Crystal's MCW Coder Hub🧬 ICD-10 CM I63.333 — Cerebral Infarction Due to Thrombosis of Bilateral Posterior Cerebral Arteries
Quick Reference
Code: I63.333 | Billable: Yes | Chapter: 9 — Circulatory | HCC Cat: 100 | MCC: Yes | POA Required: Yes
Description
ICD-10 CM I63.333 identifies an ischemic stroke caused by thrombotic occlusion of both posterior cerebral arteries (PCAs) simultaneously. The posterior cerebral arteries are the terminal branches of the basilar artery, supplying the occipital lobes, thalami, midbrain, and medial temporal lobes bilaterally. Thrombotic bilateral PCA occlusion is a high-acuity, high-mortality event producing devastating bilateral posterior circulation deficits including cortical blindness, severe memory impairment, thalamic dysfunction, and altered consciousness.
The mechanism is thrombosis — distinguishing this code from embolic occlusion (I63.433) and unspecified occlusion/stenosis (I63.533). Mechanism documentation by the provider is essential for correct code assignment and is one of the most frequent CDI query triggers in stroke coding.
Code Structure & Hierarchy
Code Tree
- Chapter: 9 — Diseases of the Circulatory System (I00-I99)
- Block: I60-I69 — Cerebrovascular Diseases
- I60 — Nontraumatic subarachnoid hemorrhage
- I61 — Nontraumatic intracerebral hemorrhage
- I62 — Other nontraumatic intracranial hemorrhage
- I63 — Cerebral infarction ← this category
- I63.0 — Thrombosis of precerebral arteries
- I63.1 — Embolism of precerebral arteries
- I63.2 — Unspecified occlusion/stenosis of precerebral arteries
- I63.3 — Thrombosis of cerebral arteries ← this branch
- I63.4 — Embolism of cerebral arteries
- I63.5 — Unspecified occlusion/stenosis of cerebral arteries
- I63.6 — Cerebral venous thrombosis, nonpyogenic
- I63.8 — Other cerebral infarction
- I63.9 — Cerebral infarction, unspecified
Mechanism Matters — Thrombosis vs. Embolism vs. Unspecified
Mechanism Bilateral PCA Code Thrombosis I63.333 ← this code Embolism I63.433 Unspecified occlusion/stenosis I63.533 Unspecified mechanism I63.9 — use only as last resort Provider documentation must explicitly state the mechanism. If only “occlusion” is documented without thrombosis or embolism specified, query the provider or use I63.533.
Instructional Notes
Excludes1 — Mutually Exclusive
Cannot be coded together with I63.333 under any circumstance:
- Transient ischemic attacks and related syndromes (G45.-) — TIA by definition resolves without infarction; if imaging confirms infarct, code I63.333
- Traumatic intracranial hemorrhage (S06.-) — traumatic mechanism changes the coding pathway entirely
Excludes2 — Not Included Here, May Co-exist
May be coded in addition to I63.333 when separately present and documented:
- Cerebral infarction due to embolism of bilateral posterior cerebral arteries (I63.433) — separate mechanism, separate event
- Sequelae of cerebral infarction (I69.3-) — used for residual neurological deficits from a prior (not current) stroke encounter
Use Additional Code — Required Add-ons
Always code the following when applicable:
- Z92.82 — Status post tPA administration at a different facility within 24 hours prior to current admission (critical for transfer stroke patients)
- R29.7- — NIH Stroke Scale (NIHSS) score — assign the specific score code (R29.700-R29.742) documented at time of admission
- T36-T50 with 5th/6th character 5 — if stroke is adverse effect of a drug
- Hypertension (I10, I11.-, I12.-, I13.-) — code as secondary diagnosis when present and managed
- Atrial fibrillation (I48.-) — code separately; has independent HCC weight and impacts sequencing considerations
- Hyperlipidemia (E78.-), diabetes (E11.-) — code when present and managed during the encounter
Clinical Description
Bilateral posterior cerebral artery (PCA) territory infarction is among the most severe stroke presentations. The PCAs originate from the basilar artery at the top of the basilar (tip-of-the-basilar syndrome) and supply critical posterior brain structures.
