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I63.332

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🧠 ICD-10 CM I63.332 - Cerebral Infarction Due to Thrombosis of Left Posterior Cerebral Artery

Quick Reference

Code: I63.332 Type: ICD-10-CM | Status: ✅ Billable & Valid FY2026 Description: Cerebral infarction due to thrombosis of the left posterior cerebral artery Combination Code: ❌ No — this code identifies mechanism (thrombosis) and vessel (left PCA) but does NOT bundle a separate upstream vascular condition Circulation: Posterior (Vertebrobasilar system) MDC: MDC 01 - Diseases and Disorders of the Nervous System

⚠️ Critical Coding Clinic Alert (AHA Q1 2022)

Per AHA Coding Clinic First Quarter 2022, if posterior cerebral artery infarction is documented WITHOUT a specified mechanism (no mention of thrombosis, embolism, occlusion, or stenosis), the correct code is I63.89 (Other cerebral infarction) — NOT I63.532. To assign I63.332, the provider must explicitly document “thrombosis” of the left PCA as the causative mechanism.

📋 Clinical Overview

ICD-10 CM I63.332 represents an ischemic stroke caused by thrombosis — the in-situ formation or propagation of a blood clot — within the left posterior cerebral artery (PCA). The PCA is an intracranial vessel belonging to the posterior (vertebrobasilar) circulation, which is anatomically and clinically distinct from the anterior carotid circulation. This is a mechanism-specific, laterality-specific code.

Unlike the precerebral combination codes (e.g., I63.231), this code does not function as a combination code — it identifies the arterial mechanism and location without simultaneously bundling an upstream carotid or vertebral stenosis. The “thrombosis” designation means the occlusion originated locally within the PCA itself (e.g., atherosclerotic plaque rupture with thrombus formation), as opposed to an embolus that traveled from a distant source.

For accurate assignment of I63.332, the treating physician must explicitly document:

  1. A cerebral infarction (not just “posterior circulation symptoms” or “TIA”)
  2. Thrombosis as the mechanism (not merely “occlusion,” “stenosis,” or unspecified)
  3. The left PCA as the affected vessel

🫀 Anatomy & Pathophysiology

Posterior Cerebral Artery — Origin & Segments

The posterior cerebral arteries (PCAs) are the terminal branches of the basilar artery, which itself is formed by the convergence of the two vertebral arteries at the pontomedullary junction. This makes the PCA anatomically part of the vertebrobasilar (posterior) circulation, not the carotid (anterior) circulation.

The left PCA is divided into functional segments:

SegmentLocationStructures Supplied
P1From basilar bifurcation → posterior communicating artery (PComA)Midbrain (cerebral peduncle, substantia nigra), thalamic perforators
P2Beyond PComA → around midbrainThalamus (lateral geniculate body), hippocampus, parahippocampal gyrus, posterior temporal lobe
P3Calcarine fissurePrimary visual cortex (V1), occipital lobe
P4Terminal cortical branchesOccipitoparietal and posterior temporal cortices

Why Thrombosis of the Left PCA Occurs:

  • Atherosclerosis of the basilar artery or proximal left PCA (most common in the P1 segment)
  • In-situ thrombosis on atherosclerotic plaque at the PCA origin
  • Basilar artery disease with clot propagation into the PCA
  • Small vessel disease (lipohyalinosis) affecting distal PCA branches
  • Hypercoagulable states (antiphospholipid syndrome, polycythemia vera)
  • Arterial dissection (vertebral artery dissection with propagation)

Thrombosis vs. Embolism — The Mechanism Distinction

Thrombosis = clot forms in place at the diseased vessel wall (atherosclerotic, inflammatory, or hypercoagulable mechanism) embolism = clot travels from a distant source (cardiogenic AFib, valvular disease, or artery-to-artery embolism from the aorta or vertebrals) Documentation MUST specify which mechanism. If cardioembolic stroke is documented, use I63.432 instead.

🧬 Clinical Presentation of Left PCA Territory Infarction

Left PCA infarction produces a characteristic constellation of posterior circulation deficits that differ markedly from anterior (carotid) strokes. The left PCA primarily serves the left occipital lobe, left thalamus, left medial temporal lobe, and parts of the left midbrain.

