Transabdominal Ultrasound for Follow-Up of Incidentally Detected Low-Risk Pancreatic Cysts: A Prospective Multicenter Study

OBJECTIVE. The purpose of this study is to investigate the detection rate of transabdominal ultrasound (TAUS) for pancreatic cysts incidentally detected on CT or MRI as well as the factors that influence detection rates. SUBJECTS AND METHODS. Fifty-seven patients with low-risk pancreatic cysts (n = 77; cyst size, 5 mm to 3 cm) that were incidentally detected on CT or MRI were prospectively enrolled at five institutions. At each institution, TAUS was independently performed by two radiologists who assessed detection of cysts, cyst location and size, and the diameter of the main pancreatic duct (MPD). Cyst detection rates based on cyst size, location, and multiplicity and the body mass index of the patient were compared using the Mann-Whitney test. Kappa statistics and the interclass correlation coefficient were used to evaluate interobserver agreement regarding cyst detection and consistency of cyst size and the diameter of the MPD on TAUS versus prior CT or MRI. RESULTS. The detection rate for known low-risk pancreatic cysts was 81.8% (63/77) and 83.1% (64/77) for TAUS conducted by each of the two radiologists. The detection rate for larger (≥ 10 mm) cysts was significantly higher than that for smaller cysts (89.0% vs 63.6% for TAUS performed and interpreted by radiologist 1 [TAUS 1] and 89.0% vs 68.2% for TAUS conducted and interpreted by radiologist 2 [TAUS 2]; p < .05). A higher detection rate was noted for cysts located outside the tail of the pancreas compared with those located in the tail (89.5% vs 65.0% for TAUS 2; p = .01), and the detection rate was also significantly higher for single cysts than for multiple cysts (90.9% vs 69.7% for TAUS 1; p = .02). However, no significant difference was observed for body mass index. Interobserver agreement was excellent regarding the size of the detected cysts (inter-class correlation coefficient: 0.964 [95% CI, 0.940-0.979] for CT, TAUS 1, and TAUS 2 and 0.965 [95% CI. 0.924-986] for MRI, TAUS 1, and TAUS 2) and the diameter of the MPD (interclass correlation coefficient, 0.934; 95% CI, 0.898-0.959). CONCLUSION. TAUS could be a useful alternative imaging tool for surveillance of known low-risk pancreatic cysts, especially single pancreatic cysts and those that are of larger size (≥ 1 cm) or are located outside the tail.