Multiple focal nodular hyperplasia arising from a fatty liver. US and MR features

Clinical History

35-year-old female patient with chronic fatigue. History of hypertension and dyslipidaemia. The patient was being treated with oral contraceptives and angiotensin converting enzyme inhibitors. Physical examination was unremarkable. Laboratory findings included elevated alkaline-phosphatase, 805 IU/L (normal: 44-147 IU/L) and gamma-glutamyl-transferase, 112 IU/L (normal: 0-51 UI/L). Inflammatory and tumour markers were negative.

Imaging Findings

Abdominal ultrasound (US) showed diffuse hepatic steatosis, a large heterogeneous echogenic lesion and multiple hypoechoic lesions (more than 10), some with a hypoechoic peripheral halo (Fig. 1). On MRI, lesions were iso or hypointense on T1-weighted in-phase and hyperintense on opposed-phase imaging (Fig. 2a, b). Liver parenchyma was diffusely hypointense on T1-weighted opposed-phase imaging (Fig. 2b). Lesions presented isointense or heterogeneous hyperintense signal with central areas of very high signal intensity on T2-weighted images (Fig. 2c). After intravenous gadolinium administration, all lesions showed intense enhancement during arterial phase (Fig. 2d) and remained hyperintense on delayed phases (Fig. 2e, f). The largest lesion showed hypointense central areas with progressive enhancement during portal and late phases (Fig. 2d-f). Pathologic examination obtained from US-guided needle core biopsy of the largest lesion demonstrated focal nodular hyperplasia. All components of the hepatocytes had a normal structure (Fig. 3). Follow-up is required since biopsy was performed only for one lesion.

Discussion

Focal nodular hyperplasia (FNH) is a benign tumour-like condition usually found in young women. It is believed to represent a hyperplastic response to increased blood flow in an intrahepatic arteriovenous malformation, but the cause is not well understood [1, 2, 3].

Clinical and liver function tests are usually normal, although serum gamma-glutamyl-transpeptidase levels may be slightly increased [2]. Because no risk of bleeding or malignant transformation exists, resection is not required [1, 2]. This implies a need for a noninvasive investigation capable of establishing the diagnosis.

Most cases present as a circumscribed solitary lesion less than 5 cm, multiple lesions occur in 20–25% of cases. On US, FNH appears iso or hyperechoic. In fatty livers, some lesions can be hypoechoic. The characteristic central scar is only visible in 15-33% of cases [4]. On MRI, FNH is isointense to hypointense on T1 and slightly hyperintese to hyperintense on T2. The central scar is hypointense on T1-weighted images and hyperintense or hypointense on T2-weighted images. After gadolinium administration, the enhancement pattern parallels that of contrast-enhanced CT. Dense enhancement is seen in the arterial phase; the lesion becomes isointense during the portal venous phase and isointense on delayed images. Late and prolonged enhancement of the central stellate scar occasionally occurs [1, 2, 3, 4]. In our case, decreased parenchymal signal intensity and gadolinium-enhancement of diffuse fatty liver at fat-saturated T1W images, could be one explanation to persistently delayed enhancement of FNH.

Differential diagnosis between FNH and liver adenoma is critical to ensure proper treatment. However, FNH may represent a diagnostic challenge, especially in situations with multiple lesions or atypical findings [5].

Our case showed atypical FNH features that are often seen in inflammatory liver adenoma (ILA). This tumour is the most common subtype of hepatocellular adenomas, characterized by multiplicity, lack of a central scar, lesion heterogeneity, hyperintensity on T1-weighted images, strong hyperintensity on T2-weighted images, and persistent contrast enhancement on delayed contrast-enhanced CT or T1-weighted images [6]. The typical inflammatory markers of ILA (fever, leukocytosis, and elevated serum levels of C-reactive protein) were absent in our case.

Because multiple atypical FNH may share imaging features with the inflammatory form of liver adenomatosis and patients with sporadic adenomas or adenomatosis may have coexistent FNH [7], achieving a confident imaging and histopathology diagnosis of each lesion can be challenging. In these cases, close follow up is essential, and surgical therapy should be considered especially in symptomatic patients [5].

Differential Diagnosis List

Final Diagnosis

Multiple focal nodular hyperplasia arising from a fatty liver

URL:	https://www.eurorad.org/case/11477
DOI:	10.1594/EURORAD/CASE.11477
ISSN:	1563-4086