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The authors have generally performed a minimal hair shave along the incision line and course of the OA. The patient is prepared and draped in the usual sterile fashion. The skin incision is performed with the goal in mind of preserving the OA in continuity while skeletonizing it from the distal above the superior nuchal line to proximal just medial to the mastoid groove end Fig. Dissection of the OA is considerably more difficult than the dissection of the superficial temporal artery and meticulous attention to detail is a prerequisite.
First, the midline avascular plane is identified. As the skin incision is extended laterally, the point at which the OA crosses the skin incision is noted. As this point is approached, a small curved hemostat is used to dissect over the OA and protect it as the incision is carried across it. The course of the artery is then followed proximally using Jamieson scissors. A generous periadventitial cuff is left along the OA. Small branches from the OA are coagulated using bipolar forceps at low current and sectioned at a distance from their origin from the OA trunk itself.
Although the authors have used the microscope to perform this dissection, loupe and headlight magnification may be easier and more efficient. The OA is typically surrounded by a venous plexus and runs with the occipital nerve in a fascial sheath. A large muscular branch of the OA is often encountered proximally and should be coagulated and sectioned.
This vessel can be anticipated from the preoperative angiogram and must not be confused with the main trunk itself. The OA should be dissected proximally until its entrance into the muscular bed at the mastoid groove. Through this dissection, the OA will have ample length and will follow a straight path from the mastoid groove to the site of anastomosis with the PICA.
Illustration of the skin incision, bone removal, and course of the OA in the procedure. The skin incision is outlined in dark blue.
The descending limb of the incision toward the mastoid groove is made if it is necessary for the OA dissection. The bone removal can be extended laterally and superiorly if a far-lateral approach will be incorporated. The OA is dissected from above the superior nuchal line down to the mastoid groove and left in continuity. Used with permission from B. The dissection of the OA is performed in stages corresponding to the muscle and skin flap dissection.
A suboccipital craniotomy or craniectomy is performed extending from the side of interest just across midline. If a far lateral approach is required as part of the procedure, to trap or occlude a PICA aneurysm for example, additional bone is resected to expose the sigmoid sinus. The posterior third of the condyle and the arch of C-1 are removed more laterally to the side of approach for a far lateral transcondylar approach.
Attention should be paid to any opened mastoid air cells, as the eventual passage of the OA graft through the dura prevents a watertight dural closure at the end of the surgery. Bone cement or bone wax can be used to seal the air cells to minimize the risk of a postoperative CSF leak. After the dura is exposed and meticulous hemostasis is obtained, the dura is opened in a curvilinear fashion from the midline at C-1 extending superolaterally to the top of the exposure.
An additional incision is made superomedially and the dural margins are sutured to the adjacent tissue.
Under the operating microscope, the medullary loop of the PICA is identified as it travels around the brainstem before coursing to the vermis and cerebellar hemisphere. Sharp dissection at high magnification is performed to free the caudal loop for performance of the anastomosis. The authors have encountered perforators to the medulla even at this distal PICA segment, and these should be preserved and the site of anastomosis adjusted accordingly.
A mm segment of the PICA should be prepared for the anastomosis. This step is routinely performed to allow performance of a side-to-side PICA anastomosis as a second option for revascularization of the PICA territory should the neurosurgeon encounter difficulty with any step in the performance of an OA-PICA anastomosis.
If there are no perforating vessels tethering this portion of the PICA, the background may be sutured to the soft tissue or dura superiorly and inferiorly to elevate the artery and isolate the segment. Suturing of the rubber background to the soft tissue was adopted from the work of Dr. Illustration of the preparation of the recipient and donor vessel.
The tonsillomedullary segment of the PICA has been isolated. A rubber background has been placed under the artery and sutured to the overlying soft tissue. The OA has been skeletonized, leaving a periadventitial cuff.
The OA, which has been left in continuity, is freed of adventitia and soft tissue under the microscope for a 10—mm segment at a distal portion of the OA, allowing enough graft length to comfortably perform the anastomosis. Although the artery can be freed of adventitia after it is sectioned, the turgor of the vessel when it is left in continuity usually facilitates the dissection. The dissection is performed with fine microscissors and jeweler forceps. The OA is then secured distally with a hemoclip and sectioned in an oblique fashion proximal to the clip.
Excellent run-off should be obtained from the OA and a temporary aneurysm clip is applied proximally. We prefer to place the temporary clip at a point along the proximal half of the artery, where the adventitia has not been dissected. Although this may necessitate a larger clip, we believe it limits the damage to the vessel wall, and increases the freedom of movement of the anastomotic site.
A gauge blunt tip needle is then used to irrigate the lumen of the OA as the temporary clip is removed and then reapplied. Care must be taken to ensure the needle is truly in the lumen and the injection is performed gently to avoid dissection or injury of the OA. The anesthesia team is then asked to raise the patient's blood pressure to above the patient's baseline—or systolic blood pressure to — mm Hg in the setting of a ruptured aneurysm—and barbiturate burst suppression is induced. Once both of these parameters are reached, temporary clips are applied proximally and distally on the recipient PICA.
Using a sharp arachnoid knife or alternatively a gauge needle, an arteriotomy is started and extended with microscissors. The lumen of the recipient vessel is irrigated with heparinized saline.
A nylon suture Ethicon with a BV needle Ethicon is used for the anastomosis as the muscular wall of the OA may bend the needle of the 10—0 nylon suture Fig. An interrupted suture technique is generally used and may allow future enlargement and maturation of the anastomotic site compared with a running suture technique, although a running suture technique may be substituted, particularly when both arteries are large. A stitch is placed first at the heel and toe of the donor artery, anchoring the graft to the recipient at both of these locations.
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Both anchoring sutures are tied and cut. Attention is then turned to performance of the anastomosis of the back wall, as this is usually the more difficult side to perform. Care is taken to avoid grasping the intima of either vessel. Rather, the forceps are used to support the artery as the needle is passed through.
Attention must be paid to avoid catching other portions of the recipient vessel wall. A single suture may be used multiple times and is more efficient as long it is handled appropriately.
As the last few stitches are being placed, the suture may be trimmed to a suitable length but not tied to facilitate placement of the subsequent stitch. Alternatively, the needle may be left in place between the donor and recipient wall as the next suture is placed. Eventually all sutures are tied. The OA is then rotated to expose the front wall that must be sutured. The inner lumen of the PICA is inspected to ensure accurate suturing of the back wall before beginning the front wall closure.
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