End-to-Side Anastomosis

Anastomoses are the connections that join arteries together to create a bypass. The Greek roots of the word translate to “furnish with a mouth,” which in this case means creating an outlet in one tube that connects with an opening in another tube to form a branching network. Arterial bypasses, no matter their complexity, are all built with just three simple anastomoses: end to side, side to side, and end to end. The application of these three anastomotic techniques in different locations, with different donor–recipient pairings, in unique combinations, and with subtle variations, yields the immensity and elegance of microsurgical bypasses.

The end-to-side anastomosis is the convergence of donor and recipient arteries that redirects donor flow destined for another territory into the recipient. This anastomosis is the opposite of an arterial bifurcation: whereas bifurcations divide trunks into diverging branches that distribute blood flow peripherally, end-to-side bypasses unite separate branches into converging streams that augment or replace flow in the recipient. Arterial convergence is unusual in circulatory systems; it is seen intracranially only at the confluence of the vertebral arteries, on the exiting side of arterial fenestrations, and in leptomeningeal networks in watershed zones. Therefore, this Y-shaped anastomosis is a strikingly surgical construct.

It is also an efficient construct because the connection between donor and recipient can exceed the diameter of each, unlike conventional end-to-end reanastomosis. A linear arteriotomy in the recipient can be made two to three times the diameter of the recipient to encourage flow through the anastomosis by lowering its resistance. Similarly, the donor artery can be widened with a “fish-mouth” arteriotomy, or an oblique transection at a 60-degree angle and a longitudinal linear incision in the sidewall equal to the length of the oblique transection. Fish-mouthing transforms the circular end of the donor artery into a quadrangular opening with four linear sides that enlarges the donor orifice. Poiseuille’s law describes the relationship between flow (Q), perfusion pressure (P), radius of an artery (r), length of an artery (L), and viscosity (η): Q = π Pr⁴/ηL. The only variable impacting flow through an anastomosis under the surgeon’s direct control is the radius, and this dominant variable can be easily increased with well-crafted arteriotomies. A generous arterio tomy in the recipient artery and a fish-mouthed arteriotomy in the donor artery also create mostly linear tissues that are easily matched in length and caliber.

Technique

The sequence of steps in an end-to-side anastomosis is illustrated with a right-angled or T-anastomosis between a radial artery graft and PICA as part of a left V3 VA-RAG-p2 PICA bypass in a patient with vertebrobasilar ischemia (Fig. 1.1). Although much less common than a STA-MCA bypass, this IC-IC interpositional bypass does not require a fish-mouth arteriotomy in the donor and deploys a larger-caliber graft that displays its circular lumen better than the smallercaliber STA. The donor is harvested as a free graft and prepared by tying off leaky branches, stripping adventitia from the distal end, and making a fresh perpendicular transection at the distal end.

The recipient PICA remains stationary in the cerebellomedullary cistern throughout the anastomosis because a RAG is easily transported to the recipient site. An accessible segment is selected that is reasonably sized, without brainstem perforators, and tolerant to temporary clipping (Fig. 1.1). Branches or perforators that lie at the recipient site within the temporary clips will back-bleed during the suturing and obscure the field. Twigs at eloquent locations are vigorously protected, whereas those at non-eloquent sites might be temporarily clipped or cauterized safely. Circumferential dissection under the recipient artery enables passage of a protective rubber dam, or piece of background material, and a suction catheter as part of the surgical stage.

Temporary clips are applied to the recipient artery, which interrupts cerebral blood flow and begins the ischemia time (Fig. 1.2). The smallest possible temporary clips are used (typically 3-mm straight clips) to lower the clip profile and keep its large shanks from snagging suture. Clips are applied at an oblique angle or laid down in the field to displace the shanks away from the anastomotic site. The trapped recipient segment should allow space for the arteriotomy and for the bites at the ends of the arteriotomy. The recipient artery is marked with ink to guide the arteriotomy and, more importantly, to visualize the edges of its incised walls, which otherwise become translucent after the arteriotomy.

Fig. 1.1 The sequence of steps in an end-to-side anastomosis is illustrated with a right-angled or T-anastomosis between a radial artery graft and PICA as part of a left V3 VA-RAG-p2 PICA bypass in a patient with vertebrobasilar ischemia. The recipient artery is exposed (Step 1) through a left far lateral craniotomy (inset) with the recipient artery just above the vagoaccessory triangle (surgeon’s view with the patient in the three-quarter prone position, the cranial vertex to the bottom right, the foramen magnum to the top left, the posterior petrous face at the top right, and the retracted cerebellum at the bottom left).

Fig. 1.2 Step 2. The recipient artery is temporary clipped, with inking of the linear arteriotomy. Note that the surgical stage has been set with a blue rubber dam, a soft rubber suction catheter beneath the dam (not seen), a retractor to secure the suction catheter, and Telfa strips to protect the cerebellum.

The artery is pierced parallel to its long axis with the beveled tip of a 25-gauge needle bent at a 45-degree angle (Fig. 1.3). The puncture site provides entry for one blade of a fine, right-angled microscissors, which then extends the arteriotomy in both directions (Fig. 1.4). Smooth cuts make a clean arteriotomy rather than a jagged, saw-toothed one, with a length three times that of the arterial diameter. Lifting the luminal blade of the microscissors under the arterial wall visualizes its tip through the translucent tissues and keeps it from catching the back wall. The lumen is flushed with heparinized saline to clear the lumen and identify back-bleeding through clips or unrecognized branches.

The first of two stay sutures joins the donor and recipient arteries (Fig. 1.5). There is little difference between the first and second stay sutures with this perpendicularly transected graft. However, a fish-mouthed donor artery takes the shape of a foot, with its toe at the distal tip at the end of the oblique angled cut and its heel at the proximal end of the longitudinal cut. The “heel stitch” is placed first with a fish-mouthed donor, taking the first bite of the heel stitch from outside to inside the donor artery and flipping the donor foot to visualize the donor lumen. The donor artery is then rolled back into its downward-facing position for the remainder of the anastomosis, and the heel stitch is completed with a second bite from inside to outside the recipient artery. When the “toe stitch” is placed first, the donor lumen faces downward and the rest of the foot covers the heel, making the bite through the heel awkward. The toe stitch prevents flipping the donor foot to visualize the donor lumen during the first bite of the subsequent heel stitch. A surgeon’s knot is used with stay sutures to keep the arteries together between the first and second throws of the knot (Fig. 1.6).