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Comprehensive overview of the interpretation of CT scans in ischemic stroke

Updated: Jan 23

Comprehensive overview of the interpretation of CT scans in ischemic stroke, outlining the various stages and corresponding radiological signs. Here's a summary of the key points:

  1. Etiologies and Classification of Ischemic Stroke:

  • Large artery atherosclerosis

  • Cardioaortic embolism

  • Small artery occlusion

  • Other causes

  • Undetermined causes

  1. CT Imaging in Ischemic Stroke:

  • Non-contrast CT is the mainstay in acute stroke settings.

  • CT is used to exclude intracranial hematoma, identify early ischemic changes, rule out other pathologies, and evaluate the ASPECT score.

  1. Timing of Stroke and Corresponding CT Findings:

  • Hyperacute (<12 hours): The CT may appear normal in 50-60% of cases. Early signs include a hyperdense artery, loss of grey-white differentiation, and signs of brain edema.

  • Acute (12 to 24 hours): Similar findings to hyperacute stage, but more pronounced.

  • Subacute (1 day to 1 week): A well-demarcated area of hypodensity with mass effect may appear. Hemorrhagic transformation can occur, and post-contrast images may show gyral enhancement.

  • Late Subacute (1 week to 2 months): Resolution of mass effect and the "fogging effect" (transient normal density of infarcted brain) may be observed.

  • Chronic (>2 months): Marked low density, volume loss, and, in rare cases, calcification.

  1. Specific Signs on CT:

  • Hyperacute Stage: May show hyperdense artery sign, indicating a clot in a vessel, and loss of grey-white matter differentiation.

  • Subacute Stage: A well-defined area of low density indicating brain tissue death, possible hemorrhagic transformation, and gyral enhancement on contrast-enhanced scans.

  • Chronic Stage: Shows low-density areas indicating old infarcts, brain volume loss, and occasionally, calcification.

  1. Conclusion: The document emphasizes the importance of recognizing the temporal evolution of ischemic stroke on CT scans. The findings vary with the stage of the stroke and are crucial for appropriate management.

Understanding these CT findings is essential for medical students and practitioners in diagnosing and managing ischemic stroke effectively.

Grouping the CT signs of ischemic stroke by affected brain anatomy and the related arteries or veins can provide a more structured understanding. Here's a breakdown:

  1. Cerebral Arteries and Related Signs:

  • Hyperdense Artery Sign: Commonly seen in the Middle Cerebral Artery (MCA). Indicates a thrombus in the artery.

  • Dense Triangular Sign: aka. wedge shaped Often associated with large artery infarctions like those in the MCA or Anterior Cerebral Artery (ACA) territories. Represents acute ischemic changes.

  1. Basal Ganglia and Deep White Matter:

  • Low-Density Basal Ganglia (BGG) Sign: Indicates ischemia in deep structures like the internal capsule and basal ganglia, often related to small vessel disease or occlusions in smaller branches of the MCA or ACA.

  • Lentiform Nucleus Sign: Specifically refers to ischemia in the lentiform nucleus, typically due to small vessel disease or occlusion of lenticulostriate arteries branching from the MCA.

  1. Cortical Regions:

  • Loss of Grey-White Matter Differentiation: Common in cortical strokes, which could involve the MCA or ACA territories. Indicates cytotoxic edema.

  • Asymmetric Cortical Sulci Sign: Seen in swelling due to ischemic events in cortical areas, often related to the MCA territory.

  • Swelling of the Gyri: Also associated with cortical strokes, particularly in the MCA territory.

  1. Subcortical Structures:

  • Hypodensity of the Posterior Limb of the Internal Capsule: Indicates ischemia in the region supplied by the lenticulostriate arteries (branches of MCA).

  1. Venous Structures:

  • Cord Sign and Empty Delta Sign: Indicative of cerebral venous thrombosis, affecting venous sinuses such as the superior sagittal sinus or transverse sinuses.

