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We present measurements of the angular broadening of OH masers in W49N, made by very long baseline interferometry. We observe a lower cutoff to the distribution of observed sizes of maser spots, at about 50 mas. Individual maser spots are significantly elongated with typical axial ratios between 2 and 3. We attribute these effects to anisotropic interstellar scattering. Alignment of the major axes of the scattered spots suggests the presence of a strongly ordered component to the ambient interstellar magnetic field. We also present preliminary measurements of the spectrum of the fluctuations in electron density responsible for interstellar scattering.
