operative nuances of side to side in situ.21

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Operative Nuances of Side-to-Side In Situ PosteriorInferior Cerebellar Artery-Posterior InferiorCerebellar Artery Bypass Procedure

BACKGROUND: An intracranial posterior circulation revascularization procedure in theform of a side-to-side in situ posterior inferior cerebellar artery (PICA)-PICA bypassoperation was introduced in 1991. This elegant and apparently low-risk operation isperformed infrequently. Thus, the operative nuances used in this procedure have notbeen well reported, limiting the scope of treatment modalities of vertebral artery-PICAaneurysms and vertebral dissections.

OBJECTIVE: To repair an incidental right-sided PICA aneurysm noted in a 51-year-oldwoman in magnetic resonance imaging and subsequent angiography.

METHODS:The patient underwent side-to-side in situ PICA-PICA bypass surgery.

RESULTS:Immediate indocyanine green angiography suggested that the PICA distal tothe aneurysms was filling in a retrograde fashion through the bypass. On the followingday, the patient was taken for coil embolization of the aneurysm. However, angiographyimages revealed that the aneurysm was spontaneously thrombosed, the proximal PICAwas patent, and the PICA distal to the aneurysms was filling in a retrograde fashion, assuspected in intraoperative indocyanine green angiography. No further treatments weredone. The patient recovered fully.

CONCLUSION:We describe in detail the preoperative evaluation, decision process, andoperative techniques for a side-to-side in situ PICA-PICA bypass operation, which isa relatively safe and elegant posterior circulation bypass procedure.

KEY WORDS: Anastomosis, Aneurysm, Bypass, In situ, PICA-PICA

Neurosurgery 67:[ONS Suppl 2]ons471ons477, 2010 DOI: 10.1227/NEU.0b013e3181f7420e

Cranial bypass surgeries should be per-formed without compromising bloodflow to involved vascular territories.

A straightforward nonocclusive bypass procedurewithout a considerable risk of intraoperative orpostoperative bypass occlusion would be theoptimal cerebrovascular revascularization opera-tion. Unlike in the anterior circulation, non-

occlusive bypass options do not exist in theposterior circulation. Cerebral revascularization

in the posterior circulation must be recognized asan important adjunct to the treatment strategiesof, for example, complex intracranial aneurysms,especially when direct treatment of theseaneurysms could lead to a sacrifice of a majorvessel in the posterior circulation.

A side-to-side in situ posterior inferior cere-bellar artery (PICA)-PICA bypass operation,1-5 a

rare anastomosis type, may be described as arelatively straightforward PICA revascularizationprocedure. This procedure appears to have a lowrisk of occlusion,1-5 at least in the short term,and a relatively low risk of procedure-relatedcomplications.1-5 In this report, we discuss theoperative nuances of the side-to-side in situPICA-PICA bypass procedure to reinvigorate itsinclusion in the discussion of treatment ofcomplex posterior circulation pathologies.

Miikka Korja, MD

Department of Neurosurgery,

Helsinki University Central Hospital,

Helsinki, Finland

Chandranath Sen, MD


Roosevelt Hospital,

New York, New York

David Langer, MDDepartment of Neurosurgery,

Roosevelt Hospital,

New York, New York

Reprint requests:

Dr Miikka Korja,


Helsinki University Central Hospital,

PO Box 266,

FI-00029 HUS, Finland.

E-mail: [email protected]

Received,August 25, 2009.

Accepted,April 5, 2010.

Copyright 2010 by the

Congress of Neurological Surgeons

ABBREVIATIONS: OA, occipital artery; PICA, pos-terior inferior cerebellar artery; VA, vertebral artery

Supplemental digital content is available for this article.

Direct URL citations appear in the printed text and are

provided in the HTML and PDF versions of this article on

the journals Web site (www.neurosurgery-online.com).

NEUROSURGERY VOLUME 67 | OPERATIVE NEUROSURGERY 2 | DECEMBER 2010 | ons471

CEREBROVASCULAR Operative Nuances

Copyright Congress of Neurological Surgeons. Unauthorized reproduction of this article is prohibited.


