CHAPTER 18 Rejoining the transected ends of two arteries after excising aneurysmal pathology reconstructs the vascular anatomy and restores the original blood flow, without an interposition graft, a graft harvest, or a second anastomosis. End-to-end reanastomosis works beautifully with small and mediumsized fusiform aneurysms with one afferent and one efferent artery, but excision of large or giant aneurysms leaves a gap that may not be closed. Reanastomosis requires enough slack on the two cut ends to bring them back together again without tension. With tension, knots cannot approximate the ends, the lumen closes on itself, and sutures pull through the walls. Therefore, successful reanastomosis depends on finding the right aneurysm with the right anatomy, and resecting all of the pathology without losing all of the slack. End-to-end reanastomosis is like a game of chicken: you win only if all of the pathology is resected, but too much resection prevents arterial ends from rejoining. Pathological tissues are stitched into the anastomosis with conservative resection, whereas knots pull and shred arterial ends with aggressive resection. Normal arteries are built with enough length, and little extra, to follow their ordained paths and conduct blood flow to those regions of the brain. However, certain arteries have stereotypical curves and loops that can be straightened to close the arterial gaps. Tortuosities and redundancies are often exaggerated in older patients or in patients with underlying vascular pathology or unique anatomic variations. Applying reanastomosis techniques requires the recognition and exploitation of these caches of extra arterial tissue. An arterial genu is a reservoir of redundant artery that can be released for reconstructions. Just as a right triangle’s hypotenuse connects two points over a shorter distance than its orthogonal legs, reconnecting trimmed arterial ends diagonally across a genu recovers lost length (Fig. 18.1). The MCA has three bends that generate extra arterial length for reanastomosis. The first is the genu of the limen insula, which is a 90-degree turn between the M1 sphenoidal segment coursing laterally and the M2 insular segment coursing superiorly, overlying the limen insulae. The second is the genu of the insular cleft, which is a 180-degree turn between the M2 insular segment coursing superiorly over insular cortex and the M3 opercular segment coursing inferiorly over the frontoparietal operculum, contained within the circular sulcus. The third is the genu of the opercular cleft, which is another 180-degree turn between the M3 opercular segment coursing laterally around the inferior margin of the frontoparietal operculum and the M4 cortical branches on the lateral convexity, where the arteries exit the Sylvian fissure. Arteries lying below the Sylvian fissure in the inferior limb of the insular cleft have a less tortuous course that those lying above the Sylvian fissure in the superior limb. Straightening the genu of the limen insulae provides length for a M1 reanastomosis, straightening the genu of the insular cleft provides length for a M2 reanastomosis, and straightening the genu of the opercular cleft provides length for a M3 reanastomosis. The ACA follows a tight path around the limbic structures with lots of curvature but little extra length for reanastomosis. The same can be said about the PCA and SCA in their course around the midbrain. In theory, end-to-end reanastomosis can be performed anywhere in the cerebral circulation that an excisional gap can be successfully closed. In practice, however, the lack of genua, tortuosities, and redundancy in the ACA, PCA, and SCA limits the application of the reanastomosis technique in these regions and increases its failure rates if attempted. The PICA has two official loops and one unofficial loop that generate extra length in its course around the medulla (Fig. 18.2). The unofficial loop is the curvy and highly variable (sometimes upward and sometimes downward, sometimes lateral and sometimes medial) course of the anterior medullary (p1) and lateral medullary (p2) segments as they pass through the hypoglossal and glossopharyngeal, vagal, and accessory rootlets (so-called loop