Nova QU Vulpeculae 1984, with a peak visual magnitude of 5.7 (ref. 1) was one of the brightest and most unusual novae of recent times. Infrared spectrophotometry2,3 showed an extremely strong [Ne II] line at 12.8 μm and revealed the formation of silicate dust grains in the ejecta 240 days after outburst. The implied high abundance of neon and oxygen prompted the suggestion that nova QU Vul 1984 belongs to a proposed new class of novae in which the underlying system contains an oxygen-neon-magnesium (ONeMg) white dwarf4. Radio observations in May 1986 by the Very Large Array (VLA)5 provided the first image of the ejecta, 497 days after outburst. We present here new high-resolution radio images, showing that the ejecta have evolved from a bipolar shape to a spherical configuration with a central hole. The brightness temperature profiles of the new images are well fitted by models with a thick expanding shell of ionized gas with a 1/r2 density distribution, and the fitting yields values for the total mass of emitting gas and the expansion rate of the inner and outer edges of the shell.