2027 ICD-10-CM Diagnosis Code I66.8Occlusion and stenosis of other cerebral arteries

ICD-10-CM Codes›I00–I99›I60-I69›I66

ICD-10-CM I66.8
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

I66.8 is a billable ICD-10-CM diagnosis code for occlusion and stenosis of other cerebral arteries. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 61 through 63, 67 through 68, 791, 793. Coders also document this condition as cerebral ischemic stroke due to small artery occlusion. 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
I66.8
Billable Status
Yes — Valid for Submission
Code Describes
Occlusion and stenosis of other cerebral arteries
Short Description
Occlusion and stenosis of other cerebral arteries
Same as the full description in the CMS dataset.
Parent Code
I66
Occlusion and stenosis of cerebral arteries, not resulting in cerebral infarction

Code Classification

ChapterI00–I99Diseases of the circulatory system
SectionI60-I69Cerebrovascular diseases
CategoryI66Occlusion and stenosis of cerebral arteries, not resulting in cerebral infarction
This CodeI66.8Occlusion and stenosis of other cerebral arteries

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Cerebral ischemic stroke due to small artery occlusion
  • Embolus of circle of Willis
  • Ophthalmic artery occlusion
  • Thrombosis of posterior communicating artery

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to I66.8: its own notes plus those printed at I66, block I60-I69, and Chapter 9. A note printed at a category, block or chapter applies to every code under it.

Includes

Further defines, or gives examples of, the content of the category.

From I66 Occlusion and stenosis of cerebral arteries, not resulting in cerebral infarction applies to 15 codes
  • embolism of cerebral artery
  • narrowing of cerebral artery
  • obstruction (complete) (partial) of cerebral artery
  • thrombosis of cerebral artery

Applicable To

Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.

  • Occlusion and stenosis of perforating arteries

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

From I66 Occlusion and stenosis of cerebral arteries, not resulting in cerebral infarction applies to 15 codes
  • Occlusion and stenosis of cerebral artery causing cerebral infarction (I63.3-I63.5)
From Block I60-I69 Cerebrovascular diseases applies to 410 codes
  • traumatic intracranial hemorrhage (S06.-)

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Chapter 9 (I00-I99) Diseases of the circulatory system applies to 1,433 codes
  • certain conditions originating in the perinatal period (P04-P96)
  • certain infectious and parasitic diseases (A00-B99)
  • complications of pregnancy, childbirth and the puerperium (O00-O9A)
  • congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
  • endocrine, nutritional and metabolic diseases (E00-E88)
  • injury, poisoning and certain other consequences of external causes (S00-T88)
  • neoplasms (C00-D49)
  • symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)
  • systemic connective tissue disorders (M30-M36)
  • transient cerebral ischemic attacks and related syndromes (G45.-)

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From Block I60-I69 Cerebrovascular diseases applies to 410 codes
  • code to identify presence of:
  • alcohol abuse and dependence (F10.-)
  • exposure to environmental tobacco smoke (Z77.22)
  • history of tobacco dependence (Z87.891)
  • hypertension (I10-I1A)
  • occupational exposure to environmental tobacco smoke (Z57.31)
  • tobacco dependence (F17.-)
  • tobacco use (Z72.0)

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name I66.8, its category, or a range that includes it.

Excludes2 1

These codes carry an Excludes2 note naming I66.8: its condition is not part of those codes, and both may be reported when the patient has both.

  • I74 Arterial embolism and thrombosis
    cerebral embolism and thrombosis (I63.3-I63.5, I66.-) names I66.-, which includes this code

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

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 I66.8 to ICD-9-CMHistory

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

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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About I66.8Overview

What is the ICD-10 code for occlusion and stenosis of other cerebral arteries?

The ICD-10-CM code for occlusion and stenosis of other cerebral arteries is I66.8 (sometimes written as I668). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is I66.8 a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report occlusion and stenosis of other cerebral arteries on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does I66.8 group to?

When occlusion and stenosis of other cerebral arteries is the principal diagnosis on an inpatient stay, it groups to MS-DRG 793, 791, 68, 67, 61, 62, 63, with relative weights from 0.9011 to 4.2192 depending on complications. Higher weights mean higher Medicare reimbursement.

Can I66.8 be reported with a code from S06?

Not as a rule. The Excludes1 note at block I60-I69, which applies to I66.8, lists "traumatic intracranial hemorrhage (S06.-)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).

What is the ICD-9 equivalent of I66.8?

Under the General Equivalence Mappings, occlusion and stenosis of other cerebral arteries converts to ICD-9-CM 434.90 (crbl art oc NOS wo infrc). The mapping is approximate, so confirm the match fits the documentation.