What is ICD-10 code D43.1?

D43.1 is the ICD-10-CM diagnosis code for Neoplasm of uncertain behavior of brain, infratentorial. A growth in the lower part of the brain (below the tentorium, a membrane dividing brain regions) that cannot yet be classified as definitely cancer or definitely benign. D43.1 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. D43.1 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. D43.1 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. D43.1 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

What is the V28 vs V24 difference for D43.1?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. For D43.1, V28 maps to Melanoma and Other Skin Cancers at RAF 0.251 while V24 mapped to Breast, Prostate, and Other Cancers and Tumors at RAF 0.150. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting D43.1?

Infratentorial refers to structures below the tentorium cerebelli (cerebellum and brainstem); ensure this anatomical distinction is documented This code is for uncertain behavior lesions; confirmed malignant brain tumors use different C-codes Because D43.1 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.

D43.1 ICD-10 Code: Neoplasm of uncertain behavior

ICD-10-CM Code View

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Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.

Code lookupD43.1Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Neoplasms (C00-D49) / Neoplasms of uncertain behavior, polycythemia vera and myelodysplastic syndromes (D37-D48)

D43.1

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

Neoplasm of uncertain behavior of brain, infratentorial

A growth in the lower part of the brain (below the tentorium, a membrane dividing brain regions) that cannot yet be classified as definitely cancer or definitely benign.

Buddy Insight

Neoplasms of uncertain behavior in the infratentorial brain involve structures below the tentorium cerebelli, including the cerebellum and brainstem.

CMS-HCC V28

Mapped

HCC 23

Melanoma and Other Skin Cancers

RAF 0.251

CMS-HCC V24

Mapped

HCC 12

Breast, Prostate, and Other C...

RAF 0.150

ACA/HHS

Not risk-adjusted for this model/period.

RAF 0

ESRD/PACE

Mapped

HCC 12

Breast, Prostate, and Other C...

RAF 0.0

RXHCC

Mapped

HCC 22

Cancer, Other Specified Sites

RAF 0.0

Code Trumping

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Code Book Path

Official

D43Neoplasm of uncertain behavior of brain and central nervous system

D43.1Neoplasm of uncertain behavior of brain, infratentorial

Inclusion Terms

Official

Neoplasm of uncertain behavior of brain stem
Neoplasm of uncertain behavior of cerebellum
Neoplasm of uncertain behavior of fourth ventricle

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for D43.1 in this effective period.

Related Child Codes

Official

D43.0Neoplasm of uncertain behavior of brain, supratentorial

D43.2Neoplasm of uncertain behavior of brain, unspecified

D43.3Neoplasm of uncertain behavior of cranial nerves

D43.4Neoplasm of uncertain behavior of spinal cord

D43.8Neoplasm of uncertain behavior of other specified parts of central nervous system

Includes

Official

ICD-10-CM does not list Includes notes for D43.1 in this effective period.

Excludes 1

Official

neoplasm of uncertain behavior of peripheral nerves and autonomic nervous system (D48.2)

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for D43.1 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for D43.1 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for D43.1 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Documentation must specify the infratentorial location (cerebellum or brainstem), supported by neuroimaging.

Pathology should describe features that preclude definitive benign or malignant classification.

Document any neurological symptoms including gait abnormalities, coordination deficits, or signs of increased intracranial pressure.

MEAT Support

HCC Buddy guidance

Documentation must specify the infratentorial location (cerebellum or brainstem), supported by neuroimaging.

Pathology should describe features that preclude definitive benign or malignant classification.

Document any neurological symptoms including gait abnormalities, coordination deficits, or signs of increased intracranial pressure.

Audit Caution

HCC Buddy guidance

Posterior fossa tumors in adults are more likely to be metastatic, which would require different coding.

Ensure the tumor is a primary lesion with uncertain behavior, not a metastasis.

Do not confuse infratentorial brain tumors with spinal cord tumors (D43.4), as the brainstem transitions to the spinal cord at the foramen magnum.

Common Mistakes

HCC Buddy guidance

D43.0 (supratentorial brain) involves structures above the tentorium.

D33.1 (benign neoplasm, infratentorial brain) is used when pathology confirms benign behavior.

C71.6 (malignant neoplasm of cerebellum) and C71.7 (brainstem) are used for confirmed malignancies.

D43.2 (brain, unspecified) should not be used when infratentorial location is documented.

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 D43.1 an HCC code?

Yes. D43.1 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

V28HCC 23, Melanoma and Other Skin Cancers

0.251

V24HCC 12, Breast, Prostate, and Other Cancers and Tumors

0.150

ESRDHCC 12, Breast, Prostate, and Other Cancers and Tumors

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 D43.1

For D43.1to 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 D43.1 during that encounter, not just copy-forwarded from a problem list.

What This Code Means

D43.1 is the ICD-10-CM diagnosis code for neoplasm of uncertain behavior of brain, infratentorial. A growth in the lower part of the brain (below the tentorium, a membrane dividing brain regions) that cannot yet be classified as definitely cancer or definitely benign. D43.1 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, D43.1 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, D43.1 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 refers to structures below the tentorium cerebelli (cerebellum and brainstem); ensure this anatomical distinction is documented. Because D43.1 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 D43.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Infratentorial refers to structures below the tentorium cerebelli (cerebellum and brainstem); ensure this anatomical distinction is documented
•This code is for uncertain behavior lesions; confirmed malignant brain tumors use different C-codes

Clinical Significance

Neoplasms of uncertain behavior in the infratentorial brain involve structures below the tentorium cerebelli, including the cerebellum and brainstem. These tumors are particularly concerning due to their proximity to vital structures and may present with ataxia, cranial nerve deficits, or hydrocephalus from cerebrospinal fluid obstruction.

Documentation Requirements

✓Documentation must specify the infratentorial location (cerebellum or brainstem), supported by neuroimaging.
✓Pathology should describe features that preclude definitive benign or malignant classification.
✓Document any neurological symptoms including gait abnormalities, coordination deficits, or signs of increased intracranial pressure.

Commonly Confused Codes

•D43.0 (supratentorial brain) involves structures above the tentorium.
•D33.1 (benign neoplasm, infratentorial brain) is used when pathology confirms benign behavior.
•C71.6 (malignant neoplasm of cerebellum) and C71.7 (brainstem) are used for confirmed malignancies.
•D43.2 (brain, unspecified) should not be used when infratentorial location is documented.