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Older-generation computed tomography (CT) scanners proved too insensitive for a negative scan to rule out the diagnosis of subarachnoid hemorrhage (SAH), making lumbar puncture (LP) necessary in patients with negative scans. In a retrospective chart review, researchers evaluated the sensitivity of newer-generation multidetector CT scanners for diagnosing SAH in 499 patients with suspected SAH who were referred to a Dutch neurosurgical unit from 2000 through 2005.
All patients underwent head CT. Patients with negative CT scans underwent LP (≥12 hours after onset of symptoms), and cerebrospinal fluid (CSF) samples were analyzed for xanthochromia by spectrophotometry. Patients with positive scans underwent angiography. SAH was diagnosed in 296 patients, based on angiography or CSF findings. Overall, CT scanning had a sensitivity of 99.7% and a specificity of 100% for diagnosing SAH. Sensitivity was 100% for scans performed 1 to 5 days after symptom onset and 96% for those performed thereafter.
Cortnum S et al. Determining the sensitivity of computed tomography scanning in early detection of subarachnoid hemorrhage. Neurosurgery 2010 May; 66:900.
Comment
This study suffers from referral bias, with an extremely high proportion of patients ruling in for subarachnoid hemorrhage (almost 60%). Although newer-generation multidetector CT was highly sensitive, the authors note that CT alone should be used to exclude SAH only on days 1 to 3 after symptom onset and scans should be reviewed by a neuroradiologist or neurosurgeon. Although this study takes us a step closer to eliminating the need for lumbar puncture in patients with suspected SAH, keep those LP trays handy until these results are duplicated in a community emergency department setting.