In horses, a keratoma is a benign epithelial tumor of the hoof capsule. There are two variations:
Cylindrical keratomas look like columns (see cylindrical keratoma image) and are found deep to the hoof wall, oriented parallel to the horn tubules.
Courtesy of Dr. Brian Beasley.
Spherical keratomas are less common and have been reported in the frog, in the sole, and above the coronary band.
Etiology and Pathophysiology of Keratomas in Horses
The etiology of keratomas in horses is unknown; however, they might develop as a result of localized chronic irritation, inflammation, or trauma to the germinal layers of the epithelium of the hoof. The tumor develops into an expansile mass that usually remains deep to the hoof capsule.
Keratomas are described histologically as rings of squamous epithelial cells containing abundant keratin. This poorly structured soft horn may be more susceptible to microbial colonization than is normal horn. Keratomas may exert pressure and cause lysis of the underlying coffin bone or distortion of the overlying hoof capsule. If the keratoma is not infected and does not impinge on any sensitive tissues, it may be clinically inapparent.
Clinical Findings of Keratomas in Horses
A change in the contour of an area of the white line is often the only initial clinical sign of a keratoma in a horse. This sign is most often noticed by the farrier while trimming the foot. Lameness results when there is an associated infection or the tumor exerts pressure on sensitive tissue. Recurrent foot abscesses in the same location are common in the histories of horses with keratomas.
Diagnosis of Keratomas in Horses
A presumptive diagnosis of a keratoma is often based on the appearance of a well-circumscribed round or oval area of horn visible on the ground surface of the foot. Radiographic evidence of a keratoma can be a well-demarcated circular or oval area of lysis in the solar margin or parietal surface of the coffin bone (see keratoma radiographic image).
Courtesy of Dr. Valerie J. Moorman.
Advanced imaging with CT or MRI is effective for identifying keratomas and enables improved planning for surgical approaches to treatment.
A biopsy with histological evaluation is needed for a definitive diagnosis of a keratoma.
Differential diagnoses include other rare hoof tumors, chronic hoof wounds, and abscesses.
Treatment and Management of Keratomas in Horses
Surgical removal is the preferred treatment of keratomas in horses if the tumor is associated with lameness or recurrent infection. Depending on its location, the tumor is excised through the sole or via a partial hoof wall resection. The surgery can be performed either in a standing horse with sedation and perineural analgesia or under general anesthesia. Application of a tourniquet is advisable to avoid extensive bleeding.
After removal of the keratoma, the wound is bandaged and the defect is allowed to heal by second intention. Perioperative antimicrobials and NSAIDs are generally indicated. The hoof capsule may require some type of stabilization, depending on the extent and location of the partial hoof wall resection.
The prognosis after uncomplicated complete surgical excision of keratomas in horses is good.
Key Points
A keratoma is a benign epithelial tumor of the hoof capsule.
Keratomas can exert pressure and cause lysis of the underlying distal phalanx or distortion of the overlying hoof capsule.
Recurrent foot abscesses in the same location are common in horses with keratomas.
Surgical removal is the preferred treatment if the tumor is associated with lameness or recurrent infection.
For More Information
Pritchard L. Management of equine keratomas. Vet Times. 2015.
Also see pet health content regarding keratomas in horses.