Cortical (Distal / P3-P4 Occlusion) Manifestations:

  • Right homonymous hemianopia — most common presentation; due to infarction of the left calcarine cortex (primary visual area V1); patient may be unaware of the field cut
  • Prosopagnosia — inability to recognize familiar faces; due to infarction of the left fusiform gyrus
  • Alexia without agraphia — patient cannot read but can write; caused by disconnection of the splenium of the corpus callosum from the left visual cortex (classic left PCA finding)
  • Color anomia / achromatopsia — inability to name or perceive colors in the right visual field
  • Visual object agnosia — inability to recognize objects visually despite intact primary vision

Thalamic / Deep (Proximal / P1-P2 Occlusion) Manifestations:

  • Right-sided hemisensory loss — thalamic infarction (VPL nucleus) producing contralateral pain, temperature, and proprioception deficits
  • Thalamic pain syndrome (Dejerine-Roussy) — delayed central post-stroke pain syndrome in the contralateral limbs
  • Memory impairment — left thalamic and hippocampal involvement
  • Homonymous hemianopia — lateral geniculate body infarction

Midbrain Manifestations (P1 Occlusion):

  • Ipsilateral CN III palsy — left oculomotor nerve involvement (ptosis, mydriasis, “down and out” gaze)
  • Contralateral hemiplegia — cerebral peduncle involvement (Weber syndrome)
  • Vertical gaze palsy — dorsal midbrain involvement
  • Altered consciousness — if both PCAs or basilar apex is involved

NIHSS Considerations for PCA Stroke:

Important

Left PCA strokes are classically under-scored by standard NIHSS because the scale heavily weights motor and language deficits, while PCA strokes predominantly cause visual and sensory/cognitive deficits that receive fewer NIHSS points. A patient with dense right homonymous hemianopia and alexia may have an NIHSS of only 2-4 yet have significant functional impairment. Document this clinical nuance carefully.

🗂️ Code Classification / Hierarchy

I00-I99  ............ Diseases of the Circulatory System
  I60-I69  ......... Cerebrovascular Diseases
    I63  ........... Cerebral Infarction
      I63.3  ....... Cerebral infarction due to thrombosis of cerebral arteries
        I63.31  .... Thrombosis of middle cerebral artery
        I63.32  .... Thrombosis of anterior cerebral artery
        I63.33  .... Thrombosis of posterior cerebral artery
          I63.331 .. Right PCA (BILLABLE)
          I63.332 .. Left PCA (BILLABLE) ← YOU ARE HERE
          I63.333 .. Bilateral PCA (BILLABLE)
          I63.339 .. Unspecified PCA (BILLABLE)
        I63.34  .... Thrombosis of cerebellar artery
        I63.39  .... Thrombosis of other/unspecified cerebral artery

🌳 Full Code Tree - I63.3 Thrombosis of Cerebral Arteries

CodeDescriptionVesselLaterality
I63.311Cerebral infarction due to thrombosis of right middle cerebral arteryMCARight
I63.312Cerebral infarction due to thrombosis of left middle cerebral arteryMCALeft
I63.319Cerebral infarction due to thrombosis of unspecified middle cerebral arteryMCAUnspecified
I63.321Cerebral infarction due to thrombosis of right anterior cerebral arteryACARight
I63.322Cerebral infarction due to thrombosis of left anterior cerebral arteryACALeft
I63.329Cerebral infarction due to thrombosis of unspecified anterior cerebral arteryACAUnspecified
I63.331Cerebral infarction due to thrombosis of right posterior cerebral arteryPCARight
I63.332Cerebral infarction due to thrombosis of left posterior cerebral arteryPCALeft ← YOU ARE HERE
I63.333Cerebral infarction due to thrombosis of bilateral posterior cerebral arteriesPCABilateral
I63.339Cerebral infarction due to thrombosis of unspecified posterior cerebral arteryPCAUnspecified
I63.341Cerebral infarction due to thrombosis of right cerebellar arteryCerebellarRight
I63.342Cerebral infarction due to thrombosis of left cerebellar arteryCerebellarLeft
I63.343Cerebral infarction due to thrombosis of bilateral cerebellar arteriesCerebellarBilateral
I63.349Cerebral infarction due to thrombosis of unspecified cerebellar arteryCerebellarUnspecified