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PREOPERATIVE EVALUATION

Although the PICA originates from the intracranial portion of thevertebral artery (VA) in 80% to 95% of cases (on average, 8.6 mmabove the foramen magnum and approximately 1 cm proximal to thevertebrobasilar junction),6,7 the PICA origin varies because of the

rather complex, tortuous, and variable course of the PICA.7

In thesenior authors (C.S., D.L.) institute, the gold standard for visualizingthe PICAs has been a vertebrobasilar angiography, which has to beperformed for both vertebral arteries. Three-dimensional rotationalangiography can also be helpful in determining the anatomic re-lationship of PICA to PICA. We have no experience in the imagequality of 3-T magnetic resonance angiography pictures for visualizingboth PICAs, but most of the time, 1.5-T magnetic resonance

angiography images do not provide the image quality necessary for insitu PICA-PICA bypass purposes. Computed tomography (CT)angiography images can be helpful for operative planning. However,scant filling of the PICA vessels on CT angiography can result in poorvisualization of the relevant PICA anatomy, prohibiting the preciseevaluation of the PICA routes and proximity.

DECISION PROCESS

Indications for bypass surgery in the posterior circulation maybe more ambiguous than those in the anterior circulation, but thecurrent lack of published data should not hamper the decisionprocess when revascularization of the PICA territory needs to beconsidered. Although collateral networks in posterior fossa are

FIGURE 1. Inferior, posterior, lateral, and midsaggital views of the segments of the posterior inferior cerebellar artery as depicted by Lister et al 7 in 1982. In theposterior view, the left half of the cerebellum is removed. 4V, fourth ventricle; A.I.C.A., anterior inferior cerebellar artery; Ant. Med. Sed., anterior medullary segment;B.A., basilar Artery; Ch. PL, choroid plexus; Cort. Seg., cortical segment; F. Luschka, foramen Luschka; F. Magendie, foramen Magendie; Inf. Cer. Ped., inferiorcerebellar peduncle; Inf. Coll., inferior colliculi; Inf. Med. Vel., inferior medullary velum; Int. He. A., intermediate hemispheric artery; Lat. He. A., lateralhemispheric artery; Lat. Med. Seg., lateral medullary segment; Lat. Tr., lateral trunk of the PICA; Med. He. A., medial hemispheric artery; Med. Ve. A., medianvermian artery; Med. Tr., medial trunk of the PICA; Paramed. Ve. A., paramedian vermian artery; P.C.A., posterior cerebral artery; Mid. Cer. Ped., middlecerebellar peduncle; S.C.A., superior cerebellar artery; Sup. Cer. Ped., superior cerebellar peduncle; Sup. Med. Vel., superior medullary velum; Tel. Vel. Ton. Seg.,telovelotonsillar segment; Tel. Vel. Ton. Fiss., telovelotonsillar fissure; Ton. A., tonsillar artery; Ton. Med. Seg., tonsillomedullary segment; Ton. Ped., tonsillarpeduncles; V.A., vertebral artery.

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robust for hemispheric perfusion, the sacrifice of the PICA canresult in significant ischemic injury because of the uniqueanatomy of the proximal PICA segment. This proximal PICAsegment maintains the origin of relatively small but extremelycritical perforators feeding the medulla oblongata and cerebel-lum.7 To ease the preoperative decision process regarding the

need for PICA revascularization, the imaged PICA should bedivided into 5 segments and 2 loops (Figure 1) as suggestedpreviously7,8: (1) the anterior medullary segment, which extendsposteriorly from the origin of the PICA at the VA to the inferiorolivary prominence and passes near the hypoglossal rootlets; (2)the lateral medullary segment, which begins at the site where thePICA passes the most prominent point of the inferior olive andends at the origins of the 9th, 10th, and 11th cranial nerves; (3)the tonsillomedullary segment, which begins at the point wherethe PICA passes posterior to the 9th, 10th, and 11th cranialnerves and then extends medially across the posterior aspect of themedulla to the level of the tonsillar midportion, before whichthe PICA forms a so-called caudal loop at the caudal pole of thetonsils (the mean diameter of the caudal loop, which is one of thelargest distal cerebellar arteries, is approximately 1.7 mm)9; (4)the telovelotonsillar segment, which begins at the middle sectionof the ascent of the PICA along the medial surface of the tonsilsand extends to the suboccipital cortical surface of the cerebellumand includes the so-called cranial loop; and (5) the corticalsegment, which extends to the cerebellar vermis and hemisphere.Because the anterior medullary, lateral medullary, and tonsillo-medullary segments may give rise to critical perforators, trappingof VA-PICA aneurysms or PICA occlusion distal to the tonsil-lomedullary segment usually can be done without revascul-arization of the PICA.8 In other words, a PICA revascularization

