Intraosseous epidermoid cyst in a horse.

This research article presents a unique case of an intraosseous epidermoid cyst in a 21-year-old female American Saddle Horse, detailing the diagnosis, treatment, and successful recovery post-surgery.

Background

• The researchers examined a 21-year-old female American Saddle Horse that had a significant swelling on the ventral aspect (lower side) of the right hemimandible (half of the lower jaw).
• The horse also showed radiographic evidence of a bone cyst, signaling a potential health problem to be investigated.

Surgical Exploration and Microscopic Examination

• The surgeons performed an exploration of the cyst cavity, revealing mucinous (mucus-like) fluid and sheets of keratin (a type of protein usually found in skin, hair and nails).
• Upon microscopic examination, the cyst was found to be lined by well-differentiated squamous epithelium (the thin layer of cells lining cavities and channels in the body, such as the esophagus and blood vessels) which displayed varying levels of hyperkeratosis (thickening of the outer layer of the skin) and parakeratosis (abnormality in the cornification process of the skin).

Histological Features and Diagnosis

• The stromal (connective tissue) component ranged from scarce areas where the epithelium was closely adhered to the bone to wider regions of denser connective tissue housing fragments of keratin surrounded by foreign-body giant cells (immune response cells that form when several macrophages fuse together).
• The histologic features confirmed the diagnosis of an intraosseous epidermoid cyst, a rare type of cyst formed from the keratocyte cells in the bone.

Treatment and Post-Surgical Outcome

• After the diagnosis, the veterinary team carried out a curettage of the cyst, a procedure used to scrape the cyst off the bone, and repulsion of the second premolar tooth, presumably associated with the cyst, to establish drainage.
• Postoperatively, iodine flushes were given to prevent infection.
• Nine months after the surgery, the horse showed no signs of drainage and the size of the right hemimandible had decreased by approximately a quarter indicating significant recovery and a decrease in the swelling initially observed.