Middle age female with abdominal pain

Middle age female with abdominal pain. Ultrasound shows multiple stones in GB. Normal wall thickness. Negative sonographic Murphy sign. Cyst was noted in body of spleen with echogenic debris. No mural nodules or septa. Atrophy of pancreatic tail. Hiatus hernia was also noted. On CT the cyst shows thin wall no septa or mural nodule. Peripancreatic fat stranding was noted. Ddx for cyst was pseudocyst VS. MCN. what should be done to make final diagnosis? Follow up and repetition of CT to see the changes in size after 1 month or endoscopic ultrasound and aspiration of cyst for amylase, mucin and markers?