We have recently demonstrated a high-speed null polarimeter [ Opt. Express 30 , 18889 ( 2022 ) 10.1364/OE.454193 OPEXFF 1094-4087 ] based on passive polarization optics and using a fast swept-wavelength laser source. We report here its implementation in a laser-scanning microscope setup, enabling highly sensitive linear retardance imaging with a pixel dwell time of 10 μ s. The instrument is also able to measure light depolarization induced by the sample. Images of biological samples, including cancerous tissue and cells, illustrate its performances.