Alterations in hepatic uptake and distribution of organ-specific superparamagnetic MRI contrast media: clinical findings and classification according to pathogenesis

Purpose. The aim of this study was to classify the alterations in the liver uptake and distribution of superparamagnetic contrast media that could potentially lead to diagnostic errors. These alterations, referred to as SPIO-LUDA for convenience,may be caused by a variety of disorders, such as cirrhosis, vascular thrombosis, hepatitis and liver steatosis, that interfere with the normal uptake of the contrast material. These conditions can give rise to focal or diffuse areas of hyperintensity or hypointensity which may mimic the presence of neoplastic lesions or hinder the detection or characterisation of neoplasms. Materials and methods.We retrospectively reviewed the hepatic MR examinations of 412 patients performed to detect hepatocellular carcinoma in 349 cases and metastases in 63 cases, with the aim of identifying conditions corresponding to the definition of SPIO-LUDA. All the examinations were performed using a 1.5 Tesla MR unit with SE and GE sequences, T1 and T2 weighted images, and SPIO as a contrast agent, in 402 cases ferumoxide (Endorem, Guerbet) and in 10 cases SHU- 555-A (Resovist, Schering). The SPIO-LUDA were classed into two groups: due to reduced uptake (cell replacement, reduced vascular flow and cellular inhibition) and due to increased uptake (Kupffer cell hyperactivity or increased vascularity). From a quantitative point of view we evaluated the percentage of signal loss (PSIL) of the SPIO-LUDA relative to the surrounding healthy parenchyma, as an expression of increase or reduced uptake of contrast material. Results. In 54 patients we identified potentially misleading SPIO-LUDA: 41 were due to reduced uptake and 13 to increased uptake. In 16 cases, all of which cases of reduced uptake, the alteration significantly limited the diagnostic effectiveness of the MR examination. The reduced-uptake SPIO-LUDA were caused by fibrosis in 31 cases, by portal vein thrombosis in 3, by suprahepatic vein thrombosis in 2, by peritumoural vascular shunts in 3 and by hepatitis in 2. The increased-uptake SPIO-LUDA were caused by focal steatosis in 2 cases and by dysplastic nodules in cirrhosis in 11. The reduced-uptake SPIO-LUDA exhibited 30% lower PSIL values than the normal liver (range 15-45%); the increased-uptake SPIO-LUDA displayed 19% higher PSIL values than the surrounding liver (range 15-23%). Out of a total of 412 patients, the alteration of SPIO uptake was so severe as to prevent detection or exclusion of focal lesions in 4% of cases. Conclusions. SPIO-LUDA constitute a diagnostic challenge. The recognition and correct interpretation of these alterations are fundamental for avoiding confusion with other diseases and to obtain further clues for the interpretation of abnormal patterns detected at MRI or other imaging modalities.