Diagnostic Impact of Bone-Subtraction CT Angiography for Patients with Acute Subarachnoid Hemorrhage

Abstract

Background and purpose: Detection and evaluation of ruptured aneurysms is critical for choosing an appropriate endovascular or neurosurgical intervention. Our aim was to assess whether bone-subtraction CTA is capable of guiding treatment for cerebral aneurysms in patients with acute SAH and could replace DSA.

Materials and methods: We prospectively studied 116 consecutive patients with SAH with 16-detector row bone-subtraction CTA and DSA before intracranial aneurysm treatment. Two independent neuroradiologists reviewed the bone-subtraction CTA blinded to DSA (reference standard). We determined the accuracy of bone-subtraction CTA for aneurysm detection and the measurement of aneurysm dimensions and compared the radiation doses of the 2 imaging modalities.

Results: Seventy-one patients (61%) had 74 aneurysms on DSA. Bone-subtraction CTA detected 73 of these aneurysms, but it detected 1 additional aneurysm. On a per-aneurysm basis, sensitivity, specificity, and positive and negative predictive values for bone-subtraction CTA were 99%, 98%, and 99% and 98%, respectively. For aneurysms of ≤3 mm, sensitivity was 94% (95% CI, 73%-99%). Bone-subtraction CTA slightly overestimated neck and dome diameters by <0.2 mm and overestimated the dome-to-neck ratios by 2% on average. Dose-length product was 565 ± 201 mGy × cm for bone-subtraction CTA and 1609 ± 1300 mGy × cm for DSA.

Conclusions: Bone-subtraction CTA is as accurate as DSA in detecting cerebral aneurysms after SAH, provides similar information about aneurysm configuration and measures, and reduces the average effective radiation dose for vascular diagnostics by 65%. Diagnostic equivalence in association with dose reduction suggests replacing DSA with bone-subtraction CTA in the diagnostic work-up of spontaneous SAH.

Fig 1.

A 78-year-old-female patient with symmetric infraclinoid aneurysms of the ICA. A, Volume-rendering of BSCTA displays both aneurysms (arrowhead: right aneurysm; arrow: left aneurysm). B and C, DSA confirms both aneurysms in size and configuration.

Fig 2.

False-negative bone-subtraction CTA findings of an aneurysm of the right anterior cerebral artery in a 50-year-old woman. A, The right anterior oblique projection DSA shows a small broad-based aneurysm (arrow). B, On volume-rendering reconstruction, the aneurysm (arrow) appears fusiform. The white surface in the lower part of the image represents the bone-to-vessel boundary of the bone-removal processing.

Fig 3.

False-positive bone-subtraction CTA findings in an aneurysm (2.5 mm) of the left middle cerebral artery distal to the trifurcation in a 50-year-old man with 2 aneurysms. A, Volume-rendering of bone-subtraction CTA depicts the aneurysm (anteroposterior view) that was missed by DSA. B, 3D-DSA image of the initially missed M2 MCA trifurcation aneurysm (left anterior oblique view) that was confirmed in retrospect.

Fig 4.

Bland-Altman plots show the relationship between differences and means of DSA and BSCTA in aneurysm dome (A) and neck (B) measurements and dome/neck ratios (C). The black dotted line indicates the regression line of the differences. The 2 thin black lines represent the 95% confidence interval for the regression line of the differences. A, Bone subtraction CTA tends to overestimate aneurysm domes by 0.17 mm (95% CI, 0.04–0.39 mm) and has a mild trend toward higher values for dome diameters with larger values. The colored rectangular boxes highlight manual measurements with interpolation of DSA results because DSA millimeter calibrations were not transferred with the other DSA data. The outlier case is 1 large 14.0-mm aneurysm that was overestimated by 6.0 mm and belongs to the manually calculated measurements. B, Bone-subtraction CTA measurements of the aneurysm neck are in good agreement with DSA (0 ± 1.96 mm). Outlier cases are small 2.5- and 2.7-mm aneurysms that were underestimated by −1.5 and −1.2 mm. The third outlier was a 2.7-mm aneurysm that was overestimated by 1.5 mm. C, Bone-subtraction CTA slightly overestimates dome/neck ratios compared with DSA (mean, 0.04; 95% CI, 0.08–0.16). Four of the 6 outliers belong to the manually calculated DSA measurements (colored rectangular boxes).