Drs. Levy and Wiersema have provided an authoritative review of the role of endoscopic ultrasonography in the diagnosis and staging of pancreatic cancer. As outlined in their article, endoscopic ultrasound has emerged as an important tool in the diagnostic evaluation of many patients with suspected pancreatic neoplasms. We concur that endoscopic ultrasound is part of the standard preoperative evaluation of patients with biochemically confirmed insulinoma and gastrinoma syndromes and of at-risk patients with multiple endocrine neoplasia type 1. Endoscopic ultrasound and endoscopic ultrasound-guided fine-needle aspiration (FNA) can also accurately determine the etiology of a cystic pancreatic neoplasm by differentiating between mucinous, serous, and inflammatory (pseudocyst) lesions.
A major incentive for the continued development of endoscopic ultrasound technology, however, is the care of patients with presumed pancreatic and periampullary adenocarcinoma. In such patients, Levy and Wiersema correctly point out that the primary limitation of diagnostic endoscopic ultrasound is a relatively low negative predictive value. Further understanding of the limitations of endoscopic ultrasound for accurate staging of pancreatic neoplasms requires an appreciation of the three-dimensional anatomy of the proximal gastrointestinal tract and pancreas and knowledge of the criteria utilized by surgeons to assess resectability.
Assessment of Resectability: Essential Anatomic Distinctions
In the absence of radiographically visible metastatic disease, the primary goal of pretreatment staging studies is accurate definition of the relationship between the pancreatic neoplasm and adjacent vascular structures, including the celiac axis (and the common hepatic artery), superior mesenteric artery, superior mesenteric vein, and portal vein. A tumor that extends to, or involves, arterial structures such as the celiac axis or superior mesenteric artery is uniformly considered unresectable. However, a tumor with isolated involvement of the superior mesenteric vein or superior mesenteric vein/portal vein confluence is not necessarily considered unresectable. Indeed, some regional centers for pancreatic surgery perform segmental venous resection and reconstruction for management of tumors with isolated venous involvement in the absence of concurrent arterial extension.[1-3]
This anatomic distinction is important because it shifts the focus of endoscopic ultrasound from tumor-venous assessment, where endoscopic ultrasound is relatively sensitive, to the definition of tumor-arterial (celiac axis and superior mesenteric artery) relationships, where the sensitivity of endoscopic ultrasound may be lower. While characterization of the relationships of the pancreatic tumor to the superior mesenteric vein and portal vein is important, these relationships are not considered essential determinants of resectability by experienced pancreatic surgeons.[1-3]
Figure 1 illustrates these anatomic distinctions. It includes three computed tomography (CT) scans that demonstrate the spectrum of potential tumor-vessel relationships. In panel A, a low-density tumor mass is visualized within the pancreatic head with a clearly definable tissue plane between the medial edge of the tumor and both the superior mesenteric vein and superior mesenteric artery. In contrast, panel B demonstrates a lesion that extends to or involves the superior mesenteric vein without involvement of the superior mesenteric artery (located slightly posterior and medial to the superior mesenteric vein). Levy and Wiersema’s opinion notwithstanding, such a lesion is indeed resectable at a treatment center with surgeons experienced in vascular resection and reconstruction at the time of pancreaticoduodenectomy. Panel C depicts a locally advanced tumor that involves both the superior mesenteric artery and superior mesenteric vein; this tumor is unresectable.
Most regional centers are currently utilizing contrast-enhanced multidetector helical CT to accurately define these critical tumor-vessel relationships. In centers where vascular resection and reconstruction are performed routinely, endoscopic ultrasound may provide minimal staging benefit over high-quality helical CT. However, if high-quality CT is unavailable, or there is no capacity for vascular resection and reconstruction at the time of pancreaticoduodenectomy, endoscopic ultrasound may be of value in identifying patients with CT-occult vascular involvement. Such patients can then be referred to a regional center with experience in vascular resection and reconstruction during pancreaticoduodenectomy.