The satellite sign is a radiological sign seen on non-contrast CT of the brain in the setting of intracerebral haemorrhage, and refers to a small haemorrhage adjacent to, and separate from, the main haematoma. It is a predictor of haemorrhage expansion. 

Epidemiology

The satellite sign can be seen in ~40% of patients with intracerebral haemorrhage scanned within 6 hours of symptom onset ^1-3. There is an association with hypertension and intraventricular haemorrhage ¹.

Pathology

Following a haemorrhagic insult, the tissues adjacent to the haematoma are thought to develop cytotoxic oedema, eventually resulting in local ischaemia 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 haemorrhagic focus that is clearly separated from the main haematoma 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 haematoma 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 haemorrhage expansion and is therefore a marker of poor outcome. Several single-centre studies report a moderate sensitivity (59-66%) and specificity (58-69%) for predicting haemorrhage 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 haemorrhages 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