**5. Alternative microcatheterization of target vessel via a collateral route**

The circle of Willis provides a natural conduit to access contralateral or carotid to basilar (or vice-versa) circulations. In the vast majority of cases, adequate access may be obtained through direct ipsilateral routes; however, due either to proximal vessel occlusion or distal vessel entry angles, these alternate routes through the circle of Willis provide easier microcatheter entry angles.

Similar patterns of distal arterial collateralization can often be expected in PICA, AICA and SCA circulations. In cases of PICA ruptured dissections or dissecting aneurysms, proximal PICA can be occluded without needs of microsurgical bypass anastomosis. (Figure 21).

Fig. 12. A 38-year-old man with a left PCA territory embolic infarct was found to have a traumatic giant left VA dissecting aneurysm and DAVF from a fall 2 years prior to

**5. Alternative microcatheterization of target vessel via a collateral route** 

The circle of Willis provides a natural conduit to access contralateral or carotid to basilar (or vice-versa) circulations. In the vast majority of cases, adequate access may be obtained through direct ipsilateral routes; however, due either to proximal vessel occlusion or distal vessel entry angles, these alternate routes through the circle of Willis provide easier

giant aneurysm.

microcatheter entry angles.

treatment. (A and B) Three-dimensional and two-dimensional angiograms show a giant left VA dissecting aneurysm and a DAVF. (C) The right VA angiogram demonstrates competent flow in the right VA. (D and E) Due to extremely high flow in the giant aneurysm, the DAVF was unable to be catheterized until occlusion of the left VA at the origin of the aneurysm. The left traumatic vertebral DAVF was catheterized from the right VA through the VB junction to the left VA. The *black arrow* indicates the fistula. *Open arrows* indicate the microcatheter route. (F) The fistula and residual filling of the giant aneurysm were treated successfully with coil occlusion through the contralateral VA to the left vertebral DAVF and

Fig. 13. A 48-year-old woman with a subarachnoid hemorrhage due to a left P2–P3 junction ruptured aneurysm. (A and B) Lateral view and anteroposterior (AP) view of original VA angiogram (*arrow in B*). (C and D) Left ICA AP and lateral angiography. (E and F) Left PCA P2 TBO. The left ICA angiogram, while the left P2 was occluded with a balloon, revealed left ACA to PCA cortical collateralization (*black arrow*) with retrograde opacification during the late arterial phase. In F, *open arrow* indicates the balloon; *arrowhead* indicates the retrograde partially opacified P2-P3 aneurysm. (G and H) Ultimately, this aneurysm was coil embolized completely with balloon-remodeling technique; and the distal PCA branches were preserved anterogradely.

A sharp reversely angulated origin of a vessel makes superselective ipsilateral catheterization difficult. For instance, access to the PICA or anterior inferior cerebellar artery (AICA) from the VA can be occasionally difficult, or in cases in which the carotid or bilateral VAs are occluded, the PCoA offers a distinct advantage. In these situations, if the caliber of the PCoA is adequate, effective catheterization of the desired vessel can be achieved (Figures 14 and 15). Naturally, a microcatheter can also go from one VA to the other through the VB junction (Figure 12, 16).7 Similarly, during treatment of broad-based aneurysms at the basilar or ICA terminus, ipsilateral placement of a stent may be inadequate for complete coverage of the aneurysm neck, necessitating a Y-configuration with increased risk of thromboembolic complications. In these cases, the following strategies offer distinct advantages: access from the contralateral carotid artery to pass a stent across the AcoA so

Intracranial Arterial Collateralization: Relevance in Neuro-Endovascular Procedures 193

Fig. 15. A 70-year-old woman presented with multiple events of VB insufficiency. Evaluation revealed bilateral VA occlusions. A) Injection of the left ICA (C) revealed the PCoA (B) as the principal supply to the BA (A) and the PCA (D). (B) A road-map angiogram reveals a guide catheter in the left ICA (B) with a microwire through the PCoA (C) and through the proximal BA (A) across an obvious stenosis into the distal VA. (C) After retrograde BA angioplasty, an ICA (A) angiogram reveals robust filling through the PCoA (B) into the basilar artery with markedly improved flow across the stenotic lesion into the BA junction (C), bilateral PICA, and VA (E, F). *With permission from Chiam PT, Mocco J, Samuelson RM, Siddiqui AH, Hopkins LN, Levy EI: Retrograde angioplasty for basilar artery stenosis: bypassing bilateral vertebral artery occlusions. J Neurosurg 110:427-430, 2009* 

