First described by Klemperer and Rabin in 1931 , solitary fibrous tumors/hemangiopericytomas (SFT/HPC) are an uncommon group of rarely metastasizing tumors of fibroblastic mesenchymal origin. Although commonly perceived as intrathoracic (most often involving the visceral pleura and submesothelial connective tissues), in reality some 60% of these tumors arise outside the thoracic cavity, including the central nervous system, and are now recognized to occur anywhere in the body . These tumors are considered rare – less than 2 percent of all soft tissue tumors in one of the largest retrospective series , the most common single site being the pleura, with 900 cases reported worldwide up to 2005 . 16% of SFTs/HPCs occur in the head and neck, including the central nervous system (CNS) . SFTs/HPCs of the central nervous system are rare, usually
dural-based, and account for less than 1 percent of all primary CNS neoplasms [4, 5]. These tumors typically occur at younger patients compared with other SFTs/HPCs. No known environmental or genetic risk factors are currently identified for SFTs/HPCs . Of note, since the discovery of a unique and recurrent gene fusion for both SFTs and tumors histologically classified as hemangiopericytomas, the use of the latter term is discouraged in clinical practice, with restructuring of solitary fibrous tumor and hemangiopericytomas as one entity [5, 6].
Grossly, SFTs/HPCs are usually well circumscribed and rarely invade adjacent sites. Microscopically, these tumors are relatively hypocellular and include a thick network of collagen fibers. Mitotic activity is minimal and anaplasia occurs in less than 1% of cases. In contrast, the more aggressive phenotype (previously termed 'hemangiopericytoma' by neuropathologists) is highly cellular and tends to recur locally and metastasize [5, 7]. Immunohistochemical testing includes CD34, Bcl2, CD99, vimentin, and the highly specific STAT6 staining. Molecular testing includes the NAB2-STAT6 fusion gene – which appears to be a unique feature of SFTs/HPCs [8, 9].
While SFTs/HPCs are uncommon in the CNS (with only 112 reported cases worldwide until 2012) , SFTs/HPCs arising from the spine are very rare, with only 68 cases documented worldwide between 2000 and 2017 . Based on recent reports, these tumors can be divided into 4 subtypes – vertebral, paravertebral, spinal cord and mixed, of which pure spinal cord SFTs/HPCs constitute the minority of cases. Complete surgical resection is the treatment of choice in most cases, as residual tumors may recur in 10–50% of patients and worsen prognosis and overall survival [10, 12, 13].
We hereby present a rare case of an intradural SFT of the cervical spine.