False negative hepatic CT for metastases - "fatty" liver

Case contributed by Dr Chris O'Donnell

Presentation

Colorectal cancer. On chemotherapy for liver metastases. Apparent response. Assess for resection

Patient Data

Age: 60
Gender: Male

Fatty liver (HU density of 19) showing focal fatty sparing in the posterior left lobe but no mass lesion to indicate metastases.

MRI

Delayed post Primovist (Gadoxetate disodium) contrast enhancement - contemporary with CT

Marked loss of signal intensity (133 to 47) on the out of phase sequence is due to intravoxel fat (fatty liver). Delayed post Primovist scans of the liver demonstrate multiple non-cystic mass lesions without contrast enhancement but with restricted diffusion indicative of metastases in both lobes.

Case Discussion

As a result of the generalized reduction in parenchymal density of the liver that occurs with fatty infiltration, lower density mass lesions such as metastases can be "lost" as there is very little density difference between the mass and the adjacent fatty liver. Primovist is taken up by hepatocytes in the liver irrespective of fatty change whereas the malignant cells do not, thus there is a signal intensity difference and the lesions are visible. The metastases also show restricted diffusion due to the presence of tightly bound water molecules in the cytoplasm of malignant cells with large nuclei.

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Case information

rID: 34519
Case created: 24th Feb 2015
Last edited: 14th Jan 2016
Inclusion in quiz mode: Included

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