Multiple glucagon-producing pancreatic neuroendocrine tumors in a horse (Equus caballus).

This research article reports the first known occurrence of several glucagon-producing pancreatic neuroendocrine tumors in a horse. The findings were incidental during a postmortem exam following the euthanization of the animal due to a severe local infection after tooth extraction.

Overview of Case

• The horse in the study was euthanized because of severe local infection, which occurred after a tooth extraction. During the postmortem examination of the horse, multiple white nodules, with a diameter of up to 4 cm, were discovered in the pancreas.

Histologic and Electron Microscopy Observations

• These nodules had signs of neuroendocrine neoplasms based on histological assessment. This means that the nodules were tumors formed from the cells in the pancreas that have neuron-like characteristics and produce hormones, particularly glucagon.
• Through immunoreactivity testing, the neoplasms tested positive for key markers such as glucagon, synaptophysin, chromogranin A, and neuron-specific enolase, supporting their identification as neuroendocrine tumors.
• Electron microscopy revealed numerous electron-dense granules, similar to those found in normal pancreatic alpha cells, in the neoplastic cells. Alpha cells are the ones responsible for producing glucagon in the pancreas.

Additional Findings

• Beyond the pancreas, the left adrenal gland of the horse showed multiple hyperplastic foci and adenomas in the medulla. These were identified as pheochromocytomas, a type of tumor that develops from the adrenal glands’ chromaffin cells.

Conclusions

• The combination of morphologic appearance and immunohistochemical staining patterns led to the diagnosis of the nodules as multiple glucagon-producing neuroendocrine tumors.
• The unique aspect of this case is that such tumors are quite rare in domestic animals, making this supposed to be the first report of such occurrence in a horse. This finding could be crucial in expanding our knowledge and research on neuroendocrine tumors in domestic animals, particularly horses.