Contingency Planning

A reality of aneurysm surgery is that the technical skill and surgical experience do not eliminate the risk of intraoperative aneurysmal rupture. The dangerous combination of aneurysm fragility and surgical manipulation sometimes precipitates rupture, and the neurosurgeon must prepare for this catastrophe. Vascular control is a simple concept: afferent arteries that supply antegrade blood flow to an aneurysm, and efferent arteries that might supply retrograde blood flow, are exposed for occlusion with temporary clips. In practice, vascular control can be difficult because of limited operative exposure, anatomic obstacles, or interfering aneurysm domes.

Successful aneurysm management begins with the development of a systematic contingency plan. With each case, before entering the operating room, the neurosurgeon must envision intraoperative disaster in every conceivable form and then develop strategies to deal with it. Forethought enables the neurosurgeon to prepare the patient, exposing the patient’s neck for proximal carotid control or suction decompression, harvesting a donor vessel for possible bypass, or inserting a groin sheath for intraoperative angiography. Forethought reminds the neurosurgeon early during the dissection to gain proximal and distal control, preselect temporary and permanent clips, and protect the brain with barbiturates. Forethought replays in the neurosurgeon’s mind the microsurgical maneuvers to control aneurysmal rupture: direct tamponade with a cottonoid, suction, temporary clipping, trapping, and permanent clipping of the aneurysm. Deliberate thoughts about disaster permeate the operation, readying the neurosurgeon and the operative team for a swift response. Negative thoughts are usually suppressed by surgeons, but must be addressed. Over time, this process of contingency planning becomes instinctive, and the microsurgical mechanics of the rupture response become almost a reflex. Still, we must always pause to consider the elements of vascular control that lie outside of the immediate surgical field to prepare them in advance.

Proximal Control

Points of proximal control are identified preoperatively on angiography, exposed early, and prepared thoroughly enough to place a temporary clip under duress or under blood. Points of proximal control include the ophthalmic segment of the supraclinoid internal carotid artery (ICA) for posterior communicating artery (PCoA) aneurysms, the M1 segment for middle cerebral artery (MCA) aneurysms, the bilateral A1 segments for anterior communicating artery (ACoA) aneurysms, the A2 segment for pericallosal artery (PcaA) aneurysms, the cervical ICA for ophthalmic artery aneurysms, the basilar trunk for basilar bifurcation aneurysms, and the intradural vertebral artery (VA) for posterior inferior cerebellar artery (PICA) aneurysms. Some aneurysms have additional proximal supply that can feed an aneurysm, like retrograde flow in PCoA with PCoA aneurysms, or retrograde flow in ophthalmic artery (OphA) with OphA aneurysms.

Special moves are needed with some aneurysms to gain proximal control. The falciform ligament can be cut to move proximally on the ICA for proximal PCoA and some OphA aneurysms. The genu of the corpus callosum can be resected to expose the A2 segment for PcaA aneurysms. The posterior clinoid process can be removed to expose the basilar trunk for control of basilar bifurcation aneurysms. The extradural VA can be exposed to control PICA aneurysms that abut the dural ring. There is a range of proximal control, from proximal-proximal control to distal-proximal control. Proximal-proximal control may be distant from the aneurysm and enable collateral arteries to supply it (e.g., cervical ICA occlusion with ophthalmic aneurysms). In addition, temporary occlusion at more proximal points can compromise blood flow in perforators that lie between the temporary clip and the aneurysm (e.g., proximal M1 segment occlusion and diminished perfusion of lenticulostriate arteries with MCA aneurysms). Distal-proximal control adjacent to the aneurysm is usually more complete and preferable.

Distal Control

Temporary occlusion of efferent branch arteries is only needed in certain situations: persistent back-bleeding after intraoperative aneurysm rupture controlled with temporary clips on all proximal arteries; persistent aneurysm turgor after temporary occlusion of proximal arteries that prevents aneurysm collapse or further dissection; aneurysm trapping for suction decompression; and deliberate opening of the aneurysm for deflation, thrombectomy, or coil extraction. The ease of gaining distal control depends on aneurysm location and is often inversely related to the ease of proximal control. For example, the proximal control of VA is straightforward with most PICA aneurysms, but the distal VA vanishes into the depths of the exposure and is obscured by lateral medulla. Conversely, the distal PcaA and the callosomarginal artery (CmaA) may be easy to control for most PcaA aneurysms, but the proximal A2 segment may vanish below the genu and rostrum of the corpus callosum. As with proximal control, points of distal control are identified preoperatively on angiography, exposed early, and prepared thoroughly enough to place a temporary clip under duress or under blood. Their exposure does not occur as early as that for points of proximal control. Distal control occurs naturally because dissecting efferent arteries is part of defining an aneurysm neck. Distal control can be challenging when efferent arteries are hidden behind the dome of an aneurysm (like the inferior trunk with laterally projecting MCA aneurysms, or the contralateral A2 segment with superiorly projecting ACoA aneurysms), or when they are deep in the surgical field (like the contralateral P1 segment with some basilar bifurcation aneurysms). As with proximal control, dome avoidance is critical.

No Control

In some cases, vascular control may be inaccessible. A low-lying basilar bifurcation aneurysm may have a basilar trunk that remains out of reach despite drilling away the posterior clinoid process and the dorsum sella. A calcified, atherosclerotic ICA harboring a PCoA aneurysm may be accessible, but the proximal parent artery wall may not collapse with temporary clipping. Inability to gain control may be disquieting enough to halt the operation. Contingency plans may need to be activated, such as exposing the cervical ICA to control the PCoA aneurysm on the atherosclerotic ICA or deploying a balloon-tipped catheter to temporarily occlude the basilar trunk to control the low-lying basilar bifurcation aneurysm. More elaborate measures, such as using hypothermic circulatory arrest for an uncontrolled basilar bifurcation aneurysm, may require aborting the operation and revising the surgical plan. Alternative therapies, such as endovascular therapy, might have increased appeal at these moments. The neurosurgeon faces a choice between establishing vascular control, aborting the operation, or continuing without control. If the decision is to proceed without vascular control, the dissection must focus on the aneurysm neck and meticulously avoid the dome, and the surgeon must be ready to place a permanent clip if the aneurysm ruptures prematurely.