Three sign | Radiology Signs

The Three Territory Sign (TTS) represents bilateral acute ischemic diffusion-weighted imaging (DWI) lesions involving both the anterior and posterior cerebral circulations. This pattern is highly associated with malignancy-related ischemic stroke, also known as Trousseau syndrome, which results from a hypercoagulable state induced by malignant disease. The TTS is 6 times more frequently observed in malignancy-related ischemic stroke compared to atrial fibrillation-related ischemic stroke, making it a highly specific radiographic marker of cancer-associated thromboembolism. The sign reflects multiple acute infarcts occurring simultaneously across different vascular territories due to the prothrombotic effects of malignancy, which promotes widespread thromboembolic events.

Why is it called so?

The sign is named for the involvement of three distinct cerebral vascular territories: bilateral anterior circulation (left and right) combined with posterior circulation involvement. This tri-territorial distribution distinguishes it from single-territory or two-territory stroke patterns and serves as a distinctive nomenclature highlighting the characteristic widespread nature of malignancy-associated stroke.

Pathophysiology

Malignancy induces a hypercoagulable state through multiple mechanisms including tissue factor expression by tumor cells, increased platelet aggregation, activation of coagulation cascades, and endothelial dysfunction. This systemic prothrombotic environment predisposes patients to multiple simultaneous thromboembolic events affecting different vascular territories. The bilateral and multicirculation involvement reflects the systemic nature of cancer-induced hypercoagulability rather than a single embolic source, distinguishing it from cardioembolic strokes that typically produce more localized infarction patterns.

Alternative names:

Trousseau syndrome sign (when specifically referring to malignancy-associated stroke)