D33.1
BillableBenign neoplasm of brain, infratentorial
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is D33.1 an HCC code?
Yes. D33.1 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 D33.1
For D33.1 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 D33.1 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
D33.1 is the ICD-10-CM diagnosis code for benign neoplasm of brain, infratentorial. A non-cancerous tumor located in the lower portion of the brain below the tentorium cerebelli, including the cerebellum and brainstem. D33.1 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering benign neoplasms, except benign neuroendocrine tumors (d10-d36).
Under the CMS-HCC V28 risk adjustment model, D33.1 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, D33.1 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.
Infratentorial tumors are located below the tentorium; ensure this distinction is documented. Because D33.1 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 D33.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Infratentorial tumors are located below the tentorium; ensure this distinction is documented
- •These tumors may present with different symptoms than supratentorial tumors due to their location
Clinical Significance
Benign neoplasm of the infratentorial brain encompasses benign tumors below the tentorium cerebelli, primarily in the posterior fossa including the cerebellum, brainstem, and fourth ventricle. Common benign infratentorial tumors include pilocytic astrocytomas, hemangioblastomas, and epidermoid cysts. These tumors can cause hydrocephalus, cerebellar dysfunction, and cranial nerve palsies due to the confined posterior fossa anatomy.
Documentation Requirements
- ✓MRI brain documenting the posterior fossa tumor location with imaging characteristics.
- ✓If resected, pathology must confirm benign histology.
- ✓Document the specific infratentorial location (cerebellum, brainstem, fourth ventricle), tumor size, degree of hydrocephalus if present, and neurological examination findings.
- ✓Include treatment plan and surveillance schedule.