of the medullary rootlets). The first established loop is the caudal loop of the tonsillomedullary (p3) segment that forms a 180-degree turn at the inferior pole of the tonsil between the retro-olivary sulcus and the medial surface of the tonsil. The second established loop is the cranial loop of the telovelotonsillar (p4) segment that forms a 180-degree turn overlying the central part of the inferior medullary velum. Like the MCA’s genua, the PICA’s loops are reservoirs of redundant artery that can be released for reconstructions. Straightening the loop of the rootlets provides length for a p1 and p2 reanastomosis, straightening the caudal loop provides length for a p3 reanastomosis, and straightening the cranial loop provides length for a p4 reanastomosis. The extra length in an arterial tortuosity can be extracted for successful reanastomosis after excising a nearby aneurysm. Whether the aneurysm is proximal, distal, or right at a genu does not matter; straightening an adjacent genu pulls that extra length into the repair, closing the arterial gap and shortcutting the reconstructed route around the bend. The MCA’s bends and the PICA’s loops create many opportunities for repairing defects with a reanastomosis almost anywhere along these arteries’ course. More tortuous arteries yield greater length for reanastomosis. Children and young adults tend to have straight, linear arteries with little redundancy. Older patients with atherosclerotic degeneration can have dramatic elongations, dilations, and tortuosities with much more redundancy. Preparation for reanastomosis requires the usual dissection of the afferent and efferent ends of the parent artery, release of arachnoid adhesions, and division of insignificant twigs. Generous dissection along afferent and efferent limbs is perhaps more important with reanastomosis than with other techniques because of the harmful effects of axial tension. Dissection of the limbs adds mobility to the length extracted from a genu or loop and should be performed before temporary clipping. Reanastomosis is critically dependent on the complete resection of all pathological tissue, be it aneurysm, arterial dissection, traumatic injury, or atherosclerosis. Even when ends rejoin easily, their reanastomosis will fail if the pathology is retained. As difficult as it is to resect more diseased length from an arterial end to reach healthy tissues and possibly make the gap unbridgeable, incorporating weakened or thrombogenic tissues into the suture line will ruin the bypass. Resection must get beyond the pathology and then close the gap by mobilizing more length from the ends. An MCA reanastomosis was performed in nearly one third of all reanastomoses along sphenoidal, insular, and opercular segments (Table 18.1; Fig. 18.3). An M1 reanastomosis involves large-caliber, muscular arteries that hold sutures well, but lenticulostriate arteries on the efferent limb do not tolerate cross-clamping for long. In addition, M1 aneurysm resection might jeopardize an associated lenticulostriate, which can be costly to the putamen, the upper part of the internal capsule, the globus pallidus, or caudate head and body. Redundancy of the genu of the limen insulae enables a reanastomosis with small aneurysms on the sphenoidal segment (Case 18.1). Slack ends can be created with giant aneurysms by deflating or debulking the aneurysm with thrombectomy (Case 18.2). Lenticulostriate arteries are often displaced by giant aneurysms to the proximal or distal ends, where they can tether the stumps. Table 18.1 Summary of Clinical Experience with IC-IC Reanastomosis
Reanastomosis
Reanastomosis
Microsurgical Anatomy
Sylvian Triangle
Falco-Frontal and Tentorial-Oculomotor Triangles
Vago-Accessory Triangle
Donor and Recipient Dissection
Reanastomosis Technique
MCA Reanastomosis
Reanastomosis Type | N | % |
MCA reanastomoses |
|
|
M1 MCA | 1 | 3 |
M1 MCA-M2 MCA | 2 | 6 |
M2 MCA | 4 | 11 |
M3 MCA | 3 | 9 |
AChA | 1 | 3 |
ACA reanastomoses |
|
|
A3 ACA | 1 | 3 |
A4 ACA | 1 | 3 |
PCA/SCA reanastomoses |
|
|
P4 PCA | 1 | 3 |
a3 AICA | 1 | 3 |
ATA | 1 | 3 |
PICA reanastomoses |
|
|
p1 PICA | 1 | 3 |
p2 PICA | 8 | 23 |
p3 PICA | 7 | 20 |
p4 PICA | 2 | 6 |
V3 VA | 1 | 3 |
Total | 35 |
|
