The Significance of A Necropsy
Barry Rickman, VMD, PhD, DACVP
Barry Rickman, VMD, PhD, DACVP
A necropsy is postmortem examination, which is defined as a thorough, orderly dissection of a deceased pet or animal. At the time of an animal’s death, especially a pet, an owner often does not want to consider a necropsy. This is definitely understandable however there are times that a necropsy is worth considering and this article explains the importance of a necropsy.
The most common reason to perform a necropsy is to determine the cause and manner of death. In some cases, we might already know the disease that is contributing to an animal’s death, but a necropsy can reveal additional information regarding the disease process, the extent of disease, as well as the presence of other underlying conditions. Often veterinarians might want to perform a necropsy to learn and understand how treatment (i.e. surgery, radiation, and chemotherapy for cancer) played a role in the disease course. In some cases animals do not respond to treatment and only the necropsy can explain why. In some cases the necropsy can explain a completely different disease process occurring, or it might reveal other contributing factors to the illness or death of the animal. Other reasons for performing a necropsy include medicolegal cases (forensic necropsy), public health concerns, new and emerging diseases, herd health, shelter health, zoo health, breeding animals and genetics, insurance and/or malpractice, and anesthetic death. It can also provide closure for the animal owner and family.
Determining the cause of death without a complete necropsy provides the animal owner only with an educated guess to why the animal died in many cases. A multitude of diseases leading to death can manifest with similar clinical signs, and a veterinarian might rule out only the most common causes of death, without considering less common disease processes, that if found, might have important implications. For example, a seizing middle-aged dog might be due to epilepsy, a brain tumor, trauma, emboli, toxins, diabetes or infection (such as bacterial infection or viruses such as distemper or rabies), to name a few. If the dog died from the seizure without previously being examined in the clinic, only the clinician’s best educated guess would help with a presumptive diagnosis. If that dog was exposed to a certain toxin that caused the seizures and it was not suspected or diagnosed, then there might be a risk to other pets or wildlife in the vicinity.
Another significant example is with West Nile Virus, a recently emergent viral disease transmitted by mosquitos that was not present in the United States 20 years ago. It was only diagnosed by a veterinary pathologist that was aware of a die off of birds in the NYC area, and linking it with critically neurologically ill people in NYC. It was not on the radar of public health officials at the time. Since then, it has become a public health concern for people across the country, as well as for animals - ranging from horses to wildlife.
One necropsy review discusses that although new technological tools have diminished the differences between clinical diagnosis of disease and necropsy findings, major diagnostic discrepancies were found in 14 – 39% of cases (Gutierrez 2009). In another study in human hospitals, it cites that at least 1/3 of death certificates to be incorrect and 50% of autopsies produce findings unsuspected before death (Roulson 2005). This article also states that over 20% of clinically unexpected autopsy findings, including 5% of major findings, can be correctly diagnosed only by histological examination. Another goal of the necropsy is to understand the disease process and mechanism in order to improve the quality of patient care.
A complete necropsy consists of a few components. A thorough history and diagnostic tests ( i.e. bloodwork, radiographs) can aid the pathologist in evaluating the cause of death. In some cases sudden death occurs and there are no diagnostic tests involved - this alone is an important piece of the history. A gross necropsy is a systemic, complete examination of the deceased animal, both externally and internally, with the naked eye. Every tissue and organ is grossly evaluated. Tissues and organs are surgically sampled in order to further examine microscopically. Additional testing for microbiology, parasitology, toxicology, and genetic testing are sampled and performed when needed. A formal report is then written with photodocumentation.
There are a small percentage of cases where necropsy does not reveal the cause of death grossly or histologically. These can include idiosyncratic drug reaction, metabolic/electrolyte disturbances and abnormalities, electrical instability related to neurohumoral and central nervous system influences, electrophysiologic abnormalities, and certain toxin exposures.
In summary, the animal necropsy and histologic examination are the gold standard to accurately determine the manner and cause of death and to correlate the accuracy of clinical diagnosis and diagnostic tests. Improved accuracy of new diagnostic methods could be achieved through closer collaboration between veterinarians, radiologists, and clinical and anatomic pathologists (Gutierrez 2009).
Ermenc B. Comparison of the clinical and postmortem diagnoses of the causes of death. Forensic Sci Int. 2000 Nov 13;114(2):117-9.
Gutierrez PS, de Brito T, Sampaio Lopes MB, Ferreira Alves VA. The value of necropsy in quality control of medical diagnosis – the gold standard for years to come. Clinics 2009;64(3):161-2
Roulson J, Benbow EW, Hasleton PS. Discrepancies between clinical and autopsy diagnosis and the value of post mortem histology; a meta-analysis and review. Histopathology 2005 Dec;47(6):551-9.
Thomas HS. A necropsy: when is it important? California Thoroughbred 2006 Nov; 87.