Diagnosis of Subarachnoid Haemorrhage (SAH)

Fig 1: Subarachnoid Haemorrhage

CT brain scan is normal in up to 30% of patients with SAH, so that a negative scan cannot be used to exclude the diagnosis if suspected clinically. However, a positive CT brain scan enables the diagnosis to be made non-invasivally.

Fig 2: CT and MRI brain show Subarachnoid Haemorrhage (SAH)

Absence of red blood cells, or the absence of xanthochromia is sensitive for the exclusion of SAH. Where lumbar puncture (LP) is traumatic, the presence of large numbers of red cells may complicate interpretation. In this situation, spectophotometric analysis of the supernatant for red cell pigments may be helpful. 

Bilirubin and oxyhaemoglobin take 12 hours to appear in the cerebrospinal fluid (CSF) following a bleed, and for this reason LP should usually be delayed until more than 12 hours from the onset of symptoms. 

Because of the invasive nature of cerebral angiography, and relatively high complication rate, it is usually reserved for patients whose other investigations are positive.

Fig 3:
a) CT showing subarachnoid haemorrhage,
b) Cerebral angiograms demonstrating 13 aneurysms,
b)3 in the right anterior circulation
c) 5 in the left anterior circulation, and
d) 5 in the posterior circulation.
Arrow heads, aneurysms;
arrow, ruptured aneurysm

Source: Fig 1, Fig 2, Fig 3,