Solitary fibrous tumor (SFT) comprises a histologic spectrum of fibroblastic mesenchymal neoplasms that rarely metastasize.¹ Although Wagner² provided the first detailed histologic description of a SFT tumor of the pleura in 1870, the lesion was only recognized as a distinct clinical entity by Klemperer and Rabin in 1931.³ It has been recognized under several different names in the past, including benign mesothelioma, localized mesothelioma, solitary fibrous mesothelioma, pleural fibroma, submesothelial fibroma, subserosal fibroma, and localized fibrous tumor.

Hemangiopericytoma (HPC) was first described in 1942 and initially believed by Stout and Murray⁴ to be a vascular tumor related to smooth muscle pericytes. However, over the years since its original description, it has become evident that HPC is simply a descriptive term to characterize a heterogeneous group of neoplasms that share a common growth pattern.⁵ Three categories have been individualized within this heterogeneous group of HPC-like neoplasms. One corresponds to some non-HPC neoplasms that occasionally display HPC-like features, such as synovial sarcoma, infantile liposarcoma, and leiomyosarcoma. Another contains lesions that show evidence of myoid/pericytic differentiation such as glomangiopericytoma/myopericytoma, infantile myofibromatosis, and some sinonasal tumors.⁵ The final category is the SFT group, which includes SFT and related lesions ranging from heterogeneous, multinodular, partially sclerotic tumors to monotonous, highly cellular ones.⁶,⁷,⁸,⁹,¹⁰ Proposed variants of SFT include the fibrous variant (conventional SFT), cellular variant (conventional HPC), a fat-forming variant (lipomatous HPC), and a giant cell-rich variant (giant cell angiofibroma).⁵ With the discovery of a unique fusion gene in SFT and other tumors histologically identified as HPC, these two tumor groups are now generally considered to be the same entity with the term “SFT” as the preferred name.¹,¹¹

SFT has an equal distribution among men and women¹²,¹³ and occurs in adults of all ages, most commonly in the fifth and sixth decades.¹²,¹³,¹⁴ They may be found in almost any site of the body with intrathoracic being the most common location where the pleura is most often involved, followed by lung parenchyma, mediastinum, and the diaphragm.¹²,¹⁵ The most common extrapleural site is the abdomen,⁶,¹²,¹⁶ followed by the trunk, extremities, head and neck, and intracranial sites.¹⁷,¹⁸,¹⁹,²⁰,²¹,²²,²³,²⁴,²⁵ SFT arising in the head and neck most often arises in the sinonasal tract, oral cavity, orbit, or intracranially from the meninges.²⁶,²⁷,²⁸,²⁹,³⁰ Primary eyelid SFT is uncommon with fewer than 40 cases reported.¹⁰,³¹,³²,³³,³⁴,³⁵,³⁶,³⁷,³⁸ However, the majority of the lesions involving the eyelids represent anterior extensions or coexisting eyelid lesions associated with orbital tumors.³³,³⁹,⁴⁰,⁴¹,⁴²

Most SFTs behave benignly, but a minority of patients will develop metastatic disease to the lungs, bones, and liver.⁴³ In lesions arising from the pleura, 13% to 23% are classified as malignant, whereas most extrapleural SFTs behave in a more benign fashion.⁷ Larger tumor size (>10 cm), high mitotic rates, increased cellularity, pleomorphism, hemorrhage, and necrosis are predictive of a greater potential for recurrence, local invasion, and metastatic spread.¹⁵,⁴⁴