It is entirely possible that this tiny cyst was missed on the CT scan. You can either repeat the ultrasound in 6 months (to assess for signs of interval enlargement), or see if your GI doctor thinks that an endoscopic ultrasound (with fine needle aspiration of the cyst, if technically feasible) should be performed. By the way, the vast majority of pancreas cysts this small will turn out to be benign.
Sincerely/ Robert A. Wascher, MD, FACS
www.doctorwascher.com
www.oncoguard.com