ICD-10 Code H70.012 – Subperiosteal abscess of mastoid, left ear (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code H70.012 – Subperiosteal abscess of mastoid, left ear
What it is
This code identifies a localized pus collection beneath the periosteum over the left mastoid bone, usually as a complication of mastoid or middle ear infection. It documents the left-sided anatomic site and the abscess location.
Clinical signs
Typical findings include postauricular swelling, tenderness, redness, and protrusion of the ear. Clinical features vary; refer to documentation for evidence of mastoid involvement or abscess formation.
When to use this code
Use H70.012 when the record clearly states a subperiosteal abscess of the left mastoid. It is appropriate when the clinician documents the side and confirms the abscess as a distinct mastoid complication. If the note only says mastoiditis or ear infection, check documentation before coding this diagnosis.
Do not use for
Do not use this code for unspecified mastoid abscesses or infections without left-sided documentation. Do not assign it when the chart only describes otitis media, mastoiditis, or postauricular swelling without confirming a subperiosteal abscess.
Coding tip
Verify laterality and the exact phrase “subperiosteal abscess” in the provider note before assigning H70.012.