Vascular territory supplied by the PCA:
- Primary visual cortex (calcarine cortex) — bilateral involvement causes cortical blindness
- Posterior thalamus and pulvinar — bilateral thalamic infarcts cause profound memory loss, hypersomnia, and altered consciousness
- Hippocampus and parahippocampal gyrus — bilateral involvement causes dense anterograde amnesia
- Midbrain and upper pons (via perforating branches)
- Posterior limb of internal capsule and posterior corona radiata (via perforating branches)
Classic clinical presentations of bilateral PCA occlusion:
- Cortical blindness with Anton syndrome (patient denies blindness, confabulates visual experiences)
- Bilateral visual field defects (bilateral homonymous hemianopia → tunnel vision or complete cortical blindness)
- Top-of-the-basilar syndrome — cortical blindness + oculomotor abnormalities + altered consciousness + memory impairment
- Bilateral thalamic infarction — hypersomnia, memory loss, behavioral changes, vertical gaze palsy
- Balint syndrome — simultanagnosia, optic ataxia, oculomotor apraxia (rare, with bilateral parieto-occipital involvement)
Common thrombotic etiologies to document:
- Large artery atherosclerosis of the basilar artery or PCA origin (most common)
- Hypercoagulable states (antiphospholipid syndrome, factor V Leiden, protein C/S deficiency)
- Vertebrobasilar dissection propagating to PCA
- In-situ thrombosis in the setting of severe hemodynamic compromise
Coding Guidelines
Official Guideline Reference
ICD-10-CM Official Guidelines FY2025, Section I.C.9.d — Cerebrovascular Disease
- Assign I63.- for ischemic stroke (cerebral infarction). The category includes occlusion and stenosis of cerebral arteries resulting in infarction.
- If a patient is admitted with stroke and expires, the stroke code is still assigned as the principal diagnosis.
- During the inpatient acute stroke encounter, assign deficit codes from I69.- only if the deficit is explicitly listed as a residual from a prior stroke, not the current one. Current neurological deficits (hemiplegia, aphasia, dysphagia) are captured using codes from I69.- only after discharge, or coded separately from their own categories (R-codes) during the acute stay.
- Guideline I.C.9.d.3 — When a patient has a cerebral infarction and hypertension, assign both I63.- and the appropriate hypertension code as secondary.
- Guideline I.C.9.d.4 — tPA administration: If the patient received tPA at another hospital within 24 hours, assign Z92.82 in addition to I63.333.
Sequencing Tips
- Principal diagnosis (inpatient): I63.333 is the PDx when the patient is admitted for acute ischemic stroke. Do not sequence a complication (e.g., aspiration pneumonia) as PDx if stroke was the condition that prompted admission.
- Secondary diagnoses: Hypertension, atrial fibrillation, diabetes, hyperlipidemia, and other chronic conditions actively managed during the stay should all be coded as secondary — each may carry CC/MCC or HCC weight.
- Outpatient (follow-up): Use I69.398 or other I69.3- codes for residual neurological deficits at post-stroke follow-up encounters; I63.333 is used for the acute event only.
- POA indicator: Almost always Y — acute stroke is present on admission. If stroke developed post-operatively or after admission for another reason, POA = N (and triggers HAC review — stroke as a HAC).
- NIHSS: Always capture R29.7- at admission — CMS requires NIHSS for stroke quality metrics and it supports medical necessity documentation.
HCC Mapping
HCC Risk Adjustment
HCC Relevant: Yes HCC Model: CMS-HCC v28 HCC Category: Category 100 — Ischemic or Unspecified Stroke HCC Coefficient: 0.658 Risk Adjustment Impact: High
A coefficient of 0.658 adds approximately 1,000 of base rate annually per Medicare Advantage beneficiary — one of the highest-weighted neurological HCC categories.
HCC Capture Tips
- Stroke under I63.- maps to HCC Category 100, one of the highest-weighted categories in v28 — accurate and complete coding is critical for MA plan risk adjustment
- Recapture: Chronic stroke sequelae coded under I69.3- also map to HCC 100 at follow-up encounters — ensure sequelae are coded at every visit where they are assessed or treated
- Comorbidity stacking: Atrial fibrillation (I48.-) maps separately to HCC 96 — code both when present to capture full RAF
- Diabetes + stroke combination: Type 2 diabetes (E11.-) maps to HCC 37 — coding all relevant chronic conditions at each encounter maximizes legitimate risk capture
- Do not use I63.9 (unspecified cerebral infarction) when vessel and mechanism are documented — specificity to I63.333 confirms HCC Category 100 mapping and defends against audit
MS-DRG Mapping
DRG Assignment
MS-DRG Description MDC GMLOS 061 Ischemic Stroke, Precerebral Occlusion or Transient Ischemia with Thrombolytic Agent, with MCC MDC 1 5.6 062 Ischemic Stroke, Precerebral Occlusion or Transient Ischemia with Thrombolytic Agent, with CC MDC 1 4.1 063 Ischemic Stroke, Precerebral Occlusion or Transient Ischemia with Thrombolytic Agent, without CC/MCC MDC 1 3.2 064 Intracranial Hemorrhage or Cerebral Infarction with MCC or tPA in 24hrs MDC 1 5.9 065 Intracranial Hemorrhage or Cerebral Infarction with CC or tPA in 24hrs MDC 1 4.1 066 Intracranial Hemorrhage or Cerebral Infarction without CC/MCC MDC 1 2.8
CC/MCC Status
- MCC status: Yes — I63.333 itself qualifies as an MCC when present as a secondary diagnosis on another principal diagnosis, driving DRG upgrade
- CC status: N/A — MCC supersedes CC
- HAC designation: Yes — Stroke/cerebral infarction is a CMS Hospital-Acquired Condition when POA = N (stroke that develops after admission). POA accuracy is essential.
