Satellite sign

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. 

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

Non-contrast 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