procedure should be considered if lesions to be treated occurproximal to the telovelotonsillar segment, when the plannedtreatment may potentially occlude patent PICA circulation. Theabsence of perforating arteries along the very proximal portion ofthe anterior medullary segment does permit direct clip or coilocclusion of the PICA at its origin. Because we are not aware ofany definite preprocedural assessments, like reliable PICA testocclusions of the sufficient collateral flow of the PICA territory,the anatomy-based planning of surgery is the most valuableevaluation tool in our hands. The most important technical pointin treating VA-PICA lesions is to preserve the critical perforatingbranches of the proximal PICA.

After we make the anatomy-based decision of whether to

revascularized the PICA, we evaluate the proximity of the leftand right PICAs. The side-to-side in situ PICA-PICA bypassrequires that both PICAs are in parallel proximity to each an-other, which is true in most cases because the tonsillomedullaryand telovelotonsillar segments usually course next to each otherdistal to the caudal loops and between the cerebellar tonsils inthe cisterna magna. The distance between parallel PICAs shouldbe less than 4 to 5 mm if possible, which allows PICA mobi-lization and the side-to-side anastomosis without harshmanipulation or significant tension placed on the vessels and

their perforators. When the PICA vessels are . 5 mm apart,increasing tension is applied to the suture line, making theanastomosis increasingly difficult. Parallel tonsillomedullary andtelovelotonsillar segments may have a rather significant differ-ence in diameter (the ratio up to 1:2), which does not hinder theprocedure. If there is any concern that the PICA-PICA

anastomosis cannot be performed, we will harvest the occipitalartery (OA). Because of the midline suboccipital approach, side-to-side in situ PICA-PICA bypass surgery can be performed ina relatively shallow and wide operative field, which makes theprocedure easier. Additionally, the operation can be performedin a dual mounted cross-table microscope setup, allowing theassistant to easily engage in the surgical field.

CLINICAL PRESENTATION

History

A 51-year-old woman was admitted to an outside hospital 6years earlier with severe idiopathic vertigo. On magnetic reso-

nance imaging years later and in subsequent angiography, anincidental right-sided fusiform PICA aneurysm was noted(minute 00:00:0500:00:14 in Video 1, Supplemental DigitalContent 1, http://links.lww.com/NEU/A336). A direct treat-ment was deferred because of the complexity of the case and thelikelihood of PICA sacrifice. The patient was transferred to theRoosevelt Hospital for further management.

Surgery

The patient underwent side-to-side in situ PICA-PICA bypasssurgery, the temporary occlusion time of which was 35 minutes.Immediately after the bypass was made, the aneurysm was ex-plored. The proximal portion of the aneurysm against the VA was

well visualized. However, because of the proximity of the cranialnerves and perforators, we felt that a clip could not be placedacross the proximal neck without cranial nerve manipulation andthe risk of perforator occlusion. In flow measurements, theproximal left PICA maintained the prebypass flow of between18 and 20 cm3/min, whereas the distal left PICA had only5 cm3/min. The contralateral distal right PICA had 15 cm3/min,whereas the proximal right PICA showed no flow. Immediateindocyanine green angiography suggested that the PICA distal tothe aneurysms was filling in a retrograde fashion through thebypass (video minute 00:04:3200:04:39).

Postoperative Course

CT control pictures on the first postoperative day revealed noischemic lesions. The patient was taken on the following day for coilembolization of the aneurysm. However, conventional angiographyrevealed that the aneurysm was spontaneously thrombosed (videominute 00:04:4000:04:50). The proximal PICA was patent, andthe PICA distal to the aneurysms was filling in a retrograde fashionthrough the bypass (video minute 00:04:4000:04:50). No furthertreatment was necessary. Aneurysm thrombosis was probably causedby temporary occlusion or a bypass-induced competitive flow distalto the aneurysm. The patient recovered fully after some

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postoperative headache problems caused by aseptic meningitis,which was treated with high-dose steroids.

