According to IMDb, it was shot in 1.33 : 1, which is the same as 4:3. On my Ghosts VCD, it's also 4:3. I think it was a deliberate choice to use that aspect ratio. I know many people consider widescreen to be 'better', but 1.33 : 1 (the ratio used in the time of silent films) is making a comeback for artistic reasons:
Why The Old-School 4:3 Aspect Ratio Is Coming Back With A Vengeance Right Now
One of the reasons it mentions, is this:
Movies are about people, not landscapes. And unlike epic landscapes (which call for a wide aspect ratio), people – or more specifically, faces – beg for 4:3. The reason is quite simple: A human head fills up more of the frame at 1.33 when compared to 2.35. A normal closeup at 2.35 is going to leave a lot of empty/negative space on the opposite side of the frame. This could of course be an excellent artistic choice for a specific project, but it won’t highlight the actor’s micro-expressions the same way a 4:3 frame will.
With this in mind, watch Ghosts one more time. And try to count the number of closeups. Soon you will discover this movie is actually more about faces than anything else. It's all about Michael's facial transformations: pulling his tongue out, crushing his face on the floor, pulling his skin off, being a fat guy, and so on. This movie is all about faces. Michael has several in this movie (his own, the skeleton, the ghoul, the mayor), but then there also all the astonishing faces of all the dancers, all with their own character and style... and there are all the frightened faces of the normal people... this story is for a large part told with closeups. And the 1.33 : 1 ratio fits that concept the best. I think it was an artistic choice.