Detection and characterization of very small cerebral aneurysms by using 2D and 3D helical CT angiography

Abstract

Background and purpose: Many cases of subarachnoid hemorrhage are due to rupture of small cerebral aneurysms. Our purpose was to evaluate the usefulness of helical CT angiography (CTA) in the detection and characterization of very small (<5 mm) intracranial aneurysms.

Methods: One hundred eighty consecutive patients underwent CTA for suspected intracranial aneurysms. All aneurysms prospectively detected by CTA were confirmed by digital subtraction angiography (DSA) or at surgery. CT angiograms and digital subtraction angiograms were reviewed by two independent blinded radiologists who performed aneurysm detection, quantitation, and characterization using 2D multiplanar reformatted and 3D volume-rendering techniques.

Results: Fifty-one patients harboring 41 very small intracranial aneurysms were included in this series. Eighty-one percent (33 of 41 aneurysms) were </=4 mm in maximal diameter, and 37% (15 of 41 aneurysms) were </=3 mm in maximal diameter. Sensitivity of CTA for very small intracranial aneurysm detection ranged from 98% to 100% (95% confidence intervals, 0.871, 0.999, 0.914, and 1.0), compared with 95% for DSA. The specificity of CTA and DSA for very small intracranial aneurysms was 100% (26 of 26 aneurysms). Positive predictive value ranged from 98% to 100%. Negative predictive value ranged from 96% to 100%. Accuracy of CTA for detection of very small intracranial aneurysms was 99% and 100% (kappa = 0.969 - 1.0 +/- 0.1221). Forty-eight percent of aneurysms were detected in the presence of subarachnoid hemorrhage.

Conclusion: The sensitivity of CTA for the detection of cerebral aneurysms </=5 mm is higher than that of DSA, with equal specificity and high interoperator reliability. High quality, noninvasive CTA aneurysm detection and characterization can be performed using routine clinical CT scanners and commercially available image processing workstations.

Fig 1.

Patient 12, aneurysm 21. Example of smallest aneurysm seen in this study. A, Midarterial phase anteroposterior projection DSA image shows a small saccular aneurysm at the supraclinoid internal carotid artery (short arrow). Note larger anterior communicating artery aneurysm (long arrow). Anterior choroidal artery aneurysm is mostly obscured by overlying internal carotid artery bifurcation (arrowhead). B, 3D posteroanterior projection CTA image with lateral angulation shows aneurysm sac (short arrow). Anterior communicating artery (long arrow) and anterior choroidal artery (arrowhead) aneurysms are also well seen.

Fig 2.

Patient 14, aneurysm 25. Example of DSA false negative finding due to overlapping MCA branches. A, Right internal carotid artery injection, midarterial phase right anterior oblique projection (one of many different projections obtained) DSA image fails to show vascular abnormality at right MCA bifurcation. B, Volume-rendered 3D direct inferosuperior projection CTA image shows a 2.7-mm aneurysm of the right MCA bifurcation with laterally projecting sac (arrow). C, Intraoperative photograph without (top) and with (bottom) labels, with sylvian fissure retracted, shows small laterally projecting saccular aneurysm of the left MCA bifurcation (arrow) and small placoid aneurysmal dilation, not well seen on CTA images. Ant, anterior; Temp, temporal; Med, medial; Lat, lateral.

Fig 3.

Patient 18, aneurysm 32. Example of CTA false negative (reader 1) finding. A, Midarterial phase right anterior oblique projection DSA image shows a small pyramidal aneurysm sac projecting inferiorly from the anterior M2 division (straight arrow). Note the small anterior temporal branch arising from the neck region (curved arrow). B, 3D lateromedial projection CTA image clearly shows the pyramidal aneurysm sac (straight arrow), along with a 0.5-mm anterior temporal branch arising from the region of the aneurysm neck (curved arrow). The aneurysm is clearly present but was overlooked during the initial reading by reader 1.

Fig 4.

Patient 6, aneurysm 9. Example of ability of CTA to visualize small aneurysms in the setting of acute severe SAH. A, Axial unenhanced CT scan shows extensive hyperattenuated blood in the sylvian and choroidal fissures and in the basal cisterns. B, Midarterial phase anteroposterior projection DSA image of the left internal carotid artery shows a small saccular aneurysm at the MCA bifurcation (short arrow) and severe vasospasm of the distal M1 and proximal M2 segments (long arrows). C, Volume-rendered 3D CTA image shows a 4.0-mm maximal diameter saccular aneurysm of the left MCA bifurcation (short arrow) and also luminal reduction compatible with severe segmental vasospasm of the distal left M1 and proximal M2 segments (long arrows).

Fig 5.

Patient 25, aneurysm 41. Example of high correlation between DSA and 3D CTA. A, Midarterial phase anteroposterior oblique projection DSA image of the left MCA shows a small MCA bifurcation aneurysm (arrow). B, 3D CTA image, obtained in a projection similar to that of the DSA image shown in A, shows a 1.9-mm maximal diameter saccular aneurysm arising from the left MCA bifurcation (arrow).

Fig 6.

Patient 19, aneurysm 33. Example of ability of 2D and 3D helical CTA to visualize intracavernous carotid aneurysms. A, Axial view 2D multiplanar reformatted image, obtained at the level of the sella turcica, shows a 2.7-mm saccular aneurysm of the left carotico-ophthalmic region (arrow). B, Sagittal view 2D multiplanar reformatted image shows an inferiorly projecting saccular aneurysm (arrow). C, Volume-rendered mediolateral projection helical CTA image shows a small inferiorly projecting aneurysm sac (arrow). D, Arterial phase lateral projection DSA image shows the small inferiorly projecting aneurysm sac shown in A–C (arrow).

Fig 7.

Characterization of injection delay times.