Table 2.

Imaging and laboratory details for the seven false negative cranial computed tomography studies.

Age	CT scanner	CT slice thickness	CSF RBCs/microliter**	Xanthochromia	Angiography results
≥90	unavailable	5mm	280000	Yes	5mm ACOM aneurysm
76	GE lightspeed VCT (64 slice)	5mm	517500	No	4mm right PCOM aneurysm
67	GE lightspeed VCT (64 slice)	5mm	408000	No	6mm left PCOM aneurysm
45	GE lightspeed VCT (64 slice)	5 mm	190000	No	4mm left ICA aneurysm
53	GE lightspeed Pro 16 (16 slice)	5mm	49750	No	2mm right PCOM aneurysm
50	GE lightspeed VCT (64 slice)	1.25mm	9960	No	10mm ACOM aneurysm
70	GE lightspeed VCT (64 slice)	5mm	55000	Yes	2mm right vertebral artery

Seven patients presenting with aneurysmal SAH had cranial CT studies performed within six hours of headache onset that were initially reported as negative for evidence of subarachnoid hemorrhage. Diagnosis of SAH was made by lumbar puncture in each case. Details of the CT technology used as well as the results of diagnostic lumbar punctures and formal cerebral angiography are presented for each case.

^**CSF RBC counts were the lowest values reported in cases where multiple tubes were analyzed.

GE, General Electric; VCT, volume computed tomography; CT, computed tomography; ACOM, anterior communicating artery; CSF, cerebrospinal fluid; RBC, red blood cell; ICA, internal carotid artery; PCOM, posterior communicating artery; SAH, subarachnoid hemorrhage