This lesson reviews necropsy technique and related topics.
Read Chapter 5 pp. 165-183 in Clincial Textbook for
Veterinary Technicians 6th edition by McCurnin and Bassert
It is helpful to review anatomy and anatomical
Optional: And if you have it you could also read chapter 10 pp 421-451 in Laboratory Procedures for Veterinary
Technicians 4th edition (by Hendrix)
There is a writing assignment at the end of the lesson. Please turn in
your answers by email.
Know indications for necropsy
Understand basic necropsy protocol
Be able to assist in specimen collection, processing, and submission
Know special procedures for rabies suspects
Be aware of necropsy procedures for small animals, horses, ruminants,
focal, multifocal, diffuse
Necropsy is the postmortem evaluation of an animal. A thorough
examination of a dead body involves the dissection and study of all
the body systems. The term used in human medicine for the same
procedure is autopsy. We often use the term autopsy with clients when
we really mean necropsy, because autopsy is a familiar term to most
people and does not require much explanation.
The purpose of necorpsy is usually to determine a
cause of death. However, in research studeis necropsy is also used
for data collection. Also, when there are large populations of
animals to manage, an animal or animals may be chosen for necropsy
procedure as a means to monitor the incidence or cause of disease
within the group from which they came. This sacrificial procedure is
a technique used in disease surveillance for research such as lab
animal colonies, or commercial operations such as that for the
Necropsy is an important diagnostic technique that is often performed
by veterinarians. Usually the role of the veterinary technician is to
sterilize and set up instruments, assist in the necropsy procedure,
record findings, and to process specimens. However, in some venues,
the veterinary technician is responsible for actually performing the
necropsy, or at least initiating the dissection. In order to be
proficient at necropsy, you must be familiar with normal anatomy and
use a standard technique in which the body systems are examined in a
sequence so that nothing is overlooked. There is no absolute right or
wrong way, just as long as it is standardized, methodical, and
systematic. There are many techniques and order of
operations used so that the necropsy technique will vary depending
upon the prosector's training and preferences as well as the type of
subject species. The body is evaluated by gross
examination and microscopic examination.
Before the necropsy
Before the necropsy, a complete signalment and history should be
acquired. The nature of the case discussed to ensure that all
supplies needed are available because the
history helps guide what tests may be needed. The history should include the date and
time of death. An
important history fact to have is if the animal bit anyone in the
previous 10 days before death. If yes, then the brain must be tested
for rabies. Make sure there is written permission to perform the
The instruments used in necropsy are somewhat different than you might
be used to seeing used for surgery. The instruments are heavier and
less delicate. For example, in necropsy a knife is used for
dissection, whereas in surgery a scalpel would be used to cut tissue.
There are also some instruments specifically used for necropsy such as
special shears used to cut bone, such as ribs or vertebrae. A basic
necropsy instrument pack includes knives, scalpel with handles,
scissors, forceps, saws, and shears. Gauze and paper towels should be
available for blotting tissue and fluids.
All work surfaces should be cleaned and disinfected.
The instruments for dissection should be sharp to lessen operator
fatigue and to decrease potential damage to any specimens that may be
collected. Dull instruments hinder the necropsy procedure and could
damage any tissue specimens, perhaps affecting the histopathology
results. The instruments should also be disinfected before cleaning,
so that you don’t splash infectious material around while cleaning the
instruments. Then the instruments are cleaned and sterilized after
use, so that contamination of any specimens from another case does not
occur when they are used again. It is ideal to use disposable
The prosector and any assistants should wear personal protective
equipment such as proper attire (gowns, aprons, shoe covers), eye
protection (goggles), mask, and gloves. All personnel working in
necropsy should have a current rabies vaccination status.
When collecting specimens, the containers chosen should be of
non-breakable material, such as some kind of plastic material.
The animal first is externally examined for any lesions, and general
condition or body scoring is assessed. Small animals may be placed on
their back or left side. All other animals are placed on their left
side, except the horse, which is often placed on the right side because of
the positioning of the digestive tract organs. A ventral midline
incision is made from the lips to the pelvis and the internal organs
are exposed. Before the thorax is entered, some prosectors puncture
the diaphragm with a blade from the abdominal side, and its movement
is observed. If air rushes into the thorax to equalize pressures
through the incision, the diaphragm will move slightly, and this means
that the pleural space was intact and maintained negative pressure
during life. Before any organs are handled or removed, the prosector
observes the position and condition of the organs as they were found,
or “in situ”. Any specimens for culture are taken aseptically before
the organs are disturbed. Then the various organs systems are
dissected out and moved onto trays for closer inspection and
processing. The organs are examined grossly for any obvious lesions
and tissue samples of each organ are submitted for histopathology.
