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are now outdated[5].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