Contributors: Phil Nicholls, Gordon Davidson, Melanie Dobromylskyj
Species: Feline | Classification: Techniques
- To determine the cause of death in a single animal (when either the owner or veterinarian wishes to understand the cause of death).
- To determine the cause of death in a multiple animal case (when such information may help prevent further deaths, or aid in determining appropriate therapy, in remaining animals within the group at risk).
- To confirm or refute the clinical diagnosis (clinical audit and quality control/morbidity and mortality investigations).
- To check whether other lesions were overlooked (clinical audit and quality control).
- To refine the diagnosis or more clearly define the extent of the lesion(s).
- To confirm or refute the validity of interpretations made using ancillary aids such as radiography, ultrasonography, clinical chemistry, MRI etc (providing feedback to allow retrospective assessment of the original data in the light of the morphological findings post-mortem).
- For research (in experimental or regulatory procedures).
- For education (in both undergraduate and post-graduate environments).
- For legal purposes, eg suspected poisoning or other malicious act, also to confirm or refute allegations of cruelty, to confirm or refute allegations of incompetence such as might occur after post-surgical or intra-operative deaths, to satisfy criteria for insurance claims.
- Aiding client grieving process after unexpected deaths, usually by providing some form of closure.
- Providing information which may prevent further deaths in other animals at risk. This is a key diagnostic step used in farm animal disease investigations and should not be overlooked in companion animal outbreaks, eg amongst litters of puppies/kittens.
- Providing an important means of quality assessment and clinical audit in diagnosis.
- Providing information which should allow more accurate interpretation of ancillary diagnostic aids, including imaging techniques, ie the provision of ground-truth data which may be used to fact check or compare to data received by other means.
- Allows discovery of new diseases, or confirmation of absence of specified diseases, such as spongiform encephalopathies in the domestic environment.
- Provides evidence for resolution of legal issues.
- The knowledge gained helps professional satisfaction and client satisfaction.
- Requires specific facilities, equipment and expertise to achieve the best outcome.
- Incurs costs (capital, professional and material).
- May spread disease if adequate precautions are not undertaken.
- Safety issues require addressing (risk of infection, risks of injury from equipment).
- Consider using a professional specialist service, such as state, commercial or university service.
- Consider restricting examination to only specified organ systems (so-called partial post-mortem examinations) if time and/or money are limiting factors.
- To cover costs of undertaking post-mortem examinations, consider various options including direct charging to the serviced client, by indirectly charging all clients through a cost-spreading or levy system (thus making PMEs available 'free' of direct charge), or by funding the provision of PMEs by contribution from practice/institute funds (since there are benefits to the practice, outlined above in Pros, from providing such a service).
- Histology techniques and histopathological interpretations are typically provided only by specialists, but consider undertaking the gross post-mortem examination yourself and collecting samples for examination by the specialist.
- Many commercial and university laboratories can provide advice on sample collection, and likely charges. Some services have different pricing schedules for examination of histological specimens collected at post-mortem examination elsewhere (so-called "post-mortem in a jar").
- Little preparation time if facilities and equipment are in place.
- Protective clothing should be worn .
- Examination of only a restricted set of organ systems, such as confirming a diagnosis or collecting a restricted set of specific tissues may be rapidly achieved in a matter of minutes, depending on the experience of the individual.
- More thorough, systematic examinations may take much longer, depending on extent of the examination, perhaps an hour or more for a systematic examination excluding the spinal cord.
- As a guideline, in professional examinations, candidates may be allowed 3 hours for a post-mortem examination of 1 or 2 animals (excluding associated histology).
Criteria for choosing test
- Consider if any conflict of interest may be present if legal issues are possible, for example if there is a question of professional negligence relating to the case
- Consider the limitations of undertaking a cosmetic examination.
- Obtain specialist advice, where appropriate, prior to the examination (advice on fixation, samples to collect, media for microbiological samples).
- Cadavers which have been frozen will have marked ice crystal distortion of histological architecture, which will severely limit the utility of histopathological examinations. However, be aware that useful information may still be obtained from post-mortem examinations, and histopathology, in many instances, despite the effects of freezing.
- A significant degree of post-mortem autolysis will limit the utility of histological examinations. However, depending on the disease, useful information may still be obtained, although extra care will be required in handling the softened tissues.
