Clinical behavior of intraocular teratoid medulloepithelioma in two-related Quarter Horses.

The research article investigates the occurrence and behaviour of a type of eye tumour – intraocular teratoid medulloepithelioma – in two related horses. The researchers present detailed clinical accounts and histopathological readings of the tumours in both horses, and offer recommendations for future procedures when this type of tumour is diagnosed.

Clinical Observation of the Horses

In this research, two related Quarter Horses with similar intraocular masses were studied:

• The first horse, a gelding, was three years old. It had a cyst-like mass in the anterior chamber of the eye and was diagnosed with glaucoma. The horse underwent a surgical procedure called enucleation to remove the eye.
• However, fifteen months later, the gelding presented swelling of the previously removed eye orbit, local lymph nodes and deformation of the skull. These symptoms were confirmed to be neuroectodermal neoplastic cells – i.e., cancerous nerve cells – indicating that the tumour had metastasized.
• The other horse, a mare aged nine (a full sibling to the gelding) also had an infiltrative mass in the eye, spread across the iris, ciliary body and into the anterior, posterior, and vitreal chambers. She had uveitis (inflammation of the middle layer of the eye) but secondary glaucoma was not present. She too underwent enucleation and was diagnosed with teratoid medulloepithelioma.

Pathological Examinations

The researchers conducted histopathologic examinations in both horses:

• In the gelding, the initial examination after the eye removal surgery revealed a teratoid medulloepithelioma – a rare and often malignant tumour that arises from the primitive medullary epithelium. However, the treatment was initially believed to have successfully removed the entire tumour.
• Additional examinations were conducted when the gelding returned showing symptoms of metastasis, confirming the return and spread of the neuroectodermal neoplastic cells.
• The mare’s post-surgical examination also revealed a teratoid medulloepithelioma but, unlike her sibling, she has shown no signs of recurrence two years after the surgery.

Recommendations for Future Cases

The researchers gave several recommendations relating to cases with teratoid medulloepithelioma:

• Affected animals should be staged — a process to determine if or how far the cancer has spread — since metastasis is a possibility.
• Full siblings of affected horses should be kept under surveillance due to the possibility of genetic predisposition, until more detailed information on the tumour’s etiology (causes) are discovered.