[Hypermetabolic multifocal steatohepatitis: a rare case of [18F]FDG PET/CT false positive mimicking a metastatic carcinomatosis].

Fatty liver disease is a common condition that rarely occurs on a multifocal mode. In this form, the differential diagnosis with hepatic carcinomatosis is not obvious, especially when a neoplastic condition coexists. Radiologically, MRI can almost systematically differentiate these two entities. However, concerning metabolic imaging with [18F]FDG PET/CT it is important to keep in mind that a multifocal hepatic steatosis may appear hypermetabolic in rare cases. By mimicking a typical presentation of metastatic carcinomatosis, it may lead to a false positive result. Here we report the case of a 73-year-old woman with a recent diagnosis of colorectal cancer. As part of the initial assessment, a MRI of the liver is performed and shows multiple lesions described as multifocal steatosis. A [18F]FDG PET/CT subsequently describes the same liver lesions but assimilates them to colorectal metastatic carcinomatosis. Due to this mismatch between the two different imaging modalities, several biopsies of the liver lesions are performed, first echoguided (two different lesions) then surgically (removal of a third lesion). The pathological analysis of the specimens fails to highlight any malignant lesion and the diagnosis of multifocal steatohepatitis is made.