Category:Necropsy

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Small Animal Necropsy

A necropsy is a post-mortem examination[1] of an animal’s carcass performed to determine the cause and manner of death. It can be requested by the owner, mandated by the state to investigate possible infectious disease outbreaks, or in forensic investigations. The procedures and protocols for conducting a necropsy on small animals may vary within different institutions, therefore, existing protocols must be thoroughly reviewed and the necropsy should be performed in accordance with these guidelines.

Hygiene Requirements and Safety Rules

As pathologists may deal with corpses harbouring zoonotic diseases, safety rules must be strictly followed. Each institution may have its own hygiene requirements that must be adhered to. In general, each case should be treated as potentially infectious, therefore, it is mandatory to wear protective clothing such as overalls, protective footwear, hats, masks, plastic sleeves, aprons, googles and at least two pairs of disposable gloves. Additionally, a change of clothes and shoes specifically designated for the necropsy hall should be worn[1].

During the necropsy, caution is essential when handling sharp instruments – these must never be left on the corpse or placed on the floor. Beware of avoiding contamination of your notes or camera with blood or other bodily fluids, as these might be infectious.

Check the protocols set up by the institution on the disposal of body parts as well as contaminated sharp or dull items. Furthermore, strictly follow the established cleaning protocols, ensuring that all organic material is removed and disposed of in the designated holding area.

Anamnesis and Carcass Registration

All data regarding carcass registration must be recorded in the protocol prior to any examination. Such data includes examination date, examination place, examiners’ information (position, name, workplace), details of any assistants present during the necropsy, the owners’ information as well as the specimen information, such as:

  • Species and breed
  • Identification number (if present) and name of the animal
  • Age
  • Sex
  • Weight
  • Coat colour and any identifying marks (e.g., cowlicks, scars etc.)

After registering this information, both anamnesis vitae and anamnesis morbi must be documented in the protocol. Anamnesis may include the type of husbandry, feeding practices, vaccination history, deworming protocols, previous diseases and their time of the onset, clinical signs, clinical findings, clinical diagnosis (if applicable), treatment type and time (if any) and the date of death or date and method of euthanasia.

External Inspection of the Carcass

  1. The animal should be thoroughly examined for post-mortem changes. Early changes include drying mucous membranes, algor mortis, rigor mortis and the muscle affected, blood clotting, autolysis or post-mortem staining such as livor mortis, haemoglobin imbibition and bile imbibition, along with their respective localization. Late changes may include maceration, mummification, skeletonization, putrefaction (involving pseudomelansis, bloating or saponification) or secondary changes due to insects. Overall, the post-mortem condition of the carcass must be classified as good, moderate or poor.
  2. The carcass should be scaled, scored and measured. Measurements may include the body length from nose to the tip of the tail, the chest circumference behind the scapula, the umbilical circumference and the lengths of forelimbs and hindlimbs. However, these may vary depending on the institutions necropsy protocol.  The Body Condition Score might be on a 1-to-5-point scale or any other scale used by the institution.
  3. The complete body (including hair coat, skin, claws, horns, mammary glands, penis or other external formations) must be examined and special attention must be given to all bodily orifices (oral cavity, nasal cavity, eyes, vagina/glans penis and anus) for secretions, excretions, prolapses or any other abnormalities. Within the oral cavity, note any missing or damaged teeth, as well as changes in the gingiva and tongue[2].

Complete or Partial Skinning

The decision to skin a carcass partial or complete depends on the level of detail required in the necropsy. Full necropsies require complete skinning, while shorter procedures (generally with a focus on a specific body system) may only require a partial skinning.

  1. The first incision should be made in a straight line from the chin, along the neck and sternum, and down to Linea alba towards the reproductive organs (udder or penis). At this point, the reproductive organ should be passed with a bilateral circular cut. The incision is then elongated towards the anus or vulva, which must also be passed with a bilateral circular cut.
  2. The next step involves making circular cuts around the base of the tail and the carpal and tarsal joints of each limb.
  3. The midline incision is then connected to each circular incision at the limbs, creating a T-shape. The skinning can then proceed systematically.
  4. Once skinning is complete, the subcutis should be examined for any abnormalities. Major muscles, such as masseter, neck, scapula, spine and the femoral muscle should be incised bilaterally to check for changes. Additionally, joints and superficial lymph nodes (parotid, mandibular, cervical superficial, inguinal superficial, poplitei, scrotal/mammary) must be assessed.

