EUS and ampullary adenoma: Why? When?

The ampullary region is a highly complex anatomic area composed of the following histologically and functionally distinct structures: the ampullary common duct or ampulla, formed by the dilated confluence of the pancreatic and common bile duct; the sphincter of Oddi; and the duodenum with the papilla of Vater, where the ampulla opens into the duodenum [1]. Due to its complexity, this small anatomic area gives rise to a heterogeneous group of tumors with different biological behaviours and spreading patterns. Ampullary tumours, although relatively uncommon, are increasingly diagnosed due to advances in imaging technology, and their management approach remains controversial. For benign ampullary adenomas, endoscopic resection has become the preferred option over surgery given its lower morbidity. However, incomplete resection may result from spreading inside the bile or pancreatic duct. Moreover, whereas endoscopic resection may be curative for selected patients with early ampullary cancer confined to the mucosa, the risk of metastatic lymph nodes arises as soon as the carcinoma invades beyond the sphincter of Oddi. Preoperative assessment of tumor depth is therefore crucial in the process of deciding between surgery and endoscopic resection. Nevertheless, owing to the complex anatomic coalescence at the ampullary region, understanding the threedimensional spreading patterns of tumors arising here is difficult. Therefore, these tumors are probably the most challenging in terms of staging [2]. The close proximity of the ultrasound transducer to the duodenum during endoscopic ultrasonography (EUS) provides high-spatial-resolution images of the ampullary region and enables clear visualization of the duodenal wall layers. EUS has been shown to be superior to computed tomography or magnetic resonance imaging for assessment of tumor depth invasion and intraductal extension in ampullary tumours [3]. In addition, when compared with surgical specimens, EUS performs similarly to endoscopic retrograde cholangiography (ERCP) in evaluating intraductal extension but without the risk of complications inherent to ERCP [4]. Although radial and linear EUS equipment have comparable accuracy for assessment of intraductal invasion, in our experience, the image of the papilla is less defined with the linear equipment. However, no study has involved a direct comparison between linear and radial EUS for Tumor staging, and the choice of using these instruments depends mostly on the operator's preferences. Only intraductal ultrasonography (IDUS) has demonstrated superiority to EUS in terms of tumor visualization and staging [5]. IDUS allows differentiation between the duodenal wall layer and the sphincter of Oddi, but its limited ultrasound penetration prevents it from exploring possible lymph nodes, and it is not widely available. EUS is now considered the modality of choice for local staging of ampullary tumors, but whether EUS should be performed in all patients with ampullary tumors is still uncertain, and some guidelines recommend EUS on a case-by-case basis [6]. This recommendation is based on expert opinions suggesting that EUS should be used only in ampullary tumours larger than 1cm or with features suggesting malignancy; however, no evidence that supports this view is available at present [7]. In this month's issue of Endoscopy International Open, Patel et al. offer an original perspective on the topic of tumor size as a predictor of invasive stage by studying the relationship between tumor size and intraductal invasion [8]. A total of 120 patients with a benign ampullary tumor on endoscopic biopsies underwent EUS before endoscopic or surgical ampullectomy. Among them, 35 tumors had intraductal invasion on EUS and were significantly larger than those without invasion on EUS (22±12mm vs 14±11mm, respectively, P >0.0001). They found that a tumor size smaller than 5.5mm had 100% sensitivity for absence of