A review of solitary fibrous tumours of the orbit and ocular adnexa

Abstract

Solitary fibrous tumour (SFT) is an uncommon spindle cell tumour of mesenchymal origin characterised by NAB2-STAT6 gene fusion. Although it was first described in the pleura, it can occur in connective tissue in any part of the body, but rarely presents in the orbit and ocular adnexa. SFT, which is part of the same disease spectrum as other fibroblastic tumours such as giant cell angiofibroma, haemangiopericytoma and fibrous histiocytoma, usually presents as a painless, slow-growing mass in any age group and generally follows a benign course, with a good prognosis after complete excision. However, malignant forms rarely occur. Even for benign tumours a more aggressive clinical behaviour is possible, with relentless infiltrative local growth, frequent recurrence following surgery, and malignant transformation with the potential for metastatic spread. Careful long-term follow-up is essential. The published literature on SFTs of the orbit and ocular adnexa is reviewed, and the aetiology, clinical presentation, epidemiology, radiological features, histopathology, immunohistochemistry, risk stratification, clinical management, and prognosis are discussed, reflecting on our own experience.

Fig. 1. Clinical presentation and progression of SFT in left superior rectus.

A 41-year-old man with a 1-year history of vertical diplopia, followed by left proptosis and frontal headache for 2–3 months. Note mild inferior displacement of left eye by superior orbital mass. B Progressive tumour growth during 5 years of observation. Note increased left proptosis, worsened hypoglobus, upper lid swelling and significant inferior scleral show. Mild diffuse left conjunctival injection is suggestive of exposure. C Contrast-enhanced coronal MRI scan on presentation revealed a well-circumscribed mass in left superior orbit. The mass is centred on the superior rectus muscle which is not identifiable separate from the mass. There is diffuse contrast enhancement with a few hyperintense streaks. Orbital biopsy confirmed a solitary fibrous tumour. D Contrast-enhanced coronal MRI scan 5 years after presentation shows significant enlargement of the left superior rectus mass, which displays avid heterogenous contrast enhancement and displaces the left optic nerve medially and inferiorly.

Fig. 2. CT scan features of SFT.

A Axial CT scan of the orbits 1 year after presentation showing a large well-circumscribed, fusiform mass in the left superior orbit extending to the orbital apex and corresponding to the superior rectus muscle. Note the lesion has similar radiodensity to brain cortex. B Sagittal contrast-enhanced CT scan. Note the avidly enhancing mass in the left superior orbit conforming to the shape of the superior rectus. The mass extends to the muscle origin at the orbital apex and the optic nerve is displaced inferiorly. C Coronal CT scan of orbits 1 year after presentation reveals a large well-circumscribed ovoid mass of brain density in the left superior orbit centred on the superior rectus. The bone is not involved but the left orbit looks expanded. There is no intralesional calcification. D The lesion enhances uniformly with contrast.

Fig. 3. MRI features of SFT.

A Hypointense well-circumscribed ovoid mass in left superior orbit on Coronal T1-weighted MRI. B Coronal T2-weighted MRI reveals intermediate density well-circumscribed lesion in left superior orbit. C Contrast-enhanced and fat-suppressed T1-weighted coronal MRI. The large left superior rectus mass enhances avidly with contrast. Note peripheral ring enhancement (superiorly and medially) and few hyperintense streaks inferiorly. D Axial T2-weighted MRI 5 years after presentation. Note large fusiform mass in left superior orbit. The mass is mostly isointense with brain with some heterogenicity. E Diffusion-weighted MRI scan at presentation showing non-restricted diffusion of the left superior orbital mass.

Fig. 4. Histopathology and immunochemistry of SFT.

A Macroscopic appearance of longitudinally cut left orbital exenteration specimen. Note the cream-coloured tumour centred on the superior rectus (arrow), infiltrating the orbital fat, and extending to the periorbita superiorly. The tumour extended to the orbital apex posteriorly. Hence the posterior margin was involved, and the orbital apex was debulked piecemeal. B Macroscopic appearance of longitudinally cut left orbital exenteration specimen stained with H + E. Note the mostly basophilic tumour centred on the superior rectus (arrow). C Low power view displaying the typical ‘patternless’ architecture of the solitary fibrous tumour with haphazard growth. H + E (magnification ×200). D High power of bland spindled cells set within a collagenized stroma. Mitotic activity is low. Note a single mitotic figure in this field (arrow). H + E (magnification ×400). E There is myxoid change within the stroma in which many thin-walled open blood vessels could be seen. H + E (magnification ×100). F Orbital solitary fibrous tumour with extraocular muscle fibres evident (arrow). H + E (magnification ×200). G High power showing a very vascular tumour with some blood vessels displaying the classical ‘staghorn’ branching arrangement (arrows). H + E (magnification ×400). H Strong and diffuse cytoplasmic CD34 immunoreactivity (magnification ×200). I Strong and diffuse STAT6 nuclear positivity on immunohistochemistry (magnification ×200).