Hi, I am Dr. Samiron Roy, Your ENT Splst.
The post aural swelling if soft can be due to lymph node, sebacious cyst, dermoid cyst
If it is bony hard it can be an Ivory Osteoma
You need 3 tests:-
2.X-ray of the mastoid bones L/R.
3. CT Scan
of the Temporal Bones.
Excision is very simple and I do it regularly.