Title Leiomyosarcoma of the portal vein : a case report and review ofthe literature

Leiomyosarcomas (LMS) are rare malignant tumours of smooth muscle origin predominately affecting females in their sixth decade. Only 2% of LMS arise from blood vessels and most are in the inferior vena cava. We present the first reported case of LMS of the portal vein in a male patient. Multidetector CT showed a large mass in the main portal vein, which was initially misinterpreted as a pancreatic cancer. Careful examination of the multidetector CT images showed radiological features of an intraluminal mass, and a preoperative diagnosis of primary LMS of the main portal vein was made. The patient underwent curative surgery and made an uneventful recovery. Awareness of this entity and recognition of the salient CT features may facilitate radiologists in making the correct preoperative diagnosis. BACKGROUND Leiomyosarcomas (LMS) are rare malignant tumours of smooth muscle origin, accounting for only 5–7% of soft tissue sarcomas. They predominantly affect females in the sixth decade of life and generally occur in the abdomen or the limbs. Only around 2% of LMS arise from the smooth muscle of the vessel wall, and the most common site is the inferior vena cava (IVC). LMS of the portal vein is extremely rare with four previous reports in the English literature, all of which were in females. In this article, we present the first reported case of LMS of the portal vein in a male patient with special emphasis on imaging findings seen on multidetector CT (MDCT) and positron emission tomography followed by a brief review of the existing literature. CASE REPORT A 67-year-old male initially underwent contrast-enhanced multidetector CT of the abdomen in Sept 2014 at another hospital, which showed an incidental 4.2 3.9 cm mass in the upper abdomen. This was interpreted as a head of pancreas mass causing portal vein compression. The patient was asymptomatic; physical and laboratory examinations were all unremarkable. The patient was lost to follow-up and did not receive any further investigation or treatment. Although still asymptomatic, he re-presented 12months later for a repeat MDCT, which showed that the mass had increased in size to 4.8 5.0 cm. Cavernous transformation of the portal vein was also observed. The patient underwent exploratory laparotomy, which showed a tumour at the upper border of the pancreas and duodenum compressing the portal vein. A 1-cm lesion in the subcapsular aspect of segment II of the liver was also seen. The presumed pancreatic tumour was deemed unresectable and multiple biopsies were taken. The liver lesion was resected and the histology of both samples showed spindle cell tumour. The patient also underwent a positron emission tomography-CT, which showed the lesion to be hypermetabolic with SUVmax of 7.3. No metastatic disease was identified. The patient was then referred to the hepatobiliary team in Queen Mary Hospital in Hong Kong for further assessment. The patient remained asymptomatic clinically with normal laboratory results including liver biochemistry (bilirubin 4mmol l, alkaline phosphatase 54 U l, alanine aminotransferase 29 U l and aspartate aminotransferase 23 U l). A repeat MDCT 2months later showed that the lesion had a soft tissue density on non-contrast scans. The mass now measured 5.3 5.9 6.4 cm, extending from the superior mesenteric vein/splenic vein confluence to the porta hepatis. It exhibited heterogeneous enhancement with feeding vessels seen on the arterial phase, both within and around the mass. On the portal venous phase, numerous collaterals were seen surrounding the mass with a sharp interface between the mass and opacified portion BJR|case reports https://doi.org/10.1259/bjrcr.20160125 © 2016 The Authors. Published by the British Institute of Radiology. This is an open access article under the terms of the Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited. of the main portal vein at the porta hepatis giving the appearance of a “beak” (Figure 1). The pancreatic duct was mildly dilated and measures 3mm. The biliary tree was not dilated. There was splenomegaly measuring 13.5 cm craniocaudally. No gastroesophageal varices or ascites was appreciated. Based on these MDCT and histological findings, a preoperative diagnosis of primary leiomyosarcoma of the main portal vein was made. The patient underwent Whipple’s procedure and portal vein reconstruction using cadaveric graft. Intraoperative findings confirmed the tumour arising from inside the portal vein and confined to the lumen with no macroscopic evidence of disease spread. Histological examination of the tumour showed spindle cells with enlarged, pleomorphic, hyperchromatic nuclei and abundant eosinophilic cytoplasm. Patchy coagulative necrosis was also seen. Mitotic figures were at 8 per 50 high power fields, and atypical mitotic figures were found. There was focal infiltration into adjacent pancreatic parenchyma. Immunohistochemical stains showed the tumour was positive for actin, h-caldesmon and desmin but negative for myogenin, c-kit and S100 protein. The final histological diagnosis was of a primary LMS of the portal vein (Figure 2). The patient made an uneventful recovery and no adjuvant radiotherapy or chemotherapy was given. He was followed up for 4 months in our institute with no complications. DISCUSSION Differential diagnoses of a portovenous mass could be “bland thrombus” or tumour thrombus from malignant aetiology including pancreatic adenocarcinoma, hilar cholangiocarcinoma and hepatocellular carcinoma. Distinguishing the two types of thrombus is essential as it significantly affects treatment options and prognosis. As in our case, enlargement of the PV and demonstration of feeding vessels within the thrombus indicate the presence of tumour thrombus rather than bland thrombus. Given the close proximity of the PV to pancreas, it is understandable that the lesion was initially misinterpreted as a primary pancreatic lesion causing portal vein thrombosis. In retrospect, the lack of concurrent dilated common bile and pancreatic ducts should make this diagnosis less likely. As for hepatocellular carcinoma and cholangiocarcinoma, tumour thrombus is often caused by direct invasion of the portal vein. Without a visible lesion in the adjacent liver Figure 1. Multiplanar contrast-enhanced multidetector CT images reveal a mass in the portal vein (*). Axial CT image (a) shows numerous collaterals around the heterogeneously enhancing mass (*). There is a rim of contrast around the mass (white arrowheads) indicating that themass has an intraluminal origin rather than tumour invasion from adjacent structures. Corresponding coronal CT image (b) shows a sharp interface with the appearance of a “beak” (white arrowheads) between the opacified main portal vein and the mass (*). Figure 2. Microscopic findings of the resected specimen showing the leiomyosarcoma arising from within the portal vein and confined in the lumen (hematoxylin-eosin, 200 magnification). BJR|case reports Chiu et al 2 of 5 birpublications.org/bjrcr BJR Case Rep;2:20160125 parenchyma or in the hepatobiliary tract, these two differential diagnoses are also less likely. The identification of a rim of contrast around the lesion and “beak” appearance at the interface between the opacified portion of the PV and the mass further support the intraluminal nature in this case. While increased fludeoxyglucose uptake suggested malignant aetiology of the lesion, the presence of cavernous transformation of the portal vein and portal hypertension points to chronicity of the portal vein occlusion, a feature of a less aggressive lesion such as LMS. These patients are often asymptomatic although they can cause Table 1. Demographics, clinical characteristics, management and outcome of previous case reports of leiomyosarcoma of the porto-