  1. Global Cerebral Effects:

  • Sulcal Effacement: A global effect due to increased intracranial pressure, not specific to any one artery.

  • Mass Effect and Midline Shift: Occurs in severe cases of swelling, not limited to a specific vessel but more common in large territory infarcts like those of the MCA.

  1. Chronic Changes:

  • Chronic Encephalomalacia: Seen in chronic stages of stroke in any cerebral territory affected by the infarct.

  • Fogging Effect in Late Subacute Stage: A transient phenomenon that can occur in any infarcted area.

  1. Hemorrhagic Transformation:

  • Hemorrhagic Transformation Sign: Can occur in any area affected by ischemic stroke, not specific to a particular artery.

Hyperdense Artery Sign:

Occurrence: This sign is most commonly observed in the Middle Cerebral Artery (MCA), but it can also occur in other cerebral arteries.

Appearance: On a non-contrast CT scan, the affected artery appears brighter or denser than its surroundings. This increased density is due to the presence of a thrombus within the artery.

Pathophysiology: The thrombus, typically composed of red blood cells and fibrin, has a higher attenuation than the surrounding brain tissue and normal blood flow. The hyperdensity is a result of the clot obstructing the artery.

Clinical Implication: Its presence is a strong indicator of acute ischemic stroke. Identifying this sign is crucial as it can guide immediate therapeutic decisions, particularly regarding thrombolytic therapy.

Location Specificity: In the MCA, this sign is significant because the MCA supplies a large portion of the lateral cerebral hemisphere, including critical areas for motor and sensory functions. An occlusion here can result in significant deficits.

Dense Triangular Sign aka. wedge shaped:

Occurrence: Commonly associated with infarctions in large artery territories, particularly the MCA and Anterior Cerebral Artery (ACA).

Appearance: It manifests as a hyperdense (bright) area on CT, usually having a triangular or wedge-shaped appearance. This shape corresponds to the vascular territory of the affected artery.

Pathophysiology: The sign indicates acute ischemic changes within the brain tissue. It represents an area of cytotoxic edema where the tissue has started to swell due to lack of oxygen and nutrients following arterial occlusion.

Clinical Implication: Early detection of this sign is crucial for stroke diagnosis. It often precedes the appearance of more obvious infarction signs like frank hypodensity (darker areas) and helps in estimating the age of the stroke, which is vital for treatment planning.

Territory Specificity: The specific appearance and location of the dense triangular sign can indicate which artery is affected. For example, in the MCA territory, it may involve the lateral surface of the cerebral hemisphere, while in the ACA territory, it involves the medial surfaces.

Low-Density Basal Ganglia (BGG) Sign:

Appearance on CT: This sign appears as a darker or hypodense area in the basal ganglia region compared to the surrounding brain tissue. The hypodensity is due to ischemic changes leading to cytotoxic edema in the tissue.

Affected Structures: It typically involves the deep brain structures such as the internal capsule and basal ganglia.

Pathophysiology: Ischemia in this area is often due to small vessel disease, which affects the tiny penetrating arteries that supply these deep brain structures. Alternatively, it can be caused by occlusions in the smaller branches of larger arteries like the Middle Cerebral Artery (MCA) or Anterior Cerebral Artery (ACA).

Clinical Significance: The identification of this sign is crucial in diagnosing ischemic strokes that affect the deep brain regions. These strokes can lead to significant neurological deficits despite the small size of the infarcted area.

Lentiform Nucleus Sign:

Appearance on CT: The lentiform nucleus sign is identified as a loss of the normal density of the lentiform nucleus on a CT scan, making it appear hypodense compared to the surrounding structures.

Affected Structure: The lentiform nucleus, part of the basal ganglia, includes the putamen and the globus pallidus.

Pathophysiology: This sign typically results from ischemia due to the occlusion of lenticulostriate arteries. These are small, deep penetrating arteries that branch from the MCA and supply blood to the lentiform nucleus and internal capsule.

