Histopathological examination of the pancreas of the koala (Phascolarctos cinereus)
Higgins, DP & Canfield, PJ 2009, Journal of Comparative Pathology, vol. 140, no. 1, pp. 217-224.
Autolysis of pancreatic tissue from koalas was previously thought to make these samples unsuitable for histopathological examination; however, this study demonstrates that many abnormalities of the pancreas can be detected using established criteria for the stages of autolysis up to 72 hours post mortem.
The purposes of this study were firstly to determine the extent to which autolysis hindered the suitability of pancreatic specimens from koalas for histopathological examination, and secondly to use these findings to describe retrospectively the pancreatic abnormalities observed during necropsies of wild koalas. Several existing koala necropsy records containing histological, clinical and pathological details were gathered. These necropsies had been performed 2, 24, 48 or 72 hours after death. For comparison, samples of normal pancreata were analysed for histological signs of autolysis at the same time intervals post mortem. The authors reported the autolytic changes occurring in these normal tissues up to 72 hours post mortem to provide controls for the analysis and description of reported abnormalities in the necropsy records. Using these control criteria, the following pancreatic abnormalities were retrospectively detected: exocrine pancreatic atrophy and fibrosis, pancreatic inflammation and necrosis, lymphosarcoma, pancreatic ductal adenocarcinoma, cryptococcoma, heterotopic pancreatic tissue, and miscellaneous lesions. The detection of these conditions suggests that abnormalities that are characterised by cellular infiltrates or structural connective tissue changes are able to be detected even up to 72 hours after death, despite the effects of autolysis.
Despite the number of diseases affecting koalas reported in the literature, only one was a pancreatic disease; namely, diabetes mellitus. Swiftly after death, autolysis occurs in the pancreas. Autolysis, meaning ‘self-digestion’, is the destruction of a cell via its own enzymes, usually in injured or dying tissue. Because of this rapid autolysis, post mortem analyses of koalas carried out between 24 and 72 hours after death may have neglected to report pancreatic abnormalities as samples were thought to be unsuitable for histological examination. Thus, the definition of criteria for stages of autolysis by the authors of this study allowed for pathological changes to be reliably detected.
The pancreatic abnormalities retrospectively described from necropsy records in this study may be the first reported for the koala, or indeed for any marsupial. This is a significant development in the fields of veterinary and comparative pathology.
Summarised by Joanna Horsfall
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