Perimesencephalic hemorrhage and CT angiography - A decision analysis

Background and Purpose-The method of choice for detecting or excluding a ve rtebrobasilar aneurysm still is a matter of debate in patients with a chara cteristically perimesencephalic pattern of subarachnoid hemorrhage (SAH) on CT. We used decision analysis to compare possible diagnostic strategies in these patients. Methods-A decision analytic model was developed to evaluate the effect of 4 different diagnostic strategies following a perimesencephalic pattern of S AH on CT: 1, no further investigation; 2, digital subtraction angiography ( DSA) by catheter; 3, CT angiography as initial modality, not followed by DS A if negative; and 4, CT angiography as initial modality, followed by DSA. We used a 4% prevalence of a vertebrobasilar aneurysm given a perimesenceph alic pattern of hemorrhage, a 97% sensitivity and specificity of CT angiogr aphy, and a 99.5% sensitivity and 100% specificity of DSA. In a prospective ly collected series, the complication rate from DSA in patients with a peri mesencephalic pattern of hemorrhage was 2.6%. We calculated the expected ut ility of each of the 4 diagnostic options and used sensitivity analyses to examine the influence of the plausible ranges of the various estimates used . Results-The expected utilities were 99.09 for CT angiography only, 98.96 fo r no further investigation, 98.22 for DSA, and 96.34 for CT angiography plu s DSA. The results of the sensitivity analysis indicate that over a wide ra nge of assumptions, CT angiography only is the most beneficial option. Only when the complication rate of catheter angiography is <0.2% is DSA the pre ferred strategy. Conclusions-Our decision analysis shows that in patients with a perimesence phalic pattern of hemorrhage on CT, CT angiography only is the best diagnos tic strategy. DSA can be omitted in patients with a perimesencephalic patte rn of hemorrhage and a negative CT angiogram.