Teaching Case

Incidental finding of a liver lesion on a follow up CT of an asymptomatic 21 year-old woman with untreated lupus. No oral contraception. CRP and other laboratory parameters were normal.

CT with intravenous contrast shows a 4 cm lesion in segment IV of the liver, hypervascular in the arterial phase and showing rapid washout in the portal and delayed phases.
On MRI, the lesion appears discretely hypointense to liver parenchyma on T1-weighted images (T1WI) and isointense on T2WI. On T1W in and out of phase sequences, a loss of signal is demonstrated between the two phases. In diffusion-weighted images (DWI), the lesion is isointense to liver parenchyma at b50 and no restriction to diffusion is demonstrated at b1000 or on the apparent diffusion coefficient (ADC) sequence. Dynamic behaviour on gadolinium enhanced T1WI is similar to the one seen on CT with hyperintensity of the lesion and homogeneous contrast enhancement in the arterial phase. A rapid washout is also seen in the portal and delayed phases.

Hepatocellular adenomas are benign liver neoplasms, typically occurring in women on oral contraception. Three distinct subtypes exist: inflammatory hepatocellular adenoma, hepatocyte nuclear factor (HNF) 1α-mutated hepatocellular adenoma and β-catenine-mutated hepatocellular adenoma[1]. Inflammatory hepatocellular adenoma is the most frequent subtype. Clinical presentation is nonspecific and may include chronic anaemia, signs of systemic inflammation and abnormal liver function tests. The main complications of hepatocellular adenoma are intratumoural haemorrhage and malignant degeneration into hepatocellular carcinoma.

MRI is the imaging modality of choice for the characterization of hepatocellular adenoma. Inflammatory adenomas are isointense or mildly hyperintense to liver parenchyma on T1-weighted images (T1WI) and are diffusely hyperintense on T2WI. No loss of signal is observed on chemical shift sequences. After gadolinium administration, there is intense enhancement during the arterial phase, which persists into the portal venous and delayed phases. HNF1α-mutated hepatocellular adenoma is hyperintense or isointense on T1WI, with diffuse loss of signal on chemical shift sequences, and is isointense to discretely hyperintense on T2WI. After gadolinium administration, there is moderate enhancement during the arterial phase, which does not persist into the portal venous or delayed phases. β-catenin-mutated hepatocellular adenomas behave unpredictably on MRI.[2]

In this case, the biopsy confirmed an adenoma with no signs of malignancy, no β-catenin mutation and no fatty component in the biopsied tissue. Despite the size of the lesion (<5cm), the decision of prophylactic surgical excision was made due to the risk of haemorrhage and also to establish a definitive diagnosis. Advantages of surgical resection include elimination of the risk of haemorrhage and malignant degeneration. Disadvantages include the usual risks associated with surgery and general anaesthesia. A conservative approach avoids therefore the risks of surgery but carries the known risks associated with adenomas. Histology of the resected specimen in this case confirmed an inflammatory telangiectatic adenoma. However, a nodule of hepatocellular carcinoma was also found.

Three take home messages emerge from this case. Firstly, it illustrates that liver adenomas can present very differently on MRI and that subtype characterization by imaging alone may not be possible. For example, the rapid washout was not specific in this case. Secondly, it shows that malignant degeneration into hepatocellular carcinoma cannot always be ruled out based solely on imaging findings. Finally, it highlights that the 5cm threshold for surgical resection suggested in the literature[3] is debateable – the decision to surgically resect a 4cm lesion, against the current recommendations, proved correct in this case.