Pseudosubarachnoid hemorrhage
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Pseudosubarachnoid haemorrhage is a sign related to apparent increased attenuation within the basal cisterns which simulates a true subarachnoid haemorrhage (SAH).
Pathology
Causes and associations
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:
- severe meningitis: breakdown of the blood brain barrier allowing mildly hyperdense proteinaceous material to leak into the subarachnoid space 3
- venous sinus thrombosis
- bilateral large subdural haemorrhage producing effacement of sulci and basal cisterns and the false impression of blood in the subarachnoid space 5
- intrathecal contrast
Radiographic features
CT
- usually symmetrical density confined to the basal cisterns (i.e. no sulcal density)
- 30-40 HU (compared with true acute SAH
~ 60HU~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.
Differential diagnosis
- true subarachnoid haemorrhage
- acute leptomeningitis mimicking a subarachnoid haemorrhage 3
-<li>30-40 HU (compared with true acute SAH ~ 60HU)</li>- +<li>30-40 HU (compared with true acute SAH ~60HU)</li>
-<li>the appearances thought to be due to a combination of<ul>- +<li>the appearances are thought to be due to a combination of<ul>
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