Crescent sign on magnetic resonance angiography revealing incomplete stent apposition: correlation with diffusion-weighted changes in stent-mediated coil embolization of aneurysms

Clinical article

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Object

Few data are available on how closely stents appose the luminal vessel wall in stent-mediated coil embolization of intracranial aneurysms and on the effect of incomplete stent apposition on procedural thromboembolic complications.

Methods

Postprocedural 3-T MR diffusion-weighted imaging and time-of-flight angiography were obtained in 58 patients undergoing stent-mediated coil embolization of aneurysms using the Enterprise closed-cell and Neuroform open-cell self-expanding intracranial microstents.

Results

A distinctive semilunar signal pattern, identified using 3-T MR angiography, represented flow outside the confines of the stent struts in patients in whom Enterprise but not Neuroform devices were used. This pattern, designated as the crescent sign, was confirmed to correspond to incomplete stent apposition by use of high-resolution angiographic flat-panel CT scanning revealing flow ingress into and egress out of the isolated luminal wedge. The presence of the crescent sign was seen in 18 of 33 Enterprise-treated but in 0 of 25 Neuroform-treated cases, and was more likely in stents delivered in the tortuous internal carotid artery (p = 0.034). The crescent sign was strongly predictive of ipsilateral postprocedural lesions seen on diffusion-weighted imaging in the entire population (OR 18, 95% CI 4.33–74.8; p < 0.0001). In the Enterprise stent subset, ipsilateral lesions were detected on diffusion-weighted imaging in 15 (45%) of 33 cases; the crescent sign was seen in 12 (80%) of 15 patients with ipsilateral lesions on diffusion-weighted imaging, but in only 6 of 18 patients without lesions (OR 8, 95% CI 1.61–39.6; p = 0.006).

Conclusions

Incomplete stent apposition is detectable on 3-T MR angiography as a crescent sign, and was found to be highly prevalent in Enterprise closed-cell design stents used to assist coil embolization of aneurysms. Incomplete stent apposition was also associated with periprocedural ipsilateral hyperintense lesions on diffusion-weighted imaging. These results identify an association between incomplete stent apposition and thromboembolic complications in stent-mediated coil embolization of intracranial aneurysms.

Abbreviations used in this paper: ACT = activated clotting time; BMI = body mass index; ICA = internal carotid artery.

Article Information

Address correspondence to: Adel M. Malek, M.D., Ph.D., Department of Neurosurgery, Tufts Medical Center, 800 Washington Street, Proger 7, Box 178, Boston, Massachusetts 02111. email: amalek@tuftsmedicalcenter.org.

Please include this information when citing this paper: published online May 27, 2011; DOI: 10.3171/2011.4.JNS102050.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    A: Schematic illustration of steps involved in stent-assisted coil embolization of a wide-necked aneurysm with good vessel wall/stent apposition. B: Two types of intracranial stents for stent-assisted coil embolization of aneurysms: the open-cell design Neuroform and the lower-profile, closed-cell design Enterprise. C: Simple manual bending highlights the different behavior of closed- and open-cell design stents: inner curve fish-scaling (arrow) and outer flaring with increased gap in the Neuroform device (yellow arrowhead); inner crimp (arrow) and ovalization with diameter loss in the Enterprise device (dashed line). D: Incomplete stent apposition (arrowheads) can occur on either the inner or outer curve of a vessel where the stent struts fail to maintain contact with the vessel wall.

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    A: Sagittal 3-T MR angiography study demonstrating the crescent sign (arrow, right) in a patient following Enterprise stent–assisted coil embolization of bilateral wide-necked carotid ophthalmic aneurysms. B: Axial high-resolution flat-panel CT scans obtained without (left) and with (center) contrast revealing Enterprise stents to be nonapposed to the vessel wall, with a corresponding crescent sign on axial 3-T MR angiography study (arrow, right). C: Magnified view of contrast-enhanced flat-panel CT scan outlines of right carotid vessel wall (solid lines), stent struts (dashed lines), and orphaned vessel lumen (arrows) resulting from the incomplete stent apposition. D: Schematic drawing of incomplete stent apposition showing arterial flow (upper arrows) through the stent struts (dashed line) into the crescent sign and back into vessel lumen.

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    Dual-volume 3D angiographic reconstruction of a wide-necked cavernous carotid aneurysm on a tight-radius 180° cavernous carotid bend (A); the lesion was treated with Neuroform stent–assisted coil embolization. A 3-T MR angiography study (B) in corresponding projection failing to demonstrate the crescent sign. Flat-panel CT scans without (C) and with (D) addition of contrast agent showing the Neuroform stent struts to be apposed to the vessel wall, with no evidence of incomplete stent apposition, and identifying a focal instance of inner-curve fish-scaling (arrow).

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    Dual-volume 3D angiographic reconstruction, in anteroposterior (A) and lateral (B) projections, of a wide-necked left superior hypophyseal carotid aneurysm treated with Enterprise stent–assisted coil embolization. Postprocedural 3-T diffusion-weighted imaging study (C) revealing a high-intensity signal of restricted diffusion in the ipsilateral left corona radiata (dashed circle). The crescent sign (arrow and arrowhead) is revealed on contemporaneous 3-T MR angiography studies obtained in the sagittal (D) and axial (E) projections, coincident with radiographic confirmation of incomplete stent apposition on contrast-enhanced flat-panel CT imaging (F) in the corresponding projection, highlighting orphaned vessel lumen (arrows). Schematic drawing (G) of flow through the stent struts into the orphaned lumen corresponding to the crescent sign, and back into the distal vessel lumen.

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    Analysis of postprocedural lesions revealed on diffusion-weighted imaging (DWI) in patients (pts) undergoing coil embolization with the aid of an Enterprise stent. Upper: Number of lesions per patient based on the presence (CS+) or absence (CS−) of crescent sign on 3-T MR angiography. Lower: Size distribution of ipsilateral lesions on diffusion-weighted imaging based on crescent sign status.

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