ICD-9-CM procedure code (retired)
20.21 — Incision of mastoid
About ICD-9-CM 20.21
20.21 is an ICD-9-CM procedure code for incision of mastoid. ICD-9-CM was retired for U.S. claims on October 1, 2015, when ICD-10-PCS took over.
The CMS General Equivalence Mappings translate it to 12 ICD-10-PCS codes, such as 099B00Z (Drainage of Right Mastoid Sinus with Drainage Device, Open Approach), 099B0ZZ (Drainage of Right Mastoid Sinus, Open Approach) and 099B40Z (Drainage of Right Mastoid Sinus with Drainage Device, Percutaneous Endoscopic Approach). All of these are approximate matches, so review the record to pick the right one.
ICD-10-PCS equivalents
- 099B00ZDrainage of Right Mastoid Sinus with Drainage Device, Open Approachapproximate
- 099B0ZZDrainage of Right Mastoid Sinus, Open Approachapproximate
- 099B40ZDrainage of Right Mastoid Sinus with Drainage Device, Percutaneous Endoscopic Approachapproximate
- 099B4ZZDrainage of Right Mastoid Sinus, Percutaneous Endoscopic Approachapproximate
- 099B70ZDrainage of Right Mastoid Sinus with Drainage Device, Via Natural or Artificial Openingapproximate
- 099B7ZZDrainage of Right Mastoid Sinus, Via Natural or Artificial Openingapproximate
- 099C00ZDrainage of Left Mastoid Sinus with Drainage Device, Open Approachapproximate
- 099C0ZZDrainage of Left Mastoid Sinus, Open Approachapproximate
- 099C40ZDrainage of Left Mastoid Sinus with Drainage Device, Percutaneous Endoscopic Approachapproximate
- 099C4ZZDrainage of Left Mastoid Sinus, Percutaneous Endoscopic Approachapproximate
- 099C70ZDrainage of Left Mastoid Sinus with Drainage Device, Via Natural or Artificial Openingapproximate
- 099C7ZZDrainage of Left Mastoid Sinus, Via Natural or Artificial Openingapproximate
Common questions about 20.21
What is the ICD-10 code for ICD-9 20.21?
- The GEMs map 20.21 to ICD-10-PCS 099B00Z, 099B0ZZ, 099B40Z, 099B4ZZ, 099B70Z, 099B7ZZ and 6 more.
GEMs are a translation aid, not a substitute for coding from the record. The 2027 ICD-10 code set has changed since the last GEMs release in 2018. Page updated September 29, 2026.