Carcass Positioning and Organ Removal

  1. Positioning: Small animals and pigs are positioned in dorsal recumbency. The muscles in the subscapular area are cut to free the forelimbs. To free the hindlimbs, the hip is exarticulated and the round ligament of the femoral head is severed. Note that the positioning of the carcass is different for large animals.
  2. Open Abdominal and Pelvic Cavity: The abdominal cavity is incised at the linea alba and extends down to the inguinal region, with bilateral transverse cuts along the last rib. The pelvic cavity is opened bilaterally, close to the acetabulum, using a saw. Any soft tissue can be cut with a scalpel. Document any fluid present in these cavities (amount, colour, transparency, contents etc.).
  3. Abdominal and Pelvic Organ Removal: Remove the spleen and omentum. Make a small incision in the duodenum where the bile duct opens. Gently compress gall bladder and check if bile flows freely from the bile duct to the duodenal loop. Free the stomach and intestines up to pelvic cavity and place the whole gastrointestinal segment between the hind limbs. Remove the adrenal glands. Free the reproductive and urinary tract until the pelvic attachment and place them between the hindlimbs. Remove the gastrointestinal, reproductive and urinary tracts simultaneously. Finally, remove the liver and the renal, lumbar, gastric and iliac lymph nodes.
  4. Open Thoracic Cavity: Cut through the costochondral joints on both sides of the sternum and subsequently remove the sternum. Gently incise the muscles at the neck. Note any fluid present in the cavity (amount, colour, transparency, contents etc.).
  5. Thoracic Organ Removal: Remove the thyroid gland. Free the upper gastrointestinal tract and the respiratory tract from their attachments, then remove both systems together. Remove the heart together with the lungs.
  6. Removal of the Brain and Spinal Cord: To remove the brain, sever head off at the atlanto-occipital joint. Using a circular saw, open the cranium bilaterally from the occipital bone to the frontal bone. With a scalpel, cut any soft tissue, taking care around the meninges. Gently remove the meninges and extract the brain by inverting the head, supporting the brain with the palm. To remove the spinal cord, clear most muscle and soft tissue surrounding the spine. Then, using a saw, cut the vertebral body longitudinally, keeping the saw medial to the spinous process[2].

Organ Evaluation and Examination

Each cavity and organ must be described separately for the following aspects[3][4]:

  • Position: relations and involvement of adjacent structures.
  • Shape: circular, oblong, ovoid, botryoid, reniform, spheroid, irregular, polypoid, wedge-shaped…
  • Size: weight, size, any enlargements…
  • Margins: well-demarcated, indistinct, pedunculated, infiltrative, villous, papillary , serrated…
  • Surface: smooth, bulging, cobblestone, corrugated, crusted, pitted, striated, verrucous, eroded, smooth, granular…
  • Colour: using only basic colour combinations (e.g. light yellow, yellow-brown). Avoid the term “in colour”. Pale structures can be described as “light coloured”. Do not use pathological terms like icteric or anaemic.
  • Consistency: hard, firm, soft, gritty, leathery, spongy, rubbery, resilient (elastic), viscous (thick, coagulated), friable (breaks easily)…
  • Odour or liquid content: quantity and relation to tissue mass percentage.
  • Cut surface


The evaluation must occur in a systematic manner and must examine all body systems specified in the necropsy request[5]:

