Adenoma and focal nodular hyperplasia

Focal nodular hyperplasia (FNH) is the second most common benign

liver lesion, primarily affecting women of reproductive age¹, with a prevalence of 0,4-3%². FNH has a typical appearance, particularly in MRI scans using gadoxetic acid: during the hepatobiliary phase, progressive contrast uptake is observed in normal functioning liver parenchyma, followed by enhancement of the bile-duct system. FNH is characterized by typical hyper/isointensity with a thin, stellar or linear hypodensity, interpreted as the central scar³.

Hepatocellular adenomas (HCA) are uncommon benign liver tumours that occur more often in female patients of reproductive age. There is a strong association with oral contraceptive (OCP) use. Other risk factors include anabolic steroid use, glycogen storage diseases, familial adenomatous polyposis, and obesity.

The incidence reported in literature is about 1/1,000,000⁴.

Inflammatory adenomas (I-HCA) are the most common subtype and they have the highest risk for haemorrhage among all adenoma subtypes. A subset of I-HCA also expresses β-catenin mutations (10%) and is at a higher risk for malignant transformation when compared with typical I-HCA⁵.

On MR imaging I-HCA may appear as a hypervascular mass with persistent enhancement during dynamic evaluation and may show a variable uptake in the hepatobiliary phase, especially at the periphery⁴. Sometimes in the hepatobiliary phase image areas of hypointensity in adenomas, mainly in the periphery, may be seen. Other subtypes of liver adenomas have similar imaging features, except unclassified adenomas (U-HCA) or β-catenin-mutated HCA (β-HCA).

As reported in ACG guidelines⁶, imaging can accurately diagnose FNH in most cases, and biopsy is not routinely needed, while in cases of HCA biopsy should be performed when hepatic adenomas have uncharacteristic appearance on imaging or change in imaging features that are concerning for malignant transformation. Even in cases of growth, resection in FNH is not required except in symptomatic cases. Instead, adenomas require interventions more frequently, particularly when they are above 5 cm in diameter⁷ or the show a significantly growth (20% from the baseline)². Adenomas of any size that have imaging features suggesting for malignant trasformation should be treated as HCC.

If these lesions are symptomatic and surgery is not an option because of comorbidities or anatomic factors, TAE could be performed to decrease size.

Today the question of the choice of the best embolization material in FNH and HCA appears unsolved: recently Wang⁸ showed that TAE performed with lipiodol-bleomycin emulsion plus polyvinyl alcohol (PVA) particles yielded better results than PVA particles alone in terms of complete resolution of FNH lesions and complete relief of the abdominal symptoms. This could be due to the sclerosing effect exerted by bleomycin, and more precisely to the formation of intraluminal microthrombi caused by the effects of bleomycin on vascular endothelium, resulting in the destruction of the feeding artery.

In non bleeding adenomas, beads or particles are the most often embolic agents used in literature, while in emergencies, gelfoam, beads, particles, glue, and (less frequently) coils could be used.

Complications of TAE of FNH and HCA are more frequently represented by liver abscess/infarction, post embolization syndrome (PES) or cholecystitis.