Hamid Chalian MD, Presenter: Grant, Siemens AG

Huseyin Gurkan Tore MD, Abstract Co-Author: Research grant, Siemens AG

Vahid Yaghmai MD, Abstract Co-Author: Nothing to Disclose

Currently an increase of 10 Hounsfield units (HU) at MDCT is considered enhancing tissue. The purpose of our study was to assess the contribution of pseudoenhancement to changes in attenuation of pancreatic masses after administration of contrast on MDCT.

This HIPAA compliant retrospective study was IRB approved. Pancreatic cysts were used as a model for nonenhancing masses. Fifty-four pathologically proven pancreatic cysts (25 pseudocyst, 20 mucinous cystic neoplasms and 9 intraductal papillary mucinous neoplasm) in 52 patients with thriphasic MDCT of pancreas were included. All lesions were more than 10 mm without septa, adjacent calcification or stent artifact. Lesion attenuation was measured on nonenhanced and pancreatic parenchymal phase with a centrally placed ROI, covering as much area of the cyst on axial plane as possible. Care was taken to avoid the cyst wall. ROI area was kept constant on different enhancement phases. The neighboring pancreatic parenchyma was used as a model of enhancing pancreatic mass. Parenchyma attenuation was also obtained by a constant ROI over different phases. Longest axial diameter was measured on pancreatic parenchymal phase. Paired t-test was used to compare the attenuation over two phases. ROC curve analysis was performed by using the parenchyma and cyst attenuation increase over two phases to define the most accurate cut-point for enhancement of viable tumors.

Mean cyst size was 35±18 mm. Cyst attenuation increased from nonenhanced: (10.9±8.3HU) to pancreatic parenchymal phase (15.5±9.0HU) as the background attenuation increased from nonenhanced (39.7±10.3HU) to pancreatic parenchymal (113.2±30.0HU) phase. Cyst attenuation was significantly different between 2 MDCT phases (p<0.001). Pseudoenhancement was found in 6 (11%) cysts. 18.6 HU was found to be the most sensitive (98%) and specific (98%) cut-point for enhancement.

In general, cyst attenuation increases about 4.5HU for 70HU increase in background attenuation. 11% of pancreatic cysts enhanced more than 10HU. 18.6HU may be a better cut-point for the definition of enhancement within pancreatic masses.

Understanding the contribution of pseudoenhancement to changes in attenuation of pancreatic masses after administration of contrast helps to assess viability of pancreatic tumors more accurately.

Chalian, H, Tore, H, Yaghmai, V, Pseudoenhancement at MDCT: Implications on Characterization of Pancreatic Masses.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11012460.html