⚕️ICD-10 CM I63.331 - Cerebral infarction due to thrombosis of bilateral vertebral arteries

Code Description

ICD-10 I63.331 represents Cerebral infarction due to thrombosis of bilateral vertebral arteries. This code specifies an acute ischemic stroke caused by a blood clot (thrombus) forming within both the left and right vertebral arteries, leading to tissue death (infarction) in the brain areas supplied by these vessels, typically the brainstem and cerebellum.^{CMS ICD-10}

Clinical Overview

The vertebral arteries supply blood to the posterior part of the brain (posterior circulation). Thrombosis in these arteries can result in lateral medullary syndrome (Wallenberg syndrome) or more extensive brainstem strokes. Symptoms may include vertigo, dysphagia, ataxia, crossed sensory deficits, and potentially locked-in syndrome if the basilar artery is also compromised. This is a medical emergency requiring immediate intervention.^NINDS

Coding Hierarchy (Code Tree)

This code exists within the following hierarchy in the ICD-10-CM structure:

Chapter IX: Diseases of the circulatory system (I00-I99)
- Block: Cerebrovascular diseases (I60-I69)
  - Category: Cerebral infarction (I63)
    - Subcategory: Cerebral infarction due to thrombosis of cerebral arteries (I63.3)
      - Sub-subcategory: Cerebral infarction due to thrombosis of vertebral arteries (I63.33)
        
        Code: Cerebral infarction due to thrombosis of bilateral vertebral arteries (I63.331)

Official Coding Guidelines & Notes

Includes

This code includes conditions specified as:

Occlusion and stenosis of bilateral vertebral arteries causing cerebral infarction
Thrombosis of bilateral vertebral arteries causing cerebral infarction^{WHO ICD-10}

Excludes1

Note: Excludes1 means “not coded here”. If the patient has this condition, do not use I63.331. Code the excluded condition instead.

Sequelae of cerebral infarction (I69.331) - Use for late effects.
Transient cerebral ischemic attacks (G45.0)
Cerebral infarction due to embolism (I63.231)^{CMS ICD-10}

Excludes2

Note: Excludes2 means “not included here”. The patient may have both conditions, but code separately.

Atherosclerosis of vertebral artery (I65.23) - Code additionally if documented as the underlying cause.
Occlusion and stenosis of vertebral artery without infarction (I65.23)^{CMS ICD-10}

Coding Tips

Acute vs. Sequelae: Use I63.331 only for acute cerebral infarction. If the patient is being seen for residual conditions (e.g., hemiplegia, aphasia) resulting from a past stroke, use codes from category I69 (e.g., I69.331).^{Coding Clinic}
Underlying Etiology: If the thrombosis is due to atherosclerosis, code the atherosclerosis (I65.23) as an additional diagnosis.
Laterality: This code specifically indicates bilateral involvement. If only one side is affected, use I63.332 (left) or I63.333 (right).
NIHSS Score: Document and code the National Institutes of Health Stroke Scale (NIHSS) score using code R29.7- if assessed.^{CMS ICD-10}
Coma/Dysphagia: Assign additional codes for associated conditions like coma (R40.-) or dysphagia (R13.1-) if present.^{CMS ICD-10}

Reimbursement & Risk Adjustment

HCC (Hierarchical Condition Category)

Status: Yes
Model: CMS-HCC V28 (2024 Model)
Category: Acute Ischemic Stroke maps to HCC categories related to Cardiovascular/Cerebrovascular Disease (e.g., HCC 53).^{CMS Risk Adjustment}
Impact: Accurate documentation of I63.331 is critical for Medicare Advantage plans. It indicates a high-risk acute event that significantly impacts the Risk Adjustment Factor (RAF) score for the encounter year.

wRVU (Work Relative Value Unit)

Value: N/A
Reason: I63.331 is an ICD-10-CM diagnosis code. wRVU values are assigned to CPT/HCPCS procedure codes (e.g., 99223), not diagnosis codes.^{AMA CPT}

