**6.2 Nuclear medicine studies**

Most HAs have a decreased uptake of Gallium and colloid, early and retained uptake of hepatobiliary agents, and no uptake on PET scanning.

If radiological studies cannot distinguish HA from HCC and FNH, a combination of radionuclide imaging, including technetium (99mTc)-sulfur colloid sulfur-colloid, Ga, and technetium-99 pyridoxyl-5-methyltryptophan (PMT) uptake may help establish the correct diagnosis [47]. Most adenomas do not take up technetium Tc-99m sulfur colloid so they appear as a "cold" spot in the parenchyma of the liver. This examination is not particularly good in diagnosing an adenoma but in distinguishing one from a FNH, which shows equal or greater uptake of the radiolabeled agent compared with surrounding liver [48]. 99mTc-labeled DISIDA (dimethyliminoacetic acid) liver scintigraphy has also been used by some authors for diagnosis of HA [47].

Positron emission tomography (PET) scanning with fluorine-18-fluorodeoxyglucose (18FDG) is useful in differentiating HAs from malignant tumors, because malignant tumors show uptake of 18FDG but not benign tumors, with some exceptions like inflammation and abscess.

Although CEUS, CT, MRI, and nuclear studies help in characterization of hepatic lesions as adenomas, the findings sometimes are nonspecific, and biopsy and/or resection may still be necessary.
