Update in imaging of cystic pancreatic masses for gastroenterologists

Preoperative contrast-enhanced computed tomographic characterisation of pancreatic cystic lesions: A prospective study

Background

Characterisation of pancreatic cystic lesions has a direct role in their management and computed tomography is the mainstay of investigation for diagnosing and characterising them.

Objectives

The aim of this study was to prospectively assess the diagnostic accuracy of contrast-enhanced computed tomography (CECT) in preoperative characterisation of pancreatic cystic lesions with histopathology as the reference standard.

Method

A total of 38 patients with cystic pancreatic lesions diagnosed after clinical, laboratory and sonographic evaluation, irrespective of age, were preoperatively evaluated with CECT. Images were reviewed for the general characteristics of the lesions on pre-contrast and portal venous phase images and overall diagnostic accuracy calculated. Imaging findings were compared with histopathology, or cytology and/or intra-operative findings.

Results

Serous cystadenoma (SCA) was the most common cystic pancreatic lesion found in 31.6% of patients followed by mucinous cystadenoma (MCA) (26.3%), solid pseudo-papillary tumour (SPT) (21.1%) and intra-ductal papillary mucinous neoplasm (IPMN) (10.5%). Three patients (7.9%) had simple cysts and one patient (2.6%) had a lymphangioma. The diagnostic accuracy of CECT for pancreatic cystic lesions was found to be 72.5.

Conclusion

The diagnostic accuracy of computed tomography (CT) was high for SCA, IPMN and pancreatic cysts, and low for MCA and SPT. Combination of a multiloculated cystic lesion with locule size of less than 20 mm, septal enhancement with relative lack of wall enhancement, central scar and lobulated outline are highly specific for SCA. Unilocular or macro-cystic pattern with locule size of more than 20 mm, female gender and wall enhancement with smooth external contour are pointers towards MCA. Solid cystic pancreatic head lesions in young females may be suggestive of SPT. A dilated main pancreatic duct in a cystic lesion with internal septations may point towards IPMN. Fluid attenuation lesions with imperceptible non-enhancing wall indicate pancreatic cysts. Lastly, pseudocysts and neuroendocrine tumours with cystic components are great mimickers of pancreatic cystic lesions, and a history of pancreatitis and hormonal profile of patients should always be sought.

Mutant proteins as cancer-specific biomarkers

Cancer biomarkers are currently the subject of intense research because of their potential utility for diagnosis, prognosis, and targeted therapy. In theory, the gene products resulting from somatic mutations are the ultimate protein biomarkers, being not simply associated with tumors but actually responsible for tumorigenesis. We show here that the altered protein products resulting from somatic mutations can be identified directly and quantified by mass spectrometry. The peptides expressed from normal and mutant alleles were detected by selected reaction monitoring (SRM) of their product ions using a triple-quadrupole mass spectrometer. As a prototypical example of this approach, we demonstrated that it is possible to quantify the number and fraction of mutant Ras protein present in cancer cell lines. There were an average of 1.3 million molecules of Ras protein per cell, and the ratio of mutant to normal Ras proteins ranged from 0.49 to 5.6. Similarly, we found that mutant Ras proteins could be detected and quantified in clinical specimens such as colorectal and pancreatic tumor tissues as well as in premalignant pancreatic cyst fluids. In addition to answering basic questions about the relative levels of genetically abnormal proteins in tumors, this approach could prove useful for diagnostic applications.

Relative accuracy of CT and MRI in the differentiation of benign from malignant pancreatic cystic lesions

AIMS

To assess the diagnostic accuracies of multidetector computed tomography (MDCT) and magnetic resonance imaging (MRI) for differentiating benign from malignant lesions and suggesting the specific diagnoses for pancreatic cystic lesions, and to assess whether review of both MDCT and MRI is beneficial.

MATERIALS AND METHODS

Patients with various neoplastic and non-neoplastic pancreatic cystic lesions that were identifiable by biopsy or surgery, who underwent both MRI and MDCT (n=63), were retrospectively reviewed by three reviewers. The likelihood of malignancy was recorded on a five-point scale, and a specific diagnosis was given. ROC analysis was performed and the sensitivity, specificity for the characterization of malignancy, and the accuracy of specific diagnoses were calculated.

RESULTS

MDCT and MRI yielded comparable results for the characterization of malignancy (Az: 0.639, 0.735, 0.806 for MDCT and 0.732, 0.753, 0.792 for MRI, for each reviewer). The accuracies of specific diagnosis based on MDCT or MRI were 61.9 versus 55.6% for reviewer 1; 76.2 versus 76.2% for reviewer 2; and 65.1 versus 61.9% for reviewer 3. There was a trend toward better prediction of malignancy (Az: 0.787, 0.745, 0.849 for each reviewer), and better accuracy in suggesting a specific diagnosis (77.8, 73, and 73% for each reviewer) for MDCT+MRI over MDCT or MRI alone, although it was statistically significant for one reviewer in the comparison of MDCT versus MDCT+MRI for the prediction of malignancy, and MRI versus MDCT for suggesting a specific diagnosis.

CONCLUSIONS

MDCT and MRI have equivalent accuracy for characterizing pancreatic cystic lesions as benign or malignant, and suggesting a specific diagnosis. Combined review of MDCT and MRI was not significantly better but may have the potential to improve diagnostic accuracy in equivocal cases.