The MRI on this horse revealed a keratoma on the solar (bottom) surface of the left front foot.
A keratoma is an uncommon tumor of the keratin producing epidermal cells of the inner hoof wall. They are considered a benign tumor, as they create problems by expanding locally, but do not spread to other areas. They are more commonly seen between the hoof wall and the coffin bone at the toe or the quarters, but have occasionally been reported between the sole and coffin bone as well.
As the keratoma grows, it starts to create pressure on the coffin bone which can result in lameness as well as resorption of the coffin bone (loss of bone density). In some cases, we will see a circular shaped area of bone loss on the edge of the coffin bone. However, not all cases will have changes that are visible on radiographs.
(Image from https://veteriankey.com/keratomas/ )
This particular case was fairly unique because of the location of the keratoma on the bottom of the horse’s foot. Additionally in this case, no radiographic changes were evident. We elected to perform an MRI on the horse’s foot because we had localized the lameness to the foot using regional anesthesia, and because the lameness had not responded to conservative therapy. In this case, the MRI was essential to obtain an accurate diagnosis of the lameness, and it allowed us to make appropriate therapy recommendations.
Keratomas require surgical removal of the abnormal tissue to resolve. The overlying hoof wall or solar surface (depending on the site of the lesion) must be removed to allow access to and removal of the tumor. Once the tumor is removed, the area is allowed to heal. The prognosis in general for keratomas is very good with surgical therapy.
Without surgery, this case would not have resolved. Without a diagnosis, the owner would be stuck with empirical therapy that would have included significant expense for specialized shoeing, anti-inflammatory medications, additional veterinary visits. Without an accurate diagnosis, all of this money would be wasted and the horse would continue to be lame.
MRI is an excellent tool to have available when other techniques to localize and diagnose lameness (physical exam, local anesthesia, radiographs, ultrasound) are not able to determine a definitive diagnosis. It is not a procedure that we use until we have exhausted these other modalities, because it requires general anesthesia and significant expense to the owner. However, for many cases getting an accurate diagnosis not only ends up with a better outcome for the horse, it ultimately ends up saving the owner a great deal in time and expense.