Intracranial epidermoid cyst in a horse.

The research paper discusses a case of an intracranial epidermoid cyst in a 12-year-old horse that presented with neurological disturbances, apathy, and fever. The large cyst, located in the brain, caused significant displacement and compression of neighboring brain structures and displayed signs that suggested a potential transition to cancer.

Background

• Intracranial epidermoid cysts are benign, slow-growing tumors originating from misplaced ectodermal tissue.
• Although these cysts are uncommon, they can become a significant health issue in horses if they grow large and compress adjacent brain structures.
• In this research, a 12-year-old gelding Haflinger horse was found to have such a cyst, diagnosed based on its symptoms of neurological disturbance, apathy, and fever.

Details and Findings of the Cyst

• The cyst measured a considerable 9 x 8 x 5 cm and was located in the region of the tentorium cerebelli, an important structure that separates the cerebellum from the inferior portion of the occipital lobes.
• Due to its size and location, it displaced the cerebral hemispheres anteriorly (forward), and compressed the cerebellum and brainstem underneath, leading to neurological disturbances.
• The cyst itself was lined by keratinizing, stratified squamous epithelium or the keratin-producing cells typically found in the outer layer of the skin and contained keratin scales, debris, focal haemorrhages, and degenerating inflammatory cells.

Morphological assessment and cancerous potential

• The cyst was enveloped by a vascularized fibrous capsule that was firmly affixed to the dura mater, one of the three meninges or membranes covering the brain and spinal cord.
• This capsule exhibited multifocal haemorrhages and moderate lymphohistiocytic infiltrations, a type of immune response usually seen in chronic inflammation or infectious disease.
• Of particular concern was the disruption in certain areas of the basement membrane of the cyst’s epithelium.
• This, along with the detection of isolated or clustered cytokeratin-positive (a type of protein indicative of epithelial cells) cells in the fibrous capsule, suggests a potential transition of the benign cyst to a malignant form or cancer.
• This finding indicates the potential for epidermoid cysts, typically considered benign, to undergo malignant transformation, emphasizing the need for careful monitoring and early intervention in such cases.