Fig. 16. A 65-year old man presented with neck-movement-related VB insufficiency. The left VA was noted to be occluded extracranially. (A) Right VA (A) angiogram revealed excellent flow into the BA with fenestration (B), a tight stenosis at the junction (C) of the left VA (D)

microballoon (A) was brought from the right VA (C) over a wire, which was placed into the left proximal VA (B). (C) Final angiogram revealing significant improvement (despite persistent stenosis) in distal left VA (A) flow noted into the proximal left VA (B) and left

with the BA, and a peak systolic angiographic jet opacifying the PICA (E). (B) A

PICA (C) following a right VA (D) injection. (E) Basilar artery.

Fig. 14. A 40-year-old man with a left intracranial VA dissection with a pseudoaneurysm just distal to the left PICA origin. (A and B) three-dimensional angiogram and lateral view of left VA two-dimensional angiogram. *Arrows* indicate the pseudoaneurysm at the dissection site. (C) Left ICA angiogram revealed robust PCoA connecting the left ICA system to the VB system. (D) Due to limited distal flow from the dissecting aneurysm to the normal PICA origin, complete occlusion of the left VA was not achieved by balloonremodeling coiling through left VA catheterization. Therefore, superselective catheterization through a left ICA-PCoA-BA-left VA route allowed us to successfully occlude the diseased segment of the VA. *Arrows* in E indicate the microcatheter route. By comparison with the angiogram in C, the 3-month follow-up angiogram with right VA (E) and left VA (F, lateral view) runs shows the left VA supplying the left PICA without evidence of recurrent aneurysm.

that it ultimately sits across the entire neck of the aneurysm in the ICA terminus (from the ipsilateral ACA to the MCA) or from the carotid artery across the PCoA so that it sits from the ipsilateral PCA to contralateral PCA (Figure 17). In cases in which there is occlusion of one or more vessels to the circle of Willis, the circle provides an optimal opportunity to access diseased segments of vessels that are proximally occluded. These routes can be used to treat a variety of conditions, such as aneurysms (Figure 18), AVMs, or AVFs. Similarly, in cases of acute occlusion, even if the proximal vessel cannot be adequately revascularized, reestablishing flow across the circle may alleviate acute cerebral ischemia (Figure 19). In other situations, the circle may allow passage of endovascular implements that, despite patency, cannot be brought up through ipsilateral routes (Figure 22 -24). This is particularly relevant to situations in which the ipsilateral vessel may have spasm after subarachnoid hemorrhage (Figure 20) or be congenitally hypoplastic.

Fig. 14. A 40-year-old man with a left intracranial VA dissection with a pseudoaneurysm just distal to the left PICA origin. (A and B) three-dimensional angiogram and lateral view of left VA two-dimensional angiogram. *Arrows* indicate the pseudoaneurysm at the dissection site. (C) Left ICA angiogram revealed robust PCoA connecting the left ICA system to the VB system. (D) Due to limited distal flow from the dissecting aneurysm to the

normal PICA origin, complete occlusion of the left VA was not achieved by balloon-

hemorrhage (Figure 20) or be congenitally hypoplastic.

aneurysm.

remodeling coiling through left VA catheterization. Therefore, superselective catheterization through a left ICA-PCoA-BA-left VA route allowed us to successfully occlude the diseased segment of the VA. *Arrows* in E indicate the microcatheter route. By comparison with the angiogram in C, the 3-month follow-up angiogram with right VA (E) and left VA (F, lateral view) runs shows the left VA supplying the left PICA without evidence of recurrent

that it ultimately sits across the entire neck of the aneurysm in the ICA terminus (from the ipsilateral ACA to the MCA) or from the carotid artery across the PCoA so that it sits from the ipsilateral PCA to contralateral PCA (Figure 17). In cases in which there is occlusion of one or more vessels to the circle of Willis, the circle provides an optimal opportunity to access diseased segments of vessels that are proximally occluded. These routes can be used to treat a variety of conditions, such as aneurysms (Figure 18), AVMs, or AVFs. Similarly, in cases of acute occlusion, even if the proximal vessel cannot be adequately revascularized, reestablishing flow across the circle may alleviate acute cerebral ischemia (Figure 19). In other situations, the circle may allow passage of endovascular implements that, despite patency, cannot be brought up through ipsilateral routes (Figure 22 -24). This is particularly relevant to situations in which the ipsilateral vessel may have spasm after subarachnoid

