MR lymphography of hepatic lymphatic system.

Abstract

Potential conflict of interest: Nothing to report. TO THE EDITOR: We read with great interest the article by Iwakiri in the September 2016 issue of Hepatology emphasizing the role of the lymphatic system in liver physiology.1 He indicated that the liver is the largest lymph‐producing organ of the body and that production of lymph markedly increases in cirrhosis with portal hypertension with likely implication of the lymphatic system in ascites formation.2 He also indicated that the study of the lymphatic vascular system is overlooked partly because of lack of established techniques for studying the lymphatic vasculature.1 We support the information provided by Iwakiri; however, we believe that the lymphatic vascular system may be analyzed by means of modern magnetic resonance (MR) techniques. Noncontrast heavily T2‐weighted three‐dimensional MR imaging, which was introduced in the early 1990s, is a completely noninvasive imaging technique that can accurately depict the morphological characteristics of the biliary and pancreatic ducts. Such sequences using very heavily T2‐weighted sequences may also be used to obtain a morphological evaluation of the lymphatic vascular system because of the high signal intensity of static or slow‐moving, fluid‐filled structures such as the lymphatic vessels, resulting in unique lymphatic vessel‐to‐background contrast.3 Given that MR cholangiopancreatography is very commonly performed in various liver diseases, we frequently observe dilated hepatic lymphatic vessels in patients with portal hypertension. Dilatation may affect both deep (Fig. 1A) and superficial (Fig. 1B) lymphatic systems, which are extensively interconnected. Iko et al. already demonstrated that cisterna chyli and thoracic duct were dilated in portal hypertension.4 We also commonly observe dilatation on hepatic lymphatic vessels in patients with long‐standing severe biliary stenosis, such as patients with severe primary sclerosing cholangitis (Fig. 1C). Dumont et al. demonstrated that after bile duct obstruction, bile was entirely regurgitated through the lymphatic vessels.5 They also demonstrated that bilirubin level was increased within thoracic duct in patients with obstructive jaundice.5 Therefore, we believe that with current improvement of MR techniques, noncontrast MR imaging may be useful to obtain an accurate anatomical evaluation of lymphatic vessels of the liver.Figure 1: Dilatation of hepatic lymphatic vessels demonstrated with noncontrast MR lymphography. (A) Dilatation of deep lymphatic vessels (arrows) in a patient with portal hypertension. Biliary ducts (arrowheads). (B) Dilatation of superficial lymphatic vessels (arrows) in a patient with portal hypertension. (C) Dilatation of deep lymphatic vessels (arrows) in a patient with severe primary sclerosing cholangitis. Dilated left biliary ducts (arrowheads).