By Rubén Anguiano, DVM, MSc, University of Guadalajara, México, WEVA Regional Ambassador

Equine otohematoma—also known as otoserohematoma, hematoma auris, and auricular pseudocyst—is an uncommon ear condition affecting horses of all ages. It is not well-described in medical and surgical equine literature, so many practitioners are unfamiliar with it.

Otohematoma is an accumulation of blood and serous fluid between the conchal cartilage (which makes up the ear) and the perichondrium (connective tissue that envelops the conchal cartilage). It can be caused by blunt or compressive trauma or horse bites, but most of the cases have an idiopathic etiology (unknown cause). Parasites, ticks, and mites can also be involved.

Fluid accumulates when the natural adhesion between the perichondrium, the cartilage, and the skin is damaged by trauma. Clinical signs include severe ear swelling, edema (fluid swelling), erythema (skin reddening), bumps under the skin, pain during palpation, frequent head-shaking and -tilting, and sometimes bloody or purulent (puslike) exudate. The separation between perichondrium and cartilage can cause necrosis (tissue death), chronic inflammation, and ear deformation, so prompt treatment is essential