Clinical Significance: This sign is important for diagnosing strokes that specifically affect the lentiform nucleus. These strokes can have a significant impact on motor and sensory functions, as the basal ganglia and internal capsule are critical for these neural pathways.

Loss of Grey-White Matter Differentiation:

  • Appearance on CT: This sign appears as a blurring or loss of the normal distinction between the grey and white matter on CT scans. The affected cortex may appear more uniform than usual, with a less distinct contrast between grey and white matter.

  • Affected Areas: This sign is commonly seen in strokes affecting cortical areas, particularly in territories supplied by the Middle Cerebral Artery (MCA) and Anterior Cerebral Artery (ACA).

  • Pathophysiology: The loss of differentiation is due to cytotoxic edema, which occurs when brain cells swell due to the failure of cellular ion pumps in the setting of ischemia. This swelling affects both neurons (grey matter) and glial cells (white matter), leading to a homogenization in the appearance of these tissues.

  • Clinical Implication: Early detection of this sign is crucial for diagnosing ischemic strokes, especially within the first few hours of symptom onset. It can guide timely therapeutic interventions, including reperfusion strategies.

Asymmetric Cortical Sulci Sign:

  • Appearance on CT: This sign involves an asymmetry in the appearance of the cortical sulci, where the sulci on one side of the brain appear more compressed or less pronounced compared to the other side.

  • Affected Areas: Often observed in swelling due to ischemic events, particularly in areas supplied by the MCA.

  • Pathophysiology: The swelling of the brain tissue due to ischemia leads to a reduction in the space occupied by the sulci. This is a manifestation of localized cerebral edema.

  • Clinical Implication: The presence of asymmetric cortical sulci is an indicator of cerebral edema and increased intracranial pressure, which are urgent findings that require prompt medical attention.

Swelling of the Gyri:

  • Appearance on CT: The gyri appear swollen and more pronounced, leading to the effacement of the adjacent sulci.

  • Affected Areas: This sign is also associated with cortical strokes, particularly those in the MCA territory.

  • Pathophysiology: Similar to the loss of grey-white matter differentiation, the swelling of the gyri is due to cytotoxic edema. The gyri swell and occupy more space, compressing the adjacent sulci.

  • Clinical Implication: Swelling of the gyri is a sign of acute ischemic stroke and can indicate the severity of the stroke. Like asymmetric sulci, it can also suggest increased intracranial pressure.

Subcortical Structures - Hypodensity of the Posterior Limb of the Internal Capsule:

  • Appearance on CT: This sign is characterized by a hypodense (darker) appearance of the posterior limb of the internal capsule on a CT scan.

  • Affected Area: The posterior limb of the internal capsule is the specific region affected, which contains important motor and sensory fibers.

  • Pathophysiology: The hypodensity signifies ischemia in this area, typically due to compromised blood flow from the lenticulostriate arteries. These small, deep penetrating arteries are branches of the Middle Cerebral Artery (MCA) and are susceptible to small vessel disease or occlusion.

  • Clinical Implication: Ischemia in this region can result in significant motor and sensory deficits, given the concentration of crucial neural tracts within the internal capsule. Recognition of this sign is important for diagnosing subcortical strokes and guiding appropriate treatment.

Venous Structures - Cord Sign and Empty Delta Sign:

  • Cord Sign:

  • Appearance on CT: Appears as a linear hyperdensity, resembling a cord, within a cerebral vein or sinus.

  • Pathophysiology: It represents a thrombosed cortical vein or sinus in cerebral venous thrombosis.

  • Clinical Implication: The cord sign is a critical indicator of cerebral venous thrombosis, a condition that requires prompt diagnosis and treatment to prevent complications like venous infarcts or hemorrhages.

  • Empty Delta Sign:

  • Appearance on CT: On contrast-enhanced CT scans, the empty delta sign

  • Affected Venous Structures: Commonly seen in the superior sagittal sinus or transverse sinuses. - Pathophysiology: This sign is indicative of thrombosis in the venous sinus. The filling defect is caused by the clot, while the enhancement around it is due to the contrast material flowing in the collateral venous channels.

