If the 1cm cystic lesion in the pancreas head does not cause any sumptoms like pain or jaundice (Yellowing of the skin due to obstruction of the bile duct by the lesion), you do not need to operate before careful work up.
You need to operate when the work up shows the cystic lesion is malignant or is carrying a high potential of malignancy. You doctor will further work up for you like the blood test for liver function, cancer markers of CA19.9 and CEA and or PET scan and endoscopic ultrasound guided biopsy if malignancy is suspected.
An one cm cystic leison which is likely benign can be obstreved and moniterored closely by doctor. If the lesion is likely or confirmed malignant, a big Whipple operation is requried which carries 3% operation mortality rate in expert center.