intracranial vascular bypass is done to maintain blood flow to region of interest. this slideshow entails the indications, various categories, types as per flow, their advantages and disadvantages

1. Intracranial Vascular Bypass
Presented By:
Dr. Rahul Jain
SR-2 Neurosurgery
Moderated by:
Dr V. C. Jha
Dr Nitish Kumar
Dr Gaurav Verma

2. • A cerebral bypass is a surgical procedure performed
to restore or revascularize blood flow to the brain.
• Involves connecting a blood vessel from another
psrt of brain or outside the brain to reroute blood
flow around an artery that is stenosed, thrombosed
or damaged.
• Main goal is to provide the blood supply to target
region of brain and prevent stroke.
• On October 30, 1967, Professor Yasargil famously
performed the first microsurgical direct flow-
augmentation bypass by anastomosing the
superficial temporal artery to the middle cerebral
artery (STA-MCA) of a 20-year-old man suffering
from Marfan’s syndrome with left M1 segment
occlusion.

3. Who is candidate
• An aneurysm, tumor, or atherosclerotic plaque that
is not treatbale by endovascular or other means.
• Failure of medical management to control TIA
symptoms or stroke.
• CTA, MRA or Angiogram suggestive of arterial
stenosis or occlusion.
• Cerebral blood flow studies like CT perfusion, PET,
SPECT showing arterial stenosis causing insufficient
blood flow to brain.

4. Cerebral bypass may be helpful in restoring blood flow
and reducing the risk of stroke in conditions such as:
• Moyamoya disease: a narrowing of the internal carotid
arteries at the base of the brain that can cause multiple
strokes or hemorrhages. A bypass can restore blood flow
to the brain and prevent future strokes.
• Aneurysm: a bulge or ballooning of an artery wall.
Some giant, fusiform, or dissecting aneurysms cannot be
treated with surgical clipping or endovascular coiling. In
such cases, the parent artery must be sacrificed and the
blood flow bypassed for the aneurysm to be effectively
treated.
• Skull base tumor: a tumor can grow where the major
vessels enter the skull and surround or invade the artery.
Removing the tumor may require sacrificing the encased
artery and bypassing the blood flow.

5. • Carotid artery stenosis or occlusion: a narrowing
or blockage of the carotid artery in the neck caused
by atherosclerotic plaque deposits in the vessel
wall.
• Intracranial arterial stenosis: a narrowing or
blockage of an artery inside the skull that supplies
blood to specific areas within the brain.

6. WHEN IS THE COLLATERAL CIRCULATION
INADEQUATE AND BYPASS NECESSARY?
Anterior Circulation
• Elective ICA occlusion has been associated with
ischemic complications in 30%–45% of cases, and
experience with Balloon Test Occlusion suggests that a
majority of patients are likely to tolerate ICA occlusion
in the short term.
• Many studies argue for a universal approach,
advocating for bypass in all patients who undergo ICA
occlusion. This strategy is intended to avoid the risk of
the BTO procedure, to mitigate the potential for false
negative BTO results, to minimize the risk for delayed or
chronic cerebral ischemia, and to avoid inducing new
aneurysms on collateral vessels.

7. Posterior Circulation
• Unclippable and uncoilable posterior circulation
aneurysms may require vertebral artery occlusion.
• Bilateral vertebral artery or basilar artery occlusion
is associated with a much higher risk for ischemia
and should be considered only if both posterior
communicating arteries are of sufficient size and
collateral flow.
• Proximal PCA occlusion for aneurysm treatment
appears to be well tolerated, with development of
an ischemic deficit, such as hemianopia, reported
in only a few cases.

8. Distal Arterial Branches
• proximal occlusion of major arteries is more likely
to be tolerated than occlusion of distal arterial
branches.
• Revascularization of these terminal branches
should be considered when these distal arteries
that supply likely eloquent areas must be occluded.
• When technically feasible, we plan
revascularization in such cases without attempting
BTO, owing to the technical difficulties and safety
concerns associated with temporary balloon
occlusion of these smaller, more distal arteries.

