ICD-10 Code C31 – Malignant neoplasm of accessory sinuses (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C31 – Malignant neoplasm of accessory sinuses
What it is
C31 identifies a malignant tumor arising in the accessory sinuses, which include the maxillary, ethmoid, sphenoid, and frontal sinuses. Use this code when the record documents cancer in one or more of these sinus sites.
Clinical signs
Clinical features vary; refer to documentation. Common findings may include nasal obstruction, facial pain or pressure, epistaxis, or swelling, but the diagnosis must be supported by imaging, endoscopy, or pathology when available.
When to use this code
Use C31 when the provider documents a primary malignant neoplasm of an accessory sinus and does not specify a more exact sinus site or subsite. It may also be used when the chart states “malignant neoplasm of paranasal sinus” without further detail. Verify laterality or exact location if the record provides it.
Do not use for
Do not use this code for benign sinus tumors, inflammatory sinus disease, or unspecified nasal cavity cancers. Check documentation if the malignancy is metastatic to the sinuses rather than arising there.
Coding tip
Review pathology and imaging reports carefully, because the exact sinus site can affect code selection and specificity.