Alphabetic Index FY2027

I66.02

Occlusion and stenosis of left middle cerebral artery

FY2027Chapter 9: Diseases of the circulatory system/I60–I69 Cerebrovascular diseases

BillableComplete code, valid to report
Care settingsHome Health Primary · Neuro Rehabilitation

I66.02 (also written I6602) is a billable ICD-10-CM diagnosis code for occlusion and stenosis of left middle cerebral artery. It is part of the FY2027 code set, effective October 1, 2026. It is one of the 15 codes in category I66 (Occlusion and stenosis of cerebral arteries, not resulting in cerebral infarction). Its coding notes include a Use additional code instruction, 2 Excludes1 entries and 10 Excludes2 entries.

Use additional code

Add the listed code as a secondary code, if known.

Also from chapter/block level (8 notes)
Inherited from I60–I69 Cerebrovascular diseases
  • 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)

Excludes1

Not coded here. The listed conditions generally should not be reported together.

Inherited from I66 Occlusion and stenosis of cerebral arteries, not resulting in cerebral infarction
  • Occlusion and stenosis of cerebral artery causing cerebral infarction (I63.3-I63.5)
Also from chapter/block level (1 note)
Inherited from I60–I69 Cerebrovascular diseases
  • traumatic intracranial hemorrhage (S06.-)

Excludes2

Not included here. Both codes may be reported if the patient has both conditions.

Also from chapter/block level (10 notes)
Inherited from Chapter 9 Diseases of the circulatory system
  • 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.-)

Care settings

How CMS programs treat this code. These are CMS claim edits and list entries, not coverage or eligibility rules.

Home Health Primary

Accepted as the primary (principal) diagnosis on a home health claim. The Home Health Grouper assigns it to the Neuro Rehabilitation clinical group.

Source: CMS Home Health Grouper Software v07.2.26, effective October 1, 2026

Includes

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

Inherited from I66 Occlusion and stenosis of cerebral arteries, not resulting in cerebral infarction
  • embolism of cerebral artery
  • narrowing of cerebral artery
  • obstruction (complete) (partial) of cerebral artery
  • thrombosis of cerebral artery