Conditions or ailments that are the cause of a problem that you see - your observation.

Your vet may diagnose

Mast Cell Tumor

Synonyms: Mastocytosis, Mastocytoma


This is a condition that usually appears as a single large lump on the limb, neck, head or trunk of horses. It is more common in Arab horses and in male horses. The cases I have diagnosed have mostly been on the lower limbs. It affects horses of all ages.

The diagnosis is made using sampling of cells, and especially biopsy and histopathology. X-ray can be helpful with diagnosis. A characteristic of these masses on the limbs of horses is a granular appearance on a radiograph.

It can also be seen as multiple skin nodules in young foals. This usually disappears spontaneously.

my vet's role


Surgical removal is usually curative. In rare cases, a malignant form can occur in which there is spread to other areas.

Related References:

Samii V, O'Brien TR, Stannard AA. Radiographic features of mastocytosis in the equine limb. Equine Vet J 1997;29(1):63-66.

Cole R, Chesen AB, Poole R, et. al. Imaging diagnosis- equine mast cell tumor. Vet Radiol Ultrasound 2007: 48(1):32-34.

Riley CB, Yovich J, Howell J. Malignant mast cell tumours in horses. Aust Vet J 1991;68(10):346-47.

Author: Doug Thal DVM Dipl. ABVP