Fig 6. (a)(100X) IHC for CD34- Tumor cells showing membranous immunopositivity, (b)(40X) Photomicrograph showing a spindle cell tumor in a hemangiopericytomatous pattern. Blood vessels are dilated and thin walled
Discussion
Solitary fibrous tumors (SFT) were first described in pleura by Lietaud in 1767, followed by Wagner in 1870.[3] Klemperer and Rabin, in 1931, classified pleural tumors into two types: diffuse mesotheliomas and localized mesotheliomas or solitary fibrous tumor [SFT]. [4] In 1991, Witkin and Rosai were the first to report a case in the head and neck region.
SFTs were classified as benign and malignant based on histopathological features. Also been referred to by numerous other names, most of which are now outdated[5]. Subsequent immunohistochemical and ultrastructural studies have suggested that SFTs are most likely derived from adult mesenchymal stem cells rather than mesothelium, ‘Solitary fibrous tumor’ is the currently preferred term.
Pleural SFTs account for about 30% of all cases followed by meninges of about 27%. The most common extra-pleural and extra meningeal locations include abdominal cavity in 20 %, trunks in 10 %, extremities in 8%, and neck in 5 %. In the head and neck, the most common site affected is the oral cavity [6]. SFT in pleura have a unique gross and microscopic appearance, wherein situation is different when it affects extra pleural sites.
Clinically extra pleural SFT may present with symptoms related to the site of origin of tumor or with systemic symptoms such as hypoglycaemia, arthralgia, osteoarthropathy and clubbing of fingers due to the production of an insulin like growth factor. The systemic symptoms usually resolve on removal of tumors. These tumors usually present as a well-defined, palpable, painless, and slowly growing mass. Extension to the parapharyngeal space to be suspected, if the patient develops compression symptoms. Sleep apnoea is reported, as a result of parapharyngeal extension of the parotid tumour [7]. Radiographic findings are non-specific. Hence, a diagnosis of SFT is based on histological and immunohistochemical findings. On IHC, SFTs are reactive to CD34, Bcl2, vimentin, CD99.
England et al. [8] defined the histological criteria, still valid today, that characterize malignant SFTs (Table 01)
To determine the risk of malignancy of each tumor, Demico in 2017[09] classified SFT into three groups according to the risks of metastasis, which is depending on the malignant potential determined for each tumor. (Table 02)
Follow-up is based on guidelines for soft tissue sarcomas of the National Comprehensive Cancer Network: Low-risk tumours, an imaging test every 6 months for 3 years, and then annually until 5 years, Medium or high-risk tests, every 3–4 months during the first 2 years and then every 6 months until the fifth year.
Surgery in these tumors should be planned with the aim of achieving complete surgical resection with optimal margins as SFT can have a potential malignant behaviour, and to avoid local recurrence.
Parapharyngeal space SFTs are very rare. Hence, they should also be considered in the differential diagnosis of parapharyngeal soft tissue tumors. This case is being reported to bring out an extremely rare vascular tumor at rare site and also represents a surgical challenge because of difficult access in parapharyngeal space with difficult planes between tumor and rest of PPS, approach to PPS is also difficult