Intra- and Extracranial Solitary Fibrous Tumor of the Trigeminal Nerve: CT and MR Imaging Appearance

Discussion

In 1931, Klemperer and Rabin⁸ reported SFT as a localized fibrous tumor arising in the pleura. The further development of electron microscopy and immunohistochemistry clarified that this tumor was not from mesothelial but rather from mesenchymal origin, and it is now referred to as a SFT, different from a mesothelial tumor. Although initially most SFTs were reported to arise within the thoracic cavity, recently they have been more frequently reported in other sites and organs. The diagnosis of SFT rests on a combination of histopathologic and immunohistochemical features. Because SFT shows such a variety of patterns on radiologic imaging, it would be difficult to make a correct presurgical diagnosis.⁹ Most SFTs present as well-circumscribed and often encapsuled lesions of 1–25 cm. On sections, they frequently show a multinodular, whitish, and firm appearance. In addition, myxoid and hemorrhagic changes are occasionally observed. Histopathologically, SFTs typically exhibit a patternless architecture characterized by the coexistence of hypo- and hypercellular areas, which are separated by fibrous stroma having hemangiopericytoma-like branching blood vessels. Immunohistochemically, SFTs tend to be positive for CD34, CD99, and BCL2. They are usually negative for S100 protein, cytokeratin, and/or desmin.⁹

On CT scans, SFTs usually appear as well-circumscribed, round, or lobulated masses with attenuation of soft tissue.^9,10 On T1-weighted MR images, they are usually isointense to the muscle.⁹ On T2-weighted images, SFTs are mainly hypointense, corresponding to fibrous stroma intermixed with prominent vascular channels.^2,9,10 In our case, SFT had rich collagenous stroma with hyalinization. After intravenous contrast administration, the tumor usually shows homogeneous enhancement but also sometimes heterogeneous enhancement, corresponding to the cellularity, stromal components, and degeneration. The enhancement can be from moderate to strong, presumably depending on the cellularity, stromal component, and vascularity. In a tumor with strong enhancement, the vascular bed may be seen as serpiginous signal-intensity voids on MR imaging.^10–12

The typical presentation of intracranial SFT strongly mimics that of a dural-based meningioma, on the basis of the likely mesenchymal origin of SFT. When located in the spine or in close relationship with the central nervous system, it may be difficult to distinguish from a schwannoma.³ Meningioma usually appears isointense relative to brain parenchyma on both T1- and T2-weighted images, and schwannoma usually appears hyperintense on T2-weighted images. On T2-weighted and postcontrast T1-weighted images, the intracranial component of jugular foramen meningioma has higher intensities and stronger enhancement than its extracranial component.¹³ These findings represent a clue to the possibility of a jugular foraminal tumor being a meningioma.¹³ In our case of SFT, different signal intensities and contrast enhancements were noted between intra- and extracranial components. Although SFT could show variable intensities on T2-weighted images, many SFTs are reported as mainly hypointense on T2-weighted images.