First the tongue, organs of the neck (esophagus, trachea, thyroid),
and thoracic organs (lungs and heart) are removed; this dissection
grouping is sometimes referred to as the “pluck”. The other organ
systems grouped for separate removal and examination are the digestive
tracts and urogenital tracts. The nervous system is studied by removal
of the eye, brain, spinal cord, and a peripheral nerve section
(usually the sciatic), and also cerebrospinal fluid may be collected.
A section of bone and muscle may be collected to assess the
musculoskeletal system. Joints may be dissected and joint fluid
collected for study. A bone marrow sample is harvested to evaluate the
hematopoietic system. Lymph nodes are collected to check the lymphatic
system. All endocrine glands are collected to study the entire
endocrine system. Because the endocrine glands are dispersed
throughout the body, and are attached to other organs in various body
systems, they are collected as they are encountered. There is so much
that needs to be collected, an organ could get overlooked, so it is
helpful to use a standard necropsy form to keep track of what needs to
A standard necropsy form should be used for keeping a complete record
of the necropsy. Gross findings should be recorded as they are
dictated during the necropsy. There will be descriptions of the size,
shape, color, texture, consistency and odor of the tissues regardless
if the organ is normal or abnormal. All comments should be recorded.
The assessment may be that the organ is normal, has postmortem
changes, or is abnormal. Postmortem changes alter the normal
appearance of an organ making it more challenging to recognize
abnormalities. Even if the assessment is that an organ is normal, most
veterinarians are more comfortable stating in the record that the
organ “appears normal” or that there are “no
visible lesions” ("NVL"). It is possible for an organ to
appear grossly normal but to exhibit abnormal histopathology.
Therefore, samples for histopathology are routinely taken of all
organs, whether they appear abnormal or normal.
Sometimes the necropsy is also documented with photography. Properly
cataloging the photographs to match up with the case written records
is a very important legal and clerical duty.
Ultimately, the gross findings will give a tentative diagnosis, or a
list of differential diagnoses, which then will be ruled out or in
depending upon the results of any laboratory tests on the specimens
collected. A list of the organs that are of clinical importance to the
diagnosis is compiled, regardless if the organs were grossly abnormal
or normal. The specimens collected and tests requested should also be
recorded on the necropsy report. Copies of the necropsy report should
be placed in the animal record and should also accompany the specimens
to the lab. Once all the results are compiled and a final diagnosis is
made, the completed report is sent to the veterinarian requesting the
As the organs are examined, representative sections are taken and
placed into 10% formalin, even if no lesions are seen. If lesions are
found, sections should be taken that include both normal and abnormal
tissue so that the pathologist has the two regions to compare. The
sections should be no more than 1 cm thick, and the formalin volume to
tissue volume should be 10 to 1. Impression smears of tissue sections
can be performed for cytology before the tissue is placed in formalin.
However, remember that formalin vapors will affect the staining of
cytology preparations, making them more basophilic. So if you are
preparing cytology slides, do this away from the preparation area
Specimens for virus or bacteria culture should be taken with the same
care and aseptic technique as with a live patient.
Ideally specimens for culture should be collected before dissection.
specimens should be protected from contamination with flora, which
sometimes is difficult to avoid in a necropsy since they are often
handled before the culture is taken. If the tissues to be cultured
have already been handled, then a quick way to sterilize the tissue
surface is to heat a spatula type instrument and sear the surface of
the tissue, effectively sterilizing the surface and
contaminants. Then the tissue beneath the seared
surface can be excised with
sterile instruments and submitted for culture. Even with these precautions, contaminant growth
is likely because of postmortem changes. After death, the body starts
to break down in an enzymatic process called autolysis, and bacteria
from the intestinal tract migrate to other organs. So the bacteria
present in a necropsy sample may not be a pathogen, but normal flora
instead that has migrated and started the decomposition process.
If serum is needed, it often can be found in the heart chambers. Fluid
from the anterior or posterior chambers of the eye may also be
collected to test for urea and electrolytes. Effusions from the
pleural or peritoneal cavity, cerebrospinal fluid, synovial fluid are
also collected. Depending on the specimen, small amounts of fluids are
collected into red top or EDTA tubes. Other fluids, such as urine or
ingesta, are collected into jars. Urine should be collected via
needle aspiration. Toxicology specimens typically require serum,
ingesta, and urine.
