The solitary fibrous tumour of the orbit is a rare spindle-cell neoplasm originating from mesenchymal fibroblast-like cells histologically identical to solitary fibrous tumours found elsewhere
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Epidemiology
Solitary fibrous tumours occur in a wide age range reported from 9 to 76 years without a convincing gender predilection, although some reports have found increased incidence in females with the male-to-female ratio of 1:2
Clinical presentation
The patients usually present with slowly progressive painless unilateral exophthalmos or swelling or palpable mass in the periocular area,
Pathology
On microscopic examination, solitary fibrous tumours are well-circumscribed, non-encapsulated tumours that show a pattern-less arrangement of alternating hypercellular and hypocellular regions of spindle cells against a collagenous background of variable vascularity. A strongly positive reaction for immune-histochemical marker CD34 is now believed to be the most important marker for diagnosis.
Solitary fibrous tumours are also immune-reactive for vimentin and B-cell lymphoma 2 (bcl-2) but negative for keratin, cytokeratin, epithelial membrane antigen, S-100 protein, smooth muscle actin, factor VIII-related antigen, and Desmin.
Radiographic features
Solitary fibrous tumour usually present as a solitary well-circumscribed ovoid mass located in intraconal and extraconal spaces of the orbit, lacrimal gland, lacrimal sac, and eyelid.
CT
Solitary fibrous tumours are well-circumscribed and iso-dense to hyperdense compared to muscle / cerebral cortex. Occasional internal calcifications and necrosis have also been reported. Although remodelling of the adjacent bones may be seen in large, long-standing lesions, frank bone destruction is an exceptional finding that should prompt suspicion for a malignant tumour.
The lesions show marked homogeneous or heterogeneous enhancement on post-contrast images very similar enhancing characteristics to those of the internal carotid artery which is attributed to high vascularity because of the prominent vascular channels within the tumour. The lesions demonstrate rapid enhancement and early washout of contrast.
MRI
These tumours exhibit the following signal characteristics:
- T1: homogeneous isointense signal intensity typically similar to cerebral cortex or muscle
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T2:
- iso- to hypointensity (the best clue to the diagnosis)
- heterogeneous mixed iso to hypointensity, reflecting fibrous tissue with high collagen content
- areas of intralesional T2 hyperintensity related to internal haemorrhage, cystic degeneration, or relatively fresh fibrosis
- T1 C+: diffuse heterogeneous vivid contrast enhancement seen on post-contrast images
Treatment and prognosis
Although local excision is usually curative, orbital solitary fibrous tumours have been reported to recur and may rarely metastasise. Local recurrences are usually related to incomplete excision. Although extremely rare, malignant degeneration has also been reported.
Differential diagnosis
The differential diagnosis is that of a highly vascular orbital lesion and includes
-
capillary haemangioma of the orbit
- during the first 6 months of life
-
cavernous haemangioma (venous malformation)
- T2 hyperintensities of containing fibrous septa and delayed pooling of contrast on dynamic studies
- orbital varix
- haemangiopericytoma
- giant cell angiofibroma