C31.3 ICD-10-CM Code: Malignant neoplasm of sphenoid sinus
C31.3 maps to CMS-HCC V28 21. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC Buddy coding tools
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FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of respiratory and intrathoracic organs (C30-C39)
C31.3
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceMalignant neoplasm of sphenoid sinus
Cancer that develops in the sphenoid sinus, an air-filled cavity deep in the skull behind the nose.
Buddy Insight
Sphenoid sinus cancer is rare and extremely dangerous due to the sinus's deep skull base location adjacent to the pituitary gland, cavernous sinus, optic nerves, and internal carotid arteries.
CMS-HCC V28
MappedHCC 21
Coefficient HCC 21: 0.671 (Community Non-Dual Aged (CNA))
CMS-HCC V24
HistoricalHistorical
Not used for CY2026 payment
ACA/HHS
MappedHCC 011
Code-level coefficient reference
ESRD/PACE
MappedHCC 11
Code-level coefficient reference
RXHCC
MappedHCC 22
Code-level coefficient reference
Code Book Path
Inclusion Terms
OfficialNo inclusion terms are included in this display for C31.3. Check the code and parent instructions in the Code Book.
Excludes 2
OfficialNo Excludes 2 notes are included in this display for C31.3. Check the code and parent instructions in the Code Book.
Related Codes
Includes
Official- malignant neoplasm of middle earInherited from C30-C39
Excludes 1
Official- mesothelioma (C45.-)Inherited from C30-C39
Code First
OfficialNo Code First sequencing instructions are included in this display for C31.3. Check the code and parent instructions in the Code Book.
Use Additional
OfficialNo Use Additional Code instructions are included in this display for C31.3. Check the code and parent instructions in the Code Book.
Code Also
OfficialNo Code Also instructions are included in this display for C31.3. Check the code and parent instructions in the Code Book.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →
Is C31.3 an HCC code?
Yes. C31.3 (Malignant neoplasm of sphenoid sinus) maps to HCC 21, Lymphoma and Other Cancers under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.671. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.
Coder answer: C31.3 is billable and maps to V28 HCC 21, Lymphoma and Other Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- C31.3
- Description
- Malignant neoplasm of sphenoid sinus
- HCC (V28)
- HCC 21 — Lymphoma and Other Cancers
- RAF reference coefficient
- 0.671
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. Weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.
Work C31.3 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →
MEAT review for C31.3
For C31.3, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.
- 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
Coder workflow notes
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What This Code Means
C31.3 is the ICD-10-CM diagnosis code for malignant neoplasm of sphenoid sinus. Cancer that develops in the sphenoid sinus, an air-filled cavity deep in the skull behind the nose. C31.3 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, C31.3 maps to Lymphoma and Other Cancers (HCC 21) with a source-labeled community, non-dual, aged reference coefficient of 0.671. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.
Sphenoid sinus cancer is rare and often diagnosed late due to deep location. For C31.3, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. 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, source-labeled coefficient references, and MEAT documentation criteria for C31.3 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Sphenoid sinus cancer is rare and often diagnosed late due to deep location
- •Document proximity to critical structures including the pituitary gland and cavernous sinus
Clinical Significance
Sphenoid sinus cancer is rare and extremely dangerous due to the sinus's deep skull base location adjacent to the pituitary gland, cavernous sinus, optic nerves, and internal carotid arteries. These tumors typically present at advanced stages because early symptoms are minimal. Surgical access is challenging, often requiring endoscopic skull base approaches.
Documentation Requirements
- ✓Pathology confirmation with histological type
- ✓MRI and CT imaging confirming sphenoid sinus as primary site
- ✓Assessment of invasion into adjacent critical structures (cavernous sinus, optic nerves, pituitary, carotid arteries)
- ✓TNM staging and treatment plan
- ✓Endocrine evaluation if pituitary involvement is suspected
Commonly Confused Codes
- •C75.1: Malignant neoplasm of pituitary gland: Sphenoid sinus tumors can invade the pituitary; confirm the primary origin
- •C31.1: Ethmoidal sinus: Adjacent sinus; ensure imaging confirms sphenoid origin
- •D35.2: Benign neoplasm of pituitary gland: Pituitary adenomas can extend into the sphenoid but are benign
- •C31.9: Accessory sinus, unspecified: Do not default to unspecified when sphenoid is documented