Regrettably, I don't think that you're going to get any answers to your main question about the cause of the abdominal swelling. This web page (which is from a reliable source, i.e. the Renal Unit of Edinburgh Royal Infirmary) basically says that doctors have no idea about the cause of your husband's problem:
http://www.edren.org/...What_is_the_loin_pain
However I hope that the links under 'More information' might be of use to you and your husband.
Chris