• Adib A Abla, Jeffrey Nelson, Helen Kim, Christopher P Hess, Tarik Tihan, and Michael T Lawton.
• *Departments of Neurological Surgery, ‡Anesthesia and Perioperative Care, Center for Cerebrovascular Research, §Radiology, and ¶Pathology, University of California, San Francisco, San Francisco, California.
• Neurosurgery. 2015 May 1; 76 (5): 592-600; discussion 600.

BackgroundArteriovenous malformation (AVM) patients present in 4 ways relative to hemorrhage: (1) unruptured, without a history or radiographic evidence of old hemorrhage (EOOH); (2) silent hemorrhage, without a bleeding history but with EOOH; (3) ruptured, with acute bleeding but without EOOH; and (4) reruptured, with acute bleeding and EOOH.ObjectiveWe hypothesized that characteristics and outcomes in the unrecognized group of silent hemorrhage patients may differ from those of unruptured patients.MethodsTwo hundred forty-two patients operated-on since 1997 were categorized by hemorrhage status and hemosiderin positivity in this cohort study: unruptured (group 1), silent hemorrhage (group 2), and ruptured/reruptured (group 3/4). Group 3/4 was combined because hemosiderin cannot distinguish acute hemorrhage from older silent hemorrhage.ResultsHemosiderin was found in 45% of specimens. Seventy-five patients (31.0%) had unruptured AVMs, 30 (12.4%) had silent hemorrhage, and 137 (56.6%) had ruptured/reruptured AVMs. Deep drainage, posterior fossa location, preoperative modified Rankin Scale (mRS) score, outcome, and macrophage score were different across groups. Only the macrophage score was different between the groups without clinical hemorrhage. Outcomes were better in silent hemorrhage patients than in those with frank rupture (mean mRS scores of 1.2 and 1.7, respectively).ConclusionOne-third of patients present with silent AVM hemorrhage. No clinical or anatomic features differentiate these patients from unruptured patients, except the presence of hemosiderin and macrophages. Silent hemorrhage can be diagnosed using magnetic resonance imaging with iron-sensitive imaging. Silent hemorrhage portends an aggressive natural history, and surgery halts progression to rerupture. Good final mRS outcomes and better outcomes than in those with frank rupture support surgery for silent hemorrhage patients, despite the findings of ARUBA.

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