- In certain cases, particularly legal cases where there is expected to be penetrating ballistic injury (eg air rifle pellets) prior radiographs or CT may be useful in narrowing down the anatomic location of such ammunition. You should be mindful of the additional costs associated with these techniques.
- CT may be used as an ancillary diagnostic tool, but it should not be used to replace a full and methodically performed postmortem examination.
- In cases of abortion, stillbirth or neonatal death, examination of the placenta is key, so it should be retained, and samples fixed and frozen. Any additional information derived from placental swabs or fresh tissue for bacteriology/mycology are extremely useful in these investigations.
- Consider and minimize health risks to veterinarian and other animals. If there is a potential for the presence of a zoonotic disease, eg tuberculosis, leptospirosis, weighing up of the risks versus the benefits should be undertaken.
- Consider and minimize health risks to owner if returning animal to client after examination. In most cases, the carcass is not returned to the owner following a complete post mortem, though ‘cosmetic post mortems’ can be performed, although they are often more limited in their investigations.
- Consider and minimize health risks associated with formalin or other fixatives (avoid skin contact, eye contact, inhalation of fumes, and ensure correct labeling of containers).
- Additional competence is required if legal issues arise.
- Histopathology is a specialist undertaking.
- A careful and systematic approach, with objective and accurate documentation of findings, plus appropriate sample collection, should enable all veterinarians to undertake a satisfactory post-mortem examination.
- Nurses may be encouraged to assist. An interested and competent nurse should be able to take on the role of post-mortem technician by undertaking much of the dissection, with the veterinarian responsible for documenting and interpreting the findings.
- Sample labeling, writing up of the (dictated) findings and other tasks may be delegated where appropriate.
- Protective clothing .
- Scalpel holder and blades (they blunt quickly, and blades may break or detach and prove hazardous).
- Rat tooth forceps.
- Saw or other instrument for cutting ribs and other bones.
- Cleaning and disinfection equipment.
- As above, plus:
- Honing steel/knife sharpening equipment.
- Good quality fixed-blade, full-tang knife (butcher's knife).
- Scales for whole animal, organ or lesion weights.
- Bone forceps.
- Bone saw.
- Necropsy saw (electrical oscillating blade type).
- Organ trays.
- Camera and flash, with some potential for close-up photography (especially for legal or insurance case). Photographs are useful if you are not practiced at describing lesions and wish to seek advice from a specialist.
- Stainless necropsy table .
- Bunsen burner and searing spatula for microbiological sampling .
- Freezer for samples.
- Plastic bags and ties for cadaver and organ disposal.
- Scalpel blades.
- Wide-mouthed containers and 10% neutral buffered formalin for tissue fixation.
- Specialized containers, depending on histological, biochemical, toxicological and microbiological requirements.
Step 1 -
- Minimize cadaver deterioration by appropriate refrigeration or minimizing delay between death and examination. As a general rule, best results are achieved if an animal can be chilled immediately after death and a post-mortem performed within 1-2 days. If not, the carcass can be frozen. If the carcass is left longer than a day at most without chilling, often limited information can be gathered by necropsy examination.
Step 2 -
- Brief owner that a diagnosis cannot always be established.
Step 3 -
- Brief owner on likely charges.
- Obtain written owner consent for examination and associated tissue retention and supplementary testing.
Step 4 -
- Discuss with owner on disposal route of body (individual cremation with/without return of ashes, or group cremation, or return to owner).
- Ensure that a thorough history has been obtained prior to the examination, and that a list of differential diagnoses has been established.
- Review the aims of the examination you are about to commence. What questions require addressing?
- Obtain specialist advice if unsure.
- Any ante-mortem tests that may prove useful in the context of the post mortem findings, eg collection of blood should be performed prior to euthanasia, if possible.
- This section assumes that a systematic examination of all major organ systems is being undertaken.
- There is no one way to examine an animal post-mortem. Develop a systematic approach that suits you.
- The following method is one example, but could be modified by omission of some steps, or inclusion of greater detail in others.
It is easy to simply get focused on the technical aspects of dissection while omitting to actually search and closely examine the organs for lesions.
Step 1 - External examination
- Weigh the cadaver.
- Examine externally, visually and by palpation, including eye, ears, mouth, perineum.