Fig. 15. A 70-year-old woman presented with multiple events of VB insufficiency. Evaluation revealed bilateral VA occlusions. A) Injection of the left ICA (C) revealed the PCoA (B) as the principal supply to the BA (A) and the PCA (D). (B) A road-map angiogram reveals a guide catheter in the left ICA (B) with a microwire through the PCoA (C) and through the proximal BA (A) across an obvious stenosis into the distal VA. (C) After retrograde BA angioplasty, an ICA (A) angiogram reveals robust filling through the PCoA (B) into the basilar artery with markedly improved flow across the stenotic lesion into the BA junction (C), bilateral PICA, and VA (E, F). *With permission from Chiam PT, Mocco J, Samuelson RM, Siddiqui AH, Hopkins LN, Levy EI: Retrograde angioplasty for basilar artery stenosis: bypassing bilateral vertebral artery occlusions. J Neurosurg 110:427-430, 2009* 

Fig. 16. A 65-year old man presented with neck-movement-related VB insufficiency. The left VA was noted to be occluded extracranially. (A) Right VA (A) angiogram revealed excellent flow into the BA with fenestration (B), a tight stenosis at the junction (C) of the left VA (D) with the BA, and a peak systolic angiographic jet opacifying the PICA (E). (B) A microballoon (A) was brought from the right VA (C) over a wire, which was placed into the left proximal VA (B). (C) Final angiogram revealing significant improvement (despite persistent stenosis) in distal left VA (A) flow noted into the proximal left VA (B) and left PICA (C) following a right VA (D) injection. (E) Basilar artery.

Intracranial Arterial Collateralization: Relevance in Neuro-Endovascular Procedures 195

Fig. 19. A 65-year-old man presented with an acute stroke with occlusion of his left ICA. He was beyond the window for intravenous thrombolysis. His ancillary studies suggested potentially viable brain in the MCA territory. However, computed tomographic

angiography suggested occlusion of the left MCA territory in addition to more proximal carotid occlusion. An emergent angiogram was planned. (A) A right carotid (D) angiogram performed to assess cross-flow reveals a left ICA terminus occlusion (A) with flow to the bilateral distal ACA circulation across the ACoA (C) but no flow to the left MCA (B). (B) Selective left ICA angiogram reveals complete cavernous occlusion (B) of the left ICA (A). (C) The occlusion (B) was carefully crossed, and a thrombectomy suction catheter (A) was advanced into the occluded left MCA. (D) Following suction aspiration, the clot was retrieved from the MCA (B), resulting in revascularization of the ICA terminus (A) and reestablishment of flow across the ACoA (C) from the right ICA (F). Both ACAs remained patent (E, D). Despite these efforts, the proximal occlusion remained recalcitrant to revascularization efforts and was therefore left occluded. The patient recovered from all

deficits.

Fig. 17. A 44-year-old man with a Spetzler-Martin Grade IV AVM post-staged embolization and Gamma Knife radiosurgery presented with a residual, broad-based basilar terminus aneurysm. (A) Combined left carotid (E) and left VA (F) angiogram reveals a robust PCoA (C). BA (A), aneurysm (B), MCA (D). (B) Road-map image of an Enterprise stent (Codman Neurovascular) being deployed via the left ICA (E) through the left PCoA (F) from the ipsilateral P1 segment of the PCA (C) across the neck of the aneurysm into the contralateral PCA (B). Deployed stent markers (A). BA (D). (C) The patient was subsequently brought for a second coil embolization session with access to the BA aneurysm achieved from the left VA (C). Angiographically, complete aneurysm obliteration (A) was obtained. The left PCoA (B) is noted.

Fig. 18. A 40-year-old man presented with a history of a bullet injury to the head and neck and surgical ligation of the left ICA and now with acute development of a carotid-cavernous fistula. He was noted to have a ruptured, giant cavernous ICA pseudoaneurysm. (A) A left VA (A) angiogram reveals filling of the aneurysm (D) across the PCoA (C) to the supraclinoidal carotid artery (B) with early venous filling of the ophthalmic vein (F) and pterygoid venous plexus (E). (B) The aneurysm was accessed through the same route from the left VA (B) across the PCoA (C) to achieve complete obliteration of the aneurysm and carotid-cavernous fistula (A). MCA (D).

