ticular, 3D reconstructions can provide as helpful overview of the vessels (Fig. 12.55). The standard method for characterizing intracranial stenosis is based on the WASID criteria, whereby percent stenosis = [(1 − (vessel diameter at the stenosis/normal vessel diameter))] × 100%.

12.2.9\ Angioplasty and Intra-arterial

Spasmolysis for Vasospasm

For symptomatic vasospasm refractory to hemodynamic therapy, endovascular techniques, such as balloon angioplasty and intra-arterial spasmolysis with papaverine or nimodipine, may be considered in order to improve cerebral perfusion. Following successful angioplasty or spasmolysis for vasospasm, imaging with CTA or MRA may be used to characterize the extent of infarction, improvement in cerebral perfusion, and luminal diameter of the affected vessels (Fig. 12.56). Otherwise, transcranial Doppler ultrasound is a convenient modality for assessing the degree of vasospasm due to its availability at the bedside.

a

12.2.10  Endovascular Stent Reconstructive Treatment for Extracranial Cerebrovascular Occlusive Disease

Carotid artery stenting is mainly reserved for patients with symptomatic carotid stenosis greater than 50% or asymptomatic stenosis greater than 70% by NASCET criteria who are otherwise poor surgical candidates for endarterectomy. The procedure consists of endovascular placement of a flexible, selfexpanding stent following angioplasty of the affected vessel and use of a distal protection device. Imaging following stent placement may be performed in order to determine if the luminal diameter following angioplasty and stent placement has improved. The standard methods for assessing stenosis at the carotid bifurcation use NASCET or ECAS criteria. Methods used to assess luminal diameter include carotid duplex ultrasound conventional angiography, MRA, and CTA (Fig. 12.57). The morphology of the stent can vary considerably depending on the design and amount of atherosclerotic disease in the vessel. For example, stents can be straight or tapered. Tapered stents can have a conical design, in which

b

Fig. 12.56  Spasmolysis. This patient developed symptomatic vasospasm involving the left middle cerebral artery after aneurysm clipping, which was documented on CTA (a). Following angioplasty of the proximal anterior

cerebral arteries with intra-arterial pharmacologic spasmolysis using calcium channel blockers, there was significant and sustained improvement in the diameter of the anterior cerebral arteries (b)

Fig. 12.57  Cervical carotid stenting. Digital subtraction angiography (DSA) color duplex ultrasound before and after angioplasty and stent placement for high-grade stenosis in a patient who had symptomatic stenosis. Both DSA and color duplex arteriography demonstrate the stenosis with high flow velocities on the carotid duplex scan

before (a, b) with resolution of the stenosis immediately after (c) and 1 month following stent placement (d). Carotid duplex ultrasound is a noninvasive means to evaluate carotid stent placement for carotid bifurcation stenosis

there is gradual decrease in caliber of the stent from proximal to distal, versus shoulder-­tapered, in which there is an abrupt change in caliber in the midportion of the stent. Atherosclerotic plaque can produce a waist in the stent. A residual waist of less than 20% of the lumen diameter is considered acceptable. Following the deployment of stents for reconstruction, there are expected artifacts that affect the imaging appearance of the treated vessel for extracranial carotid disease or carotid blowout disease.

a

b

12.2.11  Endovascular Reconstructive Treatment for Active Extracranial Hemorrhage or Pseudoaneurysm

Endovascular reconstructive treatment is currently performed using covered stents or a combination of stents and embolic material. Covered stents are deployed in circumstances where a

c

Fig. 12.58  Covered stent. CTA (a) shows a pseudoaneurysm along the midportion of the right common carotid artery (arrow). Following placement of a covered stent,

the aneurysm is no longer identified on follow-up carotid duplex ultrasound (b) and CT angiography (c)

patient has had a carotid blowout due to open communication of the parent artery with the airway or skin surface (Fig. 12.58) and it is felt that the patient would be unable to tolerate parent vessel sacrifice without high risk for neurologic deficit. Posttreatment imaging may be performed in order to assess luminal patency and intracranial events. Methods used to assess luminal diameter include carotid duplex ultrasound conventional angiography, MRA, and CTA. Patients who receive covered stents are at risk for devel-

oping blood flow around the stent or endoleak, which may result in rehemorrhage, as well as infection in the form of septic emboli with brain abscess formation.

