I66 — Occlusion and stenosis of cerebral arteries, not resulting in cerebral infarction
Is I66 billable?
No — I66 is a non-billable header code. I66 groups more specific codes and cannot be submitted on a claim. A valid ICD-10-CM code must be reported at the highest level of specificity available in its branch. Select one of the 15 billable codes beneath I66.
Billable codes under this header
- I66.3Occlusion and stenosis of cerebellar arteries
- I66.8Occlusion and stenosis of other cerebral arteries
- I66.9Occlusion and stenosis of unspecified cerebral artery
- I66.01Occlusion and stenosis of right middle cerebral artery
- I66.02Occlusion and stenosis of left middle cerebral artery
- I66.03Occlusion and stenosis of bilateral middle cerebral arteries
- I66.09Occlusion and stenosis of unspecified middle cerebral artery
- I66.11Occlusion and stenosis of right anterior cerebral artery
- I66.12Occlusion and stenosis of left anterior cerebral artery
- I66.13Occlusion and stenosis of bilateral anterior cerebral arteries
- I66.19Occlusion and stenosis of unspecified anterior cerebral artery
- I66.21Occlusion and stenosis of right posterior cerebral artery
- I66.22Occlusion and stenosis of left posterior cerebral artery
- I66.23Occlusion and stenosis of bilateral posterior cerebral arteries
- I66.29Occlusion and stenosis of unspecified posterior cerebral artery
I66 at a glance
| Code | I66 |
|---|---|
| Description | Occlusion and stenosis of cerebral arteries, not resulting in cerebral infarction |
| Billable | No — header code |
| Code set | ICD-10-CM FY2027 |
| Valid for encounters | October 1, 2026 – September 30, 2027 |
Excludes1 — never code together
The conditions below can never be reported together with I66 on the same claim. An Excludes1 note means the two conditions cannot occur in the same patient, so reporting both is a coding error.
- Occlusion and stenosis of cerebral artery causing cerebral infarction (I63.3-I63.5)
Includes
Conditions classified to I66.
- embolism of cerebral artery
- narrowing of cerebral artery
- obstruction (complete) (partial) of cerebral artery
- thrombosis of cerebral artery
Excludes1 — never code together — inherited from I60-I69
The conditions below can never be reported together with I66 on the same claim. An Excludes1 note means the two conditions cannot occur in the same patient, so reporting both is a coding error.
- traumatic intracranial hemorrhage (S06.-)
Use additional code — inherited from I60-I69
Report an additional code alongside I66 to fully describe the condition. I66 is sequenced first.
Excludes2 — not included here — inherited from Chapter 9
The conditions below are not part of I66, but a patient may have both at the same time. When documentation supports it, I66 and the excluded code may both be reported.
- 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.-)
What codes fall under I66? (6)
- I66.0Occlusion and stenosis of middle cerebral arterynot billable
- I66.1Occlusion and stenosis of anterior cerebral arterynot billable
- I66.2Occlusion and stenosis of posterior cerebral arterynot billable
- I66.3Occlusion and stenosis of cerebellar arteries
- I66.8Occlusion and stenosis of other cerebral arteries
- I66.9Occlusion and stenosis of unspecified cerebral artery
How long has I66 existed?
I66 has been in ICD-10-CM since at least FY2016, the earliest fiscal year on record here.
Derived from the official order files for FY2016–FY2026. FY2017 and FY2020 publish no order file, so those years are not covered.
Which codes are confused with I66?
ICD-10-CM declares these codes mutually exclusive with I66 — exactly one of each pair can be correct for a given encounter.