Incidental, Small (< 3 cm), Unilocular, Pancreatic Cysts: Factors That Predict Lesion Progression during Imaging Surveillance

Abstract

Objective: To explore the features that predict size increase and development of potential malignant features in incidentally detected, unilocular cystic pancreatic lesions (CPLs) less than 3 cm in diameter, during subsequent follow-up.

Materials and methods: We retrieved data of patients diagnosed with unilocular CPLs less than 3 cm in diameter during the period from November 2003 through December 2014, using a computerized search. All serial CT and MR images were analyzed to identify the number, size, and location of CPLs; dilatation of the main pancreatic duct; and occurrence of worrisome features and high-risk stigmata of malignancy in the lesion. The characteristics of CPLs were compared between the increase (i.e., size increase during subsequent follow-up) and no-increase groups. For CPLs in the increase group, subgroup analysis was performed according to the lesion size at the last follow-up (< 3 cm vs. ≥ 3 cm).

Results: Among 553 eligible patients, 132 (23.9%) had CPLs that increased in size, and 421 (76.1%) had CPLs that did not, during follow-up. Of the 132, 12 (9.1%) CPLs increased to diameters ≥ 3 cm at the final follow-up. Among the various factors, follow-up duration was a significant independent factor for an interval size increase of CPLs (p < 0.001). In the increase group, initial cyst size was a significant independent factor to predict later size increase to or beyond 3 cm in diameter (p < 0.001), and the initial cyst diameter ≥ 1.5 cm predicted such a growth with a sensitivity and specificity of 83% and 72%, respectively. No significant factors to predict the development of potential malignant features were identified.

Conclusion: Follow-up duration was associated with an interval size increase of CPLs. Among the growing CPLs, initial cyst size was associated with future lesion growth to and beyond 3 cm.

Keywords: Cancer; Cyst; Follow-up; Pancreas; Prediction; Predictor; Risk factor; Surveillance.

Fig. 1. Flowchart showing selection process for patients enrolled in this study.

Fig. 2. 68-year-old female with pathologically confirmed MCN with low-grade dysplasia.

A. Initial CT image shows 1.4 cm incidental unilocular CPL (arrow) in body of pancreas. B. Lesion (arrow) shows interval increase in size up to 2.2 cm on follow-up CT image obtained 11 months later. MCN = mucinous cystic neoplasm

Fig. 3. 71-year-old male with pathologically confirmed IPMN with low-grade dysplasia.

A. Initial CT image shows 1.6 cm unilocular CPL (arrow), which was incidentally detected. B. Follow-up CT image obtained 6 months later demonstrates no interval change of pancreatic cyst (arrow). C. Follow-up CT image obtained 12 months later reveals interval increase in size of CPL up to 3.2 cm (arrow). CPL = cystic pancreatic lesion, IPMN = intraductal papillary mucinous neoplasm

Fig. 4. 70-year-old male with pathologically confirmed ductal adenocarcinoma.

A. Initial CT image shows 0.4 cm unilocular cyst (arrowhead) in tail of pancreas. B. Follow-up CT image obtained 3 years later reveals newly developed, ill-defined low attenuated mass (arrow) in location of original cyst. C, D. MR images demonstrate no interval change of original cyst (arrowhead). Note that cyst (arrowhead) is located in vicinity of solid pancreatic mass (arrow).