Dr. Jenni Bass
Typically, however, tissue or organ samples are placed in formalin for preservation and sent to a laboratory for histological analysis. Histology is the study of tissue at the microscopic level. At the laboratory, these tiny pieces of preserved tissue will be sealed into wax blocks, which are then sliced into layers just a cell or two thick. These layers are thin enough to allow light to pass through them. They are then fixed on a glass slide, to be examined by a pathologist under a microscope. In some instances, special stains are applied to the tissues. These stains highlight features such as intracellular (within the cell) parasites or bacteria.
In some cases, a more highly specialized procedure, electron microscopy, is performed. This allows examination of structures within the cell itself, and can even allow particles as small as viruses to be seen. Virus isolation from tissue samples is possible in some instances, as some viruses can be grown and identified in the laboratory.
The Limitations of a Necropsy
If you decide to have a necropsy performed, the body of the reptile should be submitted to your veterinarian as soon as possible after its death; it should be kept cool, preferably at refrigerator temperature. If the necropsy cannot be performed for more than 48 hours, the body should probably be frozen. In the hours after death, the cells of the body begin to degenerate. This happens more quickly at higher temperatures. Bacteria within the body, particularly the high concentrations found in the digestive tract will continue to live and divide, further accelerating decomposition. Cooling slows decomposition of tissues. Freezing, although it prevents decomposition, is not ideal. As sharp ice crystals form from the water within the body, they tear delicate cell walls, distorting the microscopic appearance of tissues.
Not every cause of death will be revealed by even the most in-depth necropsy. There are many reasons for this, and veterinarians find it just as frustrating as owners do to be unable to explain or understand the death of a pet. Sometimes the cause of illness or death would have been revealed if a given test had been performed on the animal while it was alive. For example, electrical malfunction of the heart may not be detectable when the heart is examined at necropsy. It may or may not have been evident in tests when the animal was alive. Sophisticated tests such as MRI (magnetic resonance imaging) are available in only a few places, and may be cost prohibitive. In some cases our reptile patients are too small for the tests we would like to perform. In other cases, the tests do not exist for reptiles as they do for dogs, cats and people. Some disease processes are not fully understood and others have yet to be identified. There is a great deal to learn yet in the field of reptile medicine, and the more we apply science and medicine to the care of reptiles, the better that care will be.