Diagnostic Imaging

•  CT scanning: Abdominal CT scans are typically used in confirming the presence of pancreatic cancer. An important early issue is whether or not the tumor may be resectable. A key issue with respect to resectability is possible involvement of significant vascular structures as well as possible presence of hepatic metastases. Contemporary multiphase CT scanning, utilizing IV contrast followed by rapid thin cut CT imaging of the pancreas during the time of vascular and parenchymal contrast enhancement. Multidetector row helical CT scanning permits data acquisition during a single breath-hold for each phase.⁹

  • Recall that the purpose of the diagnostic CT procedure should include resolution of the following issues:

    1. (1) Determination of the presence or absence of a pancreatic tumor or tumor in the periampullary region. The periampullary region is the ampulla of Vater, the enlargement of the liver and pancreatic ducts where they converge and enter the small intestine. Periampullary cancer refers to a cancer in this region.²⁶

       1. Ampullary tumor with pancreatic invasion³⁰

          This single-section in vivo MR cholangiopancreatographic image illustrates at the arrow a filling defect at the distal end of the common bile duct and main pancreatic duct.30

    2. (2) Determination of the presence or absence of hepatic and peritoneal metastatic disease.²⁶

    3. (3) Determination of the relationship between critical venous systems and the tumor; of specific interest is the superior mesenteric vein and portal vein.²⁶

    4. (4)  Determination of the relationship between critical arterial systems and the tumor; of specific interest in this case are the superior mesenteric artery, celiac axis, and hepatic artery.²⁶ 

  • CT imaging studies should precede both biopsy and, if needed, stent placement since these procedures can, in the case of biopsy, cause inflammation and the stent can complicate image interpretation.⁹

    • The likelihood of tumor resectability can be analyzed by multiphase CT scanning as well as by other imaging modalities. With respect to CT scanning, tumor resectability is dependent on the absence of metastatic disease outside the pancreas, including the pancreatic nodal basin. Patency of the superior mesenteric vein and portal vein is also a requirement as is the presence of a clear fat plane between the superior mesenteric artery, celiac artery and the pancreatic tumor mass.⁹

    • Invasion by tumor of the superior mesenteric vein-portal vein may be a condition defining unresectable state; however, approaches with surgical resection of the superior mesenteric vein-portal vein with associated reconstruction are present at some institutions. In those cases in which the superior mesenteric vein-portal vein structures are compromised by tumor invasion, suggested by an absence of the fat plane between the pancreatic tumor and the right lateral margin of the vein, vein reconstruction during tumor resection surgery would be required.⁹

    • A classification system relating vascular CT findings and pancreatic tumor resectability has been described:

    • Classification of Vascular Involvement on CT³¹

      Type

      Criteria

      Significance

      A	Tumor is separated by an intact fat plane from adjacent vessels.	The tumor is likely resectable without venous resection in about 95% of patients
      B	Tumor separated by normal pancreatic parenchyma from adjacent vessels.	The tumor is likely resectable without venous resection in about 95% of patients
      C	Hypodense tumor exhibits a convex contact point with an adjacent vessel.	Tumor involvement with the vessel can not be reliably predicted.
      D	Hypodense tumor exhibits a concave contact point with or partially encircles the adjacent vessel.	Partial resection of vessel is required for potential tumor removal.
      E	Hypodense tumor completely encircles the adjacent vessel.	"Not possible to resect tumor with negative margin."
      F	Tumor occludes adjacent vessel.	"Not possible to resect tumor with negative margin."

    • Given the importance of vascular integrity with respect to possible tumor invasion, techniques, in addition to multiphase CT scanning may improve identification of pancreatic tumor invasion of local vasculature. Some techniques thus far assessed include CT angiography as well as curved image reformation derived from CT data.⁹

      • Helical CT imaging combined with CT angiography were utilized in identification of vascular invasion associated with periampullary pancreatic cancer. The combination of helical CT and CT angiography resulted in an accuracy level for identification of venous invasion of about 92%, an accuracy which can be contrasted to 69% when imaging was limited to transverse CT scan data. This difference was not  observed in the assessment of arterial invasion, with both techniques yielding an accuracy of about 86%.³²

