Hepatic metastasis disguised as fat spared area in the background of fatty liver: Detection on FDG PET/CT
A 65-year-old gentleman was diagnosed with carcinoma of sigmoid colon 2 years back, for which he underwent sigmoid colectomy. Histopathological analysis revealed moderately differentiated adenocarcinoma. Patient then received adjuvant chemotherapy. Serial carcino-embryogenic antigen (CEA) levels and follow-up imaging were normal until 1 year, when metastatic lesion was seen in segment VII of liver. Patient underwent transarterial chemo-embolization (TACE) and radiofrequency ablation (RFA), which led to complete regression of liver lesion. Follow-up was uneventful for 6 months, after which a rising trend was seen in CEA levels. Whole body 18 F — FDG PET/CT study was done. Maximum intensity projection (MIP) image showed diffuse tracer uptake in left side of liver [] – arrow] and a focus of abdominal uptake [– arrowhead] in midline. Axial venous phase CT images showed fatty infiltration in entire right lobe of liver [ — thick arrow], with associated post-treatment changes at the site of treated liver lesion. Left branch of portal vein was patent, with no evidence of tumor infiltration. Axial fused PET/CT image showed no tracer uptake in the right lobe. Diffuse pattern of intense tracer uptake was seen in a wedge shaped area in the left lobe of the liver [ — arrow] which, however, showed normal enhancement on CT images [ — arrow]. Maximum standardized uptake value (SUVmax in g/ml) was 17.3. No focal hypodense lesion was seen. Midline abdominal uptake corresponded to the abdominal wall metastatic nodule [Figure and — arrow]. Though FDG uptake pattern in liver favored metastasis in the background of rising CEA, the anatomical picture was not supportive. Hence, CT guided biopsy was performed, which was confirmatory for metastases from adenocarcinoma. Patient was started on alternative chemotherapy regimen, and follow-up PET/CT was done in 3 months. MIP images showed persistent hypermetabolism in the left lobe metastases [ — arrow], with mild reduction seen in metabolic activity of abdominal wall deposit [ — arrowhead]. Axial CT and fused PET/CT images showed no change in metabolic activity and extent of metastatic site in the left lobe of liver, max SUV being 16.7 [Figure , - arrows]. There was a mild reduction in metabolic activity of abdominal wall nodule, with size remaining unchanged, as seen on the axial CT [ — arrow] and fused PET/CT [ — arrow] images. In view of stable disease, with no new metastatic site, patient is being planned for left hepatectomy and abdominal nodule excision [Event chronology - ].