep the dissection field clear of blood. Locate the glenohumeral joint by depressing the forelimb, which will elevate the joint. Cut across the medial side of the joint at the highest point of the shoulder (Figure 3.6). Assess the volume, color, and viscosity of synovial fluid (see Chapter 5). Inspect and palpate the articular cartilage and examine the joint capsule insertion line for irregularities that might indicate new bone growth due to osteoarthritis. Evaluate the synovial lining and the thickness of the fibrous layer of the joint capsule.

Reflect the skin dorsally to expose the thoracic and abdominal wall from the ventral midline to the level of the vertebral transverse processes. In adult females, examine the mammary gland tissue as you reflect the skin and collect samples of any nodules or areas of thickening, as well as a section of normal gland.

Palpate the coxofemoral junction to locate the joint space and open the joint capsule. In small or thin animals, it is very easy to accidentally cut into the abdominal cavity as you are opening the coxofemoral joint, so angle the knife away from the body wall. Cut the ligament of the head of the femur (Figure 3.7) and the surrounding musculature to reflect the right hind limb dorsally. Examine the joint. Next reflect the skin past the stifle and open the knee joint. This is best accomplished by flexing the joint and making a transverse cut in the patellar ligament (Figure 3.8). Transect the lateral and medial collateral ligaments. Reflect the patella laterally in order to inspect the cruciate ligaments and menisci. This is easily done by inserting the knife into the medial aspect of the joint space, parallel to the long axis of the femur, and incising the joint capsule. Make a cut through the medial thigh muscles (sartorius and adductor) parallel and approximately 1 cm caudal to the femur to the level of the medial aspect of the biceps femoris muscle to expose the sciatic nerve (Figure 3.9). Collect a section of sciatic nerve, skeletal muscle, and skin, and affix these samples to a wooden tongue depressor or piece of cardboard (Figure 3.10). Allow the tissue to dry for 1–2 min and put the tongue depressor with attached tissues into the fixative jar (be sure the tissues are completely submerged). Clear the skeletal muscle away from the proximal end of the femur and use bone forceps or hedge clippers to make an angled cut through the metaphysis. The diagonal cut usually causes a comminuted break in the bone, allowing for collection of samples of cortical bone, cancellous bone, and bone marrow (Figure 3.11). Place the bone marrow in a labeled tissue cassette and immerse in fixative.

The next step is to open the abdominal cavity by cutting through the abdominal wall to create a flap that is reflected ventrally. The initial cut should be made just caudal to the costal arch at the highest point of the abdomen. By cutting at the highest point, any fluid within the abdomen can be retained in the cavity, allowing for collection and quantification. Use the belly of the blade and make a 4–5 cm incision through each muscle plane and the peritoneum. Once you have entered the abdominal cavity, elevate the body wall to help prevent inadvertently incising the underlying viscera. Extend the incision along the costal arch ventrally to the xiphoid process, dorsally to the lumbar vertebral muscles (longissimus), caudally to the ilium, and ventrally as close to the pubic bones as possible (Figure 3.12).

Once the abdomen is open, observe the shape of the diaphragm. The muscle should be taut and concave. Use your blade to cut through the diaphragm at the highest point, near the insertion onto the last rib (again, aim for the highest point to retain any fluid in the thoracic cavity). Once the diaphragm has been cut, the muscle should flatten out and become flaccid (Figure 3.13). In a very fresh cadaver, you may hear a rush of air into the thoracic cavity. With prolonged postmortem intervals, negative pressure will often be lost. Once negative thoracic pressure has been assessed, use your blade to cut through the entire right side of the diaphragm as close as possible to the costal arch.

In heavily muscled dogs, it is helpful to incise the muscle overlying the lines of the cut (Figure 3.14). Opening the thoracic cavity involves making two cuts through the rib cage: one though the cartilaginous attachments of ribs to the sternum and one through the dorsal aspect of the ribs, slightly ventral to the articulation with the vertebral transverse processes (Figure 3.15). In young animals, the cut adjacent to the sternum can be made with a knife or scalpel; however, bone forceps or hedge clippers are needed to cut through the dorsal aspects of the ribs. Using your nondominant hand to retract the thoracic wall as you go helps to visualize the viscera and avoid damage. Test bone strength by attempting to break the ribs by bending them against the curvature. If they break, they should snap crisply.

The third body cavity to open is the pericardium. In a normal animal, this thin sac is in close apposition to the epicardium and can be difficult to grasp or cut without damaging the underlying heart. Using rat tooth forceps or your fingers to tent the pericardium before incising it may be helpful (Figure 3.16

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