9. Categories of bypass procedures
1. Purpose of the bypass: flow-augmentation versus
flow-preservation.
• Indications for flow-augmentation bypass include
moyamoya vasculopathy, chronic steno-occlusive
disease, and acute ischaemic stroke.
• Indications for flow preservation typically include
intracranial aneurysm surgery and tumour surgery.
2. Direct, Indirect, and Combined procedures
• Indirect procedures rely on the overlay of vascularized
tissue (i.e., muscle, dura, pericranium, and omentum)
onto the cerebral cortex to promote neoangiogenesis
over time and achieve a delayed revascularization

10. • direct bypass instantly stimulates blood flow to the
brain by direct microvascular anastomosis between a
donor artery (or graft interposition, i.e., connected to a
donor artery) and an intracranial recipient artery.
• Combined procedures consist of applying both direct
and indirect techniques in the same surgical session.
A. Depending on the choice of the donor artery
(extracranial vs. intracranial donor), a direct
bypass is further classified into extra- to
intracranial (EC-IC) versus intra- to intracranial
(IC-IC).
B. Lastly, direct bypass procedures are categorized
according to the rate of flow (capacity) the
bypass can carry: low capacity (<50 mL/min),
intermediate (50–100 mL/min), or high capacity
(>100 mL/min)

12. TYPES OF REVASCULARIZATION
PROCEDURES
• Technical considerations for cerebral revascularization
include
• the donor site,
• the recipient site,
• the conduit, and
• the quantity of flow to be replaced.
• Donor sites are commonly either extracranial carotid or
vertebral arteries, or involved or adjacent intracranial
cerebral arteries. Common vessels used as a graft are
the saphenous vein in the leg or the radial or ulnar
arteries in the arm- for high flow. The other type does
not use a vessel graft but a healthy donor artery.

13. • Donor artery is detached from its normal
position on one end, redirected to the inside of
the skull, and connected to an artery on the
surface of the brain – for low flow.
• Recipient sites are generally those arteries
immediately distal to the pathology in question,
though recipient sites can also be remote to the
lesion, relying on retrograde redistribution of
flow after bypass.
• Conduit options include interposition grafts
such as radial artery or saphenous vein,
pedicled grafts such as STA or occipital artery
(OA), or direct anastomosis with no conduit at
all.
• Flow demand is typically estimated by the sum
of the flow measured in each of the recipient
branches. Permutations of these can be
classified into four types of bypass.

14. Type I Bypass: Intracranial-Intracranial
Interposition Bypass
• Connects an intracranial artery to another
intracranial artery using an interposition graft.
• Extent from the parent artery proximal to the site
of the occlusion to the point immediately distal to
the parent artery, or from a separate donor source.
• Example - intracranial petrous ICA–supraclinoid ICA
interposition bypass. It can be used when the ICA is
resected to remove skull base tumors, or to trap
giant intracavernous carotid aneurysms.

15. • Disadvantage - complex and requires a prolonged
period of ICA occlusion.
• Accordingly, it is associated with a significant
complication rate related to graft occlusion and
perioperative ischemic brain injury.
petrous-supraclinoid internal carotid artery
(ICA) skull base bypass showing a
saphenous interposition graft

16. Type II Bypass: Extracranial-
Intracranial Interposition Bypass
• interposition graft between an extracranial artery
and a major intracranial artery.
• Indication - employed when a major arterial trunk
must be occluded to treat a tumor or complex
aneurysm, and the distal collateral circulation is
grossly inadequate (as evidenced by the absence of
communicating arteries seen angiographically or
by the rapid onset of a deficit during balloon test
occlusion).
• bypass is planned to replace all of the circulation to
a major arterial territory, and therefore a large
conduit is sometimes needed.

17. • Blood flow through radial artery and saphenous
vein grafts typically exceeds 70 mL/min and can
reach well beyond 200 mL/min.
• Disadvantages of interposition grafts
• Vein grafts – lower long term atency, kinking, calibre
mismatch between larger vein and smaller intracranial
vessels.
• Arterial grafts – vasospasm, pressure dilatation
technique to counter vasospasm can cause endothelial
damage resulting in thrombosis.
• using multiple pedicled grafts is adequate for
revascularization in most cases with anterior
circulation aneurysms.

18. • Type II bypass is often required when scalp arteries
are hypoplastic or cannot reach the recipient
vessel.
• In circumstances in which only proximal occlusion is
to be performed as in the case of some
dolichoectatic and fusiform aneurysms, we prefer
the use of a type III bypass.

19. A) A clamp is passed from the cranial
incision behind the root of the zygomatic
arch to the cervical incision. (B) A chest
tube is pulled from the cervical incision to
the cranial incision.
(C) The harvested saphenous vein graft is
passed through the chest tube, which is
removed, leaving the graft in its
subcutaneous tunnel. (D) The completed
bypass after end-to-end anastomosis to
the internal carotid artery (ICA) and end-to-
side anastomosis to the MCA. (E)
Alternative technique showing end-to-side
anastomosis to the external carotid artery
(ECA)
Extracranial Carotid Artery–Middle Cerebral Artery
Interposition Graft

20. • For the distal anastomosis, we prefer an end-to-
side anastomosis to a proximal M2 branch in the
sylvian fissure. These vessels better match the size
of these interposition grafts, and provide a more
direct conduit to the entire MCA territory.
• The alignment of the vein should be marked with a
suture through the adventitia to define the proper
orientation of the vein.
• As suggested by Sundt and associates, the
intracranial anastomosis is performed first. This
sequence allows the surgeon to take advantage of
slack in the graft, which can be manipulated freely
while the back and front walls of the anastomosis
are sutured.

