A 60-year-old woman with papillary thyroid cancer, status-post total thyroidectomy and radioiodine therapy, presented with an elevated thyroglobulin level (~625 ng/ml) after a disease-free interval of approximately 7 years. The stimulated thyroglobulin level was 1500 ng/ml with thyroglobulin antibodies of less than 0.8 ng/ml. Ultrasound neck and chest X-ray did not show any neck disease or pulmonary nodules, respectively. I-131 whole-body scan was negative.
Image 1: FDG PET/CT MIP images show no abnormal uptake in the neck [A] or lungs [B]. Increased uptake is seen in a hypodense lesion in segment VI of liver [D] measuring 2.7 x 2.0 cm, SUV 5.9 [C], and a well-defined lytic lesion in right iliac bone [F] SUV 10.5 [E]. The bone lesion was suggestive of metastasis. Image 2: Various MRI sequences performed prior to the PET/CT imaging.
Hepatic adenoma, probably HNF-1α mutated.
MRI showed hypointense signal on T1, mildly hypo- to iso-intense signal on T2, and signal drop-out on T1 out-of-phase images, pathognomonic for the presence of intracellular fat. This virtually excludes a hepatic metastasis and is commonly found in the HNF-1α mutated subtype of hepatic adenomas. Hepatic adenomas are uncommon benign liver tumors that may be FDG-avid, and thus falsely interpreted as malignant on FDG PET/CT scan. They are usually solitary, often well-defined rounded pseudo-encapsulated masses, and are commonly associated with use of oral contraceptive pills, anabolic steroids and glycogen storage diseases. Complications may include spontaneous rupture and hemorrhage with rare possibility to degenerate into hepatocellular carcinoma (least likely in steatotic HNF-1α mutated subtype). Few case reports and series in literature have described FDG-avid hepatic adenomas, although the exact etiology of FDG uptake is not yet completely understood. While most FDG-avid liver lesions are malignant, some benign liver lesions may also be FDG-avid and distinguished from malignancy using features seen on CT or MR.
Benign hepatic adenomas may be FDG-avid and a cause of a false positive finding for malignancy.