Neuroepithelial tumor of the optic nerve in a horse.

The research studied a rare case where a horse developed a neuroepithelial tumor in its optic nerve, leading to severe exophthalmos (protrusion of the eye). The growth of the tumor eventually resulted in the compression of the brain stem, causing significant neurological abnormalities and ultimately necessitating euthanasia.

Presenting symptoms and initial intervention

• The nine-year-old horse showed severe signs of exophthalmos in its right eye. Exophthalmos is a condition where one or both eyes bulge out of their sockets, typically caused by an underlying disease or disorder such as thyroid issues or, as in this case, tumors.
• The horse also possessed a large mass in the vitreal cavity, the clear gel that fills the space between the lens and the retina of the eyeball.
• Due to the severity of the symptoms, the affected eye (globe) was enucleated or surgically removed.

Progression of the disease and final outcome

• Despite the removal of the affected eye, the tumor spread into the horse’s calvarium or skull.
• This growth led to the compression of the brain stem, a structure that connects the brain to the spinal cord and plays important roles in motor control, the relay of sensory information, and control of basic bodily functions such as heart rate, breathing, and consciousness.
• The brain stem compression resulted in significant neurological signs, which likely included impaired movement and organ function, altered consciousness, or other neurological abnormalities. As a result, the horse was ultimately euthanized.

Tumor examination and conclusion

• Following euthanasia, the tumor tissue was examined using light and electron microscopy, techniques which allow for detailed visualization of the biological material.
• This analysis revealed that the tumor comprised primitive neuroepithelium, a kind of stem cell found in the nervous system. The classification of tumors as ‘primitive neuroepithelium’ typically denotes an aggressive neoplasm, often found in the brains of children.
• Thus, this study describes a unique case of neuroepithelial tumor in the optic nerve of a horse, and the various complications that arose from its aggressive spread and subsequent interference with crucial neurological structures.