A 65-year-old woman on warfarin for atrial fibrillation presents with acute onset focal neurological deficit and headache. CT head shows a lobar hemorrhage. Which feature best distinguishes cerebral amyloid angiopathy (CAA)-related hemorrhage from hypertensive intracerebral hemorrhage?

## Distinguishing CAA from Hypertensive ICH ### Key Discriminating Feature **Key Point:** The distribution and pattern of microhemorrhages on gradient echo (GRE) or susceptibility-weighted imaging (SWI) MRI is the most reliable discriminator. CAA causes lobar microhemorrhages (cortical and subcortical white matter), while hypertensive ICH causes deep brain microhemorrhages (basal ganglia, thalamus, brainstem). ### Comparison Table | Feature | Cerebral Amyloid Angiopathy (CAA) | Hypertensive ICH | |---------|-----------------------------------|------------------| | **Location of acute bleed** | Lobar (cortical/subcortical) | Deep brain (basal ganglia, thalamus, pons, cerebellum) | | **Microhemorrhages on GRE/SWI** | Lobar distribution (cortical, subcortical white matter) | Deep brain distribution | | **Age of onset** | >60 years, elderly | Any age with hypertension, often younger | | **Blood pressure** | Often normal or mildly elevated | Usually markedly elevated (>180/110) | | **Recurrence risk** | High (10% per year) | Lower if BP controlled | | **Pathology** | Amyloid-β deposition in cortical vessels | Lipohyalinosis of penetrating arteries | | **Associated findings** | Microinfarcts, cortical superficial siderosis | Lacunar infarcts | ### Clinical Pearl **Clinical Pearl:** Gradient echo MRI is the gold standard for detecting microhemorrhages and distinguishing CAA from hypertensive ICH. The **lobar distribution** of microhemorrhages in CAA is pathognomonic—they cluster in cortical and subcortical regions, never in the deep basal ganglia or brainstem (which are the hallmark of hypertensive disease). ### High-Yield Mnemonic **Mnemonic:** **LOBAR CAA** = Lobar Occurrences in Basal ganglia-sparing Amyloid angiopathy Recognition - **L**obar hemorrhages (cortical/subcortical) - **O**lder patients (typically >60 years) - **B**asal ganglia **NOT** involved (distinguishes from hypertensive) - **A**myloid pathology - **A**cute lobar microhemorrhages on GRE/SWI ### Why Microhemorrhage Distribution Matters **High-Yield:** The Boston Criteria for CAA diagnosis include the presence of lobar microhemorrhages on GRE/SWI MRI. This imaging finding is highly specific for CAA and is the single best way to distinguish it from hypertensive ICH in an elderly patient presenting with lobar hemorrhage. [cite:Harrison 21e Ch 297]