A subcutaneous mass on the neck of a horse.

This research focuses on the diagnosis and treatment of a mast cell tumor found in a 25-year-old Arabian gelding’s neck. Mast cell tumors are relatively infrequent in horses, and while they’re typically benign, they require surgical removal.

Case Presentation and Diagnosis

• The study starts with the presentation of a horse with a subcutaneous neck mass. An investigation revealed mast cells of varying degrees of cytoplasmic granulation and scattered eosinophils, both types of white blood cells.
• Further histopathological examination, which involves studying tissue disease at a microscopic level, exposed a poorly defined mass consisting of sheets and bundles of mast cells, along with a significant presence of eosinophils.
• The researchers noticed that the mast cells were broken up into numerous lobules by a heavy collagenous stroma, basically a connecting and supporting structure. Signs of multifocal collagen necrosis, or cell death, were also detected.

Confirmation of Tumor

• Applying both Geimsa and toluidine blue stains strengthened the evidence for the suspected diagnosis of a mast cell tumor. These chemical stains interact with specific cell components, helping to create a clearer picture during microscopic examination.
• A Luna stain was also used to stress the infiltrated eosinophils, a type of white blood cell that can increase during inflammation or disease.

Conclusions and Treatment

• Mast cell tumors have been detected in various domestic animals but are seldom met in horses. Nonetheless, the study confirmed the existence of such a tumor through multiple diagnostic techniques.
• The research highlights that equine cutaneous mast cell tumors are generally benign, and no cases of visceral metastasis, where the disease spreads to other body parts, have been reported.
• With these characteristics in mind, researchers state that surgical removal is considered to be a curative treatment for this type of tumor in horses.