Solitary fibrous tumors of the liver (SFTL) are uncommon tumors with few cases reported in the world literature. The disease was defined as a benign tumor originating from the submesothelial tissue of the liver or other organs with histological features that include soft, uniform, fibroblast-like cells and branching hemangiopericytoma-like vessels¹. The real incidence is unknown. This rare neoplasm has been reported in less than 60 cases in the English literature^1,2. Most SFTL are benign and asymptomatic, but their malignant potential has not been defined. The presence of metastases in the published literature suggests the malignant potential of these tumors³. Surgery is the treatment of choice and there are no established guidelines about the benefits of adjuvant therapies for those cases with histological findings consistent with malignancy¹.

The reason to present this case report is the low number of cases reported in the world literature.

A 70-year-old female patient with a history of obesity, uterine leiomyomas and venous thrombosis of the lower extremities sought medical care due to a palpable mass in the abdomen with bloating. An ultrasound reported the presence of a solid and poorly vascularized irregular hypoechoic mass occupying the left liver measuring 120 x 90 mm. A contrast-enhanced computed tomography (CT) scan of the abdomen (Fig. 1) showed a solid focal lesion in segment III measuring 112 × 84 × 110 mm that compressed the gastric antrum, with heterogeneous enhancement during the arterial and portal phases and intense late enhancement. The presence of fibrosis was suggestive of solitary fibrous tumor, primary hepatic leiomyoma or intrahepatic cholangiocarcinoma. Yet, according to our experience, liver sarcoma should also be considered in the differential diagnosis. Liver functions tests, liver serology and tumor markers (CEA and CA 19-9) were within normal ranges. Surgery was indicated (left liver resection) for diagnosis and treatment. Open surgery was performed in September 2018 via a right subcostal incision with extension to the subxiphoid region. Once the peritoneum was incised, a 13-cm hepatic mass was observed in segments II and III. An intraoperative ultrasound was performed ruling out the presence of other lesions; the left liver was then mobilized. The hepatic artery and the left portal vein were dissected and were selectively clamped delineating the transection line, which was sectioned using electric scalpel and ultrasonic dissector.

Figure 1 Computed tomography scan of the abdomen (axial section at the por tal phase) and 3D reconstruction 

The accessory vein of segment IV was clamped, sectioned and ligated. The left bile duct was isolated and sectioned, and the end was closed with continuous 6-0 Prolene suture. After completing parenchymal transection, the left suprahepatic vein was selectively clamped, and liver resection was completed. The surgical specimen was removed from the field, and then the left suprahepatic vein was closed with continuous 5-0 Prolene suture. Then, the gallbladder is resected with contrast-enhanced intraoperative cholangiography with propofol, ruling out bile leakage.

The patient presented favorable outcome and was discharged on postoperative day 4 with indication of attending the outpatient clinic for follow-up. The CT scan performed one month after the surgery showed adequate regeneration, without lesions, and the presence of a collection on the cut surface that could not be drained percutaneously. A new CT scan was ordered 2 months later, which evidenced a reduction in biloma. In April, another CT scan demonstrated that the collection had resolved.

The pathological examination of the surgical specimen reported the presence of a solitary fibrous tumor measuring 15 × 10.8 × 9 cm with clear margins (Fig. 2). The liver free from the tumor presented 10% macrovesicular steatosis. The immunohistochemical staining was done on 5 microns thick tissue sections (using VENTANA BenchMark GX automated staining instrument), and was positive for vimentin, Bcl-2, CD34, CD99 with Ki-67proliferative index of 2-3%.

Figure 2 Gross examination of the surgical specimen and histological exam (magnification 10x. Inmunohistochemical staining: CD34) 

The multidisciplinary oncology committee recommended not to perform adjuvant treatments.

The patient remained free of disease 9 months after the procedure and continued with periodic follow-up with abdominal ultrasound and CT scan.

Solitary fibrous tumors are mesenchymal neoplasms of fibroblastic-type lineage, with thick bands of collagen which usually display prominent hemangiopericytoma-like patterns⁴. These tumors account for less than 2% of all soft-tissue tumors, and are most commonly located in the thorax and pleura⁴, but have also been reported in various extrathoracic organs, including the upper respiratory tract, orbits, soft tissues, abdomen, and breasts⁵. Liver tumors are extremely rare, and their incidence is unknown. Less than 60 examples are found in the literature (Pubmed/ Medline). The majority of SFTL occur in adults (mean age: 57 years) and appear to be more common in women⁵.

While most cases present as asymptomatic, some cases, such as our patient, present as a palpable mass with bloating. Radiologically, these tumors are hyperechoic on ultrasound and appear as a heterogeneous mass with irregular central enhancement on CT scan. On T1-weighted magnetic resonance imaging this tumor present as low or intermediate intensity and on T2 sequences both hypointense and hyperintense areas are seen². The definitive diagnosis is made by histopathological examination of the resected specimen based on immunohistochemical findings. A positive CD34 expression in SFTL helps in distinguishing it from other spindle cell neoplasms. They are usually positive for CD99 and Bcl-25, as in our case. Percutaneous Trucut biopsy is not recommended because of the risk of dissemination or growth.

The malignant potential is unknown, and they initially present as recurrence, metastasis or intractable hypoglycemia. Metastases occur most frequently in the lungs, bones or liver3. Complete surgical resection with clear margins is the single treatment available. R0 resection is mandatory because the malignant transformation into a high-grade sarcoma carries a poor prognosis. Malignant histopathological features include hypercellularity, cytological atypia, a high mitotic rate (4 or more mitotic figures per 10 high-power fields) and tumor necrosis⁶.

Solitary fibrous tumors of the liver are rare. The differential diagnoses include CD34 negative tumors as leiomyoma, inflammatory pseudotumor, fibrosarcoma and stromal tumor (CD34 positive)¹. The clinical presentation is usually that of a large indolent tumor or may be asymptomatic and present as an incidental finding in imaging tests. Its behavior is not completely defined. In some cases, SFTL acts as an aggressive sarcoma with poor prognosis³.

Currently, only surgery offers a therapeutic opportunity for these patients. R0 resection is mandatory because the prognosis depends on resectability rather than on tumor size of histological grading. There is no agreement about the need for adjuvant therapy.

Long-term follow-up with imaging tests is mandatory to ensure survival of patients operated on⁵ and for better understanding this uncommon condition