  • Clinical Implication: The empty delta sign is a hallmark of cerebral venous sinus thrombosis (CVST). Identifying this sign is crucial for the diagnosis and management of CVST, which is a potentially life-threatening condition requiring immediate anticoagulant therapy.

Sulcal Effacement:

  • Appearance on CT: This sign is observed as a loss or reduction in the visibility of the cerebral sulci. The normally visible grooves on the surface of the brain become less pronounced or even disappear.

  • Pathophysiology: Sulcal effacement is caused by cerebral edema, where swelling of the brain tissue leads to increased intracranial pressure. This swelling can be due to various causes, including ischemic stroke, traumatic brain injury, or other conditions leading to increased intracranial volume.

  • Clinical Implication: While sulcal effacement is not specific to any particular type of stroke or arterial territory, it is a crucial indicator of increased intracranial pressure. It necessitates immediate medical attention as it can lead to further complications, including herniation if not promptly addressed.

Mass Effect and Midline Shift:

  • Appearance on CT: Mass effect is evidenced by the compression or displacement of structures within the brain. Midline shift occurs when this effect is severe enough to push the brain's midline structures from their normal position.

  • Pathophysiology: These effects are commonly seen in large territory infarcts, particularly those involving the MCA, where significant edema causes the brain tissue to expand beyond its confined space in the skull. This can compress adjacent brain tissue and shift midline structures.

  • Clinical Implication: Both mass effect and midline shift are serious findings that signify a high risk of brain herniation, a life-threatening condition. They often necessitate aggressive medical intervention, potentially including surgical decompression to relieve intracranial pressure.

Chronic Encephalomalacia:

  • Appearance on CT: In the chronic stages of a stroke, the affected brain region appears as a well-defined area of low density (hypodense). This area corresponds to the location of the previous infarct.

  • Affected Areas: It can occur in any cerebral territory that was affected by the stroke, regardless of the specific artery involved.

  • Pathophysiology: Chronic encephalomalacia is the result of the brain tissue's healing process after an infarct. It represents the end-stage of brain infarction where the necrotic brain tissue has been resolved, leaving behind a cavity or a region of softening.

  • Clinical Implication: This finding is indicative of permanent brain damage in the affected area. It helps in assessing the extent of long-term damage post-stroke and planning rehabilitation and recovery strategies.

Fogging Effect in Late Subacute Stage:

  • Appearance on CT: During the late subacute stage of a stroke (usually 2-3 weeks after the event), the infarcted area may transiently appear isodense or similar in density to the surrounding brain tissue.

  • Pathophysiology: This effect is thought to be due to a combination of factors, including the infiltration of macrophages, resorption of necrotic tissue, and revascularization. It can give a misleading appearance of improvement or resolution of the infarcted area.

  • Clinical Implication: The fogging effect is important to recognize because it can lead to underestimation of the extent of an infarct on a CT scan. Awareness of the timing of this phenomenon is crucial for accurate interpretation of imaging findings post-stroke.

Hemorrhagic Transformation:

  • Appearance on CT: Hemorrhagic transformation is characterized by areas of increased density within a previously ischemic (low-density) region. This change indicates the presence of blood within the infarcted area.

  • Pathophysiology: Following an ischemic stroke, the weakened or damaged blood vessels within the affected area can leak or rupture, leading to bleeding into the infarcted tissue. This can occur as a natural progression of the ischemic injury or as a complication of reperfusion therapies.

  • Clinical Implication: Hemorrhagic transformation can range from minor petechial hemorrhages to large hematomas. It's a significant concern, especially in patients who receive thrombolytic therapy, as it can worsen the patient's clinical outcome. Identifying this sign on a CT scan is crucial for guiding the management and monitoring the patient's response to treatment.

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