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Endoscopic Ultrasound in the Diagnosis and Staging of Pancreatic Cancer

Endoscopic Ultrasound in the Diagnosis and Staging of Pancreatic Cancer

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.

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