Duret haemorrhage

Duret haemorrhage (also spelled, Duret hemorrhages) are small areas of bleeding in the ventral and paramedian parts of the upper brainstem, (midbrain and pons). They are secondary to raised intracranial pressure with formation of a transtentorial pressure cone in which the cerebellar tonsils are impacted in the foramen magnum by the high pressure. Kernohan’s notch is a groove in the cerebral peduncle caused by this displacement of the brainstem against the incisura of the tentorium in some cases. The resulting ipsilateral hemiparesis is a false localising sign (Collier 1904), known as the Kernohan-Woltman syndrome. This may succeed or accompany temporal lobe (uncal) herniation and subfalcial herniation secondary to a supratentorial mass.

Causes
The common causes are an acute haematoma, oedema following trauma, abscess, or tumour. The Duret haemorrhage is demonstrated at CT or MRI. It usually indicates a fatal outcome. The mechanism is uncertain but is probably caused by the displacement of the brainstem stretching and lacerating pontine perforating branches of the basilar artery; venous infarction may play a role.