I've had this problem before, too. I also was told it is "edema". I noticed only one certain type of tomatoes I started from seed had this problem. This was years ago and I got the seed from Territorial. I took the problem to them. At first, I thought it was infected seed so I asked if anyone else had brought this to their attention. They didn't know what it was. I was later informed that some plants just don't do well in hydro because they are too sensitive to an overabundance of some nutrients and water. It had something to do with cell walls expanding too fast before they are rigid enough. I can't remember exactly. Even though it wasn't Territorial's fault, Territorial sent me a different variety to try free of charge. I was impressed with that. I must say, though, that even the plants I started for the ground from that seed pack exhibited this symptom. I culled most of the plants in case it was a fungus or bacteria before I knew it was not infectious. However, the ones I didn't discard ended up doing poorly as the leaves apparently couldn't withstand the symptom and the bumps started becoming brittle and breaking the leaves. I didn't waste any further time on them at that point.