Left PCA - Full Mechanism Code Comparison:

CodeMechanismWhen to Use
I63.332ThrombosisPhysician explicitly documents “thrombosis” of left PCA
I63.432EmbolismPhysician explicitly documents “embolism” of left PCA (e.g., AFib, cardioembolic)
I63.532Unspecified occlusion/stenosisImaging or physician documents occlusion or stenosis of left PCA, mechanism not stated
I63.89Other / no mechanism statedPCA infarction documented WITHOUT any specified mechanism (per AHA CC Q1 2022)

Mechanism Must Be Documented

Do NOT assign I63.332 based solely on imaging findings (MRI showing PCA territory infarct). The physician must document “thrombosis” as the mechanism. Imaging-only with no mechanism stated → use I63.89 per AHA CC Q1 2022.

✅ Includes

Per the ICD-10-CM Tabular List, category I63 includes:

  • Occlusion and stenosis of cerebral and precerebral arteries resulting in cerebral infarction

This confirms I63.332 is appropriate when:

  • The left posterior cerebral artery (an intracranial/cerebral artery) is the documented causative vessel
  • Thrombosis is explicitly documented as the mechanism
  • The result is a cerebral infarction (not TIA, not a reversible ischemic neurological deficit)

🚫 Excludes

Excludes1 (Mutually exclusive — cannot be coded simultaneously with I63.332)

CodeDescription
P91.82Neonatal cerebral infarction — applies exclusively to the neonatal age group; I63.332 must not be assigned concurrently

Excludes2 (Not included here but may be coded additionally when clinically applicable)

CodeDescription
Z86.73Personal history of TIA and cerebral infarction without residual deficits — report when patient has a prior resolved stroke; can be coded with I63.332 for a new acute event
I69.3Sequelae of cerebral infarction — use I69.3- subcodes for residual deficits from a prior infarction; do NOT code I63.332 at chronic follow-up unless a new acute infarction has occurred

Acute vs. Post-Acute Phase

I63.332 = the active, acute infarction event only. After discharge, when the patient presents with ongoing deficits (e.g., persistent right homonymous hemianopia), transition to the appropriate I69.3- sequelae code. Assigning I63.332 at post-acute outpatient encounters without a new stroke event is a reportable coding error and may trigger payer audits.

➕ Use Additional Code (Mandatory When Available)

CodeDescriptionApplication
R29.7NIHSS ScoreAssign a subcode from R29.70-R29.74 to report the NIHSS score when documented by any licensed provider in the record. Critically important for PCA strokes, which are frequently underscored on NIHSS despite significant functional deficits.

NIHSS Subcodes:

CodeNIHSS RangeStroke Severity
R29.70Score 0No stroke symptoms
R29.71Score 1-4Minor stroke (common in isolated PCA territory)
R29.72Score 5-15Moderate stroke
R29.73Score 16-20Moderate-severe stroke
R29.74Score 21-42Severe stroke

PCA-Specific NIHSS Note

Many left PCA strokes register an NIHSS of only 1-4 (R29.71 = “minor stroke”) because the standard scale under-weights visual field deficits and cognitive deficits. Yet the patient may have profound functional impairment (can’t drive, can’t read, unsafe ambulation). CDI teams should query the provider to capture the full functional impact in the documentation even if the NIHSS score is low.

🏥 MS-DRG Assignment

I63.332 maps to the Intracranial Hemorrhage or Cerebral Infarction DRG family under MDC 01 (CMS MS-DRG v41.1, FY2026).

MS-DRGTitleAssignment Criteria
064Intracranial Hemorrhage or Cerebral Infarction with MCCAt least one qualifying MCC present as secondary diagnosis
065Intracranial Hemorrhage or Cerebral Infarction with CC or tPA in 24 HoursAt least one qualifying CC — OR — tPA/alteplase administered within 24 hours
066Intracranial Hemorrhage or Cerebral Infarction without CC/MCCNo qualifying CC or MCC present; no tPA within 24 hours

tPA Administration → Automatic DRG 065:

Important

Administration of tPA (alteplase/tenecteplase) within 24 hours of stroke onset triggers DRG 065 regardless of whether any CC or MCC is present. Additionally, Z9282 (Status post administration of tPA at a different facility within the last 24 hours) triggers DRG 065 for transfer patients. Ensure tPA administration time and route are explicitly documented.

