About Aural Haematoma

An aural haematoma is a pool of blood that collects between the skin and the cartilage of a pet’s ear flap.

It’s typically caused by overly aggressive ear scratching or head shaking that results from an ear infection. Dogs and cats can both suffer ear haematomas, though dogs (particularly those prone to skin allergies and ear infections) are more prone to them.
Treatments range from draining the haematoma with a needle, to surgical correction of the problem.

Although both dogs and cats can suffer from ear haematomas, the condition is much more common in dogs. Ear haematomas are usually caused by some kind of self-trauma - such as when a pet aggressively scratches at the ears or shakes his or her head, causing the ear flaps to slap against the skull. This trauma can cause blood to leave the vessels and pool in a pocket between the skin and cartilage components that make up the outer part of the ear flap. Usually, there’s an underlying cause for the scratching and head shaking, such as ear mites or bacterial and/or yeast infections of the ear canal.
Because dogs that suffer from skin allergies are prone to ear infections, allergic skin disease can be an important part of the underlying problem. It’s undeniably crucial to treat both the ear haematoma and the underlying parasites or ear infection and address possible allergies.

Source: http://www.vetstreet.com/care/ear-aural-hematoma