Bone metastasis often occurs in patients with breast, lung or prostate cancer, but it can also be found in most cases of advanced malignancies. Additionally, the skull and the skull base are frequent sites for bone metastasis. Bone metastasis typically involves the formation of destructive and osteolytic lesions centered in the bone on CT. It also shows hypointensly to normal bone marrow on non-contrast T1-weighted MRI [3]. The metastatic lesion at the skull base of our patient manifested as an extended infiltrative soft tissue mass with bony destruction on T1-weighted MRI, but no uptake signal at the skull base location was shown on the Tc-99m MDP whole body bone scan. The difference between the two episodes of F-18 FDG whole body tumor scan might imply that the SHC skull base metastasis did not exist before the diagnosis of primary SHC was made. In other words, these traits indicated that the lesion was most likely a metastatic tumor rather a second primary tumor, and gradually expanded into the soft tissue mass without any bone-associated activity [2].
The serum AFP level of the patient was initially within the normal limit (11.4 ng/ml) when he was diagnosed as having SHC before TACE, left liver lobectomy and RFA of the right liver lobe. This finding is compatible with the results of an 11-patient SHC case series by Koo et al [4]. In this case series, more than 50% of the patients had low or negative serum AFP levels. SHC with distant metastasis to the skull base ocurred in our patient, and serum AFP was then notably elevated (1002.2 ng/mL).
According to the literature review by Trivedi et al.,[5] only 24 cases of normal-cell type HCC with skull base metastasis were reported from 1968 to 2009. An additional two SHC cases were also reported: one with pelvic skeletal metastasis and one with peritoneal dissemination [2, 6]. Based on the above, there has never been any cases reported previously as sarcomatoid cell type HCC with skull base metastasis.
By definition, a sarcomatoid cell type of carcinoma must include both epithelial and mesenchymal differentiation at the same lesion site [1]. The typical findings of SHC have been recorded to be massive expanding or multinodular confluent type with partial encapsulation; [4] more specifically, the histopathology of primary hepatic sarcoma cells often presents with spindle shaped, clear nucleolus, acidophilic cytoplasm and significant mitotic attributes [7]. To establish a diagnosis of metastatic SHC to the skull base, pathological confirmation through EEA biopsy is required. In our case, the typical appearance of the SHC subtype was also observed in the skull base metastatic biopsy. Epidural biopsy showed sheets of tumor cells with markedly pleomorphic and hyperchromatic nuclei, frequent mitotic figures and tumor necrosis.
The prognosis of SHC is extremely poor, with 3-year survival rates reported as low as 18.2% after hepatectomy, [8] and our patient had experienced a metastatic recurrence at the skull base only 34 days after a left hepatic lobectomy. Radiotherapy, surgery and palliative care have been the options for HCC with skull metastasis in the past; [9, 10] however, EEA for decompression is now among the most optimal treatments for skull base metastasis because of its minimal invasiveness. Although EEA did not considerably prolong the life expectancy of our patient, it was able to improve neurological function and help the patient maintain his quality of life [11].
SHC with skull base invasion is such a rare condition that it has not been previously reported. Definite diagnosis of it requires neurologic findings, radiographic images and biopsy proof. Tc-99m MDP whole body bone scan and serum AFP levels were not considered definitive for monitoring bone metastasis of SHC in a previous report, these tools provided insufficient findings for diagnosis in our case. EEA for tissue biopsy and decompression is regarded as the most minimally invasive and optimal diagnostic and treatment option for skull base metastasis.