A patient is suspected of having a cystic pancreatic mass. What is your recommended for the best abdominal imaging to make the diagnosis?
Let’s turn to a valuable study in the American Journal of Roentgenology in which both CT and MRI were tested for accuracy in characterizing cystic pancreatic lesions.
The CT examinations were performed using single detector, 4- or 16-slice multidetector CT and all were obtained following administration of intravenous contrast.
The MRI examinations were performed on a 1.5 tesla scanner using a torso phased-array coil and included in- and out-of-phase T1-weighted gradient- recalled echo, T2-weighted fast spin echo fat-saturated, T2 single-shot fast spin echo, and T2 single-shot fast spin echo fat-saturated MR cholangiography sequences.
Contrast-enhanced images were obtained at 20 to 30 seconds and subsequently at one, two, and three minutes following the start of the contrast injection.
The images were reviewed by two radiologists with subspecialty interest in abdominal imaging. Each radiologists was provided only with the demographic data of age and sex of the patient and a known cystic pancreatic mass, and was asked to record specific morphologic characteristics and extra-lesional findings.
They were also asked to provide a leading diagnosis as well as the overall likelihood of malignancy, and were given the opportunity to choose a specific histologic diagnosis.Related CME:
CT and MRI were found to be equally accurate in the overall characterization of cystic pancreatic lesions as benign or malignant.
However, the accuracy for specific diagnosis of the cystic pancreatic mass was limited. The reviewers were correct in the leading diagnosis in less than half of the lesions.
The majority of the premalignant and malignant diagnoses were mucinous cystic neoplasms. Two of 13 unilocular thin-walled cysts measuring less than 4 cm were found to be malignant, one being a mucin-producing ductal adenocarcinoma and the other a mucinous cystadenocarcinoma.
Three of 13 unilocular thin-walled cysts measuring less than 4 cm were premalignant mucinous cystadenomas. Consequently, it was evident that even morphologically benign-appearing cystic pancreatic lesions are not uncommonly malignant.
These results are useful in that they demonstrate a similar accuracy of CT and MRI abdominal imaging in characterizing cystic pancreatic masses. However, the accuracy of reaching a specific histologic diagnosis is not as favorable, since few of the morphologically benign-appearing cystic pancreatic lesions were found to be malignant.
One limitation of this study is the small sample size, likely in part to the fact that only histopathologically proven pancreatic lesions were included.
Consequently, lesions with morphologically benign characteristics, such as a microcystic mass with central stellate calcification, seen with a serous cystadenoma, which were not surgically resected or biopsied, were excluded.
Reference: Brendan C. Visser, Benjamin M. Yeh, Aliya Qayyum, Lawrence W. Way, Charles E. McCulloch, and Fergus V. Coakley. Characterization of Cystic Pancreatic Masses: Relative Accuracy of CT and MRI. AJR Sep 2007; 189: 648 – 656.
Related CME: Body Imaging: Abdominal, Thoracic and Vascular
University of California, San Francisco, Department of Radiology
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