Imaging approach in focal nodular hyperplasia

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Biphasic CT scan showing typical dynamic phase imaging of an FNH. Arterial phase image (1A) demonstrates early arterial enhancement with portal phase image (1B) demonstrating portal venous washout.

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Contrast enhanced MRI also demonstrating similar features as CT scan with arterial enhancement (2A) and portal venous washout (2B)

FNH remains a largely asymptomatic disease that patients often only discover after vague abdominal symptoms or from imaging for another medical concern. The current hypothesis is that FNH occurs from a vascular origin, which is supported by the presence of associated bile ducts, veins, and the hyperperfused area of parenchyma. In comparison, a liver cell adenoma has only hepatocytes and no associated structures such as bile ducts are seen. FNH also has an association with hemangiomas, as do hepatic adenomas, but only FNH and hemangioma are associated with vasculature.

Accurate diagnosis is important in FNH as it dictates the course of treatment. It is particularly important to distinguish the diagnosis of FNH from liver cell adenomas as larger liver cell adenomas (> 4 cm) are at increased risk for bleeding or malignant degeneration. Fortunately, FNH lesions can be identified on imaging as they are well circumscribed with a central scar.
Confirmation can be made on contrast-enhanced MRI or a CT scan with MRI having the highest sensitivity and specificity (70 % and 98–100 %, respectively). On MRI, an important differentiating
factor of FNH from malignant hepatic tumors is that FNH often shows strong homogenous activity in the hepatic parenchyma due to the Kupffer cells phagocytosing the dye. Malignant tumours
will usually have no uptake at the focal defect.

The unknown pathology of FNH grouped with its benign nature has resulted in a lack of research into the best treatment for FNH. The accepted recommendations are for observation only.
After a literature review, less than 10 cases of FNH ruptures have been reported and no cases of multiple ruptures were found. The rupture of any liver tumour, including FNH nodules, can lead to
serious medical consequences, but the factors that increase the risk of rupture in a patient with an FNH are unknown. Routine imaging may be beneficial following discovery of larger or multiple lesions. Prophylactic ablation, embolization, or surgical excision could be considered in high-risk patients. The obvious question is, “What constitutes high-risk?” as no data exists to
define this group of patients.

The consequences of a ruptured FNH nodule can be very serious for patients, especially those who may not have immediate access to tertiary centres if surgical intervention is needed. Patients that
have a high risk of rupture may be considered for prophylactic hepatic resection, ablation, or embolization where appropriate.
However, the benefits of these procedures must be weighed against the generally low incidence of ruptured nodules in patients with FNH, and the invasive nature of these treatments as preventative
measures. Complications related to FNH resulting in ruptured.

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