Assistant Surgeon Payable

Status: N/A
Reason: Assistant surgeon modifiers (e.g., -80, -81, -82) apply to surgical CPT codes. Diagnosis codes do not have assistant payable status.^{CMS MPFS}

Applicability: Yes
Impact: I63.331 is a principal diagnosis driver for Stroke DRGs.
MDC: MDC 01 (Diseases and Disorders of the Nervous System).
DRGs: Typically assigns to DRG 034 (Craniotomy with Major Device Implant or Acute Complex CNS Pdx w MCC), DRG 035 (…w/o MCC), DRG 036 (Extracranial Procedures w MCC), or DRG 037-039 (Extracranial Procedures w/o CC/MCC). Specific assignment depends on procedures performed (e.g., thrombectomy) and complications.^{CMS MS-DRG}
CC/MCC: The presence of this code often triggers CC/MCC logic depending on comorbidities like mechanical ventilation or coma.

Coding Examples

Example 1: Acute Stroke Admission

Scenario: A patient presents to the ER with sudden onset vertigo and difficulty swallowing. MRI confirms acute infarction due to thrombosis of bilateral vertebral arteries. Patient undergoes mechanical thrombectomy.

Principal Diagnosis: I63.331 (Cerebral infarction due to thrombosis of bilateral vertebral arteries)
Secondary Diagnosis: I65.23 (Occlusion and stenosis of bilateral vertebral arteries) - if documented as underlying cause
Secondary Diagnosis: R13.10 (Dysphagia, unspecified)
Procedure: 61645 (Mechanical thrombectomy, intracranial artery)
Note: Ensure the procedure code matches the approach and vessels treated.^{Coding Clinic}

Example 2: Stroke Follow-Up (Sequelae)

Scenario: Patient seen 6 months post-stroke for residual dysphagia and ataxia. The acute stroke was I63.331.

Principal Diagnosis: I69.331 (monoplegia of lower limb following cerebral infarction) - Example of sequelae code
Secondary Diagnosis: I69.391 (Other sequelae of cerebral infarction) - for dysphagia/ataxia
Note: Do not use I63.331 for this encounter. Use I69 series for late effects.^{CMS ICD-10}

Example 3: Critical Care Management

Scenario: Patient with acute I63.331 requires critical care management for hemodynamic instability.

Diagnosis: I63.331
Procedure: 99291 (Critical care, evaluation and management of the critically ill or critically injured patient; first 30-74 minutes)
Note: Time must be documented to support critical care billing.^{AMA CPT}

While I63.331 does not use modifiers, associated E/M or Procedure codes might:

-25: Significant, Separately Identifiable Evaluation and Management Service by the Same Physician or Other Qualified Health Care Professional on the Same Day of the Procedure or Other Service.
-59: Distinct Procedural Service.
-50: Bilateral Procedure (if applicable to associated vascular studies, though the diagnosis itself specifies bilateral).
-RT / -LT: Right Side / Left Side (if applicable to related unilateral procedures).
-CC: Complication/Comorbidity (used in some payer contexts, though not standard CPT).
-CG: Policy requirement applied to an item or service when reported on a claim (used for PDGM in home health).^{AMA CPT}

Sources

^{CMS ICD-10} Centers for Medicare & Medicaid Services, ICD-10-CM Official Guidelines for Coding and Reporting. ^NINDS National Institute of Neurological Disorders and Stroke, Stroke Information Page. ^{WHO ICD-10} World Health Organization, ICD-10 Version:2019. ^{Coding Clinic} AHA Coding Clinic for ICD-10-CM/PCS. ^{CMS Risk Adjustment} CMS Medicare Advantage Risk Adjustment Data Processing System. ^{AMA CPT} American Medical Association, CPT Professional Edition. ^{CMS MPFS} CMS Medicare Physician Fee Schedule. ^{CMS MS-DRG} CMS Medicare Severity Diagnosis Related Groups Definitions Manual.

Explorer

I63.331