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.
AdvertisementBleeding below 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 headache.
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 (>5Ũ106/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 of headache.
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 cerebral angiography.
Thus, 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 scans.
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