2026 ICD-10-CM Diagnosis Code I66.09Occlusion and stenosis of unspecified middle cerebral artery

ICD-10-CM Codes›I00–I99›I60-I69›I66

ICD-10-CM I66.09
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

I66.09 is a billable ICD-10-CM diagnosis code for occlusion and stenosis of unspecified middle cerebral artery. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026). Coders also document this condition as asymptomatic occlusion of artery. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Occlusion or stenosis of precerebral or cerebral arteries without infarction.

Code Identity

ICD-10-CM Code
I66.09
Billable Status
Yes — Valid for Submission
Code Describes
Occlusion and stenosis of unspecified middle cerebral artery
Short Description
Occlusion and stenosis of unspecified middle cerebral artery
Same as the full description in the CMS dataset.
Parent Code
I66.0
Occlusion and stenosis of middle cerebral artery

Code Classification

ChapterI00–I99Diseases of the circulatory system
SectionI60-I69Cerebrovascular diseases
CategoryI66Occlusion and stenosis of cerebral arteries, not resulting in cerebral infarction
This CodeI66.09Occlusion and stenosis of unspecified middle cerebral artery

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Asymptomatic occlusion of artery
  • Asymptomatic occlusion of middle cerebral artery
  • Asymptomatic stenosis of intracranial artery
  • Asymptomatic stenosis of middle cerebral artery
  • Embolism of middle cerebral artery
  • Middle cerebral artery occlusion
  • Occlusion and stenosis of middle cerebral artery
  • Occlusion and stenosis of middle cerebral artery without infarction
  • Stenosis of middle cerebral artery
  • Thrombosis of middle cerebral artery

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR CIR023
Occlusion or stenosis of precerebral or cerebral arteries without infarction
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Brain Diseases

Your brain is the control center of your body. It controls your thoughts, memory, speech, and movement. It regulates the function of many organs. It's part of your nervous system, which also includes your spinal cord and peripheral nerves. The nervous system sends signals between your brain and the rest of the body.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert I66.09 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
434.00 Crbl thrmbs wo infrct
Approximate The match is approximate rather than exact.
ICD-9-CM
434.10 Crbl emblsm wo infrct
Approximate The match is approximate rather than exact.
ICD-9-CM
434.90 Crbl art oc NOS wo infrc
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About I66.09Overview

Is I66.09 (Occlusion and stenosis of middle cerebral artery) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report occlusion and stenosis of unspecified middle cerebral artery on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What is the ICD-9 equivalent of I66.09?

Under the General Equivalence Mappings, occlusion and stenosis of unspecified middle cerebral artery converts to ICD-9-CM 434.00 (crbl thrmbs wo infrct), 434.10 (crbl emblsm wo infrct), and 434.90 (crbl art oc NOS wo infrc). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.