A haematoma of the ear results from a collection of blood between the skin of the ear and the underlying cartilage. These haematoma are usually found on the underside of the external ear.
A hematoma on the ear generally causes itchiness and is characterized by a swelling of the auricle. In general, effusions are to be considered as harmless since they mostly heal on their own. In case of a blood ear, however, a veterinarian should assist. In case veterinarians do not intervene, in many cases a deformation of the outer ear will result. The result is a crippledness of the ear.
The disease is often provoked by a blunt trauma (impact, hit), such as a dog more frequently experiences during an accident or a fight with another dog. Additionally, "blood ears" more frequently develop within the course of an inflammation of the ears. The dog considers the appearing itchiness as a foreign matter which he tries to remove by heavily shaking the head. In doing so small blood vessels in the ear conch may burst resulting in the blood ear.
Relatively small blood ears can be removed by firstly injecting anti-inflammatory drugs. A few days later the blood is removed by puncture (by setting pinpricks). Possibly, another puncture is required. Larger and older blood ears required a small intervention in which the blood/secretion is either to be discharged (after a small cut) or the hematoma to be cleared out (surgically). The administration of antibiotics prevents inflammations.
Prophylactically, you may act by consulting a veterinarian already when noticing frequent scratching of your dog, above all, however, in case of intensive head shaking, and have the blood ear be treated prior to its development.