The brain is very well protected from injury by the
skull and membranes just below the skull, referred to as the meninges.
The meninges consist of 3 layers, the dura mater,
the arachnoid and the pia mater. Trauma to the head could result in bleeding
within these layers. Bleeding could also occur all of a sudden if the patient
has a ruptured dilated artery, also referred to as aneurysm.
the arachnoid layer is referred to as subarachnoid hemorrhage
The accumulated blood could press on the brain
causing headache and neurological problems.
Subarachnoid hemorrhage can be diagnosed with a CT
scan. Early treatment could result in complete recovery of the patient.
Subarachnoid hemorrhage causes headache as one of its earliest signs. A recent
study was conductedto assess the
sensitivity of modern third generation CT scan in detecting subarachnoid
hemorrhage when carried out early, that is, within six hours of the onset of
3132 patients across Canada with severe headache
suspected to be due to subarachnoid hemorrhage were included in the study. The
patients, recruited over a nine-year period between the years 2000 and 2009,
were subjected to CT scan as soon as they arrived to the emergency department.
The patients did not suffer from any neurological deficits like paralysis when
the test was conducted.
Patients were said to be positive for subarachnoid
hemorrhage if the CT scan detected a subarachnoid bleed, if their cerebrospinal
fluid (the fluid surrounding the brain and spinal cord) testing showed
xanthochromia or red blood cells (>5◊106/L), or if an aneurysm was
identified on cerebral angiography. A number of patients who were negative for
subarachnoid bleeding were followed on for 6 months to ensure that they were
not missed cases.
In the study,
researchers noted that modern CT scans were very sensitive in detecting the
presence of subarachnoid hemorrhage when conducted within 6 hours of the onset
Some false negative results (results indicating the
absence of subarachnoid hemorrhage when they were actually present) were
obtained when the CT scan was done between 8 hours to 8 days after the onset of
headache. These cases were later diagnosed with lumbar puncture and/ or
clinicians should be cautious in interpreting CT results when a scan is done
more than 6 hours after the onset of headache
The researchers also found that some emergency
physicians and radiology trainees could make mistakes while interpreting the CT
scans. Thus, besides having modern
technology, it is also necessary to have well qualified and experienced
radiologists to interpret the results and increase the sensitivity of the
1. Jeffery et al. Sensitivity of computed tomography performed within
six hours of onset of headache for diagnosis of subarachnoid haemorrhage: prospective cohort study. BMJ 2011; 343:d4277