21. Type III Bypass: Pedicled Donor Artery
Extracranial-Intracranial Bypass
• The STA or OA is commonly used.
• Advantage – readily available, only require a single
anastomosis, and have good patency rates
compared with free vein or arterial grafts.
• Chief drawback- lower flow rate—the STA supplies
an average initial flow rate of about 15–30 mL/min.
using two branches of the STA (a double-barrel
bypass) to make anastomoses to two recipient
branches in the target territory can increase the
amount of blood supplied by the graft.

22. • In general, the STA can be used to revascularize the
MCA territory, as well as the distal posterior
circulation through the superior cerebellar artery
(SCA) or PCA.
• The OA is most commonly used to bypass to the
PICA, but it can also be used to revascularize the
anterior inferior cerebellar artery (AICA).
• The preoperative angiogram should include an ECA
injection to adequately define the patency, course,
and caliber of the STA branches on the side on
which the bypass will be performed.
• STA branches are identified, largest STA branch, as
identified on the preoperative angiogram, is
selected as the donor vessel.

23. STA–MCA bypass
(A) After Doppler ultrasound identification
of the STA, a linear incision is made
over its distal aspect.
(B) The STA is exposed by cutdown
technique.
(C) After the temporalis muscle is incised,
an oval or circular craniotomy is made over
the posterior aspect of the sylvian fissure.
(D) The completed anastomosis is shown

24. • After a linear incision is made over the parietal
branch of the STA distally, the artery is identified on
the superficial surface of the galea. The artery is
exposed to the zygomatic arch, separated from the
adjacent subcutaneous tissue with an adventitial
cuff.
• The craniotomy is centered 6 cm above the
external auditory meatus (the Chater point), where
several large MCA branches emerge from the distal
sylvian fissure.
• When there are two separate MCA branches that
arise from the dome of an aneurysm, a single STA
bypass may not be sufficient. In these cases, a
doublebarrel STA bypass, using both the frontal and
parietal branches, can be performed to bypass to
two separate MCA branches.

25. • After the dura is opened and an appropriate
recipient artery (≥1 mm diameter) is selected, the
arachnoid over this vessel is opened, and a 10-mm
length of the vessel is prepared.
• The distal end of the STA is denuded, beveled, and
spatulated for the bypass. The STA is occluded and
the vessel is incised, matching the donor artery
orifice for size (approximately 3–4 mm).
• The anastomosis is completed with about four
interrupted 10-0 monofilament nylon sutures on
each of the front and back walls.
• The distal MCA temporary clip is usually opened
first, allowing backfilling of the anastomosis to
inspect for major leaks, before opening the
proximal MCA and STA clips.

26. Type IV Bypass: Direct Intracranial-
Intracranial Arterial Anastomosis
• Anastomosis between two adjacent cerebral artery
segments.
• Advantages over EC-IC bypass:-
• obviate the need for harvesting extracranial grafts.
• Useful for distant recipient locations, such as the
interhemispheric fissure
• Disadvantages –
• Long-term patency rates for these bypasses are
uncertain
• more technically demanding
• can only be applied where an appropriate donor artery
is in close proximity to the recipient artery.

27. • can involve end-to-end primary reanastomosis after
excision of an aneurysm, side-to-side anastomosis
of two adjacent intracranial arteries, or an end-to-
side anastomosis between two cerebral arteries.
• Examples of side-to-side type IV bypasses include
PICA-PICA, pericallosal-pericallosal, and MCA-MCA
between adjacent MCA branches in the sylvian
fissure.

28. Pericallosal artery–Pericallosal artery
intracranial revascularization
The arteries are exposed adjacent
to the corpus callosum, and a
side-to-side anastomosis is made
completed pericallosal artery–pericallosal
artery bypass for the treatment of a giant,
wide-necked, partially thrombosed anterior
communicating artery aneurysm (arrow)

29. Techniques for Occluding or Trapping
an Aneurysm, After Bypass
• Combined proximal and distal parent artery occlusion
immediately after the bypass is completed.
• Trapping is preferable because it isolates the aneurysm
from the circulation, avoids the risk for rupture from
retrograde filling.
• Proximal parent artery occlusion alone, which alters the
blood flow to the aneurysm, tends to be adequate to
induce aneurysmal thrombosis, while allowing for
collateral circulation and revascularization to maintain
the patency of critical branches along the artery.

