Pathology presentation dedicated to Drury Reavill.

Session #1000

Abstract

This lecture discusses the procedure of how to properly necropsy exotic companion mammals and highlights the importance of correct documentation and tissue submission to the veterinary diagnostic lab.

Introduction

Necropsies on exotic companion mammals (ECMs) can be difficult for clinicians and are rarely taught in detail in veterinary schools. This is typically due to the lack of cases of these species at these schools and their unique anatomy. Thus, most clinicians are either self-taught or learn from other exotic veterinarians. While difficult cases or cases that might have legal consequences are typically best sent to a boarded veterinary pathologist, most necropsy cases are fine for the clinician to perform. Learning how to perform a complete and thorough necropsy is paramount in improving the clinician’s diagnostic and even surgical skills.

Common Necropsy Mistakes

• Rushing through the necropsy resulting in incomplete examination.
• Failure to adequately document and record findings.
• Failure to take adequate quality photos.
• Failure to obtain tissue samples of both lesion and non-lesion tissues.
• Failure to properly preserve tissues in the correct sized containers.
• Failure to properly label containers and paperwork.
• Misidentifying normal species’ unique anatomy or tissue artifacts for true lesions.

When and How to Send a Full Necropsy to a Pathologist

It is best to send the whole body to a board-certified pathologist for difficult cases and cases that are or might become legal. These types of cases usually include multiple lesions in multiple tissues, sudden death (especially large numbers of deaths in a group), suspected zoonotic disease as the cause of death, anatomic abnormalities, and/or cases where the client might sue (either the vet or another party). It is important to attach a thorough but succinct history of the case to the pathologist; sometimes, it helps to call ahead and talk with the pathologist directly. Indicate how the animal died (natural vs. euthanized).

For small ECMs (for example, mice and rats)—The vet can open up the thoracic and abdominal cavities to take samples for future testing. This is typically for bacteriology, virology, or PCR, and tissues most often collected are small sections (not the whole organ!) of lung, liver, spleen, kidney, and occasionally GI, if indicated. Once these tissue samples are collected aseptically, they should be either sent out for testing or saved in a freezer for future testing. The top of the skull should then be removed to allow visualization of the brain; this will help with fixation. Then the whole body can be placed in a container that is large enough to fill with 10–15 times the volume of the animal in formalin.

Medium to larger ECMS (for example, guinea pigs and rabbits)—For these larger species, it is typically preferred to send out overnight to the lab. You want the body to be wrapped in multiple layers of plastic, black trash bags work great, and the body should be chilled (not frozen). This can be achieved by surrounding the body with ice packs. The diagnostic lab will process the animal from there. If you must keep the animal at the clinic overnight or for a few days, it is best to put the body in a cooler (again, not the freezer!) until you can ship it to the lab.

Necropsy in Jar

Necropsy in jar is what the diagnostic lab calls a case where the referring veterinarian performs the necropsy and sends in a container “jar” of tissue samples. This is cheaper and allows the veterinarian to get experience performing necropsies which can allow them to better understand the anatomy and gross disease presentations they noted clinically. However, this also means that the pathologist is limited to mainly relying on histology to determine the diagnosis. It is imperative that the veterinarian collects the tissues with gross lesions and/or are indicated from clinical signs. For example, if a rabbit has clinical signs indicating a spinal cord lesion, the spinal cord should be collected.

Checklist for Necropsy Set Up

• Necropsy table and/or cutting board.
• Gloves.
• Dissection kit (ruler, small- and medium-sized dissecting scissors [both sharp/sharp and sharp/blunt types], bone cutting rongeur, tissue forceps (both rat tooth and flat types), necropsy knife, scalpel, blunt probe, and rib cutters [shears] for larger species).
• 5 red top tubes or whirlpaks (saved tissues for bacterial/viral/PCR/toxin testing).
• Scale.
• Formalin jar (10% buffered formalin).
• Freeze the remainder of the body after necropsy.