OPERATIVE TECHNIQUE

Patients are put on aspirin 325 g/d 5 days before operation and

continue it for at least 6 months. Patients can be loaded withaspirin urgently or at the time of surgery if necessary. No frac-tionated or unfractionated intravenous heparin is used, except inlocal saline flush, during the operation. We routinely assess as-pirin sensitivity using the Accumetrix system.

CRANIOTOMY

Under general endotracheal anesthesia with propofol, the neu-rophysiological monitoring of brainstem auditory evoked potentialsand cortical and spinal somatosensory evoked potentials is applied,and the patient is placed in a prone position in a Sugita head frame.We perform neurophysiological monitoring in almost all cranioto-mies, although no clinical evidence exists whether cerebellar ormedullar ischemia resulting from perforator occlusion gives rise todetectable change in recorded potentials. To date, we have not seenneurophysiological changes during temporary occlusion of thePICA. The midline suboccipital and upper cervical regions arescrubbed and draped. A midline incision caudal to the nuchal lineand cranial to the C1 arch is fashioned with a No. 10 blade. Afterhemostasis, a subperiosteal dissection of the C1 arch and the sub-occipital region is carried out. Self-retaining retractors are placed inthe wound, and a burr hole is fashioned in the midline suboccipitalregion. An oval or round midline suboccipital craniotomy of the size4 to 5 3 3 to 4 cm from foramen magnum to transverse sinuses isfashioned, and the dura is opened in a V- or Y-shaped fashion and

hinged laterally and superiorly with 4-0 Nurolon sutures. Usually,good exposure of the tonsillar region of the cerebellum is obtained.There is no need to visualize the inferior edge of the transversesinuses, and the craniotomy can be kept below them.

VESSEL EXPOSURE

Under microscopic vision, the arachnoid and pia mater of thesuboccipital region are incised with microforceps, the right and/orleft cerebellar tonsil is gently retracted, and self-retaining retractorsare placed. This technique allows the tonsils to be elevated awayfrom the area just below the obex while freeing the PICAs from theirsurrounding adhesions. Subsequently, the 2 tonsillomedullary and

telovelotonsillar segments of the PICAs are well visualized at the levelof the cerebellomedullary fissure. A number of brainstem perforatorsat the tonsillomedullary and telovelotonsillar segments may be seen,and they should be preserved throughout the operation. After gentlemobilization of one or both of the vessel segments, they are broughtto close proximity for side-to-side in situ bypass. Often the PICAsare mobilized with gentle traction after all of the surrounding ad-hesions and arachnoid veil have been peeled away. Before initiationof temporary occlusion, the baseline PICA flows are measured witha flow probe. Small temporary clips (blade length, 6 mm) are placed

cranially and caudally at the anastomosis site and on perforatingvessels originating from the PICA (video minute 00:00:1600:00:29). Temporary clipping allows a complete flow arrest of the 2vessel segments at a length of 8 to 16 mm.

ARTERIOTOMY AND SUTURING

Using a back-cutting microknife (APEX Inc), we make arteriot-omies approximately 4 to 6 mm (at least double the diameter of thewider PICA) long (video minute 00:00:2800:00:43). To eliminatesmall blind arterial pouches, so-called dog ears, both arteriotomiesneed to be exactly the same length. Methylene blue is applied ex-travascularly and occasionally intravascularly to allow better visuali-zation of the arteriotomy site (video minute 00:00:4600:00:56).The lumens of the 2 vessels are aggressively irrigated with heparinizedsaline. A running anastomosis is made with a 9-0 nylon. The mostimportant step of the bypass procedure is to make tight first sutureson the back wall of the anastomosis. After approximating the 2arteries, the first (stay) suture is placed at the apex of the arteriotomyby passing the needle from outside the vessel lumen to inside thesame vessel lumen and then from inside the other vessel lumen tooutside the same vessel lumen (Figures 2A and 3A; video minute00:00:5700:02:29). This is done to have the knot outside the vessellumens. The tail of the first suture is left long enough that it can beused when tightening the final suture. After the stay suture is made,the needle is taken underneath the knot (Figures 2B and 3B; videominute 00:02:3000:02:51). Then, a running suture is started bypassing the needle very close to the stay suture (periapical) fromoutside to inside the (left or right) vessel lumen (video minute00:02:5200:03:15) and then either from inside the vessel to insidethe adjacent vessel lumen (Figure 2C; video minute 00:03:16

