2007 ICD-9-CM Procedure 20.21 Incision of mastoid 20.21 is a specific code that can be used to specify a procedure 20.21 contains 3 index entries View the full Volume 3 20.* hierarchy Index entries containing 20.21: Exploration -- see also Incision mastoid 20.21 Incision (and drainage) mastoid 20.21 Mastoidotomy 20.21