- POA exempt: No — POA indicator is required and directly affects HAC determination and CC/MCC applicability
- tPA impact: Administration of tPA (whether at this facility or within 24hrs at a transferring facility via Z92.82) triggers DRG 061-063 assignment, which carries significantly higher relative weight than DRG 064-066
CPT Crosswalk
| CPT | Description |
|---|---|
| 61645 | Percutaneous arterial transluminal mechanical thrombectomy and/or infusion, intracranial, any method, including diagnostic angiography, fluoroscopic guidance |
| 61650 | Endovascular intracranial prolonged administration of pharmacologic agents, including catheter placement |
| 70553 | MRI brain with and without contrast |
| 70498 | CT angiography, head, with contrast |
| 93880 | Duplex scan of extracranial arteries, bilateral |
| 36223 | Selective catheter placement, right common carotid or innominate, retrograde, with angiography |
| 36224 | Selective catheter placement, left common carotid, with angiography |
| 99291 | Critical care, first 30-74 minutes |
| 99223 | Initial hospital care, high complexity |
ICD-10-PCS Crosswalk
PCS Applicability
ICD-10-PCS applies in the inpatient setting only. Procedures for acute bilateral PCA thrombosis may include mechanical thrombectomy, thrombolysis, or diagnostic imaging performed as part of the inpatient admission.
| PCS Code | Root Operation | Body Part | Approach | Device | Qualifier |
|---|---|---|---|---|---|
| 03RG0JZ | Replacement | Intracranial artery, right | Open | Synthetic substitute | No qualifier |
| 03RH0JZ | Replacement | Intracranial artery, left | Open | Synthetic substitute | No qualifier |
| 3E030GC | Introduction | Peripheral vein | Percutaneous | Other therapeutic substance | Other substance (tPA) |
| B030YZZ | Fluoroscopy | Intracranial arteries | — | No contrast | No qualifier |
Character breakdown — mechanical thrombectomy (right intracranial):
- Section: 0 — Medical and Surgical
- Body System: 3 — Upper Arteries
- Root Operation: C — Extirpation (removing solid matter)
- Body Part: G — Intracranial Artery
- Approach: 3 — Percutaneous
- Device: Z — No Device
- Qualifier: Z — No Qualifier → 03CG3ZZ
ICD-10-CM Crosswalk
| Code | Description | Relationship |
|---|---|---|
| I63.331 | Cerebral infarction, thrombosis, right PCA | Unilateral equivalent |
| I63.332 | Cerebral infarction, thrombosis, left PCA | Unilateral equivalent |
| I63.339 | Cerebral infarction, thrombosis, unspecified PCA | Less specific — avoid if laterality known |
| I63.433 | Cerebral infarction, embolism, bilateral PCA | Same territory, embolic mechanism |
| I63.533 | Cerebral infarction, unspecified occlusion, bilateral PCA | Same territory, unspecified mechanism |
| I63.02 | Cerebral infarction, thrombosis of basilar artery | Upstream vessel — tip-of-basilar syndrome |
| I63.6 | Cerebral infarction due to cerebral venous thrombosis | Venous mechanism — distinct pathophysiology |
| G45.3 | Amaurosis fugax | TIA equivalent — excludes infarction |
| I65.1 | Occlusion/stenosis of basilar artery without infarction | No infarction confirmed |
| I66.3 | Occlusion/stenosis of posterior cerebral artery without infarction | No infarction confirmed |
| I69.318 | Aphasia following cerebral infarction | Sequela — use at follow-up, not acute |
| I69.398 | Other sequelae of cerebral infarction | Sequela — use at follow-up, not acute |
| R29.700 | NIHSS score 0 | Use additional — document stroke severity |
| Z92.82 | Status post tPA at outside facility within 24 hours | Use additional — critical for transfer patients |
