How to differentiate and manage a patient with hypodensity on CT brain indicating either arterial or venous ischemia?

Differentiating Arterial from Venous Ischemia on CT Brain

The key to distinguishing arterial from venous ischemia on CT is recognizing that venous infarcts are typically hemorrhagic, cross arterial territories, occur near venous sinuses, and are associated with specific venous signs (hyperdense cord sign, empty delta sign), while arterial infarcts follow vascular territories, are initially non-hemorrhagic, and show early signs like hyperdense vessel sign and loss of gray-white differentiation. 1, 2

Clinical Context: Critical First Step

The clinical presentation provides essential diagnostic clues before interpreting imaging:

• Arterial stroke presents acutely with sudden onset of focal neurological deficits corresponding to specific arterial territories, typically in older patients with vascular risk factors 1

• Venous thrombosis (CVT) presents subacutely over days to weeks (56% subacute, 37% acute, 7% chronic) with progressive headache as the dominant symptom, seizures in 40% of cases, and predominantly affects younger patients under 50 years (78% of cases), especially women on oral contraceptives or who are pregnant/postpartum 2

• Bilateral involvement or altered mental status without clear focal signs suggests deep venous system thrombosis rather than arterial stroke 2

CT Imaging Features: Arterial Ischemia

Early Signs (Within 6 Hours)

• Hyperdense vessel sign: High-density thrombus/embolus in the vessel (e.g., hyperdense MCA sign) indicating arterial occlusion 1, 3

• Parenchymal hypodensity: Loss of gray-white differentiation in cortical ribbon (particularly insular cortex), attenuation of lentiform nucleus, and sulcal effacement detected in up to 82% of MCA territory strokes 1

• Territorial distribution: Hypodensity follows specific arterial territories (MCA, ACA, PCA distributions) 1, 4

• Frank hypodensity involving >1/3 MCA territory within first 6 hours predicts cerebral edema and increased hemorrhagic transformation risk 1

Evolution Pattern

• Initially non-hemorrhagic with progressive hypodensity developing over 12-24 hours 1

• Mass effect and midline shift develop over 2-4 days in large territorial infarcts 1

• Hemorrhagic transformation, when it occurs, typically appears 24-48 hours after onset and remains within the arterial territory 1

CT Imaging Features: Venous Ischemia

Direct Venous Signs

• Hyperdense cord sign: Increased density in cortical veins or dural sinuses representing acute thrombus 1

• Empty delta sign: On contrast-enhanced CT, triangular filling defect in the superior sagittal sinus with peripheral enhancement 1, 2

• Absence of normal venous enhancement on contrast studies 1

Parenchymal Changes

• Hemorrhagic infarction is characteristic and occurs in up to 40% of CVT cases, unlike arterial stroke where hemorrhage is less common initially 1, 2

• Crosses arterial boundaries: Venous infarcts do not respect arterial territorial distributions 2

• Location near venous sinuses: Frontal/parietal/occipital lesions suggest superior sagittal sinus thrombosis; temporal lesions suggest transverse/sigmoid sinus thrombosis; deep parenchymal/thalamic involvement suggests deep venous system thrombosis 1

• Bilateral involvement: Particularly with deep venous system thrombosis causing bilateral thalamic lesions 2

Critical Diagnostic Algorithm

Step 1: Assess Clinical Presentation

• Acute onset + focal deficit + older patient → suspect arterial
• Subacute headache + seizures + young patient → suspect venous 2

Step 2: Non-Contrast CT Evaluation

• If hyperdensity in vessel: Arterial occlusion (hyperdense MCA) vs. venous thrombosis (cord sign) - location determines type 1, 3
• If parenchymal hypodensity follows arterial territory: Arterial stroke 1, 4
• If hemorrhagic lesion crosses arterial boundaries: Venous infarction 2

Step 3: When CVT Suspected

• Normal non-contrast CT does NOT exclude CVT (only 30% sensitivity) 2
• Proceed immediately to CTV or MRI/MRV - these are essential and should not be delayed when clinical suspicion is high 1, 2
• MRI with MR venography is the preferred diagnostic modality showing both venous occlusion and parenchymal changes 1, 2

Step 4: Contrast-Enhanced CT

• Empty delta sign confirms CVT 1, 2
• Helps differentiate when non-contrast CT is equivocal 1

Management Implications

Arterial Ischemia

• IV rtPA within 3 hours is indicated even with early infarct signs, unless frank hypodensity involves >1/3 MCA territory 1
• Anticoagulation is generally contraindicated in acute phase with hemorrhagic transformation 1

Venous Ischemia

• Anticoagulation is the mainstay of treatment even in the presence of hemorrhagic lesions - this is the critical management difference from arterial stroke 1, 2
• Heparin or low molecular weight heparin should be initiated once diagnosis is confirmed 2

Common Pitfalls to Avoid

• Assuming normal CT excludes CVT: Non-contrast CT has only 30% sensitivity for CVT; always pursue CTV or MRV when clinical suspicion exists 2

• Misinterpreting hemorrhagic venous infarct as primary hemorrhage: The presence of hemorrhage crossing arterial territories near venous sinuses should prompt evaluation for CVT 1, 2

• Delaying diagnosis: Median time from symptom onset to CVT diagnosis is 7 days due to variable presentation; maintain high index of suspicion in young patients with headache and seizures 2

• Withholding anticoagulation in hemorrhagic CVT: Unlike arterial stroke, anticoagulation is indicated in CVT even with hemorrhage present 2

• Over-relying on hypodensity timing: While hypodensity typically indicates established infarction, rare cases show reversal with treatment, particularly in vasospasm or eclampsia contexts 5, 6