Orbital solitary fibrous tumor: A clinicopathologic correlation and review of literature.

Orbital solitary fibrous tumor (SFT) is a rare tumor originating from the mesenchyme. Initially described in the pleura and subsequently in other mesenchymal structures, orbit continues to be one of the uncommon extrapleural sites. The diagnosis of orbital SFT cannot be made with certainty on clinical or radiological evaluation and requires histologic studies with immunohistochemical confirmation for which CD 34 is the most specific diagnostic test. We describe clinical presentations, radiological and operative findings, and pathological features of a patient with orbital SFT along with a review of literature.

Introduction

Solitary fibrous tumors (SFTs) are uncommon spindle-cell tumors of mesenchymal origin that most often arise from the pleura but may also occur in various other sites including lungs, peritoneum, pericardium, kidneys, liver, and infrequently in the head and neck region.[1] The origin from the mesothelial differentiation has been questioned and SFT cells instead have shown mesenchymal and/or fibroblastic differentiation.[2] Orbital SFT was virtually nonexistent or misdiagnosed until its characteristic features, particularly the strong and diffuse immunoreactivity to CD 34 were first described by Westra et al.[3] It is possible that orbital SFTs were underdiagnosed earlier because of its rarity in the extrapleural sites and histologic similarity to other spindle-cell tumors. Orbital SFT typically causes insidious, painless proptosis developing over an average of 2 years in patients mostly in the fourth decade (age range, 9–76 years).[4-6] As a general rule, orbital SFT shows an indolent and nonaggressive clinical course, and a complete cure can usually be achieved with complete resection.[7]

Case Report

A 22-year-old man presented with progressive and painless protrusion of the right eyeball associated with downward displacement since the past 6 months. There were no visual symptoms. Physical examination revealed 6 mm of proptosis and 3 mm downward displacement of the eyeball [Figure 1a]. The visual acuity and the fundus examination were normal in both the eyes. Ocular movements were normal other than restricted elevation in the right eye. A soft compressible, nontender, nonpulsatile mass with well-defined margins was palpable in the superior orbit.

Figure 1

(a) Clinical photograph of the patient showing right proptosis with a downward displacement of the right eyeball. (b) CT coronal view, showing a well-defined heterogenous mass in the extraconal superior orbit. (c) CT axial view, showing a moderately enhancing well-circumscribed mass in the superior orbit. (d) Gross photograph of the tumor following excision. Note the pinkish color, areas of hemorrhages, and the thin overlying capsule

Computed tomography (CT) showed a well-defined, lobulated mass in the right extraconal superior orbit above the superior rectus - levator palpebrae superioris complex displacing the eyeball downward [Figure 1b]. The mass lesion was heterogenous with numerous internal hypodense areas, showed moderate contrast enhancement, and measured 31 × 28 × 15 mm extending up to posterior limits of mid orbit [Figure 1c]. However, there was no evidence of local bone remodeling, globe indentation, or optic nerve compression. A differential diagnosis of neurofibroma, schwannoma, and hemangiopericytoma was considered.

The lesion was approached extraperiosteally through a sub-brow incision. The mass was located within a clear dissecting plane isolated from the surrounding extaocular muscles without any evidence of local infiltration which facilitated a complete excision along with the overlying capsule. The postoperative period was uneventful, with resolution of proptosis, eyeball displacement, and ocular movement restriction. At the time of last examination 6 months postoperatively, no evidence of recurrence was observed. The patient remains under close follow-up.

Histopathology

Gross examination showed an oval pinkish mass measuring 22 × 21 × 11 mm [Figure 1d]. Cut section was pinkish-gray with multiple areas of hemorrhage. Microscopic examination showed a well-circumscribed, encapsulated tumor with cellular and cystic areas. The tumor cells were spindle shaped arranged in whorls form pattern with moderate nuclear pleomorphism, vesicular nucleus, inconspicuous to prominent nucleoli, and moderate amount of cytoplasm with indistinct cell boundaries [Figure 2a]. Areas of cystic degeneration were seen; however, no necrotic areas were noted. The tumor showed vessels of varying caliber, dilated to compressed, lined by flattened endothelium [Figure 2a]. However, stag horn channels and giant cells were not noted. There was minimal atypia with very few mitotic figures of 1 per 10 high-power fields (HPF). Immunohistochemistry showed tumor cells to be strongly positive for CD 34 [Figure 2b] and BCL-2 [Figure 2c]. The tumor cells showed positive staining with CD99 [Figure 2d] and background positivity for vimentin [Figure 2e]. However, smooth muscle actin (SMA)was negative [Figure 2f] and S-100 was inconclusive. The morphological and immunohistochemical features were consistent with a diagnosis of orbital SFT.

Figure 2

(a) Microphotograph of the tumor showing interlacing bundles of spindle cells interspersed with slit-like vascular channels and fibrocollagenous tissue (H and E, ×100). (b) Immunohistochemistry microphotograph showing diffuse and strong positivity with CD 34 (×100). (c) BCL-2 positivity. (d) CD 99 positivity. (e) Vimentin positivity. (f) SMA negativity

Discussion

Orbital SFT most commonly presents in middle-aged patients with gradual unilateral progressive proptosis and mass effect. Predominantly located in the superior part of the orbit, it is usually unassociated with features of pain or entrapment like nerve palsies.[468] The tumor has been described in various reports as one with variable growth, nontender, nonpulsatile with symptomatic duration ranging from a month to several years, occasionally associated with visual disturbances, ocular motility restriction, palpable mass, or blepharoptosis.[469] Tumor invasion into adjacent bone or soft tissue is also uncharacteristic although recurrent tumors have been reported to invade surrounding tissues.[5] Rarely intracranial extension and invasion into sinus cavities produce associated symptoms.[10] The major differential diagnosis include hemangioperictyoma, fibrous histiocytoma, optic nerve sheath meningioma, neurofibroma, and schwannoma.[4-9] SFT demonstrates great variability in its morphology and shares histