Subarachnoid haemorrhages are where there is an extravasation of blood into the space between the arachnoid and pia. Subarachnoid haemorrhages often develop as a result of rupture of a cerebral aneurysm (most often arising from the circle of Willis or the middle cerebral artery bifurcation) or consequent to severe head trauma. Patients with subarachnoid haemorrhage secondary to aneurysmal bleeding often present with sudden onset severe headache which is classically described by the patient as “the worst headache of my life“.
The series of non-contrast cranial CT scans shown here (Figures 1 to 6) are from a patient who presented with sudden onset of severe headache. Subarachnoid haemorrhage is present and blood can be seen at the basal cisterns . An urgent CT angiogram was arranged and a saccular aneurysm was noted at the left middle cerebral artery bifurcation. The Neurosurgical colleagues were then consulted urgently for neurosurgical intervention.
It should be noted that the sensitivity of a non-contrast cranial CT scan in detecting subarachnoid haemorrhage reduces significantly with time, particularly if the subarachnoid haemorrhage is small. If subarachnoid haemorrhage is strongly suspected, the patient should undergo a lumbar puncture to delineate whether the presence of xanthrochromia is present. If present, this means that there are presence of red cells in the cerebro-spinal fluid. With time, the red cells breakdown, releasing haeme, which is subsequently degraded into the yellow-green pigment bilirubin causing the characteristic yellow colour in patients with xanthochromia. In contrast, if red blood cells enter the cerebrospinal fluid due to a “traumatic tap” (i.e. a small blood vessel was damaged during the lumbar puncture), there is inadequate time for the red cells to degrade and thus xanthochromia would not be present.
The non-contrast CT scans shown here are from 2 different patients with a right-sided subarachnoid haemorrhage (Figures 7 to 15). Blood could be seen at the sulci of the right parietal lobe in both cases and in the latter case (Figures 8 to 15), blood could also be seen at the sulci of the right temporal lobe as well as the right sylvian fissure .