00:03:31) or from inside to outside the same vessel lumen (Figure2C). After these most crucial steps of the anastomosis (Figures 2Athrough 2C and 3A through 3C), the back wall of the bypass can besutured in a running fashion from the intravascular side (Figures 2Dand 3D). When the other apex of the anastomosis is reached, theneedle is passed from inside to outside the apex and then from outsideto inside of the adjacent apex (Figures 2D and 3D; video minute00:03:3200:04:12). Then, the anterior wall is sutured from outsidethe lumen with a continuous suture (Figures 2E and 3E). Once thesutures attaching the entire anterior wall are loosely placed, the bypasslumen is inspected with a small nerve hook (video minute 00:04:1300:04:21) and flushed with heparinized saline. If the anastomosis iswidely patent, the continuous suture can be tightened with the long

end of the very first suture (Figures 2F and 3F). Interrupted suturesmay also be used for the final suture or two. Temporary occlusiontime typically varies between 20 and 60 minutes.

RECIRCULATION

Temporary clips are first removed distal to the bypass, thenproximal to the bypass, and finally from the perforators. Whencontinuous sutures are used, anastomosis leakage should be minimal.On recirculation, bilateral flow volumes and directions are measured

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proximal and distal to the bypass with a flow probe. Flows in therange of 8 to 12 cm3/min are usually measured in both PICA limbsproximal and distal to the site of the anastomosis. Flow measure-ments are repeated a few times before and after an intraoperativeindocyanine green angiogram, which confirm the patency of thebypass (video minute 00:04:3200:04:39). Flow measurementsdistal to the bypass can be done after a test occlusion of the proximalPICA, and a flow decrease of , 25% in the occluded limb isstrongly suggestive of the functional bypass if the PICA origin has tobe sacrificed. If the PICA origin has to be occluded, the newly madeanastomosis allows the contralateral PICA to supply the ipsilateralanteromedullary segment of the PICA in a retrograde fashion. In

other words, the main idea of the bypass is to provide sufficientblood flow into the anteromedullary segment of the PICA. Theo-retically, if an immediate bypass failure in the form of occlusion takesplace, the sutures should be opened, the lumens flushed withheparinized saline, and the anastomosis resutured.

CLOSURE

After the final inspection of the bypass, a watertight duralclosure is of great importance. A dural patch can be used

together with tissue glue. If any doubt of the water tightness ofthe dura exists, we recommend using a postoperative lumbardrain for a minimum of 2 to 3 days to prevent postoperativecerebrospinal fluid leakage. The bone flap is replaced andsecured with titanium microplates, or a titanium mesh is usedto cover the craniectomy defect. The wound itself is thenclosed with 0-0 absorbable Vicryl sutures for the deep muscleand muscle fascia, 2-0 absorbable Vicryl sutures for the sub-cutaneous tissue, and interrupted or continuous 3-0 Ethilonsutures for the skin closure.

POSTOPERATIVE COURSE

Patients undergo CT examination and interventional angi-ography on the first postoperative day. At this time, the inter-ventionalist can use intravenous heparinization withouta significant risk of postoperative bleeding complications.However, if intraoperative bleeding is of any concern, it is rea-sonable to postpone any endovascular procedures for a few days.If no clinical symptoms of ischemic complications occur, addi-tional control imaging studies are not necessarily needed.

FIGURE 2. A detailed illustration showing the manner of suturing the side-to-side in situ posterior inferior cerebellar artery-posterior inferior cerebellar artery anastomosis. All steps are described in detail in the Arteriotomy and Suturing section.





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DISCUSSION

The ability to revascularize an intracranial artery createstreatment options beyond direct clipping or coiling when treatingcerebrovascular lesions. Since Ausman and colleagues10 per-formed the first PICA revascularization procedure in the form ofan OA-PICA bypass, the OA-PICA bypass has been the mostcommon revascularization procedure in the posterior circulation.Even though the OA is a relatively suboptimal donor because ofits early branching, rapid loss of diameter, laborious and tedious

harvesting, and potentially higher susceptibility to occlusions,3

the side-to-side in situ PICA-PICA anastomosis has remainedunfamiliar to neurosurgeons. In situ bypasses, in general, areappealing and elegant bypass choices because they are entirelyintracranial, are less vulnerable to injury, probably have betterpatency rate than graft-using bypasses, do not require extracranialvessel harvesting, have arteries with similar diameters, and requirejust 1 site of anastomosis. An in situ bypass procedure can be usedfor revascularization of the most critical portion of the PICA, ieanterior medullary segment, after occlusion of its proximal origin.