Fig. 12.59  Endovascular cerebral venous thrombolysis. The MR venogram (a) shows thrombosis of the internal cerebral veins, straight sinus, and basal vein of Rosenthal. The T2-FLAIR MRI (b) demonstrates associated edema within the bilateral thalami and to a lesser extent in the basal ganglia. The patient deteriorated and the degree of edema worsened as depicted on the T2FLAIR MRI 24 h

later despite anticoagulation (c). The patient underwent embolectomy using penumbra device, and recanalization of the previously thrombosed vessels (arrows) was achieved, as demonstrated on the follow-up CT venography (d) and the edema regressed on the T2FLAIR MRI (e). Susceptibility-­weighted imaging (f) demonstrates a few microhemorrhages within the thalami

12.2.12  Endovascular Treatment

for Intracranial Venous

Stenosis and Occlusion

Endovascular treatment for symptomatic internal cerebral vein thrombosis or dural sinus thrombosis may include fibrinolytic infusion and mechanical embolectomy. Imaging typically demonstrates resolution of cerebral edema following successful therapy (Fig. 12.59). Alternatively, venous sinus stenting can be performed to treat stenoses that are unresponsive to medical therapy, most commonly in the transverse sinus (Fig. 12.60). The procedure can be performed for restoring patency of transverse sinuses in patients with

idiopathic intracranial hypertension. Stenting is most appropriate if a pressure gradient of more than 10 mmHg exists across a stenosis. Either self-expandable or balloon-­expandable stents can be used. The most common­ complications include in-stent thrombosis, headache, and hearing loss.

12.2.13  Complications Related

to Endovascular Procedures

Access Site Complications.  Non-neurologic complications related to head and neck endovascular interventions are uncommon, occurring in 0.14% of cases who undergo femoral artery

Fig. 12.62  Hyperperfusion syndrome. The initial digital subtraction arteriography (a) demonstrates a long-­ segment high-grade stenosis (arrow). Following the stent placement, the left internal carotid artery dilated to its normal diameter (b). Although the patient was doing well initially, the patient experiences seizure following the pro-

cedure, as well as right hemiparesis and aphasia. Susceptibility-weighted imaging (c) demonstrates punctate left cerebral hemisphere microhemorrhages (arrows). CT perfusion cerebral blood flow map (d) demonstrates relatively higher blood flow to the left hemisphere (encircled)

access. Such complications include femoral abscess, occlusions of the femoral artery with leg ischemia, dissection and pseudoaneurysm formation, retroperitoneal hemorrhage requiring transfusion, or a combination of these. CT/CTA is a reasonable option for evaluating patients with suspect vascular compromise and hemorrhage in the emergent setting (Fig. 12.61).

Cerebral Hyperperfusion Syndrome.  Cerebral hyperperfusion syndrome classically occurs within the first few days following carotid artery revascularization for severe stenosis. Patients present with severe headache or neurologic deficits. It is often accompanied by seizures and may result in intracranial hemorrhage. In general, patients with severe stenosis have chronic maximal dilation of the intracranial vasculature, which

Fig. 12.63  Intraprocedural aneurysm rupture. Digital subtraction angiography (a) shows aneurysm rupture as evidenced by contrast extruding beyond the confines of the aneurysm (arrow), which was treated by immediate

deployment of a balloon and continued embolization using coils. CT obtained immediately following the procedure (b) demonstrates scattered subarachnoid hemorrhage, which was not present before the procedure

Fig. 12.64  Intraparenchymal hemorrhage due to anticoagulation. Digital subtraction arteriogram (a) shows embolization of a right middle cerebral artery aneurysm. The patient was on anticoagulation and double antiplatelet

treatment during the procedure, and 16 h following embolization, the patient suddenly deteriorated due to a remote hemorrhage in the cerebellum, as shown on CT (b)

Fig. 12.65  Intracranial hemorrhage complicating flow diversion. The patient presented with right-sided weakness after treatment of a left cavernous carotid aneurysm.

The coronal CT image (a) shows a left intracranial artery Pipeline stent (arrow). The axial CTA image (b) shows a large left frontoparietal hematoma with a hematocrit level

does not immediately reverse at the time of reperfusion by stenting. This results in a hyperperfusion phenomenon. Imaging can be performed to evaluate for associated hemorrhage, and the diagnosis is supported by the finding of increased perfusion ipsilateral to the stented vessel (Fig. 12.62).

