Nova outbursts are among the most energetic phenomena in binary star systems, driven by thermonuclear runaway on the surface of a white dwarf. In symbiotic systems, where the companion is a red giant, the explosion propagates through a
dense circumbinary environment, offering a unique laboratory for high-energy astrophysics. In this talk, I will explore the structural and physical evolution of symbiotic novae, using the 2021 outburst of RS Ophiuchi (RS Oph) as a primary case study. As the
first nova ever detected at very-high energies (E>100 GeV), RS Oph provides a unique window into particle acceleration and shock dynamics. I will present high-resolution monitoring from the European VLBI Network (EVN) at 1.65 and 5 GHz, spanning 14 to 65 days
post-explosion. These observations allow us to characterize the expanding bipolar ejecta and the surrounding medium in unprecedented detail, enabling us to constrain critical system parameters for symbiotic stars, including outflow velocities, the white dwarf
accretion rate, the red giant mass-loss rate, the circumbinary density profile, and the properties of the orbital-plane density enhancement.
