Solitary fibrous tumor (SFT) is a rare spindle cell tumor originating from dendritic stromal cells expressing CD34 antigen. Both SFT and hemangiopericytoma (HPC) showed 12q13 inversion, NAB-2 and STAT-6 gene fusion. The two were combined as SFT/HPC in 2016 WHO central nervous system tumor classification[1, 2]. SFTP is a rare neoplasm accounting for less than 5% of primary pleural tumors. It derives from the submesothelial mesenchymal layer and usually appears to arise from visceral pleura, and rarely from the parietal pleura. Whereas benign SFTP are often small pedunculated tumors, most malignant SFTP may reach more than 10cm in diameter[2, 3]. However, when the tumor diameter is greater than 15 cm or when the tumor occupies more than 40% of the hemithorax, it can be defined as giant SFTP . The case we described had tumor growth of more than ten years, consistent with the benign tumor growth pattern. Finally, the tumor was surgically removed. The maximum diameter of the tumor was 23 cm, which could be regarded as a giant SFTP. Almost 80% of SFTPs are benign, and more than 50% of their course is asymptomatic. It is generally believed that whether SFTP causes clinical symptoms may be related to tumor size, and most SFTP patients are asymptomatic when the tumor size is small. When SFTP tumor size is large enough to cause compression of adjacent structures and lung tissue, patients may have chest pain, chest tightness, cough or dyspnea and other symptoms[5, 6]. It is known that some SFTP patients may develop so-called "paraneoplastic syndrome," including refractory hypoglycemia, digital clubbing, and pulmonary hypertrophic osteoarthropathy. In our case, the patient had repeated chest tightness and cough for more than two months, which may be a typical clinical manifestation for SFTP.
Thoracic CT is the standard radiological modality for investigating patients with SFTP. It is a useful diagnostic method, which can clearly identify the location and size of the lesion and help surgeons to assess the possibility of resecting the SFTP. These tumors are usually large, well-defined, lobulated, solid and vascular masses, often with a prominent feeding vessel. The enhancement pattern can vary depending on cellularity, vascularity and density of the collagenous or fibrous stroma. Central hypoenhancing or non-enhancing areas may be seen in the tumour, which represents necrosis or cystic change. It often reveals the proliferation of fibrous tissues as well as tumor and adjacent tissue details. Giant SFTPs are usually more likely to cause myxoid or cystic degeneration, hemorrhage, or necrosis. Thus, patchy inhomogeneous enhancement is common in gigantic SFTP with enhancement scanning. This imaging characteristic is often called ‘map sign’. The larger the tumor, the more inhomogeneous the enhancement. Calcification is rare and can be seen in large benign or malignant tumors [8, 9]. Tumors can demonstrate remarkable heterogeneity, with variable degrees of enhancement, necrosis or hemorrhage, and these appearances are not found to differentiate between benign and malignant lesions accurately. SFTPs larger than 10 cm in diameter are usually more likely to be malignant. However, it is difficult to determine the origin of the tumor when the SFTP tumor is giant and occupies the chest cavity. MRI multi-plane scans may be helpful for localization. MRI can provide more information in aiding distinction between benign and malignant lesions, with heterogeneous signal intensity and heterogeneous contrast uptake found to correlate with malignancy. If there is any suggestion of mediastinal invasion, MRI can be useful for surgical planning. Besides, some investigators have suggested that CT-guided aspiration biopsy is not advisable as a reliable tool due to its low diagnostic sensitivity. In our case, imaging features of SFTP are consistent with previous literature reports, and there is no significant specificity. However, the patient had a CT-guided biopsy of the lesion10 years ago in the local hospital, and the result may have been that the necrotic tissue was obtained by puncture, which was misdiagnosed as a pulmonary abscess. This false-negative result of puncture is what we need to pay attention to.
SFTP is a primary tumor arising from CD34-positive dendritic mesenchymal cells and accounts for <5% of all pleural tumors. Immunohistochemically, SFTP is positive for vimentin, CD34, CD99, and Bcl2. Thus tumors tend to grow into a huge mass before local compression symptoms develop, especially in patients without routine physical examinations.