Clinical features and MRI progression of small duct primary sclerosis cholangitis (PSC)
Kristina I. Ringe, Annika Bergquist, Henrike Lenzen, Nikolaos Kartalis, Michael P. Manns, Frank Wacker, Arsteidis Grigoriadis.
European Radiology – May 2020
Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disorder with fibrosis of the intrahepatic and/or extrahepatic bile ducts. Histologically periductal fibro-obliterative “onion skin” concentric fibrosis and bile duct strictures are characteristic of the disease, with cholangiographically identifiable duct changes being the hallmark of PSC. Its course is very variable and in a minority of cases can be benign, however in the majority of cases, PSC is a progressive disease, eventually leading to cirrhosis and potential development of cholangiocarcinoma.
To this day it is uncertain whether small duct PSC (sdPSC) represents an early stage of large duct PSC, a mild variant of it or a separate disease condition altogether.
SdPSC is characterized by clinical and histological features of large duct PSC, but with a normal cholangiogram on endoscopic retrograde cholangiopancreatography (ERCP) or magnetic resonance cholangiopancreatography (MRCP). Currently there is no specific disease marker for sdPSC, and histology remains the cornerstone of diagnosis. Histologic features of sdPSC are the same as those of PSC, surrounding the small interlobular and medium-sized bile ducts, along with a reduced number of interlobular bile ducts.
SdPSC is much less common than large duct PSC and has a favorable disease course, with a lower risk of hepatobiliary malignancy, liver transplantation or death.
The aim of this study was two-fold, first to evaluate and describe the clinical and MRI progression of patients with sdPSC, and second to evaluate MRI features associated with disease progression to large duct PSC.
A retrospective dual-center study was carried out from records of 16 patients with a known diagnosis of sdPSC and available MR imaging. Imaging and liver function tests were reviewed in consensus by two radiologists at baseline and follow-up. Due to the retrospective design, the MR protocol was not standardized. In all patients 3D MRCP, 2D MRCP or single shot MRCP sequences were available for dedicated bile duct evaluation. Some patients also had additional imaging in the form of diffusion-weighted sequences (DWI), T2w and T1w pre and post-contrast imaging (liver specific or extracellular). Images were evaluated for bile duct changes, gallbladder findings, parenchymal changes and associated findings such as hilar lymphadenopathy, ascites, varices, portal vein thrombosis and spleen volume.
Baseline MRI showed the commonest findings, with regards to sdPSC, to be inhomogeneous diffusion-weighted signal and enhancement, altered liver morphology and periportal lymphadenopathy. These changes showed pronounced manifestation at follow-up imaging. Unfortunately, no prognostic MRI marker for prediction of large duct PSC development could be determined at baseline imaging.
The progression rate in this study was high in comparison to previously published data, with 55.5% of sdPSC patients with available follow up imaging, progressing to large duct PSC, supporting the theory that sdPSC may be an early stage of large duct PSC, not a seperate entity. The largest study to date, which included 83 patients with sdPSC, showed a progression rate to large duct PSC of 22.9% in a median of 7.4 years. Ringe et al. (2020) propose the longer follow up period (median 10.6 years) and the fact that all available MRCPs were reviewed (not just those of symptomatic patients), as a possible reason for this discrepancy.
The authors highlight a number of limitations within the study, such as the study population being relatively small, the fact that follow-up imaging for sdPSC is not yet standardized and that due to the retrospective aspect of the study, the MRI protocol was very heterogenous.
The major strength of this study is that it is the first to describe MRI findings beyond cholangiographic changes in patients with sdPSC. The authors strongly suggest that assessment should not only be focused on MRCP images and cholangiographic images, but also on evaluation of parenchymal changes, inhomogeneous enhancement and associated findings (eg: hilar lymphadenopathy).
REFERENCES
- J. Ludwig, (1991) Small-duct Primary Sclerosing Cholangitis, Semin. Liver Dis. 11(1):11-7. doi: 10.1055/s-2008-1040417
- Small duct primary sclerosis cholangitis without inflammatory bowel disease is genetically different from large duct disease.
- E. Bjornsson, r. Olsson, A. Berquist et al (2008) The natural history of small-duct primary sclerosing cholangitis, gastroenterology 134: 975-980
- E. Bjornsson, K.M. Boberg, S. Cullen, K. Fleming, O.P. Clusen, O. Fausa, E. Schrumpf, R.W. Chapman (2002) Patients with small duct primary sclerosis cholangitis have a favourable long term prognosis, Gut 51 (5): 731-735. doi: 10.1136/gut.51.5.731
Dr. Ruth Gatt is a second-year radiology resident at Mater Dei Hospital, Malta. She completed her undergraduate medical degree at the University of Malta in 2016 and joined the Medical Imaging Department in 2018 where she is undertaking training in diagnostic and interventional radiology.
Comments may be sent to ruth.d.gatt@gov.mt