Radial EUS imaging of the liver: A pictorial guide

Systematic radial EUS imaging can provide a detailed evaluation of most of the liver segments, liver hilum, and hilar and intra-hepatic vascular and ductal anatomy. Innumerable scan planes are possible, and the endosonographers must reference the intra-hepatic vascular structures and ligaments, surface landmarks such as the gallbladder, and adjacent organs such as cardiac chambers and kidneys to define the liver segments. There is no strict demarcation between the adjacent segments, and all estimates are rough approximations. Radial EUS cannot sample detected lesions but can comprehensively evaluate the liver for any pathology. In particular, the superior part of the right anterior sector (S8), S4, and S6 are better seen with the radial than linear EUS probe. Unlike common belief, the liver hilum can also be well evaluated with the radial EUS probe from the mid and upper gastric body, similar to linear probe EUS imaging. Radial EUS imaging of the liver is carried out from three stations: gastroesophageal junction, upper-mid gastric body, and antrum-duodenal bulb. We describe a step-by-step approach to radial EUS description of liver anatomy in this pictorial review.