Common MCCs for DRG 064 Elevation:

  • Acute respiratory failure requiring mechanical ventilation
  • Sepsis (any type)
  • Coma or depressed level of consciousness
  • Acute kidney injury
  • Status epilepticus
  • Severe (protein-calorie) malnutrition
  • Concurrent acute MI

Common CCs for DRG 065 Elevation:

  • Dysphagia — post-stroke (R13.10-R13.19); PCA strokes may cause dysphagia if brainstem or midbrain is involved
  • Hemiplegia or hemiparesis following cerebral infarction
  • Aspiration pneumonitis/pneumonia (J69.0)
  • Urinary tract infection
  • Atrial fibrillation (I48.11, I48.19, or other I48.- subcodes)
  • Hypertensive heart disease
  • Dehydration

CDI Note for PCA Strokes:

Posterior circulation strokes frequently present with subtle findings (visual field cuts, memory changes, sensory loss) that may not initially be appreciated as MCC/CC-level comorbidities. CDI query opportunities include thalamic involvement, memory impairment severity, aspiration risk secondary to brainstem involvement, and whether dysphagia is present — all can significantly affect DRG tier.

📊 HCC Risk Adjustment

I63.332 maps to HCC 96 (CMS-HCC V24) and HCC 224 (CMS-HCC V28) under Medicare Advantage risk adjustment.

ModelHCCHCC DescriptionStatus
CMS-HCC V24HCC 96StrokeHigh-weight; suppresses less-specific stroke codes in same hierarchy
CMS-HCC V28HCC 224Ischemic or Unspecified StrokeV28 fully implemented in 2026; replaces V24 blended calculation

V28 Full Implementation (2026)

CMS phased the V28 model in at one-third in 2024, two-thirds in 2025, and fully in 2026. For plan year 2026, V28 is the exclusive risk adjustment model for Medicare Advantage. HCC 224 under V28 captures ischemic stroke codes including I63.332.

HCC Capture Best Practices:

  • Annual re-documentation required: The HCC is only credited in the year it is coded. A stroke documented in 2025 does NOT automatically carry to 2026 — re-document and re-code every year.
  • Hierarchy suppression: HCC 96/224 suppresses less-specific stroke codes (e.g., I63.9) within the same hierarchy. Always code to the highest specificity available.
  • Specificity value: Using I63.332 (thrombosis, left PCA) rather than I63.9 maximizes HCC capture accuracy, CDI credit, and risk adjustment integrity.
  • Post-acute HCC: Use I69.3-series sequelae codes (if residual deficits persist) or Z86.73 (if no residual deficits) for post-acute chronic care — do NOT continue using I63.332.

💵 wRVU & Assistant Payable

FieldValue
wRVU⚠️ Not Applicable - I63.332 is a diagnosis code. Work RVUs (wRVUs) are assigned to CPT procedure codes and E/M services billed by the treating provider. The wRVU earned is tied to the CPT code reported, not this diagnosis code.
Assistant Payable⚠️ Not Applicable - Assistant surgeon payability is a function of the CPT procedure code used for any surgical intervention, not the diagnosis. For any neurovascular intervention, consult the individual CPT code’s assistant surgeon indicator in the CMS Medicare Physician Fee Schedule.

Common CPT Procedures Associated with This Diagnosis

The following CPT codes may be reported by the profee team in connection with I63.332 (verify current CPT guidelines and payer policies):

  • 37195 - Thrombolysis, cerebral, by intravenous infusion (IV tPA)
  • 61645 - Percutaneous arterial mechanical thrombectomy and/or infusion for thrombolysis, intracranial (endovascular thrombectomy)
  • 70553 - MRI brain with and without contrast
  • 93886 - Transcranial Doppler (TCD) study, intracranial arteries, complete
  • 99221-99223 - Initial hospital care E/M
  • 99231-99233 - Subsequent hospital care E/M
  • 99291-99292 - Critical care E/M (if applicable) (Always verify current CPT coding guidelines, assistant surgeon indicators, and modifier requirements individually.)

