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Background: There is evidence that macrophage infiltration in the tumor microenvironment promotes vestibular schwannoma (VS) growth. Efficacy of bevacizumab in NF2-associated VS demonstrates the value of therapies targeting the microvascular tumor microenvironment, and tumor-associated macrophages (TAMs) may represent another druggable target., Objective: To characterize the relationship between growth, TAM infiltration, and circulating monocyte chemokines in a large cohort of patients with VS., Methods: Immunostaining for Iba1 (macrophages), CD31 (endothelium), and fibrinogen (permeability) was performed on 101 growing and 19 static sporadic VS. The concentrations of monocyte-specific chemokines were measured in the plasma of 50 patients with growing VS and 25 patients with static VS., Results: The Iba1 + cell count was significantly higher in growing as compared with static VS (592 vs 226/×20 HPF, P =<0.001). Similarly, the CD31 + % surface area was higher in growing VS (2.19% vs 1.32%, P = .01). There was a positive correlation between TAM infiltration and VS growth rate, which persisted after controlling for the effect of tumor volume (aR2 = 0.263, P =<0.001). The plasma concentrations of several monocytic chemokines were higher in patients with growing rather than static VS., Conclusion: There is a strong positive correlation between TAM infiltration and volumetric growth of VS, and this relationship is independent of tumor size. There is a colinear relationship between TAM infiltration and tumor vascularity, implying that inflammation and angiogenesis are interlinked in VS. Chemokines known to induce monocyte chemotaxis are found in higher concentrations in patients with growing VS, suggestive of a potential pathophysiological mechanism., (Copyright © Congress of Neurological Surgeons 2022. All rights reserved.)

Background: Bilateral vestibular schwannomas (VS) are pathognomonic of neurofibromatosis type 2 (NF2), but the diagnostic criteria also include unilateral VS (UVS) in combination with multiple meningiomas (MM) and other schwannomas, as well as MM without VS., Objective: To investigate the diagnostic value of these criteria and establish the presence of other genetic conditions in patients presenting in this manner., Methods: The Manchester International NF2 database was accessed to obtain information on patients presenting with a UVS and MM or ≥2 nonintradermal schwannomas (NIDS). We gathered data on patients diagnosed with NF2 due to MM without VS and on patients presenting with MM without meeting NF2 criteria. Analysis was performed for pathogenic variants (PVs) in NF2, SMARCE1, SMARCB1, and LZTR1., Results: A total of 31 of 131 patients presenting with a UVS and MM had a nonrefuted diagnosis of NF2 after molecular studies, in comparison with 85 of 96 patients presenting with UVS and ≥2 NIDS (P ≤ .00001). Fifty percent of patients presenting with a UVS and ≥2 NIDS with NF2 developed bilateral VS, compared with only 26% of those who presented with a UVS and MM (P = .0046). In total, 11 of 152 patients presenting with MM without fulfilling NF2 criteria were found to have a PV in SMARCE1, and 7 of 152 were confirmed to have mosaic NF2., Conclusion: Patients presenting with UVS and MM are significantly more likely to have a nonrefuted diagnosis of NF2 than patients presenting with UVS and ≥2 NIDS, but significantly less likely to develop bilateral VS. Seven percent of those presenting with MM without meeting NF2 criteria had PV in SMARCE1, and 5% had mosaic NF2., (Copyright © Congress of Neurological Surgeons 2022. All rights reserved.)