Fig. 17. A 44-year-old man with a Spetzler-Martin Grade IV AVM post-staged embolization and Gamma Knife radiosurgery presented with a residual, broad-based basilar terminus aneurysm. (A) Combined left carotid (E) and left VA (F) angiogram reveals a robust PCoA (C). BA (A), aneurysm (B), MCA (D). (B) Road-map image of an Enterprise stent (Codman Neurovascular) being deployed via the left ICA (E) through the left PCoA (F) from the ipsilateral P1 segment of the PCA (C) across the neck of the aneurysm into the contralateral PCA (B). Deployed stent markers (A). BA (D). (C) The patient was subsequently brought for a second coil embolization session with access to the BA aneurysm achieved from the left VA (C). Angiographically, complete aneurysm obliteration (A) was obtained. The left PCoA

Fig. 18. A 40-year-old man presented with a history of a bullet injury to the head and neck and surgical ligation of the left ICA and now with acute development of a carotid-cavernous fistula. He was noted to have a ruptured, giant cavernous ICA pseudoaneurysm. (A) A left

supraclinoidal carotid artery (B) with early venous filling of the ophthalmic vein (F) and pterygoid venous plexus (E). (B) The aneurysm was accessed through the same route from the left VA (B) across the PCoA (C) to achieve complete obliteration of the aneurysm and

VA (A) angiogram reveals filling of the aneurysm (D) across the PCoA (C) to the

carotid-cavernous fistula (A). MCA (D).

(B) is noted.

Fig. 19. A 65-year-old man presented with an acute stroke with occlusion of his left ICA. He was beyond the window for intravenous thrombolysis. His ancillary studies suggested potentially viable brain in the MCA territory. However, computed tomographic angiography suggested occlusion of the left MCA territory in addition to more proximal carotid occlusion. An emergent angiogram was planned. (A) A right carotid (D) angiogram performed to assess cross-flow reveals a left ICA terminus occlusion (A) with flow to the bilateral distal ACA circulation across the ACoA (C) but no flow to the left MCA (B). (B) Selective left ICA angiogram reveals complete cavernous occlusion (B) of the left ICA (A). (C) The occlusion (B) was carefully crossed, and a thrombectomy suction catheter (A) was advanced into the occluded left MCA. (D) Following suction aspiration, the clot was retrieved from the MCA (B), resulting in revascularization of the ICA terminus (A) and reestablishment of flow across the ACoA (C) from the right ICA (F). Both ACAs remained patent (E, D). Despite these efforts, the proximal occlusion remained recalcitrant to revascularization efforts and was therefore left occluded. The patient recovered from all deficits.

Intracranial Arterial Collateralization: Relevance in Neuro-Endovascular Procedures 197

Fig. 21. A 24-year-old man presented with subarachnoid hemorrhage due to proximal right PICA dissection. After superselective micro-balloon test occlusion, it was clear that there are

procedure. The distal branches remains filling after the proximal PICA occlusion. (A) Right

anastomoses from right SCA and AICA to right PICA distal branches. Therefore, the dissecting segment right PICA was successfully occluded with coils without the need of microsurgical bypass procedure, and the patient revealed no deficits following the

vertebral artery angiogram lateral view and (C) anterior-posterior view prior to the treatment. The *black arrows* point to the dissected proximal PICA. (B) Right vertebral artery angiogram lateral view and (D) anterior-posterior view after occlusion of proximal right PICA with coils. The *solid white arrows* indicate coil occlusion of the dissected proximal

PICA. *Open white arrows* indicate the distal right PICA filling from collaterals.

Fig. 20. A 42-year-old man presented with a ruptured ACoA aneurysm, which was treated via coil embolization. On Day 6, he developed severe symptomatic spasm, which remained refractory to maximal medical therapy. He had severe spasm of his left ACA, which resulted in the use of the ACoA artery as a conduit to angioplasty the left distal ACA. (A) Right carotid angiogram reveals a microcatheter and wire across the right ACA (A), AcoA, and aneurysm (C) into the left distal ACA (B). Right distal ACA (D). (B) Non-subtracted angiogram revealing the relationship of the aneurysm and the inflated balloon in the left distal ACA (A). AcoA (B), right distal ACA (C). Access microcatheter in the right ICA (D).

