MATERIALS AND METHODS
Undetermined pancreatic cystic lesions detected by any examination were prospectively evaluated for possible study enrollment. The inclusion criteria were as follows: 1) being at least 18 years old; 2) undergoing CEUS examination; 3) undergoing CT or MRI examination; and 4) surgicaopathologically diagnosed with PCNs. The exclusion criteria were as follows: patient with acute pancreatitis; patient being allergic to the intravenous contrast agent; patient with pseudocyst, which is highly suspected clinically.
The ultrasound instrument was Sequoia 512 (Siemens Ultrasound, Mountain View, CA, USA); the probe frequency was 1–4 MHz; and the mechanical index was lower than 0.12. SonoVue (Bracco, Milan, Italy), the contrast agent, was dissolved in 5 mL saline, and a bolus of 2.4 mL of this solution was injected into the antecubital vein quickly, followed by a 5 mL saline flush. A GE Lightspeed 64-slice spiral CT scan or Siemens SOMATOM Sensation 64-Slice CT scanner was applied with a slice thickness of 5 mm. Plain CT was followed by contrast-enhanced CT with nonionic iodinated contrast material. Philips Achieva 1.5 T machine or GE3.0T machine was applied for MRI examination. Postgadolinium contrast-enhanced images were obtained in all cases.
There were several reference standards for our study. 1) The location of the lesion was categorized into 2 groups: head and body/tail location, and the superior mesenteric vessels were the dividing landmark, whose right part defined as the head portion of the pancreas encompassed the uncinate, head, and neck portion; and the left aspect included body and tail. 2) For tumor size, the cross-section plane and coronal section plane on CT or MRI both need to be measured, and the larger dimension was selected as the size of the cyst. Otherwise, CEUS was conducted through various planes, and the longest one was selected as its size. 3) When the widest part of the pancreatic duct was more than 3 mm, it was defined as duct dilatation. 4) Regular shape was defined when the lesion was approximately round or oval, and the rest were irregular. 5) A septum was identified as a fibrous structure that started from the wall and ended at the other side, and a nodule was identified as a solid component from the wall protruding into the inner cyst.
Patient who was suspected of having pancreatic cystic neoplasm was recommended to undergo CEUS, CT, and MRI. CT and MRI images were individually read by radiologists who had more than 10 years of experience and were aware of our study design. US and CEUS were performed by two ultrasound physicians who were blinded to the CT and MRI results—one with more than 20 years and the other with more than 10 years of experience with CEUS diagnoses.
ALL patients underwent CEUS, most patients (n = 85) underwent MRI, and 69 patients performed CT. A total of 53 patients underwent both CT and MRI. Once all of the confirmed PCNs were enrolled, the sensitivity and accuracy of CEUS, MRI and CT in diagnosing the cysts were assessed. When the lesion was diagnosed as “cyst lesion” or “cyst-solid lesion”, it would be categorized as an undetermined PCL; when the lesion was diagnosed with “cystadenoma” or “cyst tumor”, it would be categorized as an unclassified PCN.
All statistics were analyzed using the SPSS 17.0 software package (SPSS, Chicago, IL). The Pearson chi-square test, Fisher’s exact test and continuity correction were applied to compare the differences in numbers between two groups. Quantitative data are expressed as the mean or median; differences were tested using a nonparametric test or a t-test. A two-tailed P-value of less than 0.05 was considered statistically significant.
From April 2015 to July 2019, 96 patients were evaluated for the presence of PCLs, and 90 patients (66 women, 24 men; mean age 42.6±13.3 years; 18–71 years) who were pathologically diagnosed with PCNs were enrolled. The other six PCLs included 2 pseudocysts, 2 retention cysts, 1 epidermoid cyst and 1 lymphoepithelial cyst. Among the 90 enrolled patients, 36 patients had SCAs, 29 had MCAs, 11 had IPMNs, 8 had SPNs, 3 had NENs, and 3 had cystadenocarcinomas. Ten patients were examined because of abdominal pain, 12 were detected due to abdominal distension, and 68 had no symptoms. The cysts were detected in the head location in 35 patients and in the body–tail location in 52 patients. Two patients had diffuse involvement of IPMNs, and one had multiple cysts. Cyst size was assessed by CEUS for 90 cysts, 85 by MRI and 69 by CT. One patient had multiple cysts, and only the largest cyst was assessed using both MRI and CEUS. The mean size was 4.6 cm (1.6–13 cm; 2.5 cm) by CEUS, 4.1 cm (1.2–13.5 cm; 2.9 cm) by MRI, and 4.9 cm (2.3–10.7 cm; 2.1 cm) by CT. There was no statistically significant difference in the assessment of cyst size using these three imaging techniques (Table 1).
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