The organ to look out for is the duodenum. With some diabetics you can see the swollen duodenum through their clothes as a pointy swelling below the sternum. I believe that T2DM is caused by Clostridium novyi Type A the alpha toxin of which causes oedema. If the internal organs are infected then you can expect them to be enlarged. The stomach appears to be unaffected because the toxin binds irreversably to L-DOPA which is present in the sub-mucosal; layer of the stomach ready to produce the dopamine signal when food enters the stomach You may also see fluid in the abdomenal cavity due to leaky intestines.

If you are seeing this effect in sterile mice I would very much like to know.

This of course indicates that another body component has decreased in size. What this is likely to be depends on the model you are using. However, in many instances changes in adipose  or muscle mass will be respoinsible. The opposite change would likely result in an obese type 2 diabetes model, while it may be in this case that the animals have lost a lot of mass due to the development of acute diabetes or relative starvation.

In type 1 diabetes in rats, I did not see a decrease in heart weight when I normalize with the body weight of the animal.