Computed Tomography and Magnetic Resonance Imaging of an Epidermoid Cyst in a Foot of a Horse.

This study discusses the case of an 18-year-old horse with foot lameness due to an epidermoid cyst, providing an overview of the multi-modal diagnostic imaging methods used to identify the cyst, and recommending the cyst to be considered as a possible source of chronic lameness after a foot injury in horses.

Case Presentation

An elderly mare of the Quarter Horse breed was taken in for examination after having moderate left forelimb lameness for a period of 4 weeks. The medical team found that the lameness was localised to the distal end of the mare’s forelimb. Additional observations were swelling around the coronary band area, more specifically, on the dorsal and lateral sides.

Diagnostic Process

The healthcare team carried out a variety of steps when making their diagnosis:

• Preliminary examinations that helped determine the lameness was confined to the lower part of the limb.
• Perineural analgesia, a numbing method, was used to support the preliminary findings.
• An array of imaging techniques including Radiography, ultrasound, magnetic resonance imaging (MRI), and computed tomography (CT) was used in the foot examination. These imaging modalities revealed a well-encapsulated soft tissue mass causing deformation of the dorsolateral border of the middle phalanx (the second segment of the horse’s toe).

Treatment & Follow-Up

In terms of treatment, the healthcare team suggested surgery to remove the mass and further stabilize the interphalangeal joint. However, before the treatment could commence, the horse was put down on the owner’s decision. Post-mortem histopathological examination confirmed the mass to be an epidermoid cyst, characterised by multi-layers of keratin encased by stratified squamous epithelium.

Conclusions

From their findings, the team concluded that an epidermoid cyst, although rare, could be a potential source of chronic lameness in a horse’s foot post-trauma and, inter alia, should be considered in differential diagnosis for any horse presenting with such symptoms. This case report in particular serves to illustrate the potential appearances of an epidermoid cyst, as revealed by multiple types of advanced imaging studies.