| I48.0 | Paroxysmal atrial fibrillation | Common comorbidity — code separately |
| I10 | Essential hypertension | Code separately when managed during stay |
Coding Examples
Example 1 — Acute Bilateral PCA Stroke with tPA Transfer, Inpatient
Scenario: A 71-year-old Medicare patient presents to a community ED with sudden onset cortical blindness, confusion, and bilateral visual field loss. CT angiography confirms bilateral posterior cerebral artery thrombotic occlusion. tPA is administered at the outside facility. Patient is transferred to a comprehensive stroke center for mechanical thrombectomy consideration. MRI confirms bilateral occipital and thalamic infarction. Hypertension and atrial fibrillation are managed during the stay. NIHSS score on admission is 18. Principal Dx: I63.333 — Cerebral infarction due to thrombosis of bilateral posterior cerebral arteries Secondary Dx: Z92.82 — Status post tPA at outside facility within 24 hours Secondary Dx: R29.716 — NIHSS score 16-19 (use specific score code per documentation) Secondary Dx: I48.0 — Paroxysmal atrial fibrillation Secondary Dx: I10 — Essential hypertension PCS: 03CG3ZZ — Extirpation, intracranial artery, percutaneous (mechanical thrombectomy) POA: Y — all diagnoses present on admission DRG: 061 — Ischemic Stroke with Thrombolytic Agent, with MCC (I48.0 = MCC) Notes: Z92.82 is critical for DRG 061-063 assignment when tPA was given at the transferring facility. Without it, the case drops to DRG 064-066. NIHSS must match the documented admission score precisely.
Example 2 — Bilateral PCA Stroke, No tPA, Severe Deficits, Inpatient
Scenario: An 83-year-old patient is admitted directly from clinic with a 6-hour history of confusion, inability to see, and inability to ambulate. MRI DWI confirms bilateral occipital and posterior thalamic infarction. CTA shows bilateral PCA thrombotic occlusion. Patient is outside the tPA window. Aspiration pneumonia develops on day 2. Type 2 diabetes with CKD stage 3 also managed. Principal Dx: I63.333 — Cerebral infarction due to thrombosis of bilateral posterior cerebral arteries Secondary Dx: J69.0 — Aspiration pneumonia (POA = N — developed after admission) Secondary Dx: E11.65 — Type 2 diabetes with hyperglycemia Secondary Dx: N18.3- — CKD stage 3 (MCC) Secondary Dx: R29.730 — NIHSS score 20-24 (document specific score) Secondary Dx: I10 — Hypertension POA: I63.333 — Y; J69.0 — N DRG: 064 — Intracranial Hemorrhage or Cerebral Infarction with MCC (N18.3 = MCC) Notes: J69.0 with POA=N triggers HAC review — aspiration pneumonia is not on the stroke HAC list, but document clinical justification. N18.3 (CKD stage 3) is an MCC driving DRG 064. Accurate CC/MCC capture is essential here.
Example 3 — Post-Stroke Follow-up, Outpatient
Scenario: Patient seen in neurology clinic 6 weeks after discharge for bilateral PCA stroke (I63.333). Residual cortical blindness and short-term memory impairment persist. Hypertension and atrial fibrillation follow-up also addressed. First-listed Dx: I69.398 — Other sequelae of cerebral infarction (covers residual cortical blindness and memory impairment from prior stroke) Additional Dx: I48.0 — Paroxysmal atrial fibrillation Additional Dx: I10 — Essential hypertension CPT: 99214 — Office visit, established patient, moderate complexity Notes: I63.333 is NOT used at the follow-up visit — the acute stroke has resolved; I69.3- codes capture the residual deficits. I69.398 also maps to HCC Category 100, maintaining RAF capture at follow-up.
