Getting the best from your pathologist. Post-mortems and surgical biopsies. Tips and tricks for vets in practice
Alison Lee (BSc MVB MRCVS DipACVP) and Danilo Wasques (MV MSc)
Trevor Whitbred (BSc BVSc DipECVP MRCVS) will take part in Q&A following the presentation
Post mortem examination (PME) can be a useful service provided by clinicians for the purposes of investigating sudden unexplained death or cases in which a diagnosis was not reached before the animal died/was euthanased. However, forensic/welfare cases or cases in which infectious/zoonotic diseases are suspected are best referred to qualified veterinary pathologists. Little in the way of extra or expensive equipment is required to carry out a PME. Consent from clients should be sought and arrangements made for disposal of the body. To avoid artefacts secondary to autolysis, PME should be carried out ideally within 24 hours of death and freezing of the body should be avoided. The body should be weighed and scanned for a microchip and radiographs may be taken in cases where death due to trauma is suspected. A number of different methods by which PMEs are carried out exist, but the exact technique does not matter so long as all organs are examined systematically. Notes describing (rather than interpreting) lesions should be made and photographs taken. Samples should be taken for histopathology of the liver, lung, kidney and any lesions in all cases. If no lesions are present, additional samples of heart and brain ideally should be taken. Samples of liver, kidney, stomach content, lung, and fat may be frozen for analysis in cases of suspect intoxication.
Surgical biopsies are essential for reaching a precise diagnosis before planning treatment in a living patient. This is especially true for neoplastic conditions, commonly seen in small animals. These can be classified as incisional biopsy (IB), performed with diagnostic intent, and excisional biopsy (EB), which is both diagnostic and potentially curative, and allows for evaluation of surgical margins. Although fine needle aspirates (FNA) are often sufficient to reach a diagnosis, there are some conditions in which a more accurate test is required for clinical decision-making. These include cases in which radical surgery is anticipated (e.g. limb amputation for osteosarcoma, maxillectomy for oral melanoma) or for lesions which are not easily assessed by FNA (e.g. feline alimentary lymphoma). Incisional biopsy is also useful for diagnosing inflammatory conditions which cannot be reliably assessed by FNA (e.g. hepatitis, cholangitis, dermatitis, gastroenteritis…).
Surgical margins of EBs should always be properly identified by the surgeon. If a large specimen (e.g. limb, spleen) cannot be submitted in its entirety, samples of the relevant lesion should be submitted instead, and in this case regional lymph nodes should also be submitted for staging. The surgeon should retain the surgical specimen in formalin until a report is issued in case additional samples are needed.
Regardless of whether a sample from a PME, IB or EM is submitted, it is imperative that all relevant clinical history and differential diagnoses are communicated to the pathologist, as this information is often extremely helpful in forming and eliminating differential diagnoses.
Brooks, J.W., 2016. Postmortem changes in animal carcasses and estimation of the postmortem interval. Veterinary pathology, 53(5), pp.929-940.
Dobromylskyj, M., 2015. How to perform a small animal post mortem in practice. Companion Animal, 20(10), pp.565-571.
King, J.M., Roth-Johnson, L., Dodd, D.C. and Newsom, M.E., 2014. The Necropsy Book: A guide for veterinary students, residents, clinicians, pathologists, and biological researchers. The Internet-First University Press.
Parry, N., 2008. Sudden and unexpected death in small animal patients: Part 1. UK Vet Companion Animal, 13(8), pp.23-30.
Parry, N., 2008. Investigating cases of sudden and unexpected death in small animal patients: Part 1. UK Vet Companion Animal, 13(9), pp.31-37.