Hypostasis

Hypostasis (also called livor mortis) refers to the purplish discolouration of the superficial layers of dependent areas of the skin occurring soon after death. In reality the mechanisms causing hypostasis cause changes in every organ in the body.

Epidemiology

In one study imaging evidence of hypostasis was seen in 52% of post-mortem CT scans .

Pathology

Due to the stasis of blood occurring after death, blood separates into serum and erythrocytes . Erythrocytes being heavier undergo sedimentation and form a dependent layer (or hematocrit level) in the superficial tissues, internal organs and large blood vessels. Sedimentation occurs within 2 hours post mortem .

Radiographic features

CT

Hypostasis appears as a gradient of increasing hyperdensity when moving from non-dependent to dependent regions of organs, tissues or the great vessels. Subtle dermal thickening may also be present in dependent areas .

MRI

• T1: a gradient of increasing hyperintensity in dependent regions of the organ .

Differential diagnosis

On CT imaging consider

• pulmonary embolism
  • thrombus appears non-dependent with gravity in pulmonary arteries
• pulmonary edema
  • edema appears non-dependent with gravity in lung
  • more widespread