CT perfusion in follow-up of patient with liver inflammatory pseudotumour

The patient was submitted to oncology department with jaundice and itch. Outpatient ultrasound detected left lobe liver lesion. There was no elevation of AST and ALT. In blood the direct bilirubin level was 20,7 mkmol/l (normal range 0- 3,4 mkmol/l).

On contrast-enhanced CT triangle wedge shaped isodense hypovascular lesion in left liver lobe was detected (Fig. 1-3). That lesion demonstrated progressive enhancement with maximum HU on delay phase images, size 5,1 х 5,6 х 3,6 sm. Also dilatation of intrahepatic biliary ducts was seen. On CT perfusion series there was increase of blood flow (mean slope of increase maps), mean transit time and permeability surface (Fig. 7-10). On MRI, lesion showed low-signal intensity on T2- and T1-weighted images with restriction of diffusion on DWI (b=900) (Fig. 4-6). Progradient contrast-enhancement was revealed on three phases contrast MRI.

Background
The pathogenesis of inflammatory pseudotumour (IP) is not clear yet. Some authors assume inflammatory pseudotumour as a low-grade fidrosarcoma with lymphomatous cells. Another point of view describes IP as an autoimmune process [1]. Some authors add trauma and infection as a possible causes of IP in the liver [2].  
Clinical and Imaging Perspective
IP of the liver is a great mimicker of intrahepatic cholangiocarcinoma and atypical hepatocellular carcinoma [3]. In our case, due to progressive enhancement and hypovascularity on CTA, the cholangiocarcinoma was suspected [4]. Malignant cells were not found by ultrasound guided biopsy. Only the diagnostic laparoscopy with liver biopsy confirmed the diagnosis of inflammatory pseudotumour.
Increase of blood flow, blood volume on CT perfusion maps is a common finding in metabolic active lesions [5]. In our case, the unusual findings were predominantly portal vein supply of the lesion and decrease of blood volume. Those CTP features are not typical for cholangiocarcinoma [6]. In contrary, the uptake of Fluorine-18-fluorodeoxyglucose in IP of the liver, described in literature was abnormal. [7] This is the sign of intensive metabolic activity in the inflammatory lesion. So the elevation of blood flow, mean transit time on PCT was expected in our case of hepatic IP.
CT angiography and MRI findings are not specific in this case. By means of CT angiography and MRI, we are ready to diagnose mass-forming cholangiocarcinoma. Nevertheless, CT perfusion features appeared to be not typical for cholangiocarcinoma.

Outcome
Laparoscopic biopsy confirmed the diagnose of hepatic inflammatory pseudotumour (Fig. 11).
Histology: Among hepatic tissue cells there are fusiform and stellate cells with big nuclei and blurred borders. Irregular intensive inflammatory lymphoplasmacytic infiltration with eosinophils is detected. Atrophied and deformed bile ducts are surrounded by fibrous tissue, in single bile ducts there is obvious epithelium proliferation. Big cells with enlarged nuclei and small nucleoli are determined among fibroblasts.
Immunohistochemical exam. There is irregular diffuse expression SMA in miofibroblast-like cells. Intensive inflammatory infiltration (CD45+) with equal amount of T- lymphocytes (CD3+, CD5+) and B- lymphocytes (CD20+), inclusion of plasma cells (CD138+) is detected. There is no IgG4 – expression in plasmacytes. Negative reaction with antibodies CD117 and ALK (Clone5A4).
Treatment with antibiotic and steroids was provided. Four months later, on CT and MRI, we observed decrease of IP sizes (Fig. 12-15). On perfusion CT, decline of blood flow, blood volume, permeability surface was detected (Fig. 16,17). This was explained as decrease inflammation in the liver lesion. CT perfusion findings became an additional confirmation of therapeutic treatment effectiveness.

Teaching Points
- The main CT features of hepatic peripheral mass-forming cholangiocarcinoma: hypovascular heterogeneous mass with irregular well-defined margins, retraction of adjacent hepatic contours. After contrast administration, there is progressive enhancement with heterogeneous to delay enhancement of central scar. Key finding on CT perfusion: increased of blood flow, blood volume and decreased portal supply.
- Hepatic inflammatory pseudotumour usually low-attenuated well-defined lesion with different enhancement patterns: homogenous, heterogeneous with delayed central scar filling or no enhancement. In our case, the CTP-findings were predominantly portal vein supply of the lesion and decreased of blood volume, low blood flow.
- In some cases, mix of patterns is determined. Special CTP-features of inflammatory pseudotumour in comparison with cholangiocarcinoma, association with progressive enhancement on CTA-images is confusing. Therefore, we can speculate that biopsy is essential modality for confirming the diagnose.
- Abdominal CT perfusion is useful tool for the evaluation of patients with hepatic inflammatory pseudotumour under conservative treatment.

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