ICD-10 Code I66.09 – Occlusion and stenosis of unspecified middle cerebral artery (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code I66.09 – Occlusion and stenosis of unspecified middle cerebral artery
What it is
This code identifies narrowing or blockage of a middle cerebral artery when the affected side is not specified. It refers to an arterial circulation problem in the brain, not a stroke subtype by itself.
Clinical signs
Clinical features vary; refer to documentation. Commonly recorded findings may include focal neurologic deficits such as weakness, speech disturbance, or sensory changes, with imaging showing MCA narrowing or occlusion.
When to use this code
Use this code when the provider documents occlusion or stenosis of the middle cerebral artery but does not identify the right or left side. It is also appropriate when imaging confirms the lesion and the record supports an unspecified MCA location. If the side is documented, choose the more specific code.
Do not use for
Do not use it for stenosis or occlusion of a different cerebral artery, or when the record specifies the right or left middle cerebral artery. Check documentation if the note only describes stroke symptoms without confirming arterial narrowing or blockage.
Coding tip
Verify whether the documentation names the side; unspecified codes are correct only when laterality is not available.