-

Intracranial Hemorrhage.  Hemorrhagic complications may include intraprocedural aneurysm rupture (Fig. 12.63), intraparenchymal hemorrhage related to anticoagulation and/or antiplatelet treatment (Fig. 12.64), and hyperperfusion syndrome with revascularization procedures, as mentioned before. Furthermore, delayed ipsilateral intraparenchymal hemorrhage has been described as a potential complication following flow diversion of anterior circulation aneurysms, perhaps due to decreased arterial wall compli-

ance and altered Windkessel effect. The intraparenchymal hemorrhages in such cases can be large and contain hematocrit levels (Fig 12.65), since the patients are typically anticoagulated. CT tends to be the modality of choice for evaluating post-procedure hemorrhage, even if metal artifact may degrade the images in some cases.

Stent Steno-occlusive Disease.  Patency of the stent can be evaluated using MRA, CTA, or Doppler ultrasound. Velocity criteria for extracranial­ internal carotid artery stents have been proposed as follows:

•\ Residual stenosis ≥20%: peak systolic velocity ≥150 cm/s and ICA/CCA ratio ≥2.15

•\ In-stent restenosis ≥50%: peak systolic velocity ≥220 cm/s and ICA/CCA ratio ≥2.7

•\ In-stent restenosis ≥80%: peak systolic velocity 340 cm/s and ICA/CCA ratio ≥4.15

Intimal hyperplasia is the process of endothelial regrowth after injury and can occur within the lumen of stents, usually with a thickness of 1 or 2 mm. However, intimal hyperplasia is sometimes more extensive and can lead to hemodynamically significant stenosis. On ultrasound, intimal hyperplasia is typically homogeneously hypoechoic, and on

Fig. 12.69  Stent kink. CT curved planar reformat shows a focal angulation (arrow) in the lateral aspect of this curved supraclinoid internal carotid artery stent, which is otherwise intact

Fig. 12.70  Stent compression and fracture. Coronal CT MIP image demonstrates deformity and a gap between fragments of a subclavian artery stent at the thoracic outlet (encircled). The ends of the stent adjacent to the fracture are compressed

CT it appears as mural hypoattenuation (Fig. 12.66).

Significant stent restenosis is a fairly common complication, occurring in about 15% of cases within several months of the procedure. Restenosis is more likely with self-expandable stents than balloon-expandable stents. CTA can demonstrate filling defects in the lumen of the stent (Fig. 12.67). Catheter angioplasty is more

sensitive and allows further treatment, such as angioplasty, to be performed.

Stent occlusion is a serious complication that can result from in-stent thrombosis. As before, several modalities can be used to evaluate this complication. CTA with delayed imaging can be helpful for differentiating high-grade stenosis versus occlusion (Fig. 12.68).

Fig. 12.72  Coil compaction. Pre-procedure CT angiography curved planar reformatted image (a) shows a large basilar tip aneurysm (*). Immediate post-embolization catheter angiogram (b) shows near-complete occlusion of

the basilar tip aneurysm with metal coils. Follow-up digital subtraction angiogram (c) shows interval coil compaction with substantial aneurysm filling (arrow)

Mechanical Stent Failure.  Mechanical stent failure can manifest as indentation, compression, kinking, and/or fracture (Figs. 12.69 and 12.70). Deformed stents can lead to vascular occlusion and/or embolization, which can be depicted on Doppler ultrasound and/or angiography imaging. This complication is less likely with self-expand- ing stents than with balloon-expanding stents. Treatment consists of inserting smaller caliber stents into the damaged stent lumen or retrieving

the fractured device. Anatomy of the stented vessel plays an important role in stent deformity, such that this phenomenon tends to occur along curvatures, such as in the carotid siphon region. Flat-panel CT is reported to be more sensitive for depicting stent deformities than is digital subtraction angiography.

