This is called an aural hematoma. That hot pocket in the ear flap is full of blood. The pinna (ear flap) has 2 layers of cartilage and a hematoma happens if a blood vessel bursts and separates the layers of cartilage.
Why does this happen? Often these dogs have a chronic history of ear issues. Sometimes they have an ear infection and marked inflammation so they have been head shaking, scratching and rubbing. And sometimes their ears look completely perfect and the hematoma just happened.
Is it an emergency? It is not a life-or-death emergency, no. But it is uncomfortable and your pet should be checked out as soon as possible so we can ensure there are no other issues within the ears.
How do we fix it? Our method of choice is to place a teat cannula (yes, a teat cannula for a cow) into the hematoma so it can be drained multiple times a day. We prefer this method because our success rate is high, complication rate is low and it can often be placed without sedation, depending on the personality of the patient!! It DOES require some home care. The hematoma needs to be drained, initially twice a day then once a day. It is often in place for 4 weeks or so. Basically the 2 layers of cartilage need to be healed together and there is not to have been any significant discharge for a week before we pull the cannula. And yes, we want these patients to go home with an E collar on, at least initially.
Are there other methods? Yes! There is surgical repair which involves a general anesthesia and placing multiple holes in the underside of the ear flap and then suturing the top and bottom of the ear flap together.
There is medical therapy—steroids, usually a 6 week tapering course of prednisone. Most vets feel this works 50-60% of the time and does take some time. There will be some side effects from the medication and not all dogs are a candidate due to preexisting conditions.
What if you just drain it? Well, it fills back up again!