Black hole sign | Radiology Signs

Answer:

Black hole sign represents a hypoattenuated (dark) area encapsulated within a hyperattenuated (bright) hematoma with a clearly defined border. It indicates active bleeding and ongoing hematoma expansion in patients with spontaneous intracerebral hemorrhage. The sign is found in approximately 14.6% of intracerebral hemorrhage patients on admission CT scans performed within 6 hours of symptom onset. Patients presenting with black hole sign are significantly more likely to experience early hematoma expansion compared to those without the sign (31.9% versus 5.8%). The presence of black hole sign on admission CT independently predicts hematoma expansion alongside baseline hematoma volume and time-to-admission CT scan. Clinical significance includes poor patient outcomes associated with hematoma expansion. The sign demonstrates sensitivity of 31.9%, specificity of 94.1%, positive predictive value of 73.3%, and negative predictive value of 73.2% in predicting early hematoma growth.

Why is it called so?

The sign is named for its appearance on CT imaging – the hypoattenuated region appears as a dark or “black” area resembling a hole within the surrounding bright hematoma. The descriptive terminology reflects the visual contrast between the low-density center and high-density periphery on non-contrast computed tomography.

Pathophysiology

The black hole sign develops as a result of active arterial bleeding within the hematoma. The hypoattenuated center represents areas of active bleeding or serum that has not yet clotted, while the hyperattenuated periphery consists of already-formed clot. This heterogeneous appearance indicates hemostasis has not been achieved and bleeding is continuing within the hematoma cavity. The density difference of at least 28 Hounsfield units between the two regions reflects the different compositions – liquid blood and serum centrally versus formed thrombus peripherally. This ongoing bleeding process explains why black hole sign is such a strong predictor of hematoma expansion; the sign directly visualizes the mechanism of growth.

Alternative names:

None commonly used in clinical practice.

Other associated named signs:

Swirl sign – appears as areas of low or iso-attenuation within hyperattenuated hematomas but does not independently predict hematoma growth. Blend sign – another CT imaging marker that predicts hematoma expansion with potentially higher accuracy than black hole sign.