Margin status following pancreaticoduodenectomy for pancreatic adenocarcinoma: Implications of R status

Margin assessment is necessary to determine the adequacy of resection following pancreaticoduodenectomy. Numerous studies have reported that a positive margin of resection is an independent predictor of poor long-term survival following pancreaticoduodenectomy for pancreatic adenocarcinoma [1-10]. However, most of these studies did not describe the system or technique used for the pathologic evaluation of surgical specimens and, therefore, margin analysis, and did not distinguish margins that were grossly positive from those that were microscopically positive. For studies in which survival duration is an endpoint of analysis, and for all prospective clinical trials, the margin status of resected specimens must be determined. All pancreatic resections should be classified according to residual disease status (termed "R" factor): R0, no gross or microscopic residual disease; R1, microscopic residual disease (microscopically positive surgical margins with no gross residual disease); and R2, grossly evident residual disease [11]. The surgical margins for pancreaticoduodenectomy specimens routinely evaluated by histology include the pancreatic transection margin, the common bile duct (or hepatic duct) transection margin, the gastrointestinal transection margins, and the soft-tissue margin adjacent to the proximal superior mesenteric artery (SMA). We refer to the mesenteric soft tissue and perineural tissue to the right of the proximal 3-4 cm of the SMA as the SMA margin; some refer to this as the retroperitoneal, mesenteric, or uncinate margin (Fig. 54.1) [12]. While the pancreatic and bile duct margins may be re-resected if the intraoperative frozen section analysis suggests a positive margin, the SMA margin cannot be re-resected because in general, surgeons do not resect the SMA for adenocarcinoma. Therefore, the most common margin found to be positive after pancreaticoduodenectomy is the SMA margin [13, 14]. A microscopically positive SMA margin is usually due to perineural and lymphatic invasion along the autonomic plexus surrounding the SMA and celiac axis, and for that reason, R1 resections may occur (and be unavoidable) in up to 10-20% of patients following a grossly negative tumor resection. However, most R2 resections can be avoided by accurate interpretation of the preoperative computed tomography (CT) images. The pathologist cannot usually differentiate an R1 (microscopically positive) from an R2 (grossly positive) SMA margin in the absence of information regarding the retroperitoneal dissection, which should be included in the operative dictation. The R designation should always be listed in the dictated operative report by having the surgeon wait to sign-off on the operative report until the pathology report is available for review and therefore the status of the SMA margin determined. For example, if the surgeon states that gross tumor was encountered when completing the SMA dissection, a positive histologic margin should result in the R2 designation in the operative report and the medical record. If the surgeon states (in the operative report) that there was no gross evidence of tumor extension to the SMA margin, then a positive histologic margin should result in the R1 designation in the operative report and the medical record.