Teaching Case

A 23-year-old man presented to the emergency department with upper abdominal pain and weight loss (10kg in the last 6 months). He did not have a history of previous illness or any medication. On physical examination, there were hepatomegaly and painless mass in the upper quadrants of the abdomen

An abdominal ultrasound scan revealed a large solid mass located in the liver (figure 1). Computed tomography scan (CT) confirmed the presence of a lesion centred in the hepatic hilum, exophytic, well-circumscribed and measuring 10x12 cm, with heterogenous vascularity (figure 2). Magnetic resonance (MR) was performed to assess the invasion of adjacent structures. The lesion showed high cellularity and caused extrinsic compression in the adjacent liver parenchyma with direct invasion of the gallbladder (figure 3). On positron emission tomography / computed tomography (PET-CT) this mass exhibited 18-fluorodeoxyglucose avidity, without evidence of metastasis (figure 4).

Ultrasound-guided liver biopsy was performed. Histology revealed small, round and blue tumour cells. Immunohistochemistry showed diffuse positivity for CD99 and PAS, and focal positivity for AE1/AE3. The cytogenetic evaluation detected a rearrangement involving the EWSR1 gene (22q12). The aspects described are compatible with primary Ewing's sarcoma of the hepatic hilum.

Ewing sarcoma (ES) is an uncommon tumour, but it is the second most common primary bone malignancy of children and young adults[1,2]. About 30% of ES arise primarily in extraosseous locations, without bone involvement[3,4].

Common primary sites of extraosseous ES are the deep soft tissue around the extremities, chest wall, retroperitoneum, and visceral organs, including the pancreas and kidney (most often involved)[1-5]. Primary hepatic ES is very rare[1,3-5], with only a few cases reported in the literature, and we did not find any publication of Ewing's sarcoma of the hepatic hilum.

Most patients with extraosseous ES are younger than 30 years[4] and the incidence is equal between genders. The most frequent complaints are localized pain and swelling[4,5].

Due to the rarity of this entity, little information on the imaging features is available[1,5]. There are reported cases of primary hepatic ES manifesting as solid heterogeneous masses with haemorrhagic areas and others in which they were a multicystic lesion[1,4]. In this case, CT and MR showed a large solid mass that was hypovascular compared with normal liver.

Diagnosis requires histological, immunohistochemical, and genetic study. On histology, the tumour is composed of small blue round cells[1,4]. In the immunohistochemical study, there is usually a diffuse positivity for CD99 and PAS, but these are not specific markers[1,4-5]. The genetic study allows reaching the final diagnosis because the translocation t (11, 22) (q24; q12) is specific to Ewing sarcoma, resulting in the production of the EWS/Fli1 gene fusion, which is present in > 85% of cases[1-6].

Treatment of extraosseous ES is similar to bone ES, and usually includes multimodal chemotherapy and surgical treatment[1,6]. In this case, he underwent chemotherapy cycles with doxorubicin and cyclophosphamide, with a good response and reduction in tumour size. Subsequently, surgical resection of the remaining lesion was performed (figure 5), as well as the gallbladder that presented transmural tumour invasion.

About 30–40% of patients with ES experience recurrence[6]. Factors suggestive of a poorer prognosis included tumours greater than 8 cm, older age, metastatic disease at presentation, positive surgical margins, and poor response to chemotherapy[3,4].

Extraosseous ES is a rare tumour with a poor prognosis. Primary involvement of the liver and hepatic hilum is extremely rare, so there is little information about its imaging characteristics. This diagnostic hypothesis can be made by the radiologist in people younger than 30 years, but the final diagnosis requires histology, immunohistochemistry, and cytogenetics.

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