atrophy means a decreasing in size of an organ because of disease or other issues. I assume heterogeneity refers to the fact that the head of the pancreas is different than it should be and/or different from the rest of the pancreas... If your doctor isn't explaining things for you so you understand what is happening then make him/her. It is important for you to know these things and understand them. If you aren't happy, get a second opinion. I will say one thing... I a little taken aback by you stating you have lower addominal pain... the pancreas are by your stomach in the upper left abdominal quadrent so that seems a little wierd to me... any other symptoms?
This is a finding that you need to discuss with your doc since he will need to put this together with any other findings. In general a fatty pancreas - depending upon the amount of fatty infiltration - can suggest that dietary changes need to be made. But marked fatty atrophy is often associated with type II diabetes, and in some cases with generalized atherosclerosis, so the findings of a fatty pancreas need to be correlated with other test findings. In a similar manner, heterogenous can mean finding pancreatic tissues in areas 'outside' of the general boundaries of the normal limits, which may or may not be the finding in your case.