Three-territory sign (brain)
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The three-territory sign is a radiological sign described in ischemic stroke and is highly specific to hypercoagulability due to malignancy (Trousseau syndrome) being the etiology. However, this sign is not pathognomonic, and may be seen with cardioembolic stroke (e.g. due to atrial fibrillation, endocarditis, cardiac tumors) or stroke due to other prothrombotic states (e.g. due to COVID-19) 1-7.
The three-territory sign describes ischemic strokes involving three vascular territories including involvement of the bilateral anterior and posterior circulations 1-6. Often, the individual ischemic strokes are small, rather than being large vessel occlusions 3. The sign is best appreciated with diffusion-weighted imaging on MRI 1-6.
In one study, the three-territory sign was found to be highly specific (96.4%) but not sensitive (23.4%) for hypercoagulability due to malignancy (Trousseau syndrome) 1. Notably, in the same study, the three-territory sign was six times more likely observed in patients with underlying malignancy when compared to patients with underlying atrial fibrillation who may have had multi-territory cardioembolic ischemic stroke (i.e. embolic shower) 1. In another study, the three-territory sign was found to be an independent marker of increased mortality in patients with acute ischemic stroke in the setting of malignancy 6.