Coding Pitfalls & Tips
Common Errors
- Using I63.9 (cerebral infarction, unspecified) when vessel and mechanism are clearly documented in the record — massive specificity loss and HCC/DRG impact
- Confusing thrombosis (I63.333) with embolism (I63.433) — mechanism must be explicitly stated by the provider; do not infer mechanism from imaging alone without physician documentation
- Failing to add Z92.82 when the patient received tPA at a transferring facility — causes DRG to drop from 061-063 to 064-066, a significant reimbursement difference
- Coding I69.3- sequelae during the acute inpatient stroke encounter — I69 codes are reserved for residual deficits from prior strokes, not the current event
- Missing the NIHSS code (R29.7-) — required for stroke quality reporting and supports medical necessity; it is a “use additional code” instruction
- Not coding comorbidities (A-fib, HTN, DM) that were managed during the stay — each may carry CC/MCC weight affecting DRG assignment
- Assigning POA = N when stroke was present on admission — triggers HAC review and prevents I63.333 from functioning as an MCC on secondary DX position
Pro Tips
- The distinction between precerebral (I63.0-I63.2, e.g., basilar, vertebral, carotid) and cerebral (I63.3-I63.5, e.g., MCA, ACA, PCA) arteries is crucial — PCA is a cerebral artery, not a precerebral artery
- Top-of-the-basilar syndrome frequently involves both the basilar (I63.02) and bilateral PCAs (I63.333) — query the provider about whether both should be coded or which was the primary occlusion
- Bilateral PCA infarction in a young patient should trigger query for hypercoagulable state — if confirmed (e.g., antiphospholipid syndrome D68.61), code it separately for HCC and clinical completeness
- For transfer patients, always verify: (1) Was tPA given? (2) At which facility? (3) Within 24 hours of current admission? — all three determine Z92.82 applicability and DRG selection
- Cortical blindness as a presenting symptom of bilateral PCA stroke is frequently miscoded under ophthalmology codes — confirm neurological etiology with provider before assigning eye-specific codes
CDI Query Opportunities
CDI Flags
- Mechanism specificity: Is the stroke mechanism documented as thrombosis, embolism, or unspecified occlusion? Imaging alone (CTA showing filling defect) does not establish mechanism — physician must document. Query if only “occlusion” or “stroke” is noted.
- Vessel specificity: Is the posterior cerebral artery explicitly named, or is the documentation vague (e.g., “posterior circulation stroke,” “basilar territory”)? Query for vessel specification to support I63.333 vs. I63.02 vs. I63.9.
- Bilateral confirmation: Are both PCAs confirmed occluded/infarcted on imaging AND documented as bilateral by the physician in the assessment? Imaging alone is insufficient — physician must link findings in the clinical documentation.
- tPA administration: Was tPA given at a transferring facility within 24 hours? If yes, Z92.82 must be assigned — confirm with transfer records and document in the physician note.
- NIHSS score: Is the NIHSS score documented on admission? Required for R29.7- coding and CMS stroke quality metrics — query nursing or neurology note if missing from attending documentation.
- Atrial fibrillation: Is A-fib documented and managed? Even if it is listed as the suspected cause (embolic mechanism), if the attending documents thrombosis as the mechanism, I63.333 applies — but A-fib should still be coded separately as a comorbidity.
- Hypercoagulable state: In younger patients or those without traditional stroke risk factors, query for underlying hypercoagulable disorder — antiphospholipid syndrome (D68.61), Factor V Leiden (Z86.718), protein C/S deficiency.
- Aspiration/dysphagia: Bilateral posterior stroke frequently causes dysphagia (R13.10) and aspiration risk — if aspiration pneumonia develops, confirm POA status and document clinical circumstances clearly.
- Cortical blindness: If Anton syndrome or cortical blindness is present, query for explicit documentation — H47.631-H47.639 (cortical blindness) can be coded in addition to I63.333 when documented as a distinct clinical finding.
Related Codes
- Laterality family: I63.331, I63.332, I63.339
- Same territory, different mechanism: I63.433 (embolism), I63.533 (unspecified occlusion)
- Upstream vessels: I63.02 (basilar artery thrombosis), I63.013 (bilateral vertebral artery thrombosis)
- Without infarction: I65.1 (basilar stenosis), I66.3 (PCA stenosis without infarction)
- Sequelae: I69.318, I69.398, I69.391
- Required add-ons: Z92.82, R29.7-
- Common comorbidities: I48.0, I10, E11.-, D68.61
- CPT crosswalk: 61645, 61650, 70553, 70498, 93880
- PCS crosswalk: 03CG3ZZ, 03CH3ZZ, 3E030GC
Sources
ICD-10-CM Official Guidelines for Coding and Reporting FY2025. CMS/NCHS. ICD-10-CM Tabular List of Diseases and Injuries FY2025. CMS. CMS MS-DRG Definitions Manual v42. Centers for Medicare & Medicaid Services. CMS-HCC Risk Adjustment Model v28 Coefficients and Category Mappings. CMS, 2024. AHA Coding Clinic for ICD-10-CM/PCS. American Hospital Association. Fourth Quarter 2023; First Quarter 2024. CMS Hospital-Acquired Conditions (HAC) Reduction Program FY2025. Centers for Medicare & Medicaid Services. Powers WJ, et al. 2019 AHA/ASA Guideline for the Early Management of Acute Ischemic Stroke. Stroke. 2019;50(12). AHA/ASA Stroke Coding and Billing Guide 2025. American Heart Association.