Ear (aural) haematomas
These are fluid filled swellings of the ear flap (Pinna). In other words the aural haematoma is a collection of blood or serum, or sometimes a blood clot within the ear flap. The blood oozes out from the damaged blood muscles causing the ear flap to swell up. The swelling may involve the entire ear flap. Smaller haematomas may disappear spontaneously. The larger ones (possibly incorporating the entire ear) need veterinary intervention.
Before I go any further, it would make sense to explain the anatomy of the outer ear flap (Pinna): The ear flap is composed of a layer of skin on each side of a layer of cartilage. The cartilage gives the ear flap its shape. Blood vessels go from side-to-side by passing through the cartilage. Violent shaking causes the vessels to break as the skin slides across the cartilage.
Now that we have an idea of the ear anatomy, we can more easily understand how anything irritating the ear canal or the ear flap itself could result in the dog/cat responding by scratching or shaking its head so excessively that it causes the blood vessels to burst, resulting in bleeding. If no corrective action is taken, the bleeding itself continues, because the