Hello. Your question is excellent. Medical jargon can be absolutely confusing! The ultrasound report is not alarming and may in fact be completely normal. Underdistention means the bladder was not quite full enough (with urine) to be visualized as well as possible. If the bladder is not adequately full when the ultrasound is done, it can create the false impression that the walls are thickened. On the other hand, true thickening of the bladder walls can be caused by inflammation (such as inflammation associated with infection). Because the bladder was not fully distended, the results of the study are somewhat inconclusive. But the good news is this: Nothing worrisome showed up... no tumors, no blockages, etc.! Best of luck! Make sure your urologist explain things in an understandable way....