What are the imaging findings of Hepatic Adenoma (liver benign tumor)?

From the Guidelines

Hepatic adenomas are typically characterized by well-defined, solitary lesions on imaging studies, with distinctive features on ultrasound, CT, and MRI, as outlined in the most recent guidelines from the American College of Radiology 1.

Key Imaging Features

• On ultrasound, hepatic adenomas present as well-circumscribed, homogeneous, hyperechoic masses, with possible intralesional hemorrhage appearing as hypoechoic or echogenic signals 1.
• CT scans without contrast show isodense or slightly hypodense lesions, while contrast-enhanced CT demonstrates early arterial enhancement with subsequent washout or persistent enhancement in the portal venous phase.
• MRI reveals lesions that are hypointense on T1-weighted images and hyperintense on T2-weighted images, with significant enhancement after gadolinium administration, and possible signal dropout on opposed-phase T1-weighted images due to intralesional fat.

Clinical Considerations

• Larger adenomas (>5 cm) carry an increased risk of rupture and malignant transformation, warranting closer monitoring 1.
• The imaging appearance can vary based on the adenoma subtype, with inflammatory adenomas showing more pronounced enhancement and HNF1α-inactivated adenomas typically containing more intracellular fat.
• These imaging characteristics help differentiate hepatic adenomas from other liver lesions, such as focal nodular hyperplasia and hepatocellular carcinoma, though biopsy may be necessary for definitive diagnosis in uncertain cases.

Diagnostic Approach

• The American College of Radiology Appropriateness Criteria provide evidence-based guidelines for the characterization of incidentally detected liver lesions, including hepatic adenomas 1.
• The guidelines recommend a multimodal approach, including ultrasound, CT, and MRI, to characterize liver lesions and determine the need for further evaluation or treatment.

From the Research

Hepatic Adenoma Image Findings

• Hepatic adenomas are typically hyperintense with respect to liver on T1- and T2-weighted images, with a variable MR appearance 2
• The high signal intensity on T1-weighted images often relates to the increased fat content of these lesions, with 15 out of 15 lesions having a fat content of grade 2 or 3 being hyperintense on T1-weighted images 2
• On T1-weighted images, 51 (77%) of 66 lesions were hyperintense, 11 (17%) were hypointense, and four (6%) were isointense with respect to liver 2
• On T2-weighted images, 49 (74%) of 66 lesions were hyperintense, 12 (18%) were isointense, and five (8%) were hypointense 2
• Hepatic adenomas are generally hypointense during the hepatobiliary phase on multiphasic MRI, except for the β-catenin-mutated exon 3 subtype and up to a third of inflammatory HCAs 3

Imaging Modalities

• Ultrasonography (US) may not specifically diagnose hepatocellular adenoma, and further evaluation with computed tomography (CT) or other imaging modalities may be necessary 4
• Color Doppler US may help differentiate hepatocellular adenoma from focal nodular hyperplasia 4
• Multiphasic helical CT allows more accurate detection and characterization of focal hepatic lesions 4
• Multiphasic MRI performed with hepatobiliary contrast agents remains the best method to noninvasively detect, characterize, and monitor HCAs 3

Complications and Management

• The two most feared related complications are bleeding and malignant transformation to hepatocellular carcinoma, although the risk of these complications depends on tumor size, subtype, and clinical factors 3
• Elective surgical resection is recommended for HCAs that are persistently larger than 5 cm, adenomas of any size in men, and all β-catenin-mutated exon 3 HCAs 3
• Thermal ablation and transarterial embolization are potential alternatives to surgical resection 3
• In the acute setting of a ruptured HCA, patients typically undergo transarterial embolization with or without delayed surgical resection 3