Evaluation and Staging of Pancreaticobiliary Malignancy

Introduction

Examination of the pancreas and biliary structures by endoscopic ultrasound (EUS) can be technically challenging to master due to the need to recognize patterns of normal, benign, and pathologic anatomy. However, once these skills are learned, EUS permits the most detailed nonoperative view of the pancreas and the bile ducts. This chapter summarizes the role of EUS for the evaluation of solid malignant pancreatic and biliary neoplasms.

EUS Detection of Pancreatic Tumors

EUS is the most sensitive imaging test for the detection of all pancreatic and periampullary lesions ( Table 62.1 ). In studies that compared EUS and computed tomography (CT), the sensitivity of EUS for mass detection was superior to CT. EUS is clearly superior to conventional CT and transabdominal ultrasound (US). A few comparative studies between EUS and multidetector-row CT (MDCT) for pancreatic tumors have demonstrated the superiority of EUS for tumor detection. There are relatively sparse comparative data between EUS and magnetic resonance imaging (MRI) for tumor detection, with at least one study showing the superiority of EUS. EUS is particularly useful for identification of small tumors that can go undetected by other imaging modalities. For tumors of 30 mm or less in diameter ( Fig. 62.1 ), EUS was found in early literature to have a sensitivity of 93% compared to 53% for CT and 67% for MRI. Nowadays, with thinner slice imaging and precisely timed contrast administration coupled with multiplanar reconstruction, CT (often referred to as pancreas protocol ) may now be able to identify small pancreatic masses that previously may have been undetected by conventional or even single-detector dual-phase imaging. EUS remains the test of choice in all patients with obstructive jaundice or dual pancreatic and bile duct dilations in whom CT or MRI do not identify a lesion.

EUS has a few limitations including the potential failure to identify true pancreatic masses in patients with chronic pancreatitis, a diffusely infiltrating carcinoma, a prominent ventral/dorsal split, or after a recent episode (< 4 weeks) of acute pancreatitis. Therefore, a normal pancreas by EUS examination essentially rules out pancreatic cancer, although follow-up EUS or other studies should be undertaken in the setting of chronic pancreatitis due to impaired visualization. It is also important to remember that acoustic shadowing caused by an indwelling biliary or pancreatic stent may also impede visualization of a small pancreatic mass.

Due to the ability of EUS to provide high-resolution images, there has been increasing interest in using this technique to screen asymptomatic high-risk cohorts for early cancer detection. A consensus statement by the International Cancer of the Pancreas Screening Consortium recommended screening with EUS and/or MRI for the following groups: first-degree relatives (FDRs) of patients with pancreatic cancer from a familial pancreatic cancer kindred with at least two affected FDRs; Peutz-Jeghers syndrome; p16 or BRCA2 mutations; and hereditary nonpolyposis colorectal cancer mutation carriers with 1 or more affected FDRs. A 2016 comparative analysis highlighted the complementary roles EUS and MRI play in screening these high-risk individuals. MRI was found to be more sensitive for the detection of cystic lesions of any size; EUS, however, detected more solid lesions then MRI. The optimal screening modality, interval, need for fine-needle aspiration (FNA), and screening abnormalities of sufficient concern for surgery remain unknown, and further studies are required to answer these questions.

Autoimmune pancreatitis (AIP) may mimic pancreatic adenocarcinoma, and accurate preoperative detection may avoid unnecessary surgery. The EUS morphology of AIP may include diffuse pancreatic enlargement, a focal mass, focal hypoechoic areas, bile duct wall thickening, or peripancreatic lymphadenopathy ( Fig. 62.2 ). EUS-guided fine-needle aspiration (EUS-FNA) may demonstrate a nonspecific plasmacytic predominant chronic inflammatory infiltrate, but this finding has variable sensitivity and poor specificity. Diagnosis may be confirmed by EUS-guided core biopsies with staining for IgG4 plasma cells.

Imaging-based technologies such as contrast-enhanced ultrasonography (CE-EUS) may be able to differentiate pancreatic adenocarcinoma from pancreatic neuroendocrine tumors (PNETs) and inflammatory pseudotumors, which can all present as a hypoechoic mass. Whereas ductal adenocarcinomas typically demonstrate hypoenhancement, PNET and inflammatory pseudotumors are hyperenhancing or isoenhancing. A recent meta-analysis of 12 studies involving 1139 patients reported a pooled sensitivity, specificity, and receiver operating characteristic (ROC) of 94%, 89%, and 0.9732, respectively. EUS elastography is another emerging technique based on the different stiffness of benign and malignant tissue. In a meta-analysis of 13 studies involving 1044 patients, the pooled sensitivity, specificity, and ROC was 95%, 67%, and 0.90. However, several limitations to their routine use exist and include costs and the lack of both agent availability and expertise with the technique.