- Examine for external parasites or check for flea excrement. (A wet, white paper towel is often useful for this.)
- Photograph external lesions or sketch position on an outline diagram if needed.
- Check for any identification such as tattoos or name tags.
- Do not overlook the limbs and feet, remembering to extrude the claws manually for examination.
- Record the findings objectively (record size, color and distribution of lesions).
Step 2 - Skin, subcutis and related structures
- With the cat in dorsal recumbency incise ventral midline from chin to perineum.
- Dissect back the skin laterally to the dorsal midline, and incise through the pectoral and other muscles to allow forelimbs to lie flat on the table .
- Cut to expose and disarticulate coxofemoral joints bilaterally (consider aseptic synovial fluid collection at this point), allowing hindlimbs to lie on the table, further stabilizing the cadaver.
- Locate and examine peripheral nodes at this stage (including retropharyngeal, submandibular, axillary, prescapular and popliteal nodes).
- Examine also the salivary glands now. Incise abdomen in ventral midline, avoiding cuts to underlying viscera.
- Consider aseptic collection and volume measurement of any peritoneal fluids at this point.
- Continue around costal arch to allow dorsal reflection of abdominal wall bilaterally .
- Examine penis and section testes in males, palpate and incise mammary glands in females.
- Record findings.
Step 3 - Body cavities
- Incise abdomen in ventral midline, avoiding cuts to underlying viscera.
- Consider aseptic collection of any peritoneal fluids at this point.
- Continue around costal arch to allow dorsal reflection of abdominal wall bilaterally.
- Examine viscera in situ now, without further dissection .
- Consider aseptic culture from parenchymal organs (liver, kidney, spleen) now, before further contamination is likely.
- Examine integrity of diaphragm from peritoneal aspect , then puncture and allow lungs to collapse away from thoracic wall.
- Examine the gall bladder and gently express to determine if the bile duct is patent.
- Cut along costochondral junction to open thorax, either bilaterally to remove a ventral section including sternum , or, if in lateral recumbency, the uppermost thoracic wall can be removed by a second cut along the ribs close to the vertebrae.
- Consider aseptic pleural fluid sampling and measuring before contamination occurs.
- Examine pleural and peritoneal surfaces, and the abdominal and thoracic viscera in situ, before proceeding .
- Mentally review history and aims of PME at this point.
- Record findings.
Step 4 - Respiratory system (and related structures)
- External nares were examined in step 1.
- To remove cervical and thoracic viscera en bloc, free the tongue ventrally by bilateral incisions along medial aspect of mandibular rami in a ‘V’ shape . You may split the mandibular symphysis for better examination of oral cavity at this point.
- Free tongue, larynx, trachea and esophagus by cutting through hyoid apparatus, and further bilateral cuts and blunt dissection to allow caudal and ventral reflection of trachea, esophagus, tongue and related structures .
- Check salivary glands, and retropharyngeal nodes if you have not done so already.
- Also examine thyroids (and parathyroids) if still with the trachea (if not, find them now before you lose track of them).
- Further cuts at thoracic inlet and along dorsal mediastinum should allow thoracic viscera to be withdrawn ventrally, and removed by cuts through aorta, esophagus and caudal vena cava at the diaphragm .
- Examine the oral cavity and teeth with the cadaver then, on the removed viscera, examine tongue, soft palate (incise on dorsal aspect to examine palatine tonsils), and continue the dorsal incision to open the cervical and thoracic esophagus.
- Now open the larynx and trachea by a dorsal midline incision , continuing into left and right bronchi.
- Examine lungs visually and, more importantly, by palpation. Sections of small areas of firm lungs can be sectioned and added to water to see if they float. If not, these may be consolidated or atelectatic.
- Record findings.
Step 5 - Cardiovascular system
- You will have noted relative heart dimensions and great vessel position etc during in situ examination of thoracic viscera. Jugular and carotid arteries may be examined also at this point, and the major abdominal vessels can be examined while the abdominal viscera are still in situ.
- Now open the thoracic aorta by dorsal midline incision (scissors) from its transected diaphragmatic end.
- Continue toward the heart until the aortic arch. Note aortic outlets for segmental arteries and, in young animals you can check for the aortic opening of the ductus arteriosus using this approach. In older animals, the ductus arteriosus remains can often be detected as a flattened C-shape on the aortic luminal aspect.
