Fate of small pancreatic cysts (<3 cm) after long-term follow-up: analysis of significant radiologic characteristics and proposal of follow-up strategies.

Objective: To describe the natural history of pancreatic cysts after long-term follow-up, with an emphasis on the identifying indicators of indolent lesions.

Methods: We retrospectively sampled 95 patients with 149 cysts <3 cm detected by CT from 2003 to 2004, and followed them for more than five years (mean 117.5 ± 18.8 months). Two radiologists reviewed the initial CT images, then recorded changes after the follow-up. We compared the cysts' initial characteristics between the surgery and non-surgery patient groups, and also between non-benign lesions and benign lesions.

Results: Twelve of the 95 patients, who among them had 16 cysts, underwent surgery. Of the 133 cysts in the 83 nonsurgical patients, 57 cysts (42.9 %) enlarged, although only five cysts increased to larger than 3 cm at the end of observation. The initial size of the cyst was significantly larger in the surgery group than non-surgery group. Also, according to cyst-based analysis, ductal communication, dilatation, and shape correlated with those of non-benign cysts and the non-surgical group. No cysts < 15 mm and without p-duct change showed a significant change within three years.

Conclusion: Small pancreatic cysts, without p-duct change, and without a pleomorphic or clubbed shape, may be followed for a longer interval than current consensus.

Key Points: • Almost all small cysts < 3 cm were indolent in long term observation. • No cysts < 15 mm, without p-duct change showed significant change within 3 years. • Cyst size, ductal change and shape can be useful in predicting progress. • Only cysts with IPMN- like features and p-duct change need follow-up with cautions.