Residual and Recurrent Aneurysms.  It can be challenging or even risky to completely obliterate

aneurysms via coil embolization, particularly in cases of aneurysm rupture. However, the presence of a small residual neck does not necessarily warrant further intervention, unless there is growth of the aneurysm. Thus, surveillance imaging via MRA is typically performed to ensure

stability of the aneurysm (Fig. 12.71). On the other hand, coil compaction is deemed to be the most common cause of aneurysm recurrence after embolization and is a process whereby aneurysm coil mass volume decreases over time and is more likely to occur after embolization of

Fig. 12.75  Coil prolapse. Digital subtraction angiogram (a) and 3D angiogram in a different patient (b) depict loops of coils (encircled) that project from the coil masses

into the lumen of the adjacent vessel (ICAs). The prolapsed coils were not significantly flow limiting

Fig. 12.76  Coil malpositioning requiring removal. Reformatted CT image (a) shows a coil mass within a basilar tip aneurysm and a coil that extends inferiorly into the left vertebral artery (arrow), thereby occluding the

vessel. Digital subtraction angiogram (b) shows attempted coil retrieval using the Merci device, which is wrapped around the coil

ruptured aneurysms as well. This process can be observed on serial imaging in which there is enlargement of the aneurysm sac from baseline (Fig 12.72).

Embolic Phenomena.  Silent thromboembolic events associated with neurointerventional procedures are a relatively common occurrence, despite meticulous technique and systemic anticoagulation. This can occur due to the formation of thrombus associated with the devices used during the procedure or the introduction of intravascular air. Nevertheless, significant clinical consequences are rare. The lesions are typically small, often multifocal, and usually localize to the vascular territory of the vessel

being treated (Fig. 12.73). Distal migration of stents or coils can occur during or after the intervention and can also be associated with morbidity. However, immediate removal of the devices is often feasible and effective before clots form. Furthermore, anticoagulation can be helpful in maintaining blood flow. Beyond the immediate intraprocedural period, imaging via CTA can help localize the migrated hardware and assess for associated complications (Fig. 12.74).

Coil Malpositioning/Prolapse.  Coils in excessively packed aneurysms can potentially prolapse through the aneurysms’ neck into the parent vessels, particularly in cases of wide aneurysm necks

Fig. 12.78  Retained microcatheter. The patient underwent left temporal arteriovenous malformation embolization. Axial CT image (a) shows the serpiginous course of the intravascular catheter (arrow), which appears hyperat-

tenuating due to the presence of concentrated embolic material retained in the lumen. The microcatheter (arrow) is hypointense on the T2-weighted MRI (b)

Fig. 12.79  Retained snare. The patient is status post coil embolization of a left superior cerebellar artery aneurysm with coil migration into the basilar artery and iatrogenic retained distal fragment of snare device within the distal basilar artery while attempting to retrieve the malpositioned coil. These materials were left in situ and the patient is treated with dual antiplatelet treatment to permit endothelialization until future follow-up, due to concern

that further manipulation of this adherent fragment might have catastrophic consequences. Frontal spot image (a) at the end of the procedure shows a retained fragment of the snare device (arrow) in the basilar artery, adjacent to the coils projecting into the basilar artery. Coronal (b) CTA image shows the fractured snare (arrow) and embolization coils remain position, but the basilar artery and distal branches are patent

and partially thrombosed aneurysms. Prolapse of only a few coils is not necessarily flow limiting (Fig. 12.75). However, extension of greater lengths of coils into the parent vessels can predispose to significant thromboembolic events and may warrant removal (Fig. 12.76). A variety of devices can be used to remove the migrated coils, such as microsnares and the Merci retriever.

Hydrocephalus After Coil Embolization. 

Hydrocephalus commonly results from subarachnoid and intraventricular hemorrhage from ruptured aneurysms. Hydrocephalus can also occur following embolization of unruptured aneurysms, particularly with hydrogel coils. The mechanism by which hydrogel coils may induce hydrocephalus is not well understood. However, one possible etiology is that hydrogel coils undergo progressive expansion once exposed to the physiological environment and increase overall aneurysm filling. Another possibility is that it may be some-

how related to an exaggerated inflammatory response during aneurysm healing. MRI or CT can readily depict post-coiling hydrocephalus (Fig 12.77).

Retained Hardware.  A potential complication of endovascular procedures involving embolization material is entrapment of the microcatheter. Imaging may be obtained to evaluate the extent and location of the entrapped microcatheter, which appears as hyperattenuating on CT and low signal intensity on MRI due to the retained embolization material (Fig. 12.78). If endovascular attempts fail to remove the microcatheters, these can be removed via microsurgical retrieval. Another more unusual situation is fragmentation and retention of a snare used to retrieve malpositioned coils (Fig. 12.79). Thus, it is useful to be familiar with the imaging appearance of various devices used, in case such situations are encountered in practice.