2026 ICD-10-CM Diagnosis Code C31.1Malignant neoplasm of ethmoidal sinus

ICD-10-CM Codes›C00–D49›C30-C39›C31

ICD-10-CM C31.1
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

C31.1 is a billable ICD-10-CM diagnosis code for malignant neoplasm of ethmoidal sinus. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 146 through 148. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Head and neck cancers - all other types.

Code Identity

ICD-10-CM Code
C31.1
Billable Status
Yes — Valid for Submission
Code Describes
Malignant neoplasm of ethmoidal sinus
Short Description
Malignant neoplasm of ethmoidal sinus
Same as the full description in the CMS dataset.
Parent Code
C31
Malignant neoplasm of accessory sinuses

Code Classification

ChapterC00–D49Neoplasms
SectionC30-C39Malignant neoplasms of respiratory and intrathoracic organs
CategoryC31Malignant neoplasm of accessory sinuses
This CodeC31.1Malignant neoplasm of ethmoidal sinus

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Adenocarcinoma of accessory sinus
  • Adenocarcinoma of ethmoidal sinus
  • Carcinoma of ethmoidal sinus
  • Malignant melanoma of accessory sinus
  • Malignant melanoma of ethmoid sinus
  • Malignant neoplasm of ethmoid sinus
  • Primary adenocarcinoma of accessory sinus
  • Primary adenocarcinoma of ethmoidal sinus
  • Primary carcinoma of ethmoidal sinus
  • Primary malignant neoplasm of ethmoidal sinus
  • Primary squamous cell carcinoma of accessory sinus
  • Primary squamous cell carcinoma of ethmoidal sinus
  • Squamous cell carcinoma of ethmoidal sinus

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR NEO010
Head and neck cancers - all other types
Default principal diagnosis: inpatient Yes · outpatient Yes

Table of NeoplasmsClinical

Anatomical sites in the Table of Neoplasms that reference this code family.

SiteMalig.
Primary		Malig.
Secondary		Ca
in situ		BenignUncertainUnspec.
ethmoid (sinus)C31.1C78.39D02.3D14.0D38.5D49.1
sinus (accessory) › ethmoidalC31.1C78.39D02.3D14.0D38.5D49.1

Patient EducationClinical

Nasal Cancer

Your paranasal sinuses are small hollow spaces around the nose. They are lined with cells that make mucus, which keeps your nose from drying out. The nasal cavity is the passageway just behind your nose. Air passes through it on the way to your throat as you breathe.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert C31.1 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
160.3 Mal neo ethmoidal sinus
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About C31.1Overview

Is C31.1 (Malignant neoplasm of accessory sinuses) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report malignant neoplasm of ethmoidal sinus on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does C31.1 group to?

When malignant neoplasm of ethmoidal sinus is the principal diagnosis on an inpatient stay, it groups to MS-DRG 146, 147, 148, with relative weights from 0.7971 to 2.1174 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of C31.1?

Under the General Equivalence Mappings, malignant neoplasm of ethmoidal sinus converts to ICD-9-CM 160.3 (mal neo ethmoidal sinus). The mapping is a direct match.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.