Introduction Angiogram negative subarachnoid haemorrhage (AN-SAH) account for about 15% of all non-traumatic SAH cases. In this paper we developed a new CT based grading system for distinguishing AN-SAH vs. aneurysmal SAH (a-SAH).

Methods A new CT grading classification was developed based on the Hijdra system. Patterns of SAH in 13 cisterns were scored between 0–2 depending on the amount of haemorrhage (0 = No blood; 1 = partial; 2 = full). The patterns of blood in the interpeduncular, pre-pontine and pre-medullary cisterns were scored in one category: P score (range 0–6); the total amount of blood in the entire 13 cisterns was scored under T score (range 0–26). Initial CT scans from 148 consecutive AN-SAH and 180 a-SAH patients were reviewed and scored by two independent blinded neurosurgeons. Patients with pure cortical or traumatic SAH or those with CT scan performed >72 h after the SAH ictus were excluded. All performed angiograms (1^st, 2^ndand 3^rdlook, if performed) were reviewed for presence of aneurysms.

Results In patients with CT scan scores between P0-1;T > 9, the performed angiograms were positive in 92% (23 a-SAH vs. 2 AN-SAH), whereas in those scoring P0-1;T < 10 angiography revealed a much higher incidence of positive findings (52% a-SAH vs. 48% AN-SAH, p = 0.33). For Px; T < x+8 (x between 2–6), the angiograms were negative in 94.6% of cases (3 a-SAH vs. 53 AN-SAH), and in a subset of this category (P4-6; T < 14) the angiograms were negative in 100% of cases (n = 34). For patients scoring (P0-1; T < 10) and Px; T > x+7(x between 2–6) the scores were not predictive of angiogram results (65% a-SAH vs. AN-SAH 35%).

Conclusion The new CT scan scoring provides an estimate for the likelihood of a negative angiogram in patients with SAH. Significant blood in the pre-brainstem cisterns with minimal or modest blood in the remaining cisterns best predicts absence of aneurysm or vascular lesion on initial and follow-up angiography.

Disclosures I. Darie: None. T. Rayan: None. S. Amin-Hanjani: None. X. Du: None. V. Aletich: None. F. Charbel: None. A. Alaraj: None.