  1. Cavity Evaluation: Assess organ location (normal or atypical), content (quantity, description), mediastinum/pleura (smoothness, gloss, moisture, transparency), and serous membrane (smoothness, gloss, moisture, transparency).
  2. Musculoskeletal System: Examine joints (surrounding tissue and capsule condition), muscles (development, colour, consistency, cut surface), bones (periosteum colour, smoothness, thickness, connection with bone, and bone tissue colour and density), as well as ligaments and tendons.
  3. Blood Circulation: Evaluate blood vessels (filling, wall elasticity, smoothness, blood quality) and the heart (length, width, LV:RV ratio, septum thickness, ventricular thickness, valves, pericardium, epicardium, myocardium and endocardium).
  4. Airway and Respiratory Organs: Assess the nose, sinus (maxillary and frontal), larynx (longitudinal cut), trachea (longitudinal cut), bronchi (longitudinal cut) and lungs (multiple transverse and longitudinal cuts) for smoothness, moisture, colour, content, consistency and cut surface.
  5. Gastrointestinal Organs: Evaluate the tongue (multiple transverse cuts), pharynx (longitudinal cut), oesophagus (muscle layer condition, mucous membranes, content), stomach (cut at lesser curvature for size, shape, content, wall thickness, serous and mucous membranes), intestines (describe each section), liver (multiple cut and examination of the bile ducts), gall bladder (size, content, wall thickness, mucous membranes) and pancreas (surface, consistency, shape, colour).
  6. Urinary Organs: Examine kidneys (longitudinal cut along the curved margin for evaluation of capsule separation, renal pelvis content, and medulla and cortex condition), bladder (content, wall thickness), ureter and urethra (mucous smoothness, content).
  7. Reproductive Organs: For male animals, evaluate the scrotum, testis, epididymis, vas deferens, accessory glands, spermatic cord, inguinal canal and penis. For female animals, assess mammary glands, ovaries, oviduct, uterus, cervix, vagina and vulva. For young animals, also evaluate the umbilicus (length, colour, tissue depth).
  8. Endocrine System: Assess the thyroid and parathyroid glands (longitudinal cut) and adrenal glands (sagittal cut at the curved margin) for shape, colour, consistency, surface and internal cut surface.
  9. Nervous System: Examine the meninges (dura mater, arachnoid and pia mater), brain (shape, symmetry, consistency, grey and white matter, ventricles), spinal cord (meninges and grey and white matter), and nerves (if necessary).
  10. Lymphopoietic and Myelopoietic Systems: Evaluate the spleen (external description and internal cut surface features of white and red pulp and trabeculae), thymus (in young animals), tonsils (size and crypt content), bone marrow (if necessary, red and yellow), and lymph nodes (external description and internal cut surface features).
  11. Other Examinations: Conducted based on the necessity and availability of the institution and funding. Such examinations may include histology, parasitology, bacteriology and other relevant analyses.

Necropsy Report

The structure of the necropsy report may vary within different institutions or be different based on various requests, therefore, it must be thoroughly reviewed.

  1. General Information: Collected data during the carcass registration and anamnesis; it includes case identification, specimen identification, information about owner, information about examiner, necropsy time and place, as well as anamnesis vitae and anamnesis morbi.  
  2. Gross Changes: Include detailed descriptions of all findings (position, shape, size, weight, margin, surface, colour, consistency, cut surface, contents). Describe also organs without any changes.
  3. Microscopical Changes or other Examinations and their Results
  4. Morphological Diagnoses: A morphologic diagnosis[3] is a short summary of key aspects of the lesion based on gross and microscopic examination. It includes duration, severity, distribution, exudate (if present), type of lesion, and organ affected. List all organ and tissue changes in order of severity, starting with the most severe changes first and any agonal changes and incidental findings last.
    • Severity: minimal, mild, moderate, severe…
    • Duration: peracute, acute, subacute, chronic, chronic-active…
    • Distribution: focal, multifocal, diffuse, unilateral, bilateral, cranioventral…
    • Type of Lesion/Exudate: purulent, fibrinous, necrotizing, granulatomous…
    • Organ
    • Example: Moderate, acute, cranioventral, purulent bronchopneumonia.
  5. Interpretation: Summarise the main changes, their possible causes, pathogenesis and main differential diagnoses. Start with the primary process, followed by secondary changes. Mention incidental changes, agonal changes and artefacts of euthanasia last. If necessary, suggest extra investigations necessary for diagnosis verification. As the interpretation is written for the owner or the veterinarian, it should be understandable.
  6. Case Summary: A single sentence about cause of death. Avoid writing “death because of euthanasia”. If the cause of death is unclear, state this in the summary.
  7. Date and Signature
  1. Jump up to: 1.0 1.1 Zachary J. F. (2021). Pathological basis of veterinary disease. 7th edition. USA: Elsevier. eBook ISBN: 9780323713146
  2. Jump up to: 2.0 2.1 King J.M. (2013). The Necropsy Book. England: Independent Publisher. ISBN: 1467582123
  3. Jump up to: 3.0 3.1 VPM 152 (2006). Introduction to Pathology: https://www.animalnexus.com.pk/uploads/documents/Pathology.pdf
  4. Describing Pathological Findings: https://www.carrsconsulting.com/thepig/basicvet/clinicalpdf/post_mortem%20_findings_description.pdf
  5. Maxie G. (2015). Jubb, Kennedy & Palmer's Pathology of Domestic Animals: Volume 3. 6th edition. Edinburgh: Elsevier Saunders. eBook ISBN: 9780702068317

Subcategories

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