I do not think your plant is a Saguaro. The problem is that you or the previous owner has had the plant in poor light for so long that it has etiolated (stretched out searching for, reaching for light) that it has become unrecognisable. The growth at the base is more what the whole plant should look like. The long, thin, almost spineless cylinder on top is tragic. You may not be able to save this plant. Get it back into good light, but not direct sunlight strong enough to cause sunburn. It will probably start to fatten again but the narrow neck may not be able to sustain the recovering growth; you may have to stake it to support it at that time. Eventually you will be able to cut off the (refattened) top and root it down. The basal part will probably produce offsets. You could cut off the narrow neck now but I think it might be better to get it into more appropriate light conditions for a while first.

Poor little thing... :o(

Thanks for your help. What a shame! Oh well...

I've got a plant like that (minus the long skinny thing). I saw it in a book and it was labeled as a "Echinocactus Texensis" (spelling?) Cochemiea is right, the poor baby was severely deprived of light :( for a long time. Since it's a type of barrel cactus it should be shaped more like, well, a barrel! Hopefully with the suggestions Cochemiea gave, you can make this plant look more like nature intended. Best wishes.

It is quite possibly Echinocactus, but more likely to be E. grusonii rather than texensis. I would consider beheading it in the Spring, and seeing if you could restart the top, or get some new growths at the base.