Triphasic helical CT of hepatic focal nodular hyperplasia: incidence of atypical findings.

OBJECTIVE: The objective of this paper is to assess the findings of focal nodular hyperplasia of the liver as depicted by triphasic helical CT.
MATERIALS AND METHODS: Triphasic helical CT scans (arterial, portal vein, and delayed phase scans) in 12 patients with hepatic focal nodular hyperplasia were reviewed to assess the frequency of findings on each phase. The final diagnosis of focal nodular hyperplasia was proven by surgery or biopsy in eight cases and by additional imaging studies and clinical follow-up in four cases.
RESULTS: Only two of the 12 patients had CT features that could be considered typical of focal nodular hyperplasia. The other patients had one or more findings considered to be atypical and more suggestive of a primary or metastatic hypervascular malignant hepatic neoplasm, such as an enhancing capsule, lack of a central scar, early draining veins, rapid washout of contrast material on the portal vein phase or persistent enhancement on the delayed phase, and interim growth.
CONCLUSION: Although classic or typical triphasic helical CT manifestations of focal nodular hyperplasia do occur, atypical features are common and can mimic those of primary or metastatic hypervascular hepatic neoplasms. In these latter cases, additional imaging studies, such as a 99mTc-sulfur colloid liver scan, an MR scan, or a percutaneous biopsy, are essential for correct diagnosis.