The satellite sign is a radiological sign seen on non-contrast CT of the brain in the setting of intracerebral hemorrhage, and refers to a small hemorrhage adjacent to, and separate from, the main hematoma. It is a predictor of hemorrhage expansion.
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Epidemiology
The satellite sign can be seen in ~40% of patients with intracerebral hemorrhage scanned within 6 hours of symptom onset 1-3. There is an association with hypertension and intraventricular hemorrhage 1.
Pathology
Following a hemorrhagic insult, the tissues adjacent to the hematoma are thought to develop cytotoxic edema, eventually resulting in local ischemia and reperfusion injury. Subsequent disruption of the blood-brain barrier then manifests as the satellite sign 1.
Radiographic features
CT
The satellite sign is defined as a small intraparenchymal hyperdense hemorrhagic focus that is clearly separated from the main hematoma on at least one CT slice. This focus can exhibit any morphology but has to 4:
measure no more than 10 mm in maximum diameter
be separated from the main hematoma by no more than 20 mm
remain intraparenchymal: i.e. not within the ventricles or subarachnoid space
Treatment and prognosis
The satellite sign is a predictor of hemorrhage expansion and is therefore a marker of poor outcome. Several single-center studies report a moderate sensitivity (59-66%) and specificity (58-69%) for predicting hemorrhage expansion 1-3.
History and etymology
The term was first coined in 2017 by Shimoda et al 1.
Practical points
this sign may be confused with simultaneous intraparenchymal hemorrhages in multiple discrete locations which often occur within the deeper regions of the basal ganglia
when there are more than three satellite foci, this may be referred to as the island sign