D33.1 ICD-10-CM Code: Benign neoplasm of brain, infratentorial
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FY 2026 Apr update / Neoplasms (C00-D49) / Benign neoplasms, except benign neuroendocrine tumors (D10-D36)
D33.1
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceBenign 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.
Buddy Insight
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.
CMS-HCC V28
MappedHCC 23
RAF 0.186
CMS-HCC V24
MappedHCC 12
RAF 0.150
ACA/HHS
MappedHCC 12
Varies by metal level
ESRD/PACE
MappedHCC 12
RAF 0.045
RXHCC
MappedHCC 22
RAF 0.124
Code Book Path
Inclusion Terms
Official- Benign neoplasm of brain stem
- Benign neoplasm of cerebellum
- Benign neoplasm of fourth ventricle
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for D33.1 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for D33.1 in this effective period.
Excludes 1
Official- angioma (D18.0-)
- benign neoplasm of meninges (D32.-)
- benign neoplasm of peripheral nerves and autonomic nervous system (D36.1-)
- hemangioma (D18.0-)
- neurofibromatosis (Q85.0-)
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for D33.1 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for D33.1 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for D33.1 in this effective period.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
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 D33.1 an HCC code?
Yes. D33.1 (Benign neoplasm of brain, infratentorial) maps to Prostate, Breast, and Other Cancers and Tumors under the CMS-HCC V28 risk adjustment model (and Breast, Prostate, and Other Cancers and Tumors under V24), with a community non-dual aged RAF of 0.186. It is billable for payment year 2026.
Coder answer: D33.1 is billable and maps to V28 HCC 23, Prostate, Breast, and Other Cancers and Tumors. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- D33.1
- Description
- Benign neoplasm of brain, infratentorial
- HCC (V28)
- HCC 23 — Prostate, Breast, and Other Cancers and Tumors
- RAF
- 0.186
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
Each model's RAF is its CMS base weight for that model's standard population, so 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 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.
Work D33.1 in the Code Book — tabular path, V28 RAF, and MEAT checklist →
MEAT Criteria for D33.1
For D33.1to 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.
Coder workflow notes
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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 Prostate, Breast, and Other Cancers and Tumors (HCC 23) with a community, non-dual, aged base RAF weight of 0.186. 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.