Pseudosubarachnoid hemorrhage

Pseudosubarachnoid hemorrhage describes an apparent increased attenuation within the basal cisterns simulating true subarachnoid hemorrhage. It is usually due to cerebral edema.

Pathology

Etiology

The most common cause is cerebral edema where there is a decrease in parenchymal attenuation and engorgement and dilatation of the superficial venous structures due to an increased intracranial pressure . This is seen in hypoxic-ischemic brain injury and recent resuscitation from cardiopulmonary arrest.

Other causes include:

• severe meningitis: breakdown of the blood-brain barrier allowing mildly hyperdense proteinaceous material to leak into the subarachnoid space 
• venous sinus thrombosis
• bilateral large subdural hemorrhage producing effacement of sulci and basal cisterns and the false impression of blood in the subarachnoid space
• intrathecal contrast

Radiographic features

CT

• usually, symmetrical density confined to the basal cisterns (i.e. no sulcal density)
• 30-40 HU (cf. true acute subarachnoid hemorrhage ~60 HU)
• often seen with generalized cerebral edema or basal cistern effacement
• the appearances are thought to be due to a combination of
  • cisternal effacement
  • distention +/- thrombosis of vessels
  • adjacent brain hypoattenuation accentuating contrast difference

Given et al. reviewed 7 cases of generalized cerebral edema accompanied by increased basal cisternal attenuation which were all found not to have subarachnoid blood at lumbar puncture or autopsy .

Differential diagnosis

• true subarachnoid hemorrhage
• acute meningitis mimicking a subarachnoid hemorrhage

Siehe auch:

• hypoxischer Hirnschaden
• Hirnödem
• Subarachnoidalblutung

und weiter:

• Superfizielle Hämosiderose der Leptomeningen
• MRI appearance of subarachnoid haemorrhage