      • Multidetector row CT technology allows near arbitrary sectioning through the data sets while preserving image quality. Therefore, in addition to axial, sagittal, and coronal cross-sectional images, customized or curved reformations of the CT data volume could potentially allow enhanced appreciation of complex anatomy. One study utilizing contrast-enhanced multi-detector CT scans with curved planer reformations assessed the utility of this method in characterizing pancreatic tumors with respect to vascular involvement and resectability. Image data reformations were developed along the pancreatic duct, common bile duct, and major mesenteric vasculature. At least in this study, although interpretation time was cut by half by viewing curved planer reformatted images, these curved  reformations were found equivalent to transverse images with respect to conclusions about tumor resectability.³³

      •  Helical CT imaging is considered poor for predicting nodal involvement with further reduced accuracy subsequent to neoadjuvant treatment.⁹  

    • Drawings of the pancreas, pancreatic tumor, and relevant, localized vasculature along with corresponding CT images are available in the scientific paper "Diagnosis, Staging, and Surveillance of Pancreatic Cancer",³⁴ available online.

    • At the M.D. Anderson Cancer Center, radiographic criteria for identifying the potentially resectable, primary pancreatic tumor have been delineated. These factors include (1) an absence of extrapancreatic disease, (2) a patent (open) superior mesenteric vein and portal vein [the authors note the assumption of surgical ability to resect and reconstruct the venous confluence and (3) a clear tissue plane between the tumor and local arterial anatomy including the celiac axis and superior mesenteric artery. CT staging and other factors used in assessment of tumor resectability can result in resectability rates in the range of 75% to 80%. Comparison is made between assessment of tumors as resectable based on CT imaging and findings during surgery. Accuracy (%) represents the ratio of actually resectable tumors compared to resectable tumors identified by CT imaging prior to surgery.²⁶ At M.D. Anderson a chest CT is not part of staging workup (as reported in ref. 26, 2006); however, if chest x-rays or CT images of the lung bases suggest pulmonary nodules or other potentially concerning findings, a CT chest imaging study would be obtained. These authors suggest that bone scans and brain imaging are typically not part of routine staging examinations.²⁶

      • For an M.D. Anderson study, the accuracy was 80.0% (118/94); that is, 118 patients were identified with resectable tumors using CT imaging; 94 patients exhibited tumors that were actually resectable at operation.⁹

      • A Beth Israel Deaconess study reported an accuracy of 76.0% (68/52).⁹

      • A Barcelona, Spain study indicated an accuracy of 64.1% (39/25).⁹

      • A Liverpool, UK study reported an accuracy of 80.0% (35/28).⁹  

•  Magnetic Residence Imaging (MRI) may exhibit both sensitivity and specificity comparable to that observed with CT for pancreatic cancer assessment. Generally, MRI is not in widespread use for radiological evaluation of pancreatic cancer. However, advances in MR imaging including development of phased-array multicoils, enhanced gradients, and techniques that reduce motion artifacts permit pancreatic imaging with both excellent contrast along with reduced examination time. Additionally, pancreatic anatomical evaluation can be assisted by the use of MR pancreatography (MRP), allowing examination of the pancreatic ductal system; in addition, MR angiography (MRA) allows visualization of peripancreatic vasculature.³⁵

  • MRI evaluation of pancreatic lesions optimally involve multiple pulse sequences, providing complementary information. A combination of T1-weighted and T2-weighted sequences would be obtained. For T1 weighted imaging, a breath-hold T1 weighted spoiled gradient reversal allows a short echo time (TE), which in turn permits faster acquisition. In this case, the flip angle should be at least 70° which allows adequate T1 contrast. The most common pancreatic diseases such as pancreatitis and pancreatic adenocarcinoma exhibit longer T1 due to increased free water protons and exhibit lower signal intensity relative to normal pancreatic tissue. Fat-suppressed T1 weighted images may be best for identification of pancreatic tumors and separation of the pancreas from surrounding fat.

  • Pancreatic Adenocarcinoma³⁵

    "On a pancreatic-phase post-gadolinium T1 weighted fat-suppressed MR image, it (the tumor) is clearly separated from normal enhancing pancreatic tissue (arrow)." 35

  • For detailed characterization of MR parameters appropriate for various imaging approaches for assessment of pancreatic tumors, pancreatitis, and peripancreatic vasculature, the reader is directed to reference 35.

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