What causes island sign in intracerebral hemorrhage on computed tomography?
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Answer:
The island sign is a reliable CT imaging marker that independently predicts hematoma expansion and poor clinical outcome in patients with spontaneous intracerebral hemorrhage (ICH). It represents a special type of extremely irregularly shaped hematoma characterized by multifocal small bleeding surrounding the main hematoma. The underlying pathophysiology suggests that the main hematoma represents bleeding from a ruptured blood vessel, while the peripheral islands of blood reflect continued or multifocal hemorrhage from damaged vascular structures. The presence of the island sign is associated with significantly higher risk of early hematoma expansion. In clinical studies, the island sign was observed in 44.7% of patients with documented hematoma expansion and demonstrated a specificity of 98.2% for predicting expansion, with a positive predictive value of 92.7%. When adjusted for other clinical variables including age, Glasgow Coma Scale score, intraventricular hemorrhage presence, subarachnoid hemorrhage presence, admission systolic blood pressure, baseline ICH volume, and infratentorial location, the island sign remained an independent predictor of poor functional outcome with an odds ratio of 3.51.
Why is it called so?
The sign is named for its radiographic appearance of islands or small clusters of blood (representing multifocal bleeding) scattered around the main central hematoma, creating a pattern resembling islands within a larger landmass.
Pathophysiology
The island sign develops when active or recurrent bleeding occurs from damaged vessels adjacent to the primary hematoma, creating satellite hemorrhages in the surrounding tissue. This multifocal bleeding pattern indicates ongoing vascular disruption and hemostatic failure, distinguishing it from simple irregular hematoma margins. The presence of these peripheral islands suggests more aggressive bleeding dynamics and greater likelihood of continued hematoma expansion.
Other associated named signs: Satellite sign, spot sign (both associated with hematoma expansion in ICH)
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The island sign arises from multifocal secondary vessel rupture and active hematoma propagation, producing satellite hemorrhages around the main intracerebral hematoma, which appear as isolated “islands” on CT.
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