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C31.2 ICD-10-CM Code: Malignant neoplasm of frontal sinus

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FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of respiratory and intrathoracic organs (C30-C39)

C31.2

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Malignant neoplasm of frontal sinus

Cancer of the frontal sinus, the air-filled space in the forehead above the eyebrows.

Buddy the Bee presenting code insight

Buddy Insight

Frontal sinus cancer is uncommon among paranasal sinus malignancies.

CMS-HCC V28

HCC 21

RAF 0.545

CMS-HCC V24

HCC 11

RAF 0.306

ACA/HHS

0

0

RAF 0

ESRD/PACE

HCC 11

RAF 0.0

RXHCC

HCC 22

RAF 0.0

Code Trumping

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Code Book Path

Official
C31Malignant neoplasm of accessory sinuses
C31.2Malignant neoplasm of frontal sinus

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for C31.2 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C31.2 in this effective period.

Related Child Codes

Official
C31.0Malignant neoplasm of maxillary sinus
C31.1Malignant neoplasm of ethmoidal sinus
C31.3Malignant neoplasm of sphenoid sinus
C31.8Malignant neoplasm of overlapping sites of accessory sinuses
C31.9Malignant neoplasm of accessory sinus, unspecified

Includes

Official

ICD-10-CM does not list Includes notes for C31.2 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C31.2 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C31.2 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C31.2 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C31.2 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance
Pathology confirmation of malignancy with histological type
Imaging documenting frontal sinus as the primary site
Assessment of intracranial or orbital extension
TNM staging and treatment approach

MEAT Support

HCC Buddy guidance
Pathology confirmation of malignancy with histological type
Imaging documenting frontal sinus as the primary site
Assessment of intracranial or orbital extension
TNM staging and treatment approach

Audit Caution

HCC Buddy guidance
Coding frontal bone invasion as primary bone cancer when the sinus is the primary tumor site
Defaulting to unspecified sinus (C31.9) when imaging clearly identifies the frontal sinus
Not querying the provider for sinus specificity when documentation is vague
Failing to capture the rare occurrence of frontal sinus cancer due to its unusual presentation

Common Mistakes

HCC Buddy guidance
C31.1 — Ethmoidal sinus cancer: Frontal and ethmoidal sinuses are adjacent; imaging is needed to determine the primary site
C31.8 — Overlapping sites of accessory sinuses: Use when the tumor spans multiple sinuses
C41.0 — Bone cancer of skull: Frontal bone involvement from sinus cancer should still be coded as sinus cancer
C31.9 — Accessory sinus, unspecified: Use only if the specific sinus cannot be identified

Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.

Is C31.2 an HCC code?

Yes. C31.2 maps to Breast, Prostate, Colorectal and Other Cancers and Tumors under the CMS-HCC V28 risk adjustment model (and Colorectal, Bladder, and Other Cancers under V24).

HCC Category Mapping

V28HCC 21, Breast, Prostate, Colorectal and Other Cancers and Tumors
0.545
V24HCC 11, Colorectal, Bladder, and Other Cancers
0.306
ESRDHCC 11, Colorectal, Bladder, and Other Cancers
0.000
RxHCCHCC 22, Cancer, Other Specified Sites
0.000

RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.

MEAT Criteria for C31.2

For C31.2to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.

  • MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
  • EEvaluate: test results, medication response, or physical findings reviewed by the provider
  • AAssess: explicit mention in the assessment or plan with acknowledgment of status
  • TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed C31.2 during that encounter, not just copy-forwarded from a problem list.

What This Code Means

C31.2 is the ICD-10-CM diagnosis code for malignant neoplasm of frontal sinus. Cancer of the frontal sinus, the air-filled space in the forehead above the eyebrows. C31.2 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of respiratory and intrathoracic organs (c30-c39).

Under the CMS-HCC V28 risk adjustment model, C31.2 maps to Breast, Prostate, Colorectal and Other Cancers and Tumors (HCC 21) with a community, non-dual, aged base RAF weight of 0.545. Under the older CMS-HCC V24 model, C31.2 maps to Colorectal, Bladder, and Other Cancers (HCC 11) with a community, non-dual, aged base RAF weight of 0.306. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.

Frontal sinus cancer is uncommon; verify diagnosis and document any intracranial extension. Because C31.2 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.

HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for C31.2 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •Frontal sinus cancer is uncommon; verify diagnosis and document any intracranial extension
  • •Note involvement of adjacent structures such as the orbit or anterior cranial fossa

Clinical Significance

Frontal sinus cancer is uncommon among paranasal sinus malignancies. Due to the frontal sinus's proximity to the anterior cranial fossa and orbit, these tumors frequently present with intracranial extension. Surgical management is complex, often requiring craniofacial resection, making accurate coding important for reflecting true disease severity and resource needs.

Documentation Requirements

  • ✓Pathology confirmation of malignancy with histological type
  • ✓Imaging documenting frontal sinus as the primary site
  • ✓Assessment of intracranial or orbital extension
  • ✓TNM staging and treatment approach
  • ✓Distinction from other sinus sites if tumor extends beyond the frontal sinus

Commonly Confused Codes

  • •C31.1: Ethmoidal sinus cancer: Frontal and ethmoidal sinuses are adjacent; imaging is needed to determine the primary site
  • •C31.8: Overlapping sites of accessory sinuses: Use when the tumor spans multiple sinuses
  • •C41.0: Bone cancer of skull: Frontal bone involvement from sinus cancer should still be coded as sinus cancer
  • •C31.9: Accessory sinus, unspecified: Use only if the specific sinus cannot be identified

Child Codes

C31.0Malignant neoplasm of maxillary sinus
HCC 21
C31.1Malignant neoplasm of ethmoidal sinus
HCC 21
C31.2Malignant neoplasm of frontal sinus
HCC 21
C31.3Malignant neoplasm of sphenoid sinus
HCC 21
C31.8Malignant neoplasm of overlapping sites of accessory sinuses
HCC 21
C31.9Malignant neoplasm of accessory sinus, unspecified
HCC 21

Code Hierarchy

└C31Malignant neoplasm of accessory sinuses└C31.2Malignant neoplasm of frontal sinus
└C31.2Malignant neoplasm of frontal sinus

Because C31.2 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

C31.2 maps to CMS-HCC V28 category 21, Breast, Prostate, Colorectal and Other Cancers and Tumors. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works.

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