🔗 Related & Associated Codes

Left PCA — All Mechanism Codes Side by Side:

CodeMechanismWhen to Use
I63.332ThrombosisPhysician explicitly documents “thrombosis” of left PCA
I63.432EmbolismPhysician explicitly documents “embolism” of left PCA (e.g., AFib-related, cardioembolic)
I63.532Unspecified occlusion/stenosisImaging or physician documents occlusion or stenosis of left PCA, mechanism not stated
I63.89Other cerebral infarctionPCA infarction documented without any mention of mechanism (per AHA CC Q1 2022)

Posterior Circulation - Related Stroke Codes:

CodeDescription
I63.331Cerebral infarction due to thrombosis of right posterior cerebral artery
I63.333Cerebral infarction due to thrombosis of bilateral posterior cerebral arteries
I63.339Cerebral infarction due to thrombosis of unspecified posterior cerebral artery
I63.341Cerebral infarction due to thrombosis of right cerebellar artery
I63.342Cerebral infarction due to thrombosis of left cerebellar artery

Sequelae Codes — Post-Discharge / Chronic Follow-Up:

CodeDescription
I69.398Other sequelae of cerebral infarction (use for residual visual field defects, cognitive deficits, alexia)
I69.391Dysphagia following cerebral infarction
I69.351Hemiplegia/hemiparesis following cerebral infarction, right dominant side
I69.352Hemiplegia/hemiparesis following cerebral infarction, left dominant side
Z86.73Personal history of TIA and cerebral infarction without residual deficits
I63.9Cerebral infarction, unspecified — avoid when specificity is available

📝 Coding Guidelines & Clinical Notes

Official Guideline Highlights (ICD-10-CM FY2026):

  1. Mechanism Documentation Requirement: I63.332 requires the treating physician to explicitly document “thrombosis” as the causative mechanism. Coders and CDI specialists cannot independently infer thrombosis from imaging findings alone.

  2. AHA Coding Clinic Q1 2022 (Critical Update): The current guidance states that posterior cerebral artery infarction without a documented mechanism should be coded to I63.89 (Other cerebral infarction). A prior Coding Clinic (Q2 2017) had advised I63.532, but this was superseded by Q1 2022. Ensure your facility coding policy reflects the updated guidance.

  3. Laterality Specificity: The “left” in I63.332 refers to the left posterior cerebral artery (the vessel), not left-sided neurological deficits. Left PCA infarction typically causes right-sided visual and sensory deficits. Document vessel laterality from imaging reports.

  4. Sequelae vs. Acute:

    • Acute admission: Code I63.332 as principal (or secondary, depending on admission reason)
    • After discharge with chronic deficits: Transition to I69.3-series sequelae codes
    • After discharge, deficit-free: Use Z86.73

  5. NIHSS — Always Code When Documented: Assign the appropriate R29.7- subcode whenever an NIHSS score is documented by any provider in the record.

  6. AFib and Left PCA Infarction: Atrial fibrillation is a major stroke risk factor, but its presence does NOT automatically confirm embolic mechanism. If the physician documents thrombosis despite AFib, use I63.332 and separately code the AFib (e.g., I48.11). Only use I63.432 if embolism is explicitly documented.

  7. Bilateral PCA Infarction: If both PCAs are affected by thrombosis, use I63.333 (bilateral) rather than coding I63.332 and I63.331 separately.

🩺 Coding Examples / Clinical Scenarios

📌 Example 1 - Classic Left PCA Stroke, Minor NIHSS (DRG 066)

Clinical Scenario: A 68-year-old male presents to the ED reporting sudden inability to read (alexia) and a dark area in his right visual field. MRI confirms acute left PCA territory infarction of the left occipital lobe and splenium. MRA shows thrombosis of the left P3 segment. Attending neurologist documents: “Acute ischemic stroke due to thrombosis of the left posterior cerebral artery.” NIHSS = 3 (right visual field defect only). No significant comorbidities. No tPA administered.

Codes Assigned:

  • I63.332 - Cerebral infarction due to thrombosis of left posterior cerebral artery (Principal Dx)
  • R29.71 - NIHSS score 1-4 (Use additional code)

MS-DRG: DRG 066 - No CC/MCC, no tPA

CDI Note: Despite NIHSS of 3, this patient has profound functional impairment (alexia without agraphia, can’t drive, can’t read). Query the provider to document functional severity for care planning even if DRG tier is not elevated.

