Essay Submitted in partial fulfillment of the M.Sc. Degree in diagnostic radiology BY WALEED AHMED ABDO ALRAYIS M.B.B.Ch
Prof. Dr. Tarek Mohammed El Zayyat Dr. Amr Ahmed Mostafa
CT is the most commonly used imaging modality for the detection and preoperative staging of pancreatic tumors. 21-55% of patients were incorrectly diagnosed as having respectable tumor on CT only to be found to have un-resectable tumor at surgery ,most often, this type of misdiagnosis is due to undetected vascular invasion , small Peritoneal implants, or small hepatic metastases. MDCT facilitates the generation of multiplanar reconstructions, such as curved planar reformations, providing the potential to improve the detection and staging of pancreatic tumors
The term “pancreatic cancer” usually refers to ductal adenocarcinoma. While this entity accounts for 85% of primary pancreatic tumors, a variety of other neoplasms can arise from the range of cell types present in the normal pancreas (ducts, acini and islets).
Most patients do not develop symptoms until after the cancer has metastasized. Common presenting symptoms epigastric pain, unexplained weight loss, painless jaundice, light clay colored stool, dark urine, pruritus, and Nausea. It represents about 85% to 90% of pancreatic tumors. Ductal adenocarcinomas are mainly located in the head of the pancreas (60%), body of the pancreas (13%), tail of the pancreas (5%) and diffuse involvement (22%)
Successful imaging detection of pancreatic neoplasms is significantly improved by the use of pancreas specific examination protocols. MDCT should be used whenever possible to evaluate suspected pancreatic neoplasms because it enables large volume coverage in short imaging times. In the assessment of pancreatic tumors, there are four basic components: (a) detection of the pancreatic tumor; (b) assessment of peripancreatic arteries; (c) assessment of peripancreatic veins; (d) detection of extra pancreatic metastases (most frequently liver)
Clinical Indications Patient Preparation Radiation Dose Contrast Material Acquisition Timing and Phases of Imaging: Reconstruction and post-processing imaging modalities.
All patients suspected of pancreatic neoplasm Acute pancreatitis Chronic pancreatitis Evaluation of jaundice Severe epigastric pain Recent onset of diabetes Weight loss
Fast at least 6 hours before the examination. Spasmolytic drug to dilate duodenum and to impair peristaltic contractions of the stomach and duodenum. If spasmolytic is contraindicated the examination may be performed while the patient remains in the right lateral decubitus position.
Assures the scanner will deliver the minimum dose necessary to maintain the noise level in the images that the user finds acceptable for diagnosis. Tube current modulation software can reduce delivered dose by a factor of 30%. Patient radiation exposure decreases with increasing numbers of detector rows due to increased x-ray dose efficiency.
Oral contrast material: Critical to delineate the bowel loops adjacent to the pancreas and within the abdomen. Neutral contrast agent is preferable. Intravenous contrast material: Non-contrast enhanced studies are insufficient for detection of neoplasms, evaluation of peripancreatic vasculature or detection of distant metastases. Peak hepatic enhancement and peak pancreatic parenchymal enhancement are directly related to the injection rate. Peak hepatic enhancement and peak pancreatic parenchymal enhancement are directly related to the injection rate.
A challenge of pancreatic imaging is that the timing of peak pancreatic enhancement differs from that of other organs in the abdomen, most notably the liver. Most radiologists employ a dual-phase protocol which incorporates a pancreatic parenchymal phase and a portal venous (hepatic parenchymal) phase A single-phase acquisition can be obtained with a 4- detector row scanner if careful scan timing is used.
Scan timing can be determined with two methods: A. Automatic pumping B. Bolus tracking technique
Other concept in pancreatic imaging says that contrast-enhanced imaging of the pancreas is performed in three distinct phases: The early arterial phase Delayed arterial phase or the pancreatic phase Portal venous phase.
Current criteria for resectability include Absence of distant metastases. Lack of evidence of tumor involvement of major arteries. If there is venous invasion suitable segment of portal vein (above) and superior mesenteric vein (below) the site of venous involvement to allow for venous reconstruction.
Category Description CommentGrade 0 No contiguity of tumor with a vessel Vascular invasion in 0% of casesGrade 1 Tumor contiguous with <25% of the Vascular invasion in 0% of circumference of a vessel casesGrade 2 Tumor contiguous with 25–50% of the Vascular invasion in 57% of circumference of a vessel casesGrade 3 Tumor contiguous with 50–75% of the Vascular invasion in 88% of circumference of a vessel casesGrade 4 Tumor contiguous with >75% of the Vascular invasion in all cases circumference of a vessel or any vessel constriction
Category Description CommentType A Fat plane separates the tumor Overall resection rate: 100%. Resection rate and/or the normal pancreatic without venous resection: 95%. Conclusion: parenchyma from adjacent ‘‘Lesions with type A and B appearances are vessels likely to be resectable lesions’’Type B Normal parenchyma separates Overall resection rate: 100%. Resection rate the hypo dense tumor from without venous resection: 95%. Conclusion: adjacent vessels ‘‘Lesions with type A and B appearances are likely to be resectable lesions’’Type C Hypo dense tumor is Overall resection rate: 89%. Resection rate inseparable from adjacent without venous resection: 55%. Conclusion: vessels, and the points of ‘‘Lesions of type C vascular involvement contact form a convexity should be operated on with an intention to against the vessels resect the tumor, but the tumor may or may not adhere to the wall of the vessels’’Type D Hypo dense tumor is Overall resection rate: 47%. Resection rate inseparable from adjacent without venous resection: 7%. Conclusion: vessels, and the points of ‘‘Lesions of type D vascular involvement contact form a concavity would require pancreatic resection with a plan against the vessels or partially to perform venous resection and venous graft encircle the vessels or patch or would be unresectable for surgeons who do not have that appearance’Type E Hypo dense tumor encircles Overall resection rate: 0%. Resection rate adjacent vessels, and no fat with outvenous resection: 0%. Conclusion: plane is identified between the ‘‘Lesions of the type E and F vascular tumor and the vessels involvement are not likely to be resectable’’Type F Tumor occludes the vessels Overall resection rate: 0%. Resection rate without venous resection: 0%. Conclusion: ‘‘Lesions of the type E and F vascular involvement are not likely to be resectable’’
Category Description CommentGrade 0 Normal, with a fat plane or 100% resectable normal pancreas between the tumor and the vesselGrade 1 Loss of fat plane between the 100% resectable tumor and the vessel, with or without smooth displacement of the vesselGrade 2 Flattening or slight irregularity 92 % resectable of one side of the vesselGrade 3 Encased vessel with tumor The recommended threshold for extending around at least two predicting vascular invasion. In this sides (two-thirds of the study, resection was performed in1 of perimeter), altering its contour 10 patients with grade 3 findings, but and producing concentric or tumor along per vascular neural eccentric narrowing of the bundles was present at resection lumen margins.Grade 4 Occluded vessel No attempted surgery
Assessment of vascular invasion is an important parameter for determining resectability of pancreatic cancer. The introduction of MDCT and real-time 3D volume- rendering software has greatly improved the visualization of the pancreas and adjacent vasculature. An examination protocol should provide maximal differentiation between normal and abnormal tissue. From the point of view of the detection of vascular invasion, many studies have evaluated CT.
In a study by Wen Yi Zhao et al, The pooled sensitivity and specificity of CT in diagnosing vascular invasion were 77% and 81%. Since CT technology improved in different periods, in the recent five years (2004-2008) CT has shown a higher diagnostic accuracy, and the pooled sensitivity and specificity increased to 85% and 82%, respectively. Subgroup analysis of CT studies was made to determine the involvement of different vessels, and the pooled sensitivities for the invasion of the venous system, portal vein, and arterial system were 75%, 75%, and 68%, and the pooled specificities were 84%, 91%, and 92%, respectively. For CT imaging with vascular reconstruction, the pooled sensitivity and specificity were 84% and 85%, higher than the estimates in studies without reconstruction.
Thin-sections MDCT is an accurate technique for the diagnosis and assessment of the resectability in patient with a suspected pancreatic neoplasm. The advantages of multidetector volumetric CT allow comprehensive preoperative assessment of pancreatic carcinoma. Carefully- timed scan acquisition maximizes the difference in attenuation between the neoplasm and the pancreatic parenchyma and allows accurate staging as well as assessment of local resectability
In conclusion the MDCT technique remains the first-line imaging modality in the evaluation of the majority of patients with suspected pancreatic disease because of low cost, greater widely used and easy technical approaches and its great value in staging pancreatic masses and predicting vascular invasion which helps in choosing the appropriate management for each case.