30. • Direct surgical occlusion of the proximal parent
artery in the neck, or just proximal to the aneurysm
(hunterian ligation) is typically performed
immediately after construction of the bypass.
• In some cases, the parent artery proximal to a giant
aneurysm cannot be exposed easily during the
same procedure used for the bypass. In such cases,
coil occlusion of the parent artery immediately
following bypass can be performed.

31. OUTCOMES
1. most serious acute complication is that of early
graft occlusion.
• patency of arterial and venous grafts can be
ensured by
• gentle and meticulous surgical technique;
• Careful avoidance of twisting, kinking, stretching, or
tension of the graft;
• avoidance of graft spasm by adventitial papaverine
irrigation; and
• administration of perioperative antiplatelet therapy.
A. Complications

32. • If there is any question intraoperatively about the
patency of the bypass, as determined visually using
ICG video angiography and Doppler ultrasound,
intraoperative angiography should be performed.
• If the graft is found to be severely stenotic or
occluded, the bypass vessel or anastomosis should
be revised. Sometimes, simply repositioning the
bypass vessel is adequate.
2. Aneurysmal rupture associated with the
hemodynamic changes that accompany arterial
reconstruction with a bypass. These complications
emphasize the need to isolate the aneurysm
completely from the circulation by trapping
whenever possible.

33. 3. Ischemic neurological deficits may be evident
postoperatively. Cerebral protection with
moderate hypothermia, induced arterial
hypertension, and barbiturate administration
ordinarily minimizes this risk.
• subdural or epidural hematomas postoperatively.

34. b. Long-Term Graft Patency
• depends on several factors, with the choice of
conduit used chief among them
• Superficial temporal artery grafts tend to have the
greatest patency rates.
• The Carotid Occlusion Surgery Study showed a 96%
patency rate at a mean of 605 days’ follow-up.
• The International Cooperative EC/IC Bypass Study
of 1985 found that the postoperative patency rate
of 663 STA-MCA bypasses was 96% at an average
follow-up of 55.8 months.

35. • Long-term bypass graft failure appears to be rare
for aneurysms, estimated at 5.3%.
• Young patients in particular may benefit from the
addition of revascularization, as ICA occlusion
appears to confer an increased lifetime risk of
stroke and secondary intracranial aneurysm
formation.
• Occlusion of vein grafts increases over time. Ten
years after surgery, thrombosis occurs in about 40%
of aortocoronary grafts and in more than 50% of
femoropopliteal bypasses.
• In a study by Regli and coworkers, Long saphenous
vein grafts for cerebral revascularization, the early
patency rate was 88%, and at 13 years it was 73%.

36. C. Results of Bypass for Complex
Intracranial Aneurysms
• Using saphenous vein graft bypasses for giant
aneurysms, Sundt and associates reported an acute
graft patency rate of 94%. “Excellent” or “good”
outcomes were achieved in 80% of anterior circulation
aneurysms and in 44% of posterior circulation
aneurysms.
• Lawton and colleagues reported that 93% of 61
patients had good outcomes after revascularization for
intracranial aneurysms.
• Sen and Sekhar reported results in 30 patients who
underwent vein grafting with carotid occlusion or
resection (primarily for tumors). Their rate of graft
patency was 86% at 18 months; 4 patients sustained
ischemic injury related to the bypass procedure.

37. CONCLUSION
• Several types of EC-IC and IC-IC bypass procedures
can provide revascularization, if the treatment of
unclippable aneurysms or skull base tumors
requires major artery occlusion or sacrifice.
• The selection of the type of revascularization
procedure depends on the demand for blood flow
through the bypass and the anatomy of the vessels.
• Parent artery occlusion or trapping by surgical or
endovascular techniques, combined with EC-IC
bypass to maintain tissue perfusion, is an effective
strategy for treating such complex aneurysms.

38. Careful attention to technique can yield a high rate of
bypass patency and good clinical outcomes in those
patients not ideal for flow diversion or clip
reconstruction.

39. References
1. Youmann’s and Winn Neurological Surgery 8th Ed
2. Zhao Y, et al. Direct Bypass Surgery vs. Combined
Bypass Surgery for Hemorrhagic Moyamoya
Disease: A Comparison of Angiographic
Outcomes. 2018. Front. Neurol. 9:1121.
3. Basil E. et al. Trends in Literature on Cerebral
Bypass Surgery: A Systematic
Review. Cerebrovasc Dis 1 February 2022; 51 (1):
102–113.
4. https://mayfieldclinic.com/pe-erebralbypass.htm

40. Thank you