Understanding CT Brain Non-contrast Scans in Ischemic Stroke

Table summarizing the interpretation of CT scans in ischemic stroke:

Stage	Timing	CT Findings	Key Signs
Hyperacute	<12 hours	May appear normal in 50-60% of cases, hyperdense artery, loss of grey-white differentiation, brain edema	Hyperdense Artery Sign, Loss of Grey-White Matter Differentiation
Acute	12 to 24 hours	Similar to hyperacute stage but more pronounced	Same as hyperacute stage
Subacute	1 day to 1 week	Well-demarcated hypodensity with mass effect, possible hemorrhagic transformation, gyral enhancement post-contrast	Well-defined Hypodensity, Possible Hemorrhagic Transformation, Gyral Enhancement
Late Subacute	1 week to 2 months	Resolution of mass effect, "fogging effect" (transient normal density of infarcted brain)	Fogging Effect
Chronic	>2 months	Marked low density, volume loss, occasional calcification	Low-Density Areas, Brain Volume Loss, Occasional Calcification

Affected Brain Anatomy	Related Arteries/Veins	Key CT Signs
Cerebral Arteries	MCA, ACA	Hyperdense Artery Sign, Dense Triangular Sign
Basal Ganglia and Deep White Matter	MCA, ACA	Low-Density Basal Ganglia (BGG) Sign, Lentiform Nucleus Sign
Cortical Regions	MCA, ACA	Loss of Grey-White Matter Differentiation, Asymmetric Cortical Sulci Sign, Swelling of the Gyri
Subcortical Structures	Lenticulostriate arteries	Hypodensity of the Posterior Limb of the Internal Capsule
Venous Structures	Superior sagittal sinus, transverse sinuses	Cord Sign, Empty Delta Sign
Global Cerebral Effects	N/A	Sulcal Effacement, Mass Effect and Midline Shift
Chronic Changes	N/A	Chronic Encephalomalacia, Fogging Effect, Hemorrhagic Transformation

Introduction

Ischemic stroke, a common and potentially devastating condition, requires prompt diagnosis and treatment. One of the primary tools for diagnosis is the CT scan. This blog provides a comprehensive overview of interpreting CT scans in ischemic stroke, focusing on various stages and corresponding radiological signs.

Etiologies and Classification of Ischemic Stroke

• Large Artery Atherosclerosis

• Cardioaortic Embolism

• Small Artery Occlusion

• Other Causes

• Undetermined Causes
  

CT Imaging in Ischemic Stroke

Non-contrast CT scans are crucial in acute stroke settings for:

• Excluding intracranial hematoma.

• Identifying early ischemic changes.

• Ruling out other pathologies.

• Evaluating the ASPECT score.

Timing of Stroke and Corresponding CT Findings

Hyperacute (<12 hours)

• Normal CT in 50-60% of cases.

• Early Signs: Hyperdense artery, loss of grey-white differentiation, brain edema.

Acute (12 to 24 hours)

• Similar findings to hyperacute stage but more pronounced.

Subacute (1 day to 1 week)

• Findings: Well-demarcated hypodensity with mass effect, possible hemorrhagic transformation, gyral enhancement post-contrast.

Late Subacute (1 week to 2 months)

• Findings: Resolution of mass effect, "fogging effect" (transient normal density of infarcted brain).

Chronic (>2 months)

• Findings: Marked low density, volume loss, occasional calcification.

Specific Signs on CT

Hyperacute Stage

• Hyperdense Artery Sign: Indicates a clot in a vessel.

• Loss of Grey-White Matter Differentiation.

Subacute Stage

• Well-defined Hypodensity: Indicates brain tissue death.

• Possible Hemorrhagic Transformation.

• Gyral Enhancement on Contrast-Enhanced Scans.

Chronic Stage

• Low-Density Areas: Indicate old infarcts.

• Brain Volume Loss.

• Occasional Calcification.

Grouping CT Signs by Brain Anatomy and Related Arteries

Cerebral Arteries

• Hyperdense Artery Sign: Common in the Middle Cerebral Artery (MCA).

• Dense Triangular Sign: Often in MCA or Anterior Cerebral Artery (ACA) territories.
  

Basal Ganglia and Deep White Matter

• Low-Density Basal Ganglia (BGG) Sign: Indicates ischemia in deep structures, related to small vessel disease or MCA/ACA branches.

• Lentiform Nucleus Sign: Ischemia in the lentiform nucleus due to small vessel disease or lenticulostriate artery occlusion.
  

Cortical Regions

• Loss of Grey-White Matter Differentiation: Indicates cytotoxic edema, common in cortical strokes involving MCA or ACA territories.

• Asymmetric Cortical Sulci Sign: Indicates cerebral edema and increased intracranial pressure.

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

Subcortical Structures

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

Venous Structures

• Cord Sign and Empty Delta Sign: Indicative of cerebral venous thrombosis, affecting venous sinuses.
  

Global Cerebral Effects

• Sulcal Effacement: Indicates increased intracranial pressure.

• Mass Effect and Midline Shift: Occur in severe cases of swelling, common in large territory infarcts like MCA.
  

Chronic Changes

• Chronic Encephalomalacia: Seen in chronic stages of stroke, indicative of permanent brain damage.

• Fogging Effect in Late Subacute Stage: Transient isodense appearance of the infarcted area.

• Hemorrhagic Transformation: Areas of increased density within previously ischemic regions, indicating the presence of blood.
  

Conclusion

Recognizing the temporal evolution of ischemic stroke on CT scans is crucial for appropriate management. The findings vary with the stage of the stroke, helping medical students and practitioners in diagnosing and managing ischemic stroke effectively.