<s>[INST] I have a small hard bump at the bottom of my mastoid (?) behind my ear.  It seems to be at the base of the bone...does not hurt. Just noticed it.  Maybe pea size. What could this be? I've had like pressure in my ear for some time...like my eustacian tube is blocked. [/INST] Hi,Dear,Good evening.Thanks for your query to Health Care Magic.I studied your query indepth. In my opinion the lump on base of acute mastoiditis with chronic otitis media with Eustachian tube block due to the cholesteatoma-Treatment is a-Consult a ER ENT Surgeon who would treat it-by Mastoidectomy-i.e.incision and drainage of the abscess  causing pressure on the eardrum with blocked eustachian tube, with scraping of the .Antibiotics and NSAID under cover of ER ENT-Surgeon is the right treatment for such a bump behind the ear. Hope this answers your  query and explains the cause of the lump.Hope this would clarify the worry you had.Would love to Wellcome your queries to HCM. </s>