Equine papillary ependymoma.

The study discusses the primary outcome of a 17-year-old Arabian gelding that had developed neurological signs and was diagnosed with a rare form of a brain tumor, specifically a papillary ependymoma.

Study Subject and Initial Findings

• The subject of the study was a 17-year-old Arabian gelding displaying progressive neurological signs.
• The horse was found to have a velvety, reddish brain tumor protruding from the ventral midline caudal to the optic chiasma, a crucial part of the brain responsible for vision.

Microscopic Assessment of the Tumor

• Upon further examination under the microscope, the tumor revealed a unique structure – a papillary formation, characterized by a single layer of elongate cells radially oriented around a central fibrovascular core.
• The cells of the tumor held intracytoplasmic globular inclusions, structures within a cell, that were positive for glial fibrillary acidic protein (GFAP), an important protein in the nervous system, and weakly positive for vimentin, a type of protein often associated with cell stability and structure.

Ultrastructural Analysis

• Ultrastructural analysis of these inclusions showed that they were made up of whorling intermediate filaments, key components in cell structure and function.
• Moreover, the neoplastic cells showed features including cytoplasmic interdigitations, extensions that enable close contact between cells, and numerous zona adherens, structures that help cells adhere together.
• These cells often rested on a basal lamina, an extracellular matrix that separates epithelial cells from the underlying connective tissue.

Final Diagnosis

• Based on these complex findings indicating abnormal growth and organization of cells, the tumor was diagnosed as a papillary ependymoma, a rare type of brain tumor commonly found in the lining of the ventricles of the brain.