Clinical features of orbital SFT
With the further understanding of SFT, although it is commonly occurs within pleura, there has been an increase in its incidence in nonpleural sites in recently. SFT is reported in diverse bodily locations, and recognized to have a wider range of clinical and radiological features[4]. Orbital SFT is a kind of extrapleural SFT, and is a rare kind of orbital tumor. Due to its relatively rare, the clinical characteristics have not been fully grasped at present. Although SFT is usually considered as a clinically indolent neoplasm, the orbital SFT is usually more aggressive than pleural form, and the prognosis is substantially unpredictable[3]. Therefore, it has a great clinical significance to study the clinical characteristics and development rules of this tumor.
Orbital SFT has no obvious age preferenction, our study has been documented across a wide age range from 19 to 72 years, and children's patient has also been reported[5]. But from previous reports, as well as our findings, adult cases seem to account for the majority. It has no sex and side of affected eye predilection according to previous reports.
The common manifestations include exophthalmos and eyeball dislocation, andsome patients may be associated with eyelid swelling, visual disturbances, a palpable painless mass, epiphora, and ptosis, periorbital spontaneous pain or tenderness[6]. The majority of patients suffer minor visual impairment. But the patients of recurrent orbital SFT with compressive optic neuropathies or exposure keratitis, often result in severe impairment of visual function, or even loss of vision. In some patients, the lesions are relatively superficial in the orbit, the painless soft tissue masses can be touched. If the mass presses on the dacryocyst, symptoms of epiphora is common. Although the clinical manifestations were diverse, they are not significantly different from other orbital tumors.
Imaging features of orbital SFT
Orbital SFT usually presents as a soft-tissue mass on CT. The tumors are often outside the muscular cone, partial cases are involved in, or within the in the orbital muscle cone. Most commonly located at superomedial quadrant of the orbit, the second is inferomedial quadrant of the orbit. The masses are mostly round or oval in shape. The density of the lesions is uneven in most cases. The mean CT values range from 22.8 Hu to 66.4 Hu in our study, thus the mean CT values of the tumors on CT scans are variable. This is similar to schwannoma, but different from cavernous hemangiomas. The boundary of the tumor is most clear, but it is un clear when it is recurrent cases or the lesion is very large. Remodeling of the adjacent bones can be seen with long-standing orbital SFT[6], due to the compression of the lesions. The change of adjacent bones is found in 9 patients of our group. The disease can spread to the nasal cavity or the brain in the recurrent or long-standing cases.
Although not pathognomonic, homogeneous or heterogeneous-attenuated enhancement is reported to be the most prominent feature of SFT revealed with CT and MR imaging, which is attributed to high vascularity because of the prominent vascular channels within the tumor. And it can see a markedly enhancing mass showing the similar characteristics to those of the internal carotid artery on postcontrast CT or MR images[7]. We found that the MRI signals of orbital SFT are relatively complex in practice. It is mostly medium or low signal on T1WI, but can show arbitrary signal on T2WI, which may be related to the composition of the tumor. Consistent with previous reports, most tumors can be significantly enhanced. But in the majority of cases, it is inheterogeneous enhancement, and the lamellar unenhanced regions can also be found in this study. In a recurrent cases, we find that most lesions are not enhanced, except for cystic enhancement around the lesion.
Due to the uncertainty of lesion signal on MRI, it is necessary to distinguish from orbital hemorrhage and schwannoma. The lesions in hemorrhage is no enhanced on MRI. The composition of orbital schwannoma is complex. Secondary degenerative changes of the tumor, such as cyst formation, hyalinization, hemorrhage, are relatively common. These lead to extremely complex MRI findings of schwannomas. But the boundary of the schwannoma is very clear, and we can find that the tumor is associated with the corresponding nerve in some lesions. Other orbital tumors for differential consideration include histiocytomas, giant cell angiofibromas, and hemangiopericytomas[8].
Histopathological and immunohistochemical features of orbital SFT
Some tumor specimen has very thin capsules or pseudocapsules, and some tumor specimen has no capsules. The typical SFT phenotype is that the tumor cells are spindle-shaped, and the alternately arranged sparse and dense cells are separated by eosinophilic collagen fiber bands[9]. Normally, immunohistochemical markers are fundamental for the diagnosis, and the combination of immunohistochemical markers CD34 and Bcl-2 increase the diagnostic accuracy[10,11]. The expression of CD34 is usually diffuse and intense, but according to the report, the expression of Bcl-2 is very high in STF and negative in most malignant mesotheliomas. This is similar to our study. Expression of the Ki67 protein (pKi67) is associated with the proliferative activity of intrinsic cell populations in malignant tumors, allowing it to be used as a marker of tumor aggressiveness[12]. Although the Ki-67 labelling index is very low, most cases are <10% in our study, malignant forms with an increased propensity for local recurrence have been reported[11]. Vimentin is a key component of the cytoskeleton, and is particularly important during development and in cancer during epithelial–mesenchymal transition and metastasis[13]. Due to the high expression rate of Vimentin in orbital SFT, we must be alert for recurrence or metastasis of this tumor. In this study, 3 patients were tested for STAT6, and all were strongly positive. Studies have found that the fusion of NAB2 and STAT6 genes can make the STAT6 protein in the cytoplasm enter the nucleus so that the nucleus strongly expresses the STAT6 protein. The immunohistochemical staining method using the STAT6 protein can quickly detect the NAB2-STAT6 gene fusion status in tumor cells, and it has high sensitivity and specificity for diagnosing SFT. STAT6 has a great auxiliary effect on accurately distinguishing SFT from tumors that are similar in morphology but negative for CD34[14]. Therefore, the combined application of Vimentin, STAT6, CD34 and other markers will help the correct diagnosis of SFT.
Treatment and prognosis of orbital SFT
There are few studies examining the various treatment modalities due to its rare. The mainstay of treatment for orbital SFT is en bloc surgical resection with negative margins. If the initial excision is incomplete, the recurrent tumor tends to spread into surrounding tissues and bone, rendering a second excision much more difficult[8]. In our opinion, these tumors may recur and require even more aggressive wide excision[8]. Especially in the cases with unclear boundary of lesions, the capsule is incomplete or no capsule, noncontact excision, and thorough rinsing of the operationg area after extensive excision, may reduce the recurrence rate of the lesion. Currently, there is little evidence that adjuvant chemotherapy and radiation therapy following complete surgical resection is beneficial and thus they are not routinely performed[15,16].
Through our observations, combined with previous reports, the fairly high local recurrence rate underscores their aggressive potential and highlights the importance of prospective recognition[17]. In our case, 2 patients were found to have relapsed, with the lesions growing more rapidly and more invasive after recurrence. In the cohort of recurrent orbital hemangiopericytoma/SFT, median time to recurrence was 4 years underscoring the importance of careful continued follow-up[18]. This group were followed up from 7 months to 8 years, and the median was 2 years 10 months. Thus, a longer follow-up is needed to determine the recurrence rate of the disease, and to identify the causes of recurrence.