Bypass option for ‘unclippable’ giant cerebral aneurysms

By Eleanor McDermid, Senior medwireNews Reporter

Extracranial-intracranial bypass is a "durable" treatment option for giant middle cerebral artery aneurysms that cannot be clipped, say US researchers.

Use of the technique is associated with "an acceptable rate of complications," they report in Neurosurgery.

"Given their high rate of progression and poor natural history, giant aneurysms should be treated aggressively once identified," say Robert Spetzler (St Joseph's Hospital and Medical Center, Phoenix, Arizona) and team.

But they stress the need for "lifelong surveillance" because of the potential for aneurysm recurrence. Three of the 16 patients in their study needed reintervention during follow up averaging 58.4 months.

Two of the patients who needed retreatment had evidence of residual aneurysm filling on postoperative angiograms. Two of the patients were retreated with coiling and one with clipping; no morbidity or mortality resulted from retreatment.

All aneurysms were larger than 2.5 cm in diameter. In most cases, the decision to bypass was made during exploratory surgery, although bypass was preplanned for a few clear-cut cases, such as fusiform aneurysms or aneurysms that gave rise to critical perforators.

"The logic behind this strategy is simple," say Spetzler et al. "Reducing flow to the aneurysm promotes thrombosis while the bypass revascularizes the territory beyond the aneurysm.

"When the vessel is ligated proximal to the aneurysm, decreased intraluminal pressure reduces the risk of aneurysm rupture, while decreased retrograde flow leads to thrombosis."

The researchers most often used the superficial temporal artery for bypass, with a radial artery graft used in other patients. After bypass, they occluded the parent vessel, proximally in nine cases, distally in four, and by aneurysm trapping in one case.

"Where possible, we prefer proximal vessel occlusion because of its theoretical advantage of reducing the risk of aneurysm rupture," they comment. "However, when exposure of the proximal inflow is limited, or there are critical branches arising from the proximal portion of the aneurysm, distal parent vessel occlusion is an option that can lead to aneurysm thrombosis and obliteration."

After surgery, the bypass was patent in all but one patient, and the aneurysm was completely occluded in 12 (75%) patients.

No patient died, but five had perioperative complications, with three having symptomatic infarctions, and two developing shunt-dependent hydrocephalus. Long-term outcomes were generally good, with 15 patients having a Glasgow Outcome Scale (GOS) score of 4 or 5. The exception, with a GOS score of 3, was a patient who had lasting deficits from perioperative infarction (despite a patent bypass).

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