📌 Example 2 - Left PCA Stroke with tPA (DRG 065)

Clinical Scenario: A 72-year-old female with hypertension and basilar atherosclerosis presents with sudden right homonymous hemianopia and right hemisensory loss. CTA confirms left PCA occlusion via thrombosis. Neurologist documents: “Acute cerebral infarction, thrombosis of the left posterior cerebral artery.” IV alteplase administered 2 hours post-onset. NIHSS = 7. PMH: hypertension and type 2 diabetes.

Codes Assigned:

  • I63.332 - Cerebral infarction, thrombosis, left PCA (Principal Dx)
  • R29.72 - NIHSS score 5-15
  • I10 - Essential hypertension (Secondary)
  • E11.9 - Type 2 diabetes mellitus without complications (Secondary)

MS-DRG: DRG 065 - tPA administered within 24 hours

📌 Example 3 - Deep PCA (P1) Infarction with Thalamic Involvement + MCC (DRG 064)

Clinical Scenario: An 80-year-old male presents with acute altered consciousness, right hemisensory loss, and left CN III palsy. MRI demonstrates acute infarction of the left thalamus, left midbrain, and left occipital lobe. Attending documents: “Acute left PCA thrombosis with infarction of the left thalamus, midbrain, and occipital lobe.” NIHSS = 18. He develops aspiration pneumonitis requiring mechanical ventilation.

Codes Assigned:

  • I63.332 - Cerebral infarction due to thrombosis of left PCA (Principal Dx)
  • R29.73 - NIHSS score 16-20
  • J69.0 - Pneumonitis due to aspiration (MCC)

MS-DRG: DRG 064 - MCC present

📌 Example 4 - Incorrect Mechanism / Coding Clinic Q1 2022 Application

Clinical Scenario: A 66-year-old female is admitted with sudden right homonymous hemianopia. MRI confirms left PCA territory infarction. Radiologist documents: “Acute infarct in the left PCA distribution.” Attending discharge summary states: “Acute ischemic stroke, left PCA territory.” No mention of thrombosis, embolism, occlusion, or stenosis anywhere in the chart.

Correct Code:

  • I63.89 - Other cerebral infarction (per AHA Coding Clinic Q1 2022)

Do NOT Assign:

  • ❌ I63.332 - Thrombosis not documented by physician
  • ❌ I63.532 - Occlusion/stenosis not documented (prior Q2 2017 Coding Clinic — superseded)

CDI Query Opportunity: Send a query to the attending requesting clarification of the mechanism. If thrombosis can be specified, amend to I63.332 for HCC capture and maximum specificity.

📌 Example 5 - AFib Present but Thrombosis Explicitly Documented (Not Embolic)

Clinical Scenario: A 74-year-old male with paroxysmal AFib on anticoagulation presents with left PCA infarction. Bubble echo and monitoring show no active thrombus. Neurologist documents: “Acute cerebral infarction due to in-situ thrombosis of the left posterior cerebral artery; atherosclerotic plaque at the P1 segment with local clot. No evidence of cardioembolic source despite known AFib.”

Codes Assigned:

  • I63.332 - Thrombosis explicitly documented (Principal Dx)
  • R29.71 - NIHSS score (if 1-4)
  • I48.11 - Long-standing persistent atrial fibrillation (Secondary — comorbidity only, not the causative mechanism)

Coder Note: Do NOT change to I63.432 (embolism) simply because AFib is present. The physician explicitly documented thrombosis as the mechanism. Code what is documented.

📌 Example 6 - Annual HCC Capture at Outpatient Follow-Up (MA Patient)

Clinical Scenario: A 77-year-old Medicare Advantage patient returns to neurology 11 months post-left PCA stroke. She has persistent right homonymous hemianopia and alexia. Neurologist documents: “Status post left PCA thrombotic stroke; residual right homonymous hemianopia and alexia without agraphia persisting.”

Correct Codes:

  • I69.398 - Other sequelae of cerebral infarction (use for residual visual/cognitive deficits — I63.332 should NOT be assigned post-acute)

HCC Note: Confirm whether I69.398 maps to HCC under V28 for the current plan year against the CMS HCC mapping file. The provider documentation of chronic residual effects also supports quality metrics and STAR ratings.

