Aneurysm Occlusion

Aneurysm Attack

A bypass performed for an aneurysm empowers and emboldens the neurosurgeon. Unlike a bypass for ischemia, the completion of which marks the end of the operation, completing a bypass for an aneurysm marks the beginning of the aneurysm attack. The bypass is only the first round in a fierce fight and has no direct impact on the aneurysm, but it facilitates the stepwise deconstruction of the lesion, throttling its inflow and outflow with temporary clips, incising its walls to deflate or thrombectomize its core, and finally excluding it from the circulation with permanent clips. That simple conduit of blood flow to distal territories becomes a powerful weapon in the coming battle. Like the matador who tires and frustrates the angry bull with deft passes before finally plunging his sword, the neurosurgeon diminishes the giant aneurysm with his bypass before finally applying the clips. The bypass steels the neurosurgeon both strategically and psychologically to defeat the aneurysm.

Not performing a bypass for an aneurysm can have an equally withering effect. Those same temporary clips that deadened the aneurysm now also deprive distal territories of blood flow and stress the surgeon. Those same debulking maneuvers cannot be reversed until after the gutted aneurysm neck is reconstructed, which may be thwarted by atherosclerotic walls, complex branches, or intraluminal thrombus. Failure to reconstruct parent or branch arteries may demand a bypass under duress, already deep into the ischemic period and without a harvested donor artery. Therefore, the strategic and psychological advantages of a bypass justify a low bypass threshold for complex and giant aneurysms. The bypass changes the game, spurs aggressivity, and can dramatically improve outcomes.

Aneurysm Trapping

Trapping excludes an aneurysm from the circulation by closing all afferent and efferent arteries, rather than clipping the neck, and is the occlusion method of choice because it is controlled, complete, and predictable (Fig. 13.1). It requires access to all parent and branch arteries for clipping and avoids a direct aneurysm attack, eliminating any risk of intraoperative rupture, remnant, or recurrence. The bypass supplies the distal circulation, and the parent artery supplies the proximal circulation. Trapping is safe when perforating arteries are excluded from the trapped aneurysmal segment, but may be contraindicated when perforators cannot be excluded.

After bypass and trapping, giant aneurysms presenting with mass effect and compressed neural structures can be punctured and deflated, or opened and thrombectomized with an ultrasonic aspirator. A well-trapped aneurysm is disconnected from the circulation and will not bleed. Thrombus organized in layers of varying age and firmness is quickly broken down with the CUSA, and a limited aneurysm incision opens a keyhole into the lumen through which the thrombus is mobilized centrally into view and removed. The aneurysm’s walls protect the surrounding brain and collapse inward as the thrombus is reduced. Aneurysm decompression may create space or reveal surrounding anatomy that enables trapping clips to be readjusted to shorten the trapped segments or liberate perforators and branches included between the clips.