Fig. 20. A 42-year-old man presented with a ruptured ACoA aneurysm, which was treated via coil embolization. On Day 6, he developed severe symptomatic spasm, which remained refractory to maximal medical therapy. He had severe spasm of his left ACA, which resulted in the use of the ACoA artery as a conduit to angioplasty the left distal ACA. (A) Right carotid angiogram reveals a microcatheter and wire across the right ACA (A), AcoA, and aneurysm (C) into the left distal ACA (B). Right distal ACA (D). (B) Non-subtracted angiogram revealing the relationship of the aneurysm and the inflated balloon in the left distal ACA (A). AcoA (B), right distal ACA (C). Access microcatheter in the right ICA (D).

Fig. 21. A 24-year-old man presented with subarachnoid hemorrhage due to proximal right PICA dissection. After superselective micro-balloon test occlusion, it was clear that there are anastomoses from right SCA and AICA to right PICA distal branches. Therefore, the dissecting segment right PICA was successfully occluded with coils without the need of microsurgical bypass procedure, and the patient revealed no deficits following the procedure. The distal branches remains filling after the proximal PICA occlusion. (A) Right vertebral artery angiogram lateral view and (C) anterior-posterior view prior to the treatment. The *black arrows* point to the dissected proximal PICA. (B) Right vertebral artery angiogram lateral view and (D) anterior-posterior view after occlusion of proximal right PICA with coils. The *solid white arrows* indicate coil occlusion of the dissected proximal PICA. *Open white arrows* indicate the distal right PICA filling from collaterals.

Intracranial Arterial Collateralization: Relevance in Neuro-Endovascular Procedures 199

Fig. 23. Review of the circle of Willis appeared to demonstrate both a sizeable ACoA and PCoA arteries therefore a second groin access was established with the guide catheter in the vertebral artery (Figure 23 A, B). A microcatheter was used to catheterize the PCoA artery from the vertebral artery and thereby gain access into the aneurysm using retrograde catheterization of the proximally dislocated but distally tethered Pipeline Device (Figure

23 C, D).

Fig. 22. 64-year old woman presented with increasing headaches after a motor vehicle accident. She was neurologically intact upon presentation. Diagnostic workup revealed a giant cavernous aneurysm (Figure 22 A, B). She was enrolled in the PUFFs trial for utilization of a flow diversion Pipeline Device for treatment of large proximal carotid aneurysms. After deployment of the first device the distal access through the aneurysm was lost and despite multiple attempts to regain access through the proximal end of the stent, which had migrated laterally into the aneurysm, distal anterograde access could not be established (Figure 22 C, D).

Fig. 22. 64-year old woman presented with increasing headaches after a motor vehicle accident. She was neurologically intact upon presentation. Diagnostic workup revealed a giant cavernous aneurysm (Figure 22 A, B). She was enrolled in the PUFFs trial for utilization of a flow diversion Pipeline Device for treatment of large proximal carotid aneurysms. After deployment of the first device the distal access through the aneurysm was lost and despite multiple attempts to regain access through the proximal end of the stent, which had migrated laterally into the aneurysm, distal anterograde access could not be

established (Figure 22 C, D).

Fig. 23. Review of the circle of Willis appeared to demonstrate both a sizeable ACoA and PCoA arteries therefore a second groin access was established with the guide catheter in the vertebral artery (Figure 23 A, B). A microcatheter was used to catheterize the PCoA artery from the vertebral artery and thereby gain access into the aneurysm using retrograde catheterization of the proximally dislocated but distally tethered Pipeline Device (Figure 23 C, D).

Intracranial Arterial Collateralization: Relevance in Neuro-Endovascular Procedures 201

avoid complications that could have been prevented by a better understanding of underlying vascular anatomy. As the scope and extent of endovascular interventions for cerebrovascular and cranial disease continues to expand, the recognition of these putative anastomoses will continue to become a larger part of diagnostic evaluation and

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Fig. 24. Once the microwire was in the aneurysm a Snare was deployed to grab the microwire and the Marksman microcatheter was advanced using the snare over the microwire into the Pipeline device by pulling the microwire back out through the PCoA (Figure 24 A, B). Once distal access was reestablished additional Pipeline Devices were used to complete the endovascular reconstruction of the aneurysm. The aneurysm appeared almost completely obliterated at the end of the procedure (Figure 24 C) and remained obliterated at the 6-month follow-up (Figure 24 D).