The proximity and parallel courses of the bilateral tonsillome-dullary and telovelotonsillar segments of the PICAs usually allowtheir mobilization for side-to-side in situ bypass.

One criticism of the PICA-PICA bypass is that vessel occlusionor bypass failure could compromise circulation of both PICAterritories with a subsequent risk of bilateral or wide-rangingischemic events. Although this concern is valid, PICA-PICAbypass thrombosis would lead to occlusion of the PICAs distal tothe telovelomedullary segment; therefore, any resulting cerebellarhemispheric infarction will probably be mild as a result of the rich

anastomoses through various cerebellar arteries. Occlusion ofcritical brainstem perforators resulting from bypass thrombosis isunlikely. Because of the midline suboccipital approach in theprone position, the bypass procedure is performed quite easily.Lesions that necessitate a bypass are usually complex, and theirtreatment carries significant risks related to perforator and cranialnerve injury. A multidisciplinary approach combining the side-to-side in situ PICA-PICA bypass and endovascular aneurysmal de-construction in the treatment of complex VA-PICA lesions may beadvantageous compared with a sole microsurgical approach.

FIGURE 3. An optional manner for suturing the side-to-side in situ posterior inferior cerebellar artery-posterior inferiorcerebellar artery anastomosis. Steps C and D differ from the technique illustrated in Figure 2.

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CONCLUSION

The side-to-side PICA-PICA bypass technique is a technicallystraightforward, low-risk technique that can be used in themanagement of complex VA-PICA aneurysms and VA dis-sections. This technique is useful to microvascular neurosurgeons

treating complex VA-PICA vascular pathologies and can be usedin combination with endovascular therapies, lessening the risks ofboth open and endovascular treatments.

Disclosure

The authors have no personal financial or institutional interest in any of thedrugs, materials, or devices described in this article

REFERENCES

1. Takikawa S, Kamiyama H, Nomura M, Abe H, Saitoh H. Vertebral dissecting an-eurysm treated with trapping and bilateral posterior inferior cerebellar artery side-to sideanastomosis: case report [in Japanse]. No Shinkei Geka. 1991;19(6):571-576.

2. Lemole GM Jr,Henn J, Javedan S, Deshmukh V, Spetzler RF.Cerebral revascularizationperformed using posterior inferior cerebellar artery-posterior inferior cerebellar artery

bypass: report of four cases and literature review. J Neurosurg. 2002;97(1):219-223.3. Nussbaum ES, Mendez A, Camarata P, Sebring L. Surgical management of

fusiform aneurysms of the peripheral posteroinferior cerebellar artery. Neurosur-gery. 2003;53(4):831-834.

4. Quinones-Hinojosa A, Lawton MT. In situ bypass in the management of complexintracranial aneurysms: technique application in 13 patients. Neurosurgery.2005;57(1)(Suppl):140-145.

5. Nussbaum ES, Madison MT, Myers ME, Goddard J, Janjua T. Dissecting aneur-ysms of the posterior inferior cerebellar artery: retrospective evaluation of managementand extended follow-up review in 6 patients. J Neurosurg. 2008;109(1):23-27.

6. Fine AD,Cardoso A, Rhoton AL Jr.Microsurgical anatomyof the extracranial-extraduralorigin of the posterior inferior cerebellar artery. J Neurosurg. 1999;91(4):645-652.

7. Lister JR, Rhoton AL Jr, Matsushima T, Peace DA. Microsurgical anatomy of theposterior inferior cerebellar artery. Neurosurgery. 1982;10(2):170-199.

8. Hudgins RJ, Day AL, Quisling RG, Rhoton AL Jr, Sypert GW, Garcia-Bengochea F.Aneurysms of the posterior inferior cerebellar artery: a clinical and anatomical

analysis. J Neurosurg. 1983;58(3):381-387.9. Kawashima M, Rhoton AL Jr, Tanriover N, Ulm AJ, Yasuda A, Fujii K. Mi-crosurgical anatomy of cerebral revascularization, part II: posterior circulation.

