Multifocal nodular hepatic steatosis: Multimodality diagnostic evaluation

A 51-year-old male presented with constitutional symptoms for one year, including a 20 kg weight loss, night sweats, asthenia, and anorexia. The patient had an untreated HIV infection, leading to severe immunosuppression. He also had a history of a previously treated and cured hepatitis C virus infection.

The abdominal ultrasound revealed multiple hyperechoic nodular lesions scattered throughout the liver parenchyma, some of which were confluent (Figures 1a and 1b).

The non-enhanced computed tomography scan (CT) demonstrated multiple hypoattenuating nodules of different sizes (Figure 2a). After contrast media administration, the nodules showed an enhancement pattern similar to the normal liver parenchyma, remaining hypodense in the various phases of the dynamic study (Figures 2b, 2c and 2d).

On resonance magnetic imaging (MRI), the nodules exhibited iso-signal on the in-phase images and signal loss on opposed-phase images compared to the in-phase images (Figures 3a and 3b). In the dynamic study sequences, the nodules revealed the same enhancement behaviour as in the CT scan (Figures 4a, 4b, 4c and 4d). They were slightly hyperintense on the T2-weighted sequence (Figure 5a). No hypervascular lesions or areas of diffusion restriction were visible (Figures 5b and 5c).

The nodules had no mass effect on adjacent structures.

Background

Hepatic steatosis refers to triglyceride accumulation within the cytoplasm of hepatocytes. Risk factors include diabetes, obesity, hyperlipidaemia, and chronic alcohol abuse [1]. Six patterns of liver steatosis have been described: diffuse, geographic, perivascular, focal, multifocal, and subcapsular [2]. Multifocal nodular hepatic steatosis (MNHS) is an unusual form of hepatic steatosis, characterised by the presence of multiple nodules of fat deposition within the liver [2,3].

Clinical Perspective

MNHS is often discovered incidentally during imaging for unrelated reasons, as most patients are asymptomatic [4].

The primary clinical challenge arises from the difficulty in distinguishing MNHS from more serious hepatic pathologies, particularly metastatic disease. Thus, correct imaging evaluation is critical to prevent misdiagnosis and unnecessary interventions [5].

Imaging Perspective

MNHS presents with multiple fat nodules, typically oval or round in shape, randomly distributed throughout the liver. Recognising the characteristic imaging features of fat deposition in the different imaging modalities is the key to a correct diagnosis [2,3].

Ultrasound shows homogeneous sharply demarcated hyperechoic nodular lesions, sometimes with associated posterior acoustic shadowing. The lesions typically do not exhibit peripheral hypoechoic halo, a characteristic that has a good negative predictive value for malignancy [1].

On CT, MNHS appears as multiple hypoattenuating nodules with a similar enhancement pattern to adjacent liver parenchyma after contrast administration [3].

On MRI, the nodules are isointense or hyperintense relative to the liver parenchyma on in-phase images and show homogeneous signal intensity loss on opposed-phase images, which is highly suggestive of focal steatosis [3]. They are typically slightly T2-hyperintense and do not show diffusion restriction [6].

Other clues indicative of MHNS are the lack of a mass effect (demonstrated by no invasion or displacement of vascular and biliary structures) and size stability over time [3,7].

Outcome

The treatment of MNHS, like other forms of hepatic steatosis, generally focuses on addressing the underlying causes. Usually, management requires a multimodal strategy that targets various factors such as weight loss, lifestyle changes, and medication optimisation [4].

Take Home Message / Teaching Points

MNHS is a benign disorder that can mimic hepatic malignancies on imaging studies.

MRI is the most reliable imaging modality to diagnose MNHS. The loss of signal in opposed-phase images compared to the in-phase images and the absence of mass effect are the key imaging features on MRI.

Recognising the characteristic imaging findings of MNHS is essential to prevent misdiagnosis and the associated potential for overtreatment.

Written informed patient consent for publication has been obtained.