Crystal's MCW Coder Hub🧬 ICD-10 CM I67.5 — Moyamoya disease
Billable Code Confirmed
ICD-10 CM I67.5 is a valid, billable 4-character ICD-10-CM code for FY2026. No further specificity (such as a 5th or 6th character) is required.
Clinical Context: Active Disease vs. Sequelae
Moyamoya is a chronic, progressive condition. Unlike an acute ischemic stroke that becomes “history of” once the patient is discharged, I67.5 is a lifelong active diagnosis1. It should be coded on all encounters where the disease is being managed, monitored, or is impacting medical decision-making. If the patient has residual deficits from past strokes caused by Moyamoya, code I67.5 alongside the specific sequelae codes (e.g., I69.854 for hemiplegia).
🔍 Code Description
ICD-10 CM I67.5 classifies Moyamoya disease, a rare, progressive cerebrovascular disorder caused by the gradual narrowing and ultimate occlusion of the distal internal carotid arteries (ICAs) and their proximal branches (the Circle of Willis)2.
In response to the severe restriction of normal blood flow to the brain, tiny, fragile collateral blood vessels develop at the base of the brain in an attempt to supply the ischemic tissue. On conventional cerebral angiography, this tangle of tiny compensatory vessels resembles a “puff of smoke”—which translates to moyamoya in Japanese2.
These collateral vessels are structurally weak and highly prone to rupture (causing hemorrhagic stroke) or thrombosis (causing ischemic stroke or TIAs).
🌳 Code Tree / Hierarchy
I67 Other cerebrovascular diseases ❌ Non-billable Category
│
├── I67.0 Dissection of cerebral arteries, nonruptured ✅ Billable
├── I67.1 Cerebral aneurysm, nonruptured ✅ Billable
├── I67.2 Cerebral atherosclerosis ✅ Billable
├── I67.3 Progressive vascular leukoencephalopathy ✅ Billable
├── I67.4 Hypertensive encephalopathy ✅ Billable
│
└── I67.5 Moyamoya disease ◀ THIS CODE ✅ Billable✅ Includes
The following clinical terms and scenarios map directly to I67.5:
-
Moyamoya disease (idiopathic, familial)
-
Moyamoya syndrome (Moyamoya-like vasculopathy secondary to another condition, such as sickle cell disease, Down syndrome, or prior cranial radiation)
-
Progressive intracranial arterial occlusion
📋 Clinical Overview
Pathophysiology
The exact etiology of primary Moyamoya disease is largely unknown, though genetic factors (such as the RNF213 gene mutation) are strongly implicated, especially in East Asian populations. The disease causes intimal thickening and smooth muscle proliferation in the terminal portions of the internal carotid arteries. This progressive stenosis triggers angiogenesis, forming the classic fragile collateral network at the base of the brain. The brain exists in a chronic state of hypoperfusion, making it exquisitely sensitive to changes in blood pressure or hyperventilation (which causes vasoconstriction)2.
Clinical Presentation
Moyamoya exhibits a bimodal age distribution, presenting differently in children versus adults:
-
Pediatric Patients (Peaks at age 5-10): Most commonly present with ischemic symptoms. Transient Ischemic Attacks (TIAs) or ischemic strokes are frequently triggered by hyperventilation (e.g., crying, blowing on hot food, playing a wind instrument)3.
-
Adult Patients (Peaks at age 30-50): While ischemia occurs, adults have a much higher incidence of intracranial hemorrhage due to the rupture of the fragile moyamoya vessels under systemic arterial pressure.
-
Other Symptoms: Chronic headaches, seizures, and cognitive decline due to chronic hypoperfusion.
Diagnosis
-
Cerebral Angiography: The gold standard. Demonstrates stenosis/occlusion of the terminal ICA and the “puff of smoke” collateral network3.
-
MRI/MRA: Shows narrowed vessels, multiple small ischemic infarcts, and the “ivy sign” (prominent leptomeningeal collaterals on FLAIR imaging).
-
Perfusion Studies: Identifies areas of the brain at highest risk of ischemia to plan surgical revascularization.
💰 HCC Risk Adjustment (CMS-HCC v28)
| Field | Detail |
|---|---|
| CMS-HCC Model Version | v28 (2024-2026 Implementation) |
| HCC Assignment | ❌ Not Mapped |
| HCC Category | N/A |
| RAF Coefficient | 0.000 |
Capture the Sequelae!
While I67.5 does not carry a RAF weight, the neurological damage it causes often does. If a Moyamoya patient has chronic deficits, you must code them to ensure accurate risk adjustment.
🛠️ CPT Procedural Crosswalk
Because the underlying occlusive process cannot be reversed with medication, treatment primarily relies on surgical revascularization to bypass the blocked arteries and restore blood flow to the ischemic brain.
