Transient Hepatic Attenuation Differences (THAD)

Elderly patient presented with large hepatic mass showing large central scar. Mass is highly suspicious for malignancy.

Two THAD areas are seen; one at right lobe and smaller one on left lobe; the larger right lobe THAD is probably associated with the malignant hepatic mass and the smaller left lobe segment 3 THAD is probably due to third-inflow tract or idiopathic.

Transient hepatic attenuation difference (THAD) is an attenuation difference of the liver appearing during bolus-enhanced dynamic CT and not corresponding to mass. THAD is generally seen as an area of high attenuation on the hepatic arterial phase image that returns to normal attenuation on the portal venous phase image. THADs that are associated with hepatic tumors are generally characteristic of malignant tumors. However, benign focal lesions, such as hemangiomas, focal nodular hyperplasia, pyogenic abscesses, and focal eosinophilic necrosis, may accompany THADs. Hepatic hemodynamic alterations caused by liver cirrhosis and aberrant blood supply may show findings similar to those of THADs in focal hepatic lesions.
Radiologists should be familiar with the dual-phase CT appearancesof THADs to avoid the false-positive diagnosis of pseudolesions and not to overestimate the extent of the disease.

Another important cause of THAD is the "third-inflow tract." Aberrant gastric venous drainage into the hepatic segment IV and aberrant cystic venous drainage into the gallbladder fossa are the commonly encountered third-inflow tracts. Focal hepatic lesions are not always associated with THAD and vice versa. In some cases, it is impossible to define the specific cause of THAD