D42.9
BillableNeoplasm of uncertain behavior of meninges, unspecified
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is D42.9 an HCC code?
Yes. D42.9 maps to Melanoma and Other Skin Cancers under the CMS-HCC V28 risk adjustment model (and Breast, Prostate, and Other Cancers and Tumors under V24).
HCC Category Mapping
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 D42.9
For D42.9 to 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 D42.9 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
D42.9 is the ICD-10-CM diagnosis code for neoplasm of uncertain behavior of meninges, unspecified. A growth in the membrane surrounding the brain or spinal cord that cannot yet be classified as definitely cancer or definitely benign, but the exact location is not specified. D42.9 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering neoplasms of uncertain behavior, polycythemia vera and myelodysplastic syndromes (d37-d48).
Under the CMS-HCC V28 risk adjustment model, D42.9 maps to Melanoma and Other Skin Cancers (HCC 23) with a community, non-dual, aged base RAF weight of 0.251. Under the older CMS-HCC V24 model, D42.9 maps to Breast, Prostate, and Other Cancers and Tumors (HCC 12) with a community, non-dual, aged base RAF weight of 0.150. 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.
Use this code only when it cannot be determined whether the meningeal lesion is cerebral or spinal. Because D42.9 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 D42.9 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use this code only when it cannot be determined whether the meningeal lesion is cerebral or spinal
- •Query the provider if possible to obtain specific anatomical location (brain vs. spinal cord) for more precise coding
Clinical Significance
This unspecified code represents a meningeal tumor of uncertain behavior when the location (cerebral versus spinal) cannot be determined. Using this code limits clinical utility because treatment and prognosis differ significantly based on whether the tumor involves brain or spinal meninges.
Documentation Requirements
- ✓This code should only be used when documentation does not differentiate between cerebral and spinal meningeal involvement.
- ✓A provider query is strongly recommended to determine the specific location from imaging, operative notes, or pathology reports.
- ✓Pathology should confirm uncertain behavior classification.