- Now examine the pericardium, considering fluid sampling and measuring at this point. Incise pericardium to free the heart, still attached to the lungs.
- Transect heart one third up from the base, allowing assessment of relative thickness of ventricular walls, especially in suspected dilated or hypertrophic cardiomyopathies and examine myocardium.
- Open right ventricle further by cutting (scissors or knife) ventricular free wall close to interventricular septum, up and through the pulmonary valve, into left and right pulmonary arteries .
- Open right atrium to expose right atrioventricular valve, then continue cut into right ventricle, passing between valve cusps. This should leave the right ventricular free wall still attached by a hinge at the dorsal aspect.
- Now open left atrium and examine left AV-valve.
- Open left ventricle by cutting close to the IV septum and up through the aortic valve (you will cut across the previously opened pulmonary artery at this point).
- Record findings.
Step 6 - Alimentary system
- You have already examined oral cavity and cervicothoracic esophagus.
- Transect the colon near the rectum, and by cutting mesentery close to the viscus , remove colon, ileum (and cecum), and jejunum as a unit, cutting once more at the descending duodenum.
- The stomach and intestines may be laid out along their length in a pleated pattern to more easily examined. Consider sampling intestinal contents at this stage. Duodenum, stomach, liver and pancreas can be removed with the diaphragm as a unit , but first locate and examine the adrenals , since they may be damaged during the subsequent dissection.
- Remove duodenum, stomach, liver and pancreas by continuing the mesenteric cuts and cutting around the peripheral margin of the diaphragm.
- Open duodenum, check gall bladder patency by gentle bladder pressure to expel bile into duodenum.
- Open stomach along greater curvature, inspect mucosa and consider sampling stomach contents.
- Examine liver and make multiple deep cuts to check parenchyma. Note that, unlike the dog, the liver of the older cat does not commonly have nodular hyperplasia.
- Open gall bladder.
- Examine pancreas. Nodular hyperplasia of the pancreas is a reasonably common incidental finding in the cat.
- Record findings.
Step 7 - Lymphoreticular system
- The spleen, removed with stomach, or removed with omentum to expose abdominal viscera, is examined visually, by palpation, and multiple incisions.
- Peripheral nodes were examined in section 2 and as part of respective organ system examinations.
- Bone marrow may be examined by opening a femur with bone forceps, or transecting a rib or vertebra during examinations of musculoskeletal system.
- Marrow smears may be made by transecting a rib, then squeezing near cut end with bone forceps, to express marrow onto a slide for smearing.
- Thymus can be examined in rostral ventral mediastinum in young animals.
- Record findings.
Step 8 - Urinary system
- Expose pelvic cavity by cutting from obturator foramen rostrally and caudally on both sides, allowing removal of ventral wall of pelvis.
- Examine kidneys in situ , then dissect kidneys free from surrounding fat, transecting renal vessels, and remove with ureters, bladder and reproductive tract if desired . The lower urinary tract and reproductive tract may not need to be removed in all cases.
- Bisect both kidneys , and make further cuts if needed.
- Note the marked pallor of the normal feline kidney, and the prominent stellate veins . The markedly pale renal cortex, especially of older neutered males, should not be misinterpreted as a pathological change .
- Open ureters if indicated, and open bladder (considering aseptic sample and culture of urine at this point).
- Open urethra.
- Record findings.
Step 9 - Reproductive system
- Mammary glands, penis and testes may have been examined already, if not, do so now.
- Examine ovaries and uterus if present, opening uterus. Opening of the urethra should have allowed examination of penis, vagina and vulva.
- Record findings.
Step 10 - Musculoskeletal system
- Coxofemoral joints have been opened already, and various muscles have been exposed and cut during the course of the examination.
- Open scapulohumeral, carpal, femorotibial and other joints as indicated . Ribs may be examined at this point. Consider history and findings to decide which muscles, bones and joints require closer examination.
- Record findings.
Step 11 - Nervous system
- Peripheral nerves may be examined on opening the axilla during reflection of the forelimbs in step 2 . If indicated peripheral nerves may be exposed, examined and sampled.
- Remove the head by disarticulation at the atlanto-occipital joint.
- Remove the skin and masticatory muscles to expose the dorsal aspect of the skull .