Diagnostic Procedures
| CPT Code | Description | Clinical Application |
|---|---|---|
| 36224 | Selective catheter placement, internal carotid artery; with angiography | Gold standard diagnostic test for Moyamoya. |
| 70544 | Magnetic resonance angiography, head | Non-invasive monitoring of disease progression. |
Surgical Revascularization (Neurosurgery)
| CPT Code | Description | Clinical Application |
|---|---|---|
| 61711 | Anastomosis, arterial, extracranial-intracranial (eg, middle cerebral/cortical) | Direct Bypass: Standard Superficial Temporal Artery to Middle Cerebral Artery (STA-MCA) bypass. |
| 61250 | Burr hole(s) or trephine; with implantation of ventricular catheter, reservoir, EEG electrode(s), or other unspecified | Note: Indirect bypass procedures like EDAS (Encephaloduroarteriosynangiosis) or EMS (Encephalomyosynangiosis) do not have specific CPT codes and are often billed using unlisted neurosurgical codes (64999) or specific cranial/vascular combinations depending on payer policy. |
💊 Coding Scenarios and Examples
Scenario 1 — Pediatric Patient with TIA (Outpatient Neurology)
Clinical Vignette: A 7-year-old male with known Moyamoya disease presents for an urgent neurology follow-up. Yesterday, after crying intensely, he developed right-sided facial droop and right arm weakness that completely resolved within 30 minutes. An urgent MRI showed no acute infarction. Impression: TIA triggered by hyperventilation in the setting of Moyamoya.
ICD-10-CM:
-
G45.9 — Transient cerebral ischemic attack, unspecified (Primary reason for the urgent visit)
-
I67.5 — Moyamoya disease (The underlying chronic etiology causing the TIA)
Scenario 2 — Adult Admission for STA-MCA Bypass (Inpatient)
Clinical Vignette: A 42-year-old female with progressive right-sided Moyamoya syndrome and increasingly frequent TIAs is admitted for a planned direct revascularization. The neurosurgeon performs a right STA-MCA (Superficial Temporal Artery to Middle Cerebral Artery) anastomosis without complications.
Principal Diagnosis:
- I67.5 — Moyamoya disease
ICD-10-PCS (Inpatient Procedure):
031G0Z_— Bypass Cerebral Artery, open approach (Requires completion of the 6th and 7th characters based on the specific source and destination arteries in the operative report).
MS-DRG Assignment:
- DRG 021 (or similar tier) — Intracranial Vascular Procedures with CC. (The surgical procedure overrides the medical MDC 01 assignment).
Scenario 3 — Emergency Admission for Ruptured Moyamoya Vessel
Clinical Vignette: A 35-year-old male with undocumented medical history is brought to the ED unresponsive. CT head reveals a massive intraparenchymal hemorrhage in the left basal ganglia. Emergency angiogram demonstrates severe bilateral ICA stenosis with a massive “puff of smoke” collateral network and an actively bleeding ruptured collateral vessel. Impression: Acute intracerebral hemorrhage secondary to newly diagnosed Moyamoya disease.
Principal Diagnosis:
- I61.0 — Nontraumatic intracerebral hemorrhage in hemisphere, subcortical (The acute life-threatening event)
Additional Diagnosis:
- I67.5 — Moyamoya disease (The underlying etiology of the hemorrhage)
⚠️ Coding Pitfalls and Tips
| Pitfall or Tip | |
|---|---|
| ❌ | Do not code Moyamoya as “History of”. Even if the patient has had a successful surgical bypass and is currently asymptomatic, the underlying vascular disease of the ICA is permanent. It remains an active diagnosis (I67.5) for the patient’s lifetime1. |
| ❌ | Do not confuse with standard atherosclerosis. Do not code I67.2 (Cerebral atherosclerosis) for the stenosis seen in Moyamoya. The pathology is entirely different (fibrocellular intimal thickening, not cholesterol plaques)2. |
| ✅ | Differentiate Moyamoya Disease vs. Syndrome. “Disease” is usually idiopathic/genetic. “Syndrome” means it developed secondary to another condition (e.g., Sickle Cell D57.1, Neurofibromatosis Q85.00). If the provider documents “Moyamoya syndrome secondary to sickle cell,” code the underlying systemic condition in addition to I67.5. |
| ✅ | Code the late effects. If coding a rehabilitation or follow-up visit for a patient with left hemiparesis from a past Moyamoya stroke, use the specific combination code: I69.854 (Hemiplegia/hemiparesis following other cerebrovascular disease, left non-dominant) alongside I67.5. |
📚 Sources
1 CMS/NCHS. ICD-10-CM Official Guidelines for Coding and Reporting. Chronic diseases treated on an ongoing basis logic; Cerebrovascular Disease Guidelines.
2 Scott RM, Smith ER. Moyamoya disease and moyamoya syndrome. N Engl J Med. 2009. Pathophysiology, bimodal age presentation, and “puff of smoke” angiographic findings.
3 Ropper AH, Samuels MA, Klein JP. Adams and Victor’s Principles of Neurology. Clinical presentation, pediatric hyperventilation trigger, and surgical revascularization strategies.