Alphabetic Index FY2027

I66

Occlusion and stenosis of cerebral arteries, not resulting in cerebral infarction

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

Non-billable headerNot valid on its own. Use one of the more specific codes under it.

I66 is a non-billable ICD-10-CM code category for occlusion and stenosis of cerebral arteries, not resulting in cerebral infarction. Report a more specific code from it instead. It is part of the FY2027 code set, effective October 1, 2026. The more specific codes under it are I66.0 Occlusion and stenosis of middle cerebral artery, I66.1 Occlusion and stenosis of anterior cerebral artery, I66.2 Occlusion and stenosis of posterior cerebral artery, I66.3 Occlusion and stenosis of cerebellar arteries and 2 more. 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.

This code
  • 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.-)

Includes

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

This code
  • embolism of cerebral artery
  • narrowing of cerebral artery
  • obstruction (complete) (partial) of cerebral artery
  • thrombosis of cerebral artery

More specific codes under I66 6