What does renal collecting systems are not appreciably dilated mean on a CT scan? Cause for concern?

Normal. This is a way of saying the part of the kidneys that collect and drain urine are normal.
No. Renal collecting systems should not be dilated so this is a normal finding.
Sometimes more words. Are not better. "not appreciably dilated" means not dilated, which means normal. Perhaps there was a clinical concern regarding urinary obstruction, and the radiologist was stating a pertinent negative finding.