Utility of CT angiography in the identification and characterization of supraclinoid internal carotid artery blister aneurysms

Abstract

Background and purpose: Blister aneurysms of the supraclinoid ICA represent a rare but potentially catastrophic cause of SAH, often presenting both diagnostic and therapeutic dilemmas. We explore the utility of CTA in the identification and characterization of ICA blister aneurysms.

Materials and methods: We performed a retrospective review of catheter cerebral angiograms obtained at our institution over a 12-month period for evaluation of SAH, identifying 6 cases of ICA blister aneurysms. All patients underwent CTA and DSA for evaluation of SAH. The reports from the CTA and DSA studies were reviewed to identify aneurysms correctly diagnosed prospectively. Retrospective review of the CTA and DSA images was also performed. Review of the interpretations and images was performed for any follow-up studies.

Results: All 6 patients presented with SAH, diagnosed by head CT. All patients subsequently underwent CTA prior to DSA evaluation. All 6 aneurysms were identified prospectively on initial DSA imaging. Of the 6 blister aneurysms, 4 (67%) were identified prospectively; and 5 (83%), retrospectively on CTA. All 6 patients underwent endovascular treatment with stent placement. Four of the 6 aneurysms underwent follow-up CTA (range, 9-22 days), including the 2 aneurysms that had been unidentifiable preprocedurally. All 4 blister aneurysms were seen postprocedurally by DSA. Three of these 4 (75%) residual aneurysms were detected by CTA (both prospectively and retrospectively).

Conclusions: In the presence of SAH and otherwise negative findings on CTA, a catheter cerebral angiogram should be performed to absolutely exclude an ICA blister aneurysm.

Fig 1.

Left supraclinoid ICA blister aneurysm. Volume-rendered 3D CTA image shows the characteristic morphology of supraclinoid ICA blister aneurysms (white arrow): wide-neck shallow outpouching of the medial wall of the left supraclinoid ICA.

Fig 2.

Left supraclinoid ICA blister aneurysm. Coronal MIP CTA image (A) shows the morphology of the blister aneurysm (white arrow), which closely resembles its DSA counterpart (black arrow, B).

Fig 3.

Left supraclinoid ICA blister aneurysm posttreatment. Coronal MIP CTA image (A) shows the morphology of the residual blister aneurysm (white arrow), which again resembles its DSA counterpart (black arrowhead, B), though the dome of the aneurysm appears slightly more prominent on the DSA study (B). Note that the radiopaque tines of the overlapping stents used in the treatment are clearly seen on the CTA image (black arrows, A) but not on the DSA image.

Fig 4.

Right supraclinoid ICA blister aneurysm. At presentation, this blister aneurysm (black arrow, A) manifests as a subtle shallow outpouching, which becomes progressively larger and more saccular at 2-week (B) and 3-month (C) follow-ups, despite treatment with overlapping stents and subsequent coil embolization.

Fig 5.

Right supraclinoid ICA blister aneurysm. This aneurysm (black arrow) was not identified prospectively but appears visible on retrospective review. A, Volume-rendered 3D CTA image shows a poor imaging technique, with a relatively low resolution and prominent step-off artifacts. B, The correlative DSA clearly delineates the small blister aneurysm (black arrow).

Fig 6.

Right supraclinoid ICA blister aneurysm posttreatment. With adequate imaging and postprocessing parameters on the short-term CTA follow-up (following treatment of the blister aneurysm in Fig 5), the residual blister aneurysm (white arrow) is much more clearly identified (A and B) and closely resembled the appearance of the aneurysm on the correlative DSA (black arrow, C). Note the radiopaque tines of the overlapping stents used in the treatment identified on the CTA images (black arrowheads, A).

Fig 7.

Right supraclinoid ICA blister aneurysm, pre- and posttreatment. The blister aneurysm is not detectable on initial CTA images (A and B) but is clearly delineated on the correlative DSA image (black arrow, C). On the short-term posttreatment CTAs (D and E), the residual aneurysm remains invisible, while it is still clearly seen on the correlative posttreatment DSA image (black arrow, F).