A cursory ultrasound means an initial ultrasound to see how things look in general. It isn't a specific type of ultrasound, it is just a lets take a look initially and see what is going on in there.

15mg twice a day for a 13lb dog is too much to start at. They like to start at 1mg/1lb in total. With diabtes it is important to give twice days, so say you are doing 10mg, which is a good starting point, then you'd give 5mg in the morning and 5mg in the evening.

What was the ACTH results and the ultrasound results?