J Neurosurg. 2005;102(1):132-147.10. Ausman JI, Lee MC, Klassen AC, Seljeskog EL, Chou SN. Stroke: whats new?

Cerebral revascularization. Minn Med. 1976;59(4):223-227.

Supplemental digital content is available for this article. Direct URL citationsappear in the printed text and are provided in the HTML and PDF versions of thisarticle on the journals Web site (www.neurosurgery-online.com).

COMMENTS

The posterior inferior cerebellar artery (PICA)-PICA bypass is anelegant example of intracranial-to-intracranial bypass, which is

gradually replacing some conventional extracranial-to-intracranial by-passes because it is equally safe, more anatomical, and avoids the tediousharvest of a donor artery.1 I strongly prefer the PICA-PICA bypass over

the occipital artery-to-PICA bypass, and have used the former almostexclusively in my practice. This article provides an outstanding review ofthe microsurgical technique and a virtuoso video by Dr Langer. Theauthors use a single running suture for both suture lines. I prefer a knot ateach end of the suture line instead because it allows the deep suture line to betightened and tied before proceeding to the superficial suture line. I con-gratulate the authors for a contribution here that will surely reinvigorate theuse of PICA-PICA bypasses in treating complex PICA aneurysms

Michael T. Lawton

San Francisco, California

1. Sanai N, Zador Z, Lawton MT. Bypass surgery for complex brain aneurysms: anassessment of intracranial-intracranial bypass. Neurosurgery. 2009;65(4):670-683.

The report by Korja et al is a well written and well illustrated technicaldescription of the technique of PICA to PICA bypass by a group of

authors with a great deal of experience in bypass techniques , an includesa clear video, illustrating the technique. The authors point out some of thenuances and pitfalls in performing the technique including checking foradequately sized arteries on the pre op angio. Although the technique has

been described before in detail and other reports include descriptions inmultiple cases, this is a clear description for someone wishing to review thetechnical essentials of the procedure. The authors make the correct point that

with proximal PICA lesions, it is difficult to assess the collateral networkbefore an intervention that has a high likelihood of sacrificing the parentvessel. Most of the collateral circulation can come from the network betweenthe vermial branches of the superior cerebellar artery and the vermianbranches of PICA. These collaterals may not provide adequate collateralsupport to sacrificing PICA in all cases, and this is difficult to predict. Abypass can be warranted in this situation. The authors describe some of thepitfalls of the alternative procedure of occipital artery to PICA bypass whichare valid. One advantage of the occipital artery to PICA bypass is howeverthat there will only be one side of the cerebellum at risk if the bypass fails. Inthe case described, the authors had planned to perform an interventional

sacrifice of the proximal PICA after the bypass to occlude the aneurysm,however it occluded spontaneously obviating the need for this. One dangerin this approach is that aneurysms can rupture during the waiting periodafter distal bypass. Another alternative is to clip the PICA origin after thebypass is in place to avoid this risk.

David W. Newell

Seattle, Washington

The authors describe an elegant manner of performing revascularization ofthe PICA distribution in cases where proximal vessel sacrifice is required.

The PICA-PICA bypass is relatively straightforward and avoids utilizing theoccipital artery, isolation of which is often tedious and time consuming. Noteshould be made that one potential downside of such bypass techniques is that

it does putan otherwise normal cortical vessel at risk should the bypass fail. Inmy experience the technical difficulty is performing this type of anastomosis islies in the initial suture line along the back wall, and the importance ofpracticing this bypass routinely and gaining adequate proficiency cannot beoveremphasized. Additionally, the authors describe a midline approach. Caremust be made in cases where laterally placed pathology must be simulta-neously addressed (a fusiform PICA aneurysm arising at the VB-PICA

junction, for example) that the exposure is adequate.

Nicholas C. Bambakidis

Cleveland, Ohio

Acknowledgments

We would like to thank Professors Juha Hernesniemi andMika Niemelavery warmly for their constructive comments onthis article. We would also like to thank Jill Gregory for creatingthe definite illustration.



operative nuances of side to side in situ.21

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