An<unk>  is a round or oval<unk> sicle that lies above and separate from the body of C-2. A normal odontoid process is absent and atlantoaxial instability may be present. It must be distingushed from an odontoid fracture.
Os odontoideum
Ocellus
Cutaneos Horn
Filum terminale
Cumulus oophorus
Pilonidal sinus
Cutis rhomboidalis nuchae
Cauliflower ear