Background: There is sparse literature on the effect of flow diversion (FD) on large or giant intracranial aneurysms. We assessed the effects of FD with Pipeline stent on aneurysm sac size using MRI follow-up
Methods: All patients at our institution who underwent FD for treatment of intracranial aneurysms were retrospectively identified. Aneurysms with maximum dimension > 20mm, with pre and post treatment MRI were selected. These aneurysms were not previously treated, and did not receive adjunctive devices for current treatment. The largest diameter in 2-dimensions was measured on the MRI sequence that best demonstrated the aneurysm sac, and compared on serial scans. MRI changes were compared to DSA where aneurysm occlusion was graded by the O'Kelly-Marotta (OKM) scale.
Results: Between 6/2011-4/2015, 87 patients with 96 aneurysms were treated with FD. Eighteen patients had aneurysm >20mm. Pre and post treatment MRI were available in 12/18 (67%) patients. This included 9 (75%) females, with mean age 65.5 years. All aneurysms were unruptured and symptomatic. Nine (75%) patients had cavernous/ophthalmic aneurysms, and 3 had basilar aneurysms. Average largest aneurysm diameter was 26.7 (range 21-37) mm. Pipeline was used in all patients (mean 1.9, range 1-5 stents), with 8 (67%) requiring > 1 stent. At the first MRI follow-up (median 4, range 1-18 months), 4 (33%) aneurysms decreased in size, 6 (50%) remained stable, 1 (8%) increased in size. The stent thrombosed in the last patient. At the last MRI follow-up (median 10.5, range 1-48 months), 9 (75%) aneurysms decreased in size and 2 (16%) remained stable from baseline. No aneurysm completely resolved. DSA follow-up was available in 10 (83%) patients (median 9, range 1-25 months). Patients with decreased size on MRI had OKM grade C2, C3 or D, while aneurysms with stable size had OKM grade B3. The one patient with initial increased size on MR had corresponding OKM grade D (no filling).
Conclusion: Majority (75%) of large aneurysms decrease in size on serial MRIs after FD treatment. This corresponds with no filling or early remnant on DSA. Rare aneurysms increase in size despite no filling on DSA, which suggests caution when using only DSA follow-up post treatment. These findings require further study.