⚠️ Common Coding Errors & Pitfalls

❌ Error✅ Correct Practice
Assigning I63.332 based solely on radiology finding of PCA territory infarctionRequires physician documentation of “thrombosis” — radiology alone is insufficient
Using I63.532 when no mechanism is documented (post-2022)Use I63.89 per AHA Coding Clinic Q1 2022
Assigning I63.432 (embolism) because AFib is presentOnly use I63.432 if the physician explicitly documents embolic mechanism
Coding I63.332 at post-acute outpatient follow-up without a new acute eventUse I69.3-series for residual deficits; Z86.73 for resolved stroke
Using laterality of neurological deficits to determine vessel lateralityI63.332 = left PCA (the vessel); neurological deficits are contralateral (right-sided)
Omitting R29.7- NIHSS code when documentedAlways assign NIHSS subcode; PCA strokes often have low NIHSS despite significant impairment
Coding I63.332 and I63.331 simultaneously for bilateral PCA infarctionUse I63.333 for bilateral PCA thrombosis
Using I63.9 when vessel and mechanism are both documentedI63.332 provides maximal specificity — I63.9 is only for truly unspecifiable infarctions

📄 Documentation Requirements Checklist

  • Diagnosis: Explicit documentation of “cerebral infarction” or “ischemic stroke” (not just “TIA” or “posterior circulation event”)
  • Mechanism: Provider explicitly documents “thrombosis” of the left PCA — required for this code
  • Vessel: Left posterior cerebral artery identified as the causative vessel (from imaging, MRA, or clinical reasoning)
  • Laterality: Left PCA specifically documented (not just “posterior cerebral artery” without laterality)
  • NIHSS Score: Documented by MD/DO/NP/PA for R29.7- use additional code assignment
  • Timeline: Acute vs. sequelae delineated in the discharge summary
  • Imaging: MRI/MRA or CT/CTA findings consistent with left PCA territory infarction and/or thrombosis
  • Comorbidities: All active comorbidities affecting care documented for CC/MCC capture
  • tPA Status: Time, route, and administration documented for DRG 065 eligibility
  • Functional Impact: Especially critical for PCA strokes — document visual field deficits, cognitive changes, alexia, memory loss for accurate severity representation

🔑 Key Takeaways for Inpatient Profee Coders

  • I63.332 requires explicit provider documentation of “thrombosis” — do not infer mechanism from imaging alone
  • Per AHA Coding Clinic Q1 2022: PCA infarction without documented mechanism = I63.89, NOT I63.532
  • Left PCA strokes are in the posterior (vertebrobasilar) circulation — clinically and anatomically distinct from carotid territory strokes
  • Neurological deficits are contralateral to the vessel (right-sided deficits from left PCA) — do not confuse vessel laterality with deficit laterality
  • NIHSS frequently underscores PCA strokes — CDI opportunity to query for full functional impact documentation
  • AFib does not automatically equal embolic mechanism — if thrombosis is documented despite AFib, use I63.332
  • HCC 96 / HCC 224 annual capture is essential; re-document and re-code every plan year for MA patients
  • Post-acute follow-up: transition from I63.332 to I69.3-series sequelae codes or Z86.73

Sources: ICD-10-CM FY2026 Tabular List & Alphabetic Index — cms.gov AHA Coding Clinic Q1 2022 (PCA infarction mechanism guidance) — ahacodingclinic.org AHA Coding Clinic Q2 2017 (superseded PCA guidance) — ahacodingclinic.org CMS MS-DRG v41.1 Definitions Manual, MDC 01 — cms.gov/icd10m CMS-HCC V24 & V28 Risk Adjustment Models; V28 fully implemented 2026 — cms.gov StatPearls: Posterior Cerebral Artery Stroke — ncbi.nlm.nih.gov/books/NBK532296 Medscape: Posterior Cerebral Artery Stroke — emedicine.medscape.com Radiopaedia: PCA Infarct — radiopaedia.org AAPC ICD-10-CM Code Reference — aapc.com UASI Solutions: CVA Coding Specificity — uasisolutions.com

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