Tiny Pipes: 67 Cases of Flow Diversion for Aneurysms in Distal Vessels Measuring Less Than 2.0 mm

Flow diversion is increasingly used for off-label treatments of distal circulation aneurysms. Reports of use in sub-2.0-mm vessels are scant.A prospectively collected, institutional review board-approved cerebral aneurysm database was reviewed to identify patients who underwent flow diversion with a 2.5-mm diameter Pipeline embolization device.Sixty-seven aneurysms were treated in 67 procedures (66 [99%] successful, 64 [96%] single device, 2 [3%] with 2 devices) in 57 patients. Average age was 56 years and 60% were female. Aneurysm location was 51 (76%) anterior cerebral artery, 14 (21%) middle cerebral artery, and 2 (3%) posterior cerebral artery. Aneurysm size was 4.1 ± 3.0 mm (1-20 mm). Safety outcomes included 3 major strokes (4.5%) resulting in permanent neurologic deficit (modified Rankin Scale score 6,4,4), including 1 mortality (1.5%). Acute stent thrombosis was observed intraprocedurally or within 24 hours of each stroke. There were 2 small-volume (<10 cm3, 40 cm3) dependent intracerebral hemorrhage (3.0%) that resolved without permanent neurologic deficit. For effectiveness, 71% of patients underwent follow-up angiography. Complete occlusion was achieved by 88% at 6 months, 86% at 12 months, and 89% at last follow-up. A slight vessel diameter reduction was apparent on average 6.9 months after the procedure, which was statistically significant at the proximal (P = 0.001) but not distal (P = 0.317) device end. Preoperative average parent vessel diameter was 1.9 mm proximally (range, 1.1-2.6 mm) and 1.7 mm distally (range, 1.0-2.3 mm) of the Pipeline embolization device. Follow-up average vessel diameter was 1.7 mm proximally (range, 0.7-2.4 mm) and 1.6 mm distally (range, 0.6-2.1 mm). Flow delay associated with vessel diameter reduction occurred once. There were no cases of asymptomatic vessel occlusion.Flow diversion can be safe and effective for aneurysms originating from vessels <2.0 mm in diameter. Heightened vigilance for the prevention and management of acute stent and vessel thrombosis is warranted in these cases.