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Positron emission tomography/computed tomography manifestations of primary hepatic myxoid liposarcoma

Abstract Rationale: Computed tomography (CT) and magnetic resonance imaging (MRI) are conventional used to evaluate liver tumors. Detection of fat component is considered an important clue to the imaging diagnosis of hepatic myxoid liposarcoma. However, the positron emission tomography (PET)/CT report of hepatic myxoid liposarcoma is scarce, and the metabolic characteristics of primary hepatic myxoid liposarcoma are still unknown. Patient Concerns: In this report, we report the PET/CT manifestations of a rare case of primary hepatic myxoid liposarcoma that was confirmed by pathologic examination. A 29-year-old male patient presented with a nodule adjacent to the umbilicus that had been present for 2 weeks. PET/CT showed a hypoattenuating mass with moderate uptake (maximum standardized uptake value [SUVmax] 1.9), except for a slightly hyperattenuating focal area with intense uptake (SUVmax 3.1). Diagnoses: The final pathologic diagnosis was confirmed, by means of laparotomy, to be a primary hepatic myxoid liposarcoma with multiple extrahepatic metastases. Interventions: The lesions in the left liver and periumbilical abdominal wall were punctured. During the laparotomy, hepatic malignant tumors were confirmed and metastasized widely in the abdominal cavity. Outcomes: An abdominal CT performed 4 months after initial presentation showed extensive metastasis. Lessons: Primary hepatic myxoid liposarcoma may manifest as moderate metabolism with less fat on PET/CT. PET/CT is not only valuable in reflecting the round cell component of hepatic myxoid liposarcoma, but also in estimating its origin.


Introduction
Myxoid liposarcoma is the second most common type of liposarcoma, accounting for 30% to 40% of all liposarcomas. [1] Myxoid liposarcoma most commonly occurs in the lower extremities, followed by the buttocks, retroperitoneum, and trunk. [1] Primary hepatic liposarcoma is very rare; <12 cases have been identified to date. [2,3] Detection of fatty tissue in the tumor helps to narrow the diagnosis. Primary hepatic myxoid liposarcoma should be further differentiated from other fatcontaining masses such as angiomyolipoma, hepatocellular cancer with steatosis, and teratoma. [4] Recently, positron emission tomography (PET)/computed tomography (CT) was confirmed to be capable of differentiating hibernoma from liposarcoma in the thigh. [5] However, literature regarding PET/ CT evaluation of hepatic liposarcoma is still scarce. Furthermore, there is no report about the PET/CT findings of hepatic myxoid liposarcoma. In this case study, we discuss the PET/CT images of a pathology-confirmed rare hepatic myxoid liposarcoma.