- Remove the calvarial cap with a junior hacksaw or bone cutters by cutting transversely across the skull just caudal to the orbits.
- Continue each cut caudally to join the lateral wall of the foramen magnum at 45 degrees.
- Lever off the calvarial cap , using a chisel if necessary.
- Cut dura mater and tentorium cerebelli prior to attempting brain removal, otherwise these structures will cheesewire through the brain.
- Tap skull on table gently, with nose up, then use scalpel handle to bluntly tease olfactory lobes from the cranial vault .
- Tilt skull so that gravity applies tension on the optic nerves, allowing them to be seen from the rostral aspect and cut by insertion of a scalpel or long fine scissors along ventral aspect of the brain. Further cuts of nerve roots, coupled with gentle easing of the brain from the cranial vault, should allow the brain to be removed intact. The brain is typically fixed whole prior to serial slicing and selection of tissues for histology.
- Submit the whole brain to a histology laboratory for the pathologist to examine and slice, if you are considering histology (or, after fixation, make very careful, parallel, transverse slices of around 5-7 mm thickness with a single stroke from a long sharp knife (avoid sawing action) if you wish to examine the brain yourself).
- The spinal cord may be removed, if indicated, by dissecting away epaxial musculature and performing a dorsal laminectomy. Grasping the dura in rat tooth forceps, and applying very gentle traction, but not bending/creasing the spinal cord, cutting the spinal nerve roots should allow removal of the spinal cord. Most techniques require a degree of practice to gain competence.
- An interesting option, with obvious limitations, is to sample the brain tissue simply by pushing a cylinder with a cutting edge (perhaps a large diameter plastic drinking straw, or similar material) into the brain via the foramen magnum and direct it toward the orbit. Withdrawing the cylinder, with the free end blocked to prevent tissue core remaining behind, is likely to sample several key regions of the brain. Most pathologists would reel in horror at this suggestion and it is really only an emergency procedure, such as might be done under field conditions overseas by inexperienced personnel. This tip from http://www.canids.org/PUBLICAT/AWDACTPL/appdx2.htm#post-mortem.
Step 12 - Endocrine system
- The pituitary gland may be fixed whole, along with adrenals and thyroids/parathyroids. Pancreatic tissue may be examined histologically to evaluate islets.
Step 1 - Tissue fixation
- Handle all tissue carefully (especially gut and CNS) to avoid damage prior to fixation. Tissues should be fixed in ten times their volume of 10% neutral buffered formalin (eyes need special fixatives).
- To aid fixative penetration, thick tissues should carefully be sliced through their partial thickness. Brains and spinal cords should be fixed intact for up to a week or more, after which they will be firm enough to cut cleanly and without damage. The slices can then be fixed to completion.
- Fix representative samples of the lesions (beware necrotic centers, include margins, small lesions may be younger than larger ones).
- Sample all major organs, since many lesions are inapparent grossly.
- Many laboratories offer a special rate for examining a set of tissues from one post-mortem case.
- Submit the tissues you regard as most important, but save fixed tissue from other organs in case they are needed. You can never go back once the carcass is incinerated!
- Consider saving fresh frozen tissue (toxicological or biochemical analyses), or whether tissue for immunostaining, electron microscopy or other procedures is required.
- Conventionally frozen tissues will have marked ice crystal damage if later submitted for histology.
Step 2 - Description and the report
- A systematic objective description is essential, especially if you are submitting tissues elsewhere for histopathology, microbiology or other investigations. This helps the laboratory interpret the findings. Photographs are always useful, especially in legal or insurance work, or where description or interpretation are difficult.
- Describe what you see, measure where possible. Location, distribution, size, shape, color, texture and odor may all be useful. Later, none of these will be evident to the pathologist inspecting the fixed sample. Be careful of over-interpreting where you cannot be sure. It is better to write "The lungs were diffusely dark red and heavy (congestion? pneumonia?), than "The lungs showed pneumonia". Your descriptions and your own opinions are valuable. Make sure your description (objective) is clearly distinguishable from your own interpretation (subjective).
- A useful technique is to have a standard sheet on which to document your findings. This sheet should have sections in which the following data can be added:
- Clinic number.
- Owner details.
- Animal details (species, breed, sex, age, name).
- Date and time of death.
- Date and time of post-mortem examination.
