A 31-year-old woman was admitted to our department as outpatient to perform an MRI of the abdomen complaining of vague abdominal pain in the right flank. The pain was accompanied by a loss of appetite. Past medical history revealed a fever episode lasting 5 days about 1 month ago, treated with paracetamol. Laboratory testing results were normal with the exception of a mild leukocytosis (11,800 cells/mm3). Ultrasound examination revealed no relevant findings.
Axial T2-weighted magnetic resonance (MR) image shows a hyperintense mass located in the right hepatic lobe, close to the hilum, measuring 20 mm in the greatest dimension. The surrounding liver is normal. On T1-weighted MR images the lesion appears hypointense without showing any signal drop in the opposite phase. Diffusion-weighted image demonstrates restricted diffusion during the high b-value, mainly located in the peripheral aspect. Axial arterial phase MR image from a multiphasic study shows mild enhancement of the lesion. On portal phase and delayed phase, lesion demonstrated an intense enhancement with a “target” appearance. No washout is documented. Hepatobiliary phase image obtained 20 minutes after injection of contrast agent shows an ill-defined hypointense lesion with a slight increase in size compared to T2-images.
Inflammatory pseudotumour (IPT) is a rare benign entity that presents as a single or multiple non-neoplastic mass consisting of proliferation of polymorphous inflammatory cell infiltrates mixed with a variable amount of fibrous stroma, granulomatous reaction and necrotic tissue. It primarily occurs in the lung or in the orbit, with the liver accounting for just 8% of the extrapulmonary IPTs . Liver IPTs are categorised into two types, IgG4-related and non-IgG4-related. The first ones are associated with IgG4-related sclerosing disease, a systemic disease characterised by diffused IgG4-positive plasma cells infiltration of various tissues , whereas the non-IgG4-related variant is considered to represent the consequence of an excessive inflammatory response to triggering factors such as infection, and biliary or portal obstruction .
Patients are often symptomatic and present with abdominal pain, fever, loss of weight and fatigue. Laboratory test may reveal an inflammatory syndrome with leukocytosis and elevated ESR and CPR, while tumour markers are typically negative . Unfortunately, no pathognomonic signs of IPT have been described at imaging and findings are often non-specific, reflecting the variable amount of fibrosis and inflammatory infiltrates in the lesion and may mimic liver malignancies. Even after laboratory test and imaging investigations the diagnosis remains challenging, with many liver IPTs initially diagnosed as malignant lesions (e.g. cholangiocarcinoma) or liver abscess .
On MRI, IPT usually appears as an ill-defined and heterogenous mass, hypointense on T1-weighted images and hyperintense on T2-weighted images, with heterogeneous enhancement in the periphery of the mass at portal and delayed phase, attributable to the tumour's fibrous component. IPTs generally do not show uptake of hepatobiliary contrast agents and appear hypointense on hepatobiliary phase. However, some lesions may show hyperintensity due to retention of contrast medium in the extravascular space [1,4,6].
Liver IPT is a benign entity with an optimal prognosis and no risk of malignant transformation; indeed, when the diagnosis is confirmed, they should be managed conservatively (e.g. steroids, antibiotics, or simple surveillance) with complete regression rates of >90% .
Knowledge of hepatic IPT can prevent incorrect diagnosis and avoid surgery. Suspicion should be raised when the general imaging features of liver IPT are observed in association with inflammatory systemic disease, fever, non-elevated tumour markers, and absence of signs of chronic liver disease. The diagnosis should be then confirmed by means of liver biopsy and short-interval imaging follow-up may reveal a decrease in size or complete resolution of the lesion.
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