H70.8- vs Q18.0
H70.8 and Q18.0 are not coded together. ICD-10-CM declares them mutually exclusive with an Excludes1 note — the two conditions are not expected to occur together, so exactly one of them is normally correct for a given encounter. The Official Guidelines carve out one exception: if the two conditions are clearly unrelated to each other, both may be reported.
Other mastoiditis and related conditions
- Chapter 8
- Diseases of the ear and mastoid process
- Section
- H65-H75
Sinus, fistula and cyst of branchial cleft
- Chapter 17
- Congenital malformations, deformations, chromosomal abnormalities, and genetic disorders
- Section
- Q10-Q18
- Branchial vestige
- Branchiogenic remnant (in neck)
- Cyst › branchial (cleft)
- Cyst › branchiogenic
- Cyst › cervical lateral
- Fistula › branchial (cleft)
These two codes sit in different chapters of the Tabular List, which is usually the clearest signal that they describe different underlying processes rather than different degrees of the same one.
Excludes1 is not always absolute: where two conditions covered by the note are genuinely unrelated, CMS guidance permits reporting both. Document the reasoning rather than assuming it. More on Excludes1 vs Excludes2 · FY2027