- Differential diagnoses prior to PME.
- Mode of cadaver disposal, owner consent.
- Under this can be space for recording findings in each of the following organ systems:
- External examination, skin and subcutis, body cavities, respiratory system, cardiovascular system, alimentary system (includes liver and pancreas), lymphoreticular system (spleen, lymph nodes, bone marrow), urinary system, genital system, endocrine system, musculoskeletal system, nervous system
- If there are no abnormal findings within a system, it is useful simply to list the organs examined, so that the extent of the examination is clearly documented in the report. Another useful tip is to include an organ checklist on your reporting form, against which you can tick whether an organ has been sampled histologically, microbiologically or frozen. Such checklists act also to ensure no organ has been overlooked during the examination.
Reasons for Treatment Failure
- Not having formulated clear aims for the post-mortem examination.
- Not briefing client as to likely outcomes and costs.
- Not performing a thorough systematic examination.
- Over-interpreting minor lesions, incidental findings or agonal and post-mortem changes.
- Not documenting the findings objectively and thoroughly.
- Failing to adhere to client's request for cadaver disposal.
- Not maintaining efficient communication with all parties, especially if there are potential legal issues.
- Not collecting appropriate tissues for histology (it is simple to collect a sample of most organs routinely, and then allow the pathologist to select from these tissues as indicated from history and findings).
- Marked autolysis due to failure of prompt examination or inadequate refrigeration. Long haired or obese individuals do not cool quickly during refrigeration, and may need to have either the coat wetted down prior to chilling, or perhaps partial skinning to allow rapid cooling.
- Recent references from PubMed and VetMedResource.
- Ribas L M et al (2020) Post-Mortem CT vs Necropsy in Feline Medicine. J Feline Med Surg 22(12), 1206-1213 PubMed.
- Various authors (1986) Necropsy techniques. Vet Clin North Am Food Animal Pract 2 (1), 1-202 PubMed.
- Liu S K (1983) Post mortem examination of the heart. Vet Clin North Am Small Anim Pract 13 (2), 379-94 PubMed.
Other sources of information
- Mcdonough S P & Southard T (2017) Necropsy Guide for Dogs, Cats, and Small Mammals. Ames (Iowa), Wiley Blackwell.
- Ginsberg J R, Alexander K A, Cleaveland S L, Creel S R, Creel N M, Kock N, Malcolm J R, McNutt J W, Mills M G L & Wayne R K.The IUCN/SSC Canid Specialist Group's African Wild Dog Status Survey and Action Plan (1997) Appendix 2 Some techniques for Studying Wild Dogs (online).Available World Wide Web URL: http://www.canids.org/PUBLICAT/AWDACTPL/appdx2.htm#post-mortem (accessed 14 June 2001). (Contains a field technique for examination of wild dogs, from which the tip on sampling the brain via the foramen magnum was obtained.)
- Summers B A Cummings J F, de Lahunta A (1995) Veterinary Neuropathy. Mosby. ISBN 0-8016-6328-8. (Chapter 1 includes a section on CNS examination.)
- Jubb K V F, Kennedy P C, Palmer N (Eds) (1992) The Cardiovascular System. Pathology of Domestic Animals. 4th edn. Vol 3, Ch 1. Academic Press Inc, London, pp 7-8. (Normal cardiac weights for various species, selection of blocks for histology.)
- King J M, Dodd D C, Roth L, Newson M E The Necropsy Book. Charles Louis Davis DVM Foundation Publisher 6245 Formoor Lane, Gurnee, Il 60031 USA.
- Nicholls P K (1993) Post-mortem examination of the dog. (video, 34 minutes - University of Cambridge, UK). (An example of one method for canine necropsy, much of which is directly applicable to the cat.)
- Kelly D F, Lucke V M, Gaskell C J (1982) Notes on pathology for small animal clinicians.Wright, PSG, London. ISBN 00-7336-0657-9. (Sections on necropsy technique, agonal changes, common incidental findings and post-mortem changes.)
- Palmer A C (1976) Introduction to animal neurology. 2nd edn. Blackwell Scientific. (Contains a useful section on removal of the brain and spinal cord from several species.)
- State or National Veterinary Service.
- Forensic or analytical laboratories.
- Pathology Departments of Veterinary Schools.
- Commercial pathology services.