Baseline imaging: Ultrasound and native MRI
Without contrast agents, focal nodular hyperplasia is barely noticeable.
- Ultrasound: The lesion has slightly increased or decreased echogenicity compared to the surrounding parenchyma. It is often extremely difficult to spot during a real-time examination. Large feeding vessels may be visualized at the periphery of the nodule.
- MRI (native scans): The lesion is poorly distinguishable on non-contrast 3D T1-weighted images and fat-suppressed T2-weighted images. In general, FNH is characterized by an isointense or minimally hypointense signal on T1WI and a hyperintense signal on T2WI.
Special attention is paid to the central scar (central scar). On MRI, it appears hypointense on T1WI and hyperintense on T2WI. Interestingly, the scar may be clearly visible on MRI while being completely undetectable on CT (and vice versa).
Contrast enhancement on MRI and CT
The enhancement pattern of standard intravenous contrast agents (e.g., gadolinium-based) on T1WI in MRI is similar to that seen on computed tomography.
- Arterial phase: Marked, intense contrast agent uptake occurs.
- Portal venous and delayed phases: The lesion rapidly becomes isointense, meaning it visually "blends" with the surrounding healthy liver parenchyma.
- Behavior of the central scar: Unlike the main mass of the lesion, the scar typically begins to take up contrast specifically in the delayed phase.
MRI with hepatobiliary agents
For accurate diagnosis of FNH, special hepatobiliary contrast agents (e.g., gadoxetic acid / gadoxetic acid) are used.
The agent is taken up by normal hepatocytes and partially excreted into the biliary tract. On delayed T1WI (in the hepatobiliary phase), there is pronounced contrast uptake inside the FNH, and the lesion becomes isointense. Such retention of the agent is due to the presence of aberrant bile ducts within the hyperplastic structure.
This feature is critically important for differentiating FNH from hepatic adenoma. Adenomas lack portal tracts and bile ducts, so they do not excrete bilirubin and do not retain hepatobiliary contrast. In the delayed phase of MRI, adenomas appear hypointense (dark).
Differential diagnosis with other lesions
In addition to adenomas, the diagnostician may encounter focal lesions that mimic tumors.
- Hepatic adenoma: Prone to intracellular fat accumulation. On ultrasound, this yields increased echogenicity and clear margins, which can mimic hemangiomas. Unlike FNH, adenomas carry a risk of malignant transformation (1–5%) and are prone to dangerous hemorrhages, thus often requiring surgical resection.
- Focal fatty infiltration (focal fat): Regional variation in liver fat content. It may manifest as either focal fat accumulation or sparing areas against a background of diffuse steatosis. Typical locations of such "pseudotumors": on either side of the falciform ligament (falciform ligament), around the gallbladder fossa, and in the posterior regions of segment IV of the liver.
Briefly: answers to topical questions
What specific vascular pattern does focal nodular hyperplasia have on color Doppler ultrasound?
On ultrasound, no specific color Doppler flow pattern has been described for focal nodular hyperplasia, although it is known that large feeding vessels may be visualized at the periphery.
Additional vascularization and enhancement features:
- Portal venous and delayed phases — the lesion often blends with the parenchyma, becoming isointense.
- Central scar (central scar) — may remain visible and enhance with contrast in the delayed phases.
FNH — Forms Gadoxetic acid uptake (due to bile ducts within the nodule). Adenoma — lacks ducts, does not retain contrast.
Class and exam questions
How does the central scar of FNH appear on MRI?
On T1WI, the scar is hypointense; on T2WI, it is hyperintense. A characteristic feature is its contrast enhancement in the delayed phase.
Why use a hepatobiliary contrast agent?
Gadoxetic acid reliably differentiates FNH from hepatic adenoma. FNH has aberrant bile ducts and retains the agent, becoming isointense in the hepatobiliary phase, whereas adenoma appears hypointense.
Can FNH be easily detected on ultrasound?
No, without contrast in real-time, the lesion is difficult to visualize because its echogenicity is nearly identical to healthy parenchyma (only slightly increased or decreased).
What is the main clinical difference between FNH and adenoma?
Adenomas, unlike FNH, tend to grow, undergo necrosis, cause life-threatening hemorrhages, and carry a risk of malignant transformation (1–5%), which is why their surgical removal is frequently recommended.
What else to study on this topic
- Pathogenesis and risk factors for hepatic adenoma (role of steroids, oral contraceptives, and MODY diabetes)
- CT semiotics of complicated and uncomplicated hepatic adenomas
- Differential diagnosis of hemangiomas and fat-accumulating adenomas on ultrasound
- Focal fatty infiltration (focal fat) and areas of spared parenchyma in steatosis
- Telangiectatic histological variant of adenoma and its MRI appearance
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