Pseudocyst of the Auricle
The entity known as pseudocyst of the auricle is a relatively uncommon defect in which the cartilaginous plates that make up the auricle (the anterior and posterior leaf) do not join completely. Sometimes they are traumatically separated and form a seroma-like entity, other times it is more or less a congenital malformation. It is identified by the relatively smooth swelling, nearly always abutting the helix, but not really involving the helix, leaving it well defined. It looks deep, much like a lipoma looks deep, as opposed to the other major entity which causes auricular swelling, hemoperichondrium, which leads to cauliflower ear. Since cauliflower ear is much more superficial, it has the appearance more like a cyst would look on the skin. Other clues: cauliflower ear is much more irregular, usually multilobulated, and it usually involves the helix to some degree.
The other ddx to consider is Stahl's Ear, which is a cartilaginous abnormality of structure which causes the scapha to be flipped forward due to an abnormal additional crus of the anthelix. If you want extra credit this weekend, forward this link to someone you love who is younger than 18, and then tell me who (in general terms, e.g. your nephew or neighbor kid or whatever) you forwarded it to: http://dcmf.ca/ .