Final Dissection

Temporary clips are used occasionally to control an intraoperative aneurysm rupture, but more often to finish aneurysm dissection and prepare it for permanent clipping. Aneurysm dissection proceeds in an orderly sequence from controlling afferent arteries, finding efferent arteries, and dissecting the neck. Inevitably, this orderly progression is disrupted by the aneurysm dome. A dome that blocks the line of sight will conceal critical aneurysm anatomy in a surgical blind spot. Most of the dissection is performed in open surgical corridors with visible aneurysm anatomy; final dissection is performed in surgical blind spots after all visible anatomy has been prepared. Seeing into a surgical blind spot typically requires mobilizing the aneurysm. Pushing on the aneurysm’s base adheres to the policy of dome avoidance, but can avulse a fragile, tethered dome or dislodge a clot at the rupture site. Alternatively, the policy of dome avoidance can be ignored during final dissection, de-tethering and mobilizing the dome to see around it. A turgid, pulsatile aneurysm moves only with great force, whereas a softened aneurysm moves easily. Therefore, temporary clipping enables the neurosurgeon to manipulate the aneurysm aggressively and visualize hidden anatomy.

Temporary clipping is also used for potentially dangerous moves that have nothing to do with surgical blind spots or dome manipulation. An efferent artery stuck to the side of an aneurysm may be completely visible, but peeling this artery off the side wall and developing this cleavage plane may tear into a thin aneurysm wall. These risky maneuvers are deliberately saved for the final dissection. Similarly, delicate perforators stuck to the back of an aneurysm must allow passage of a clip blade. The cleavage plane is developed best with gentle traction on a softened aneurysm, pulling it away from the adherent perforator. Aneurysm traction widens the plane and adhesions are cut under tension. Aneurysm traction relieves a deflected perforator, rather than distorting it further. Temporary clipping and aneurysm softening give the neurosurgeon confidence for these risky moves.

Extent of Temporary Clipping

One temporary clip proximally is often all that is needed for the final dissection. Aneurysms with only one afferent artery, such as middle cerebral artery (MCA) and basilar bifurcation aneurysms, soften dramatically with a single temporary clip. Aneurysms with contrast jetting into it on preoperative angiography also soften dramatically with a single temporary clip. Aneurysms with several afferent arteries do not slacken with one temporary clip and require additional clips. Ophthalmic artery aneurysms can backfill from the posterior communicating artery (PCoA) or ophthalmic artery (OphA) despite cervical internal carotid artery (ICA) occlusion; an anterior communicating artery (ACoA) aneurysm can cross-fill from the contralateral A1 segment despite ipsilateral A1 segment occlusion; and basilar bifurcation aneurysms can fill from the contralateral PCoA despite occlusion of basilar trunk. The extent of temporary clipping is individualized according to afferent artery anatomy and how much softening is needed.

Distal temporary clips on efferent arteries together with proximal temporary clips on afferent arteries trap the aneurysm and arrest its flow, which may be necessary when final dissection calls for deliberately opening an aneurysm. Thrombotic aneurysms may require thrombectomy to debulk its mass and clip the neck; coiled aneurysms may require removal or mobilization of coils to clip the neck; and giant aneurysms may require suction decompression. Suction decompression takes aneurysm softening one step further, collapsing the aneurysm through an afferent artery outside the cranial field (such as the cervical ICA for an ophthalmic artery aneurysm), through the aneurysm dome with direct puncture, or endovascularly through a balloon-tipped catheter. Suction decompression quickly removes blind spots and greatly facilitates permanent clipping, but it requires complete aneurysm trapping to keep the aneurysm from re-expanding with blood. The aneurysm must also be soft and collapsible, which may not be the case with elderly patients and atherosclerotic aneurysms.

Temporary clipping has disadvantages too. The clip consumes precious space around the aneurysm and can interfere with deep dissection. Interruption of blood flow can cause brain ischemia, depending on the extent of temporary clipping and collateral circulation. Changes in somatosensory or motor evoked potentials may be observed and may elicit warnings from the neurophysiologist. There appears to be a direct relationship between aneurysm softening and brain ischemia: dramatic softening with temporary clipping is often followed quickly by signs of ischemia.

Unquestionably, temporary clipping adds time pressure and stress to the final dissection. Cerebral protection with barbiturates extends patient tolerance to temporary clipping, and so does raising blood pressure. However, neurosurgeon speed is most important. Technical steps during the final dissection must be clear. Contingency plans must be reviewed in advance. Instruments and permanent clips should be preselected. Preparation translates into surgical efficiency. The precious few minutes of final dissection after the temporary clips are applied are the crux of the operation, when exposure is optimized, the aneurysm is slack, risky moves must be made, and the outcome is determined. An aneurysm’s tolerance to mobilization is never clear, and a bold maneuver that might cause a catastrophe is not natural for surgeons. However, delicacy vanishes as one appreciates the difficulty of seeing an aneurysm’s blind side and the high cost of missing a deep perforator. Intraoperative rupture may be our biggest fear because it causes bleeding and demands an immediate solution. Perforator infarcts may not hurt us in the operating room, but ultimately they have no solution. Performing comfortably under pressure and becoming aggressive with aneurysms is a gradual process. The key to becoming aggressive with aneurysms is the temporary clip. The temporary clip pressures the surgeon to complete the task, but signals the right time to battle the aneurysm.