As modern CT scanners become more sensitive, the ability of scanners to discriminate smaller and small abnormalities - such as spontaneous aneurysmal subarachnoid hemorrhage - continues to increase. This BMJ paper makes another case for forgoing lumbar puncture in patients with a negative CT scan.
Specifically, they say that all the SAH in their cohort was picked up by a 3rd generation scanner as long as the scan was performed within six hours of headache onset. Unfortunately, this is another one of those studies that uses follow-up as a proxy for the gold standard evaluation - only half of their enrolled cohort underwent lumbar puncture. They followed up their patients for six months, but survival at six months doesn't rule out pathology, it only rules out death from that specific pathology, and only if an autopsy was performed.
But, CT scan is starting to get close to the point where the false negatives of CT are equivalent to the false positives of the lumbar puncture - and I would imagine the costs and harms to the patient begin to approach equivalence. It definitely changes the equation for your patients when you come back with a negative CT scan and your patient wants to know what the chances are they really need this lumbar puncture.
"Sensitivity of Computer Tomography Performed Within Six Hours of Headache For Diagnosis of Subarachnoid Haemorrhage: Prospective Cohort Study"