I66.01 (Occlusion and stenosis of right middle cerebral artery) compared with I66.09 (Occlusion and stenosis of unspecified middle cerebral artery), from the official CMS tabular data. I66.01 and I66.09 code the same condition on opposite sides.
Same condition; these differ only in which side is documented.
These codes share a category and title and differ only in the side affected. The documentation decides which applies, and a bilateral code is reported only where the code set provides one.
Source: ICD-10-CM tabular list (laterality variant derived from the code title)
Same condition, opposite side. I66.01 and I66.09 name the same condition on opposite sides of the body.
Same category and title, differing only in which side is affected — the documentation decides which one applies, and a bilateral code is reported only where the code set provides one.
| I66.01Occlusion and stenosis of right middle cerebral artery | I66.09Occlusion and stenosis of unspecified middle cerebral artery | |
|---|---|---|
| Billing status | Billable | Billable |
| Classification | I00-I99 — Diseases of the Circulatory System (I00-I99) | I00-I99 — Diseases of the Circulatory System (I00-I99) |
| Definition | Occlusion and stenosis of right middle cerebral artery is a billable ICD-10-CM diagnosis code (I66.01). | Occlusion and stenosis of unspecified middle cerebral artery is a billable ICD-10-CM diagnosis code (I66.09). |
| Includes | embolism of cerebral artery narrowing of cerebral artery obstruction (complete) (partial) of cerebral artery thrombosis of cerebral artery | embolism of cerebral artery narrowing of cerebral artery obstruction (complete) (partial) of cerebral artery thrombosis of cerebral artery |
| Use additional code | code to identify presence of: alcohol abuse and dependence (F10.-) exposure to environmental tobacco smoke (Z77.22) | code to identify presence of: alcohol abuse and dependence (F10.-) exposure to environmental tobacco smoke (Z77.22) |
Derived from the official CMS ICD-10-CM tabular data (FY2026). Not billing advice; verify sequencing rules for the encounter. All data sources