Before Necropsy

• Some mammals have unusual anatomy (for example, marsupials) and researching normal anatomy is highly recommended before necropsy.
• In the grossing notes describe any lesions and record the weight of the animal.
• Wet down hair/fur to decrease the amount of hair/fur from getting onto the tissues.

During Necropsy

• Take photos of the animal’s front, back, open chest/abdominal cavity, and any pathologic lesions.
• Most ECM species can be necropsied in right lateral recumbency, with a few being easiest to necropsy laying on the back in dorsal recumbency (for example, hedgehogs and ferrets).
• With the necropsy knife, cut the skin and top two limbs (typically left limbs) away from the body.
• Make a cut to the peritoneal cavity starting at the midline and following just behind the ribcage up to the spinal column. Then finish the cut by making a V shape and cutting down towards the region of the urinary bladder.
• Then fold the abdominal wall back and visualize the abdominal organs.
• With a scalpel or necropsy knife, puncture the diaphragm and check for negative pressure. Cut the diaphragm from midline to the spinal column.
• Remove the ribs by using rib cutters (shears).
• Once the ribs are removed, take a step back and think about what lesions you are seeing or not seeing.
• Take tissue samples for testing (typically lungs, liver, spleen, kidney, and GI).
• Take histology samples of the skeletal muscle, sciatic nerve, skin, and bone (typically a section of femur).
• Then remove the pluck (trachea, lungs, heart) and take representative samples for histology.
• For abdominal organs, remove the adrenal glands first; this is because once the organs are moved and manipulated, they can be easily lost.
• Then, take out the liver/gallbladder, spleen, and pancreas.
• Remove the entire GI tract but put it to the side and then remove the urogenital tract.
• After histology samples of the other tissues have been taken, go back to the GI tract.
• Make sure to check for lesions along this whole process.
• At this stage, clean the instruments and cutting board and then proceed to remove the head.
• Cut the skin and musculature away from the base of the skull and C1 vertebra. Then move the animal to dorsal recumbency so that the ventral aspect of the vertebrae is facing up. With a necropsy knife, cut the ligaments and spinal cord between the occipital bone and C1 vertebra.
• Once the head is removed, cut the skin at midline and fold back to the base of the ears on both sides.
• Then, use a bone-cutting rongeur to remove the dorsal skull and take out the brain and pituitary gland.
• Then, remove one or both eyes and open the nasal sinuses.

Tissues Collected at Necropsy

• Nasal sinus.
• Eye(s).
• Brain/pituitary.
• Skin/skeletal muscle.
• Bone (usually section of femur).
• Large nerve (usually sciatic nerve).
• Entire pluck for small animals; take small tissue sections for larger animals.
• Tongue, esophagus, stomach (2 tissue sections), small intestine (3 tissue sections), large intestines (2 tissue sections).
• Heart.
• Thyroid/parathyroid.
• Thymus.
• Lungs (at least 2–3 sections if large animal) and section of trachea.
• Liver (2 sections), gallbladder, spleen, and pancreas.
• Lymph nodes.
• Kidneys, adrenals, testes (if present), and urinary bladder.
• Female—ovaries, uterus, and mammary tissue.
• Any lesions—whole lesion or at least 2–3 tissue sections.

Proper Fixation and Sample Size

• Remember, samples should be fixed with ∼10–15 times their volume worth of fixative.
• Thin tissue sections fix best. Aim for ∼0.5 cm in thickness.

After Necropsy

• Clean and disinfect all instruments and workstation.
• Wash hands after all necropsies.
• Not all tissues collected need to be sent to the lab for histopathology. Think about the case and submit the necessary tissues.
• All formalin containers should be clearly labeled.
• Send samples and necessary paperwork to the diagnostic lab as soon as possible.

Disclosure statement: Dr. Biswell is the CEO/Founder of Biosphere Lab.