Pseudosubarachnoid haemorrhage

Dr Dan J Bell and Dr Andrew Dixon et al.

Pseudosubarachnoid haemorrhage is a sign related to apparent increased attenuation within the basal cisterns which simulates a true subarachnoid haemorrhage (SAH).

The most common cause is cerebral oedema where there is a decrease in parenchymal attenuation and engorgement and dilatation of the superficial venous structures due to an increased intracranial pressure 1,2. This is seen in anoxia and recent resuscitation from cardiopulmonary arrest.

Other causes include:

  • usually symmetrical density confined to the basal cisterns (i.e. no sulcal density)
  • 30-40 HU (compared with true acute SAH ~60HU)
  • often seen with generalised cerebral oedema 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 generalised cerebral oedema accompanied by increased basal cisternal attenuation which were all found not to have subarachnoid blood at lumbar puncture or autopsy 1.

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Article information

rID: 9346
Section: Signs
Synonyms or Alternate Spellings:
  • Pseudo-subarachnoid haemorrhage
  • Pseudo-SAH
  • Pseudo-subarachnoid hemorrhage
  • Pseudosubarachnoid hemorrhage
  • PseudoSAH

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Cases and figures

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    Case 1: oedema secondary to intracranial hypoxia
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    Case 2 : hyoxic or cerebral ischaemic event
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    Case 3: hypoxic-ischaemic brain injury
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    Case 4: due bilateral SDH
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    Case 5
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    Case 6
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    Case 7
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    Case 8
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