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Neoplasia affects almost one third of domestic animals at some point in their life. Reports of neoplasia in Australian native animals, while known to occur, are infrequently reported. The following case study describes an interesting case of neoplasia in a greater bilby (Macrotis lagotis).
Sunny was an eight-year-old male greater bilby, who was part of a collection at a wildlife park. He was one half of a successful breeding pair. His keepers brought him into the veterinary clinic after finding him in respiratory distress in his enclosure. Unfortunately, however, Sunny passed away en route to the clinic.
A complete post-mortem examination was performed to determine the cause of death. On post-mortem he was noted to be in good condition, with no signs of trauma or injury noted on external examination. On internal examination, the thoracic cavity was noted to have no abnormalities aside from mild post-mortem change in the lungs. Otherwise, the lungs, heart, greater vessels, pleura and diaphragm all appeared normal. No pleural effusion was noted.
On examination of the abdominal cavity, approximately 50mls of serosanguinous fluid was drained. Diagnostic testing confirmed this fluid was haemorrhagic effusion. The gastrointestinal tract, urinary tract, liver and spleen all appeared morphologically normal upon gross examination.
Bilaterally cranial to the kidneys, two roughly ovoid shaped masses were present in the abdominal cavity, measuring approximately 20mm x 30mm in diameter. These masses had a mottled pink, red and yellow discolouration. On a sagittal cut of one mass, it appeared to consist of multiple layers varying from pink to yellow, with some intermittent sections of gritty white material within the layers. The consistency and appearance of this material was suspected to be calcium deposits, however this was not able to be confirmed.
The rest of the post-mortem examination was unremarkable. The cause of the haemorrhagic effusion was not determined, as no damaged vessels were able to be visualised.
One of the two masses was sent for diagnostic testing. Histopathology determined the mass to be an undifferentiated neoplasm. At the edges of the sample in some sections there was evidence of remnant adrenal gland tissue. The histopathological appearance raised the question of whether these masses were potentially adrenal gland carcinomas, though this was difficult to confirm. However, it was confirmed that the mass was a neuroendocrine-type tumour. Immunohistochemistry was performed but was negative, ruling out most sarcomatous lesions.
The cause of death in Sunny was suspected to be an acute haem-abdomen due to the significant haemorrhagic effusion noted in the abdominal cavity. The cause of haem-abdomen was not able to be determined at post-mortem.
The bilateral suspected neuroendocrine neoplasia masses are likely to be an incidental finding.
Neuroendocrine tumours are found in a wide variety of locations in animals, but are overall a rare occurrence in both people and animals. They can affect many different organs and tissues, and can be functional or non-functional. Examples include insulinomas, gastrinomas, chemodectomas, and carcinomas. Of the 38 cases of neoplasia noted in the Medicine of Australian Mammals diagnosed in bilbies and bandicoots, no neuroendocrine neoplasias were noted.
Given the histopathology results it is difficult to draw a conclusion as to what kind of neoplasia these bilateral tumours could be. Further immunohistochemistry studies were unable to be completed, so the suspicion of bilateral adrenal carcinomas was unable to be confirmed.
As this case appears to be one of the only reported cases of neuroendocrine neoplasias in bilbies and bandicoots, it was deemed essential to report this case due to its unusual presentation and nature. Interestingly, Sunny did not have any ante-mortem clinical signs which can be seen in some active neuroendocrine neoplasias.
This case reflects the importance of performing a full post-mortem in native wildlife species that have died. A complete post-mortem allows one to not only determine the cause of death, but gives one the opportunity to report interesting or unusual findings. While we know much more about the pathophysiology of Australia’s native animals than we did before, there is always the opportunity to learn more.
Dr Jessica Bowers
BSc BVMS Marlin Coast Veterinary Hospital
Dr Jessica Bowers graduated from Murdoch University in 2017. Over the course of her career, she has developed a passion for wildlife and native animal medicine and surgery. Dr Bowers has also developed a passion for anatomic pathology.
She is currently working as a policy officer and volunteering her skills as a wildlife veterinarian at a wildlife shelter in Western Australia.