Due to the vague symptoms associated with FLC, diagnosis is usually made on the basis of both clinical presentation and diagnostic imaging studies. Imaging studies including ultrasound, computed tomography (CT) scan, and magnetic resonance imaging (MRI) may all be useful.
On ultrasound, FLC is characterized as a well-defined mass that has heterogenous echogenicity.49 Rather than ultrasound, cross-sectional imaging is the preferred mechanism to characterize most liver lesions, including FLC. CT scans that included an unenhanced phase followed by an intravenous contrast-enhanced hepatic arterial phase, a portal venous phase, and a delayed phase are recommended.50
Using contrast-enhanced CT, FLC typically presents as a large (7–20 cm), heterogeneous, welldefined mass with a lobulated outline.51 On the unenhanced phase, FLC is most often hypoattenuating with calcifications (40%–68%) and a central stellate scar (65%–75%), which is not seen in traditional HCC.49,51,52
Necrosis without intratumoral hemorrhage is also a common finding in FLC.49,51 On hepatic arterial phase, most FLC lesions appear with heterogeneous hyperattenuation due to the large hypervascular tumor cells surrounding hypovascular fibrotic bands, as well as necrosis.49,51
The portal venous-phase CT characteristics of FLC are more variable. In ∼50% of patients, FLC tumors are isoattenuating to the liver in the portal venous phase, while in 30%–40% and 10%–20%, the lesions are either hyperattenuating or hypoattenuating, respectively.50,51
In many centers, MRI is the preferred imaging modality. MRI can be quite helpful in distinguishing FLC from other liver lesions. FLC tumors are usually hypointense on T1-weighted images and hyperintense on T2-weighted images with a fibrous central scar that remains hypointense on both T1- and T2-weighted images.50,51
The hypointensity of the central scar can help differentiate FLC from benign liver masses such as focal nodular hyperplasia, which typically has a predominately hyperintense central scar on T2-weighted images. Gadolinium contrast-enhanced MRI is used by many institutions to help further characterize liver lesions.
On gadolinium-enhanced MRI, FLC is characterized by marked heterogeneous enhancement on the arterial phase that washes out and leaves an isointense or hypointense lesion on the portal venous phase.50,51
The role of 18F-FDG positron emission tomography– computed tomography (PET/CT) in the workup of FLC has not been well studied. Limited case series have suggested that PET/CT may be a useful tool in the diagnosis and monitoring of FLC as it may be FDG avid in up to 75% of patients (Figure 1).53,54
As such, FDG-PET may be especially helpful in distinguishing FLC from focal nodular hyperplasia, the latter not being FDG avid.53 Before routine utilization of PET/CT can be recommended, further investigations of the effectiveness of PET/CT in FLC are warranted.