If larval tapeworms are found, extreme caution must be taken, since
many tapeworms are zoonotic. If adult parasites are found, they should
be preserved in 70% ethanol or formalin. Some internal parasites, such
as flukes, will curl up when placed in formalin which will hinder
proper identification. For many parasites, it is better to place them
in a moist petri dish in the refrigerator for a few hours where the
cold will cause them to relax and immobilize. Then they can be placed
in preservative and their anatomic shape will be preserved. If feces
is to be collected for parasite testing, it can be placed into
antibody testing usually requires that the
specimen be preserved in Michel’s media, and not formalin. Some
immunochemistry techniques can use fixed tissue, but conferring with
the lab before the necropsy will help you plan what you need in the
way of specimen preparation for immunologic testing.
If an animal had neurologic signs before
death, encephalitis due to rabies is always a concern. Or if the
animal bit anyone within 10 days before death, it is required that the
brain be tested for rabies. Direct fluorescent antibody (DFA) testing
is the standard and most reliable test for postmortem diagnosis of
rabies in animals. Fresh brain is needed for DFA testing. Other tests
are available that can use frozen or fixed specimens, but you will
need to check with the lab in order to give them the specimen they
want for the test they will perform.
Generally, the entire body of small animals such as bats can be
submitted for rabies testing. The head and a small portion of the
upper neck are submitted from larger animals such as dogs or cats. But
you should always check with the lab first to see what kind of
specimen they will accept.
Remember rabies is a zoonosis. When working with a rabies suspect,
protective equipment is a must. It is rare, but rabies virus can be
transmitted through mucosal membranes, and not just through a wound or
a bite. Therefore, you should wear protective garments, goggles, mask,
shoe covers, and gloves, and follow strict universal precautions when
handling tissues from rabies suspects. Never advise a client to
prepare and submit a rabies suspect specimen by themselves.
Rabies testing in most jurisdictions is handled through the local
health department. However, your regional animal health laboratory can
be helpful in matters concerning potential rabies cases. The local animal
control departments should be contacted as well
for assistance in handling
situations involving rabies cases. Persons exposed to rabies suspects
should contact their physician for treatment and advice.
Many laboratories utilize a courier service for the timely shipment of
specimens. If specimens are to be shipped, they must be properly
packaged in leak-proof containers so that package handlers or the
public are not exposed to any chemicals or infectious agents. Plastic
non-breakable containers should be used as a safety precaution. There
are strict regulations regarding the shipment of clinical diagnostic
A diagnostic specimen is defined as "any human or animal material
secreta, blood and its components, tissue, and tissue fluids being
transported for diagnostic or investigational purposes, but excluding
live infected humans or animals." Specimens treated with formalin generally
do not contain infectious organisms and are usually exempt from
regulations for infectious material. However, formalin specimens must
be properly packaged in leak-proof containers and absorbent padding.
Diagnostic specimens that are subject to special regulations are
listed on the Hazardous Material Tables of Title 49 CFR. For more
information you can start by going to
Many laboratories will provide the containers, proper packaging
materials, and protocol information for the proper packaging and
transport of specimens to their lab.
There are local ordinances regarding the acceptable disposal of animal
cadavers. Even if burial is permitted, the body must be buried deeply
enough or in such a way that the remains cannot be dug up by wildlife
or roaming pets. There have been several instances in which animals
were poisoned by ingesting the remains of animals that had been
euthanized. The euthanasia solution stays in a carcass and will be
pharmacologically active for some time.
Websites of interest
Necropsy collection techniques (caution: very graphic)
Virtual Necropsy of the mouse:
Sea turtle necropsy
Pathology website: Press the continue button and go into the course
index. Then within the course, you will find images of pathology
specimens with the corresponding descriptive medical term.
Lesson 3 Writing assignment
- Name at least 3 reasons for doing a necropsy.
- List 5 safety procedures that should be
followed when performing a necropsy.
- A ruminant should be examined in left or right
- What is a cosmetic necropsy?
- What is a sacrificial procedure?
- How is the patency of the bile duct checked in
those animals with a gall bladder?
- How soon after death should fish be necropsied?
- T or F It is best to freeze cadavers if you
can’t get to doing the necropsy right away.
- T or F A pet spider lying on its back is dead
so you should instruct the client to put the little body into some
alcohol to preserve it for necropsy.
- What can you do to collect a tissue specimen
for bacterial culture if the tissue surface
has already been handled and contaminated?
- What is the recommended ratio of tissue to
- What is the best specimen for rabies testing
using direct immunofluorescence?
- What is the “pluck”?
- What is the purpose of incising the diaphragm
before opening the thoracic cavity?
- What procedure should be followed to preserve
adult internal parasites?
- What percent of formalin is
routinely used to fix tissues? Name one exception
- List at least 2 precautions
when handling formalin or other fixatives.
- List the criteria by which
lesions should be described.
- what is menat by
morphologic diagnosis- give an example.
- Name at least 3 specimens
used for toxicology testing.
- What precautions are taken
with bird necropsies?