Case presentation
A 29-year-old male presented with a small nodule above the umbilicus that was first noticed 2 weeks prior to presentation. Abdominal ultrasound examination of the lesion, performed at a local hospital, revealed a mass in the left lobe of the liver that was most likely a liver tumor with abdominal metastasis. The patient had no obvious symptoms during the course of his evaluation and treatment. He was referred to our institution for further diagnosis and treatment. Physical examination revealed a firm mobile nodule above the umbilicus. Laboratory testing revealed a slightly elevated direct bilirubin (9 mmol/L, reference range 1-7 m mol/L); other liver function indices were all within normal limits. Serum tumor markers were also within normal limits, including alpha-fetoprotein, carcinoembryonic antigen, carbohydrate antigen (CA) 199, CA 125, ferritin, and total prostate-specific antigen.
Abdominal noncontrast CT revealed a well-circumscribed hypoattenuating mass measuring approximately 9.1 Â 9.6 cm 2 in the left lobe of the liver with slight heterogeneity. Contrastenhanced CT imaging showed nodularity and ring-shaped enhancement of the hepatic mass. An additional nodule with attenuation and an enhancement pattern similar to the hepatic lesion was also observed in the middle of the anterior abdominal wall. Abdominal magnetic resonance imaging (MRI) revealed a well-circumscribed mass in the left liver lobe that was heterogeneously hypointense on T1-weighted images (T1WIs) and hyperintense on T2-weighted images (T2WIs). There was signal loss of the tumor on out-of-phase MRI. Furthermore, the mass showed slightly increased signaling in diffusion-weighted MR images (b = 800). Contrast-enhanced MRI also showed nodularity and ring-shaped reinforcement. The signal intensity and enhancement pattern of the nodule in the middle of the anterior abdominal wall were similar to the imaging characteristics of the hepatic lesion.
To further evaluate the lesions, the patient was examined with a Siemens Biograph 16 PET/CT scanner (Siemens Medical Solutions USA, Inc, Malvern, PA) with intravenous injection of fluorodeoxyglucose (FDG) at 5.5 MBq/kg. PET/CT revealed a hypoattenuating mass approximately 8.3 Â 11.0 cm 2 (11.2 HU) in the left lobe of the liver. Radioactive uptake of the mass was moderate, that is, uptake of the mass was similar to hepatic parenchyma uptake, with a maximum standardized uptake value (SUVmax) of 1.9. A small, ring-shaped, mildly hyperattenuating area of the mass showed intense uptake, that is, lesion uptake was higher than hepatic parenchyma uptake, with an SUVmax of 3.1 (Fig. 1). The SUVmax was 3.6 on the delayed scan. Multiple small hypoattenuating nodules were revealed below the umbilicus in the abdominal wall and peritoneum, which showed slight uptake with an SUVmax of 1.8.
To clarify the diagnosis, the patient underwent laparotomy. The tumor could not be excised via surgery due to extensive intraperitoneal metastasis. The diagnosis of hepatic myxoid liposarcoma was confirmed by pathology (Fig. 2). The patient then returned to the local hospital for chemotherapy. Four months later, abdominal CT showed extensive metastasis in the abdominal and pelvic cavities. The patient died a few weeks later due to extensive recurrence of the tumor.
The CT findings of hepatic liposarcomas included a well-defined hypoattenuating mass with cystic degeneration, occasional bleeding, and margin enhancement. [3,6,7,9,11,12] The MRI findings of hepatic liposarcomas included T1WI and T2WI hyperintensity of fatcontaining components, T1WI hypointensity and T2WI hyperintensity of other components, and signal loss with fat suppression. [5,9] Similarly, hepatic myxoid liposarcomas containing myxoid components and nonfat nonmyxoid components showed heterogeneous enhancement on contrast-enhanced MRI. [17] In this case, CT did not show any detectable fat component but did reveal heterogeneous reinforcement. In-phase and out-of-phase MRI confirmed the presence of a fat component in this case. The identification of a fat component of the tumor provided the basis for an image-based diagnosis of hepatic myxoid liposarcoma.
The PET/CT revealed moderate uptake of the hepatic myxoid liposarcoma, which was consistent with the hypocellularity of the mass. [17] The area of intense focal uptake on PET/CT was consistent with the MRI-identified nonfat nonmyxoid component, which reflects the nature of round cell clusters. [18] Thus, PET/CT alone could not fully reflect the molecular biologic behaviors of myxoid liposarcoma, but when combined with MRI allowed for a comprehensive evaluation of hepatic myxoid liposarcoma. The unique advantage of PET/CT was the confirmation that the tumor in this case originated from the liver, thereby excluding the diagnosis of metastatic liver liposarcoma.
Fine-needle aspiration biopsy has not been shown to be a valuable diagnostic tool when evaluating primary hepatic liposarcoma. Only 1 case was confirmed as liposarcoma with this method. [3,5,7,9] Surgical resection is regarded as the treatment of choice for primary liposarcomas, and surgical therapy can also be used to treat recrudescent resectable foci. [6] Radiotherapy is modestly effective, but can only be applied to specific areas. [3] The 5-year survival rate of hepatic liposarcomas after surgery or radiotherapy is about 50%. [7] It has also been reported that older age (>45 years), necrosis, and high histologic grading are associated with a poorer prognosis in myxoid liposarcoma patients. [19] In general, PET/CT evaluation revealed that primary hepatic myxoid liposarcomas could be represented as a moderately metabolic tumor with little fat. Primary hepatic myxoid liposarcoma should be included in the differential diagnosis of liver disease with moderate uptake on PET imaging.