Tara M. Breslin, Nora A. Janjan, Jeffrey E. Lee, Peter W. T. Pisters, Robert A. Wolff, James L. Abbruzzese, Douglas B. Evans

Pancreatic Tumor Study Group: Departments of Surgical Oncology (TMB, JEL, PWTP, DBE), Radiation Oncology (NAJ), and Gastrointestinal Oncology and Digestive Diseases (RAW, JLA), The University of Texas M. D. Anderson Cancer Center, Houston, TX

Received 6/4/98 Accepted 5/5/98

3. PRETREATMENT RADIOGRAPHIC STAGING

Stringent pretreatment staging to exclude patients with locally advanced (unresectable) or metastatic disease is critical to allow accurate interpretation of results from studies examining the value of multimodality therapy in patients with pancreatic cancer. In order to determine the extent of local-regional disease and screen for the presence of extrapancreatic metastases, patients should receive a careful physical exam, chest roentgenography, and abdominal computed tomography (CT) scan. High-quality contrast-enhanced CT is used to define the relationship of the tumor to the celiac axis and superior mesenteric vessels (12). At MDACC, we generally use helical CT in the evaluation of patients with presumed pancreatic neoplasms. The development of helical or spiral scanning has improved scan speed; the continuous rotation of the x-ray

tube around the gantry allows the entire pancreas to be imaged during the bolus phase of contrast enhancement. In addition, scan data can be processed to display images in three-dimensional and multiplanar formats. Dilute Gastrografin or 2% barium sulfate is used to opacify the stomach and small bowel before scanning. Water can be used as an oral contrast agent when it is necessary to evaluate the gastric wall or duodenum. Precontrast CT of the liver and pancreas is performed at 10-mm slice thickness to localize the pancreas. Nonionic contrast material (300 mg/dl) is then delivered intravenously by an automatic injector at a rate of 2 to 3 ml/second for a total of 150 ml. Helical CT of the pancreas is performed 60 to 70 seconds after the start of the injection. A dynamic series of scans through the pancreas is completed at 3-mm slice thickness with a pitch factor of 1.5 to 2.0, depending on the anatomic extent of the tumor. The slice thickness can be increased to 5-mm in a large patient. The rest of the abdomen is then scanned at 7-mm slice thickness.

In the absence of extrapancreatic disease, the relationship of the low-density tumor mass to the superior mesenteric artery (SMA) and celiac axis is the main focus of preoperative imaging studies. In assessing resectability, the goal is to accurately predict the likelihood of obtaining a negative retroperitoneal margin of resection. Anatomically, the retroperitoneal margin corresponds to the tissue along the proximal 3-4 cm of the SMA as shown in figure 1. The CT criteria used at MDACC to define potentially resectable disease includes: 1) the absence of extrapancreatic disease, 2) the absence of direct tumor extension to the SMA and celiac axis as defined by the presence of a fat plane between the low-density tumor and these arterial structures, and 3) a patent superior mesenteric-portal vein (SMPV) confluence (figure 2). The accuracy of this form of radiographic staging is demonstrated by a recent report by Spitz and colleagues from MDACC demonstrating a resectability rate of 80% (94/118) and a low rate of microscopic retroperitoneal margin positivity (17%) in patients with adenocarcinoma of the pancreatic head or uncinate process in patients who meet this radiographic criteria (9). The accuracy of CT in predicting unresectability and the inaccuracy of intraoperative assessment of resectability are both well established.

Figure 1. Illustration of the final step in resection of the specimen. Medial retraction of the superior mesenteric-portal vein confluence facilitates dissection of the soft tissue adjacent to the lateral wall of the proximal superior mesenteric artery (SMA). The retroperitoneal margin is defined as the soft tissue margin directly adjacent to the proximal 3- 4-cm of the SMA. This margin is identified by the surgeon immediately upon specimen removal and evaluated by the surgeon and pathologist (in the adjoining pathology suite) by microscopic examination of a 2-3- mm full-face (en-face) section of the margin. The inferior pancreaticoduodenal artery is identified at its origin from the SMA, ligated, and divided. PV, portal vein; SMV, superior mesenteric vein.

Figure 2. Contrast-enhanced CT scan demonstrating a resectable adenocarcinoma of the pancreatic head (T). Note the normal fat plane between the tumor and both the superior mesenteric artery (large arrow) and the superior mesenteric vein (arrowhead). The intrapancreatic portion of the common bile duct contains a stent (small arrow), which was endoscopically placed for biliary drainage.