Ischemic infarction — the death of brain tissue from interrupted blood supply — is the most common neuropathologic process in adults. A focal infarct produces a stereotyped sequence of changes that unfold over hours, days, weeks, and months. Recognizing where in this evolution a lesion sits is fundamental: it allows the pathologist to estimate when the injury occurred, the clinician to interpret imaging, and both to identify what other findings should and should not be present. This page covers the temporal evolution of cerebral infarction at the histologic and gross level, the patterns of infarct distribution, and the secondary findings.

The Temporal Evolution of Infarction

The classical staging of cerebral infarction:

Hyperacute (0-12 hours)

At the cellular level, an infarct is invisible under the microscope for the first few hours. Gross examination is unremarkable. The brain looks essentially normal.

• Imaging: DWI restricted diffusion within minutes (cytotoxic edema); CT often unremarkable.
• Histology: normal H&E appearance.
• This is forensically important: a person who dies within minutes of a stroke shows no histologic stroke.

Acute (12-48 hours)

• First histologic change: red neuron (ischemic neuronal change). Appears at 4-12 hours, prominent by 24-48 hours.
• Eosinophilic cytoplasm, pyknotic nucleus, loss of Nissl substance.
• Endothelial swelling.
• Cytotoxic edema with cellular swelling, especially astrocytes.
• Gross: subtle swelling of the affected territory; cortical-white matter junction loss.
• Vasogenic edema begins (peak at 3-7 days).

Subacute (3 days to 3 weeks)

• Neutrophil infiltration (24 hours to 5 days): first inflammatory response.
• Macrophage / microglial infiltration: peaks at 1-2 weeks; foamy macrophages with luxol-positive myelin debris and lipid.
• Reactive astrogliosis begins at the margin (~1 week).
• Capillary proliferation at the margin (vascular reaction, ~1-2 weeks).
• Liquefactive necrosis: the necrotic core softens and begins to break down.
• Gross: soft, pale, swollen lesion at first; later a yellow-tan softening.
• Edema peaks at 3-5 days; clinical decline often occurs at this point.

Chronic (3 weeks onward)

• Cavitation: liquefied necrotic core leaves a fluid-filled cavity.
• Reactive astrogliosis: dense gliotic wall around the cavity (“gliotic scar”).
• Foamy macrophages: persist in the cavity wall and adjacent parenchyma for months.
• Hemosiderin deposition: in areas of prior hemorrhage; Prussian blue positive.
• Atrophy of the affected region.
• Gross: well-defined cystic cavity, gliotic margin, focal atrophy.
• By 1-3 months: stable scar; the cavity is the final pathologic state.

Patterns by Vascular Territory

Infarction patterns reflect the underlying mechanism. Recognizing the pattern points to the artery and often the mechanism:

Large Artery Infarcts

• MCA territory: lateral hemisphere; face/arm/leg motor and sensory cortex, Broca/Wernicke areas. Most common large stroke.
• ACA territory: medial frontal and parietal. Leg-predominant motor; abulia.
• PCA territory: occipital and medial/inferior temporal. Hemianopia with macular sparing; amnesia if bilateral hippocampi.
• Vertebrobasilar: brainstem syndromes (Wallenberg, Weber, etc.), cerebellar infarcts, occipital.
• Watershed: between major territories; from hypoperfusion.

Lacunar Infarcts

Small (< 1.5 cm) infarcts in territory of small penetrating arteries. Pathology: lipohyalinosis or microatheroma of the small vessel; chronic state is a small fluid-filled cavity (lacune). Locations:

• Internal capsule (posterior limb).
• Thalamus.
• Basal ganglia.
• Basis pontis.
• Centrum semiovale.

Border Zone (Watershed) Infarcts

• External: ACA-MCA (anterior watershed → man-in-the-barrel); MCA-PCA (posterior watershed → Balint features).
• Internal: between perforator and surface vessel territories; “string of beads” in centrum semiovale.

Cardioembolic Infarcts

• Often multiple, in different territories.
• Often cortical with sharp borders.
• Hemorrhagic transformation common.

Hemorrhagic Transformation

Reperfusion of an infarcted territory can produce secondary hemorrhage. Two patterns:

• Petechial hemorrhage: scattered small hemorrhages within the infarct. Common, usually not clinically significant.
• Parenchymal hematoma: large confluent hemorrhage within the infarct. Can cause clinical deterioration; risk factor for poor outcome after thrombolysis.

Mechanisms of Infarction

Atherothrombotic

Atherosclerotic plaque in a large vessel ruptures or thromboses, with downstream infarction. Plaque often at carotid bifurcation, vertebral origin, or intracranial vessels.

Cardioembolic

Embolus from cardiac source (atrial fibrillation, valve disease, endocarditis, paradoxical embolism). Often produces multiple infarcts in different territories.

Small Vessel (Lacunar)

Lipohyalinosis or microatheroma of small penetrating arteries. Hypertension is the dominant risk factor.

Other Determined Causes

• Arterial dissection (carotid, vertebral).
• Hypercoagulable states.
• Vasculitis.
• Sickle cell disease.
• Fibromuscular dysplasia.
• Moyamoya.
• Substance abuse (cocaine, methamphetamine).
• Postpartum.

Cryptogenic / Embolic Source Undetermined

About 25-40% of strokes — increasingly recognized as embolic stroke of undetermined source (ESUS), often with occult atrial fibrillation, patent foramen ovale, or aortic plaque.

Gross Pathology by Stage

Special Patterns

Laminar Necrosis

Selective necrosis of cortical layers III and V (most vulnerable to hypoxia) in band-like distribution. Classic of hypoperfusion or anoxia. Imaging: cortical T1 hyperintensity (“cortical laminar necrosis sign”).

Borderzone Pattern

Multiple small infarcts in border zones; often unilateral if severe carotid stenosis, bilateral if global hypoperfusion.

Anoxic Brain Injury

Global rather than focal. Selective vulnerability pattern:

• CA1 of hippocampus (most vulnerable).
• Purkinje cells of cerebellum.
• Cortical layers III and V (laminar necrosis).
• Basal ganglia (caudate, putamen).
• Watershed cortex.

Spinal Cord Infarction

Anterior spinal artery territory most common (anterior two-thirds of cord; dorsal columns spared). Often from aortic disease.

Cerebellar Infarction

PICA, AICA, SCA territories. Important because edema can cause brainstem compression and herniation; suboccipital decompression life-saving.

Hemorrhagic Conversion

Reperfusion of an infarcted territory damages the BBB; blood extravasates into the infarcted tissue. Risk factors:

• Large infarct.
• Cardioembolic mechanism (especially atrial fibrillation).
• Thrombolysis or thrombectomy.
• Anticoagulation.
• Hypertension.
• Delayed reperfusion (24+ hours).

Pathology: petechial hemorrhages early; large parenchymal hematoma in severe cases. Hemosiderin remains in cavity walls indefinitely.

Secondary Effects

• Mass effect: peaks at 3-7 days from edema; causes midline shift, herniation.
• Hydrocephalus: from edema or hemorrhagic conversion compressing CSF pathways.
• Wallerian degeneration: of axons whose cell bodies are in the infarct; manifests in distant tracts.
• Trans-synaptic degeneration: of neurons receiving input from the infarct.
• Diaschisis: functional depression of remote regions connected to the infarct.
• Post-stroke seizures: from cortical scar, especially in chronic infarcts.

Imaging-Pathology Correlation

🔍 Did You Know?

The classical observation that histologic changes of infarction take 4-12 hours to appear has profound forensic implications. A person who dies within minutes of a clinically obvious massive stroke will show no histologic stroke at autopsy — the brain looks essentially normal. This creates a counterintuitive forensic situation: the apparent absence of stroke at autopsy does not exclude stroke as a cause of death. Multiple lines of evidence are required: imaging (DWI restricted diffusion appears within minutes), vascular imaging (the occluded vessel), the clinical history, and the cardiac evaluation. In contrast, a patient who lives for 24-48 hours after a clinical stroke will show clear histologic changes — red neurons, neutrophil infiltration starting, edema peaking. By 1-2 weeks, foamy macrophages and gliosis are well established. The temporal evolution allows the pathologist to estimate the age of the lesion with reasonable precision. This has practical value beyond forensics: in a chronically ill patient with multiple cerebral lesions, dating the infarcts can identify which one was responsible for the recent clinical event versus which represent old injuries. The neuropathology of stroke is one of the few areas where the temporal sequence of cellular changes is reliable enough to serve as a clock.

Pitfalls and Pearls

• Red neurons appear at 4-12 hours minimum. Hyperacute infarction has no histologic findings.
• Edema peaks at 3-7 days. Clinical deterioration often occurs in this window from mass effect.
• Liquefactive necrosis is the CNS pattern. Coagulative necrosis is rare in brain (unlike most other organs).
• Cystic cavity with gliotic walls: chronic infarct.
• Wedge-shaped cortical infarct with sharp borders: cardioembolic until proven otherwise. Often multiple territories.
• Lacunar infarcts reflect small vessel disease (lipohyalinosis); BP control is primary prevention.
• Watershed infarcts: hypoperfusion (cardiac arrest, severe carotid stenosis, hypotension).
• Laminar necrosis: cortical layers III and V; classic of anoxic injury.
• CA1 + Purkinje + watershed cortex damage: anoxic-ischemic encephalopathy.
• Hemorrhagic transformation: petechial or parenchymal; risk factors include cardioembolic, thrombolysis, large infarct.
• Hemosiderin: permanent marker of past hemorrhage; Prussian blue positive.
• Wallerian degeneration: distant tract degeneration from infarcted neurons.
• Cerebellar infarction can cause fatal herniation. ICU monitoring, suboccipital decompression.
• Anterior spinal artery infarct: spares dorsal columns; vibration/proprioception preserved.
• Pseudo-normalization on DWI/ADC at 5-10 days does not mean the stroke is gone; correlate with T2/FLAIR.

References

1. Love S, Budka H, Ironside JW, Perry A, eds. Greenfield’s Neuropathology. 9th ed. CRC Press; 2015.
2. Caplan LR. Caplan’s Stroke: A Clinical Approach. 5th ed. Cambridge University Press; 2016.
3. Mohr JP, Wolf PA, Grotta JC, et al, eds. Stroke: Pathophysiology, Diagnosis, and Management. 6th ed. Elsevier; 2016.
4. Garcia JH, Liu KF, Yoshida Y, Lian J, Chen S, del Zoppo GJ. Influx of leukocytes and platelets in an evolving brain infarct (Wistar rat). Am J Pathol. 1994;144(1):188-199.
5. Vinters HV, Kleinschmidt-DeMasters BK. General pathology of the central nervous system. In: Love S, et al, eds. Greenfield’s Neuropathology. 9th ed. CRC Press; 2015:1-58.