ICD-10 Code C31.9 – Malignant neoplasm of accessory sinus, unspecified (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C31.9 – Malignant neoplasm of accessory sinus, unspecified
What it is
This code identifies a malignant tumor arising in an accessory sinus, but the exact sinus site is not specified. Use it when documentation confirms cancer of a paranasal sinus without further detail.
Clinical signs
Clinical features vary; refer to documentation. Common findings may include nasal obstruction, facial pain or pressure, epistaxis, or a mass seen on imaging or endoscopy.
When to use this code
Use C31.9 when the record states malignant neoplasm of an accessory sinus and does not name the specific sinus involved. It also fits when the provider documents a paranasal sinus cancer without laterality or further site detail. Check documentation if the site can be specified more precisely.
Do not use for
Do not use this code for benign sinus lesions, inflammatory sinus disease, or cancers with a documented specific sinus site. If the record names a more exact paranasal sinus location, code that site instead.
Coding tip
Query for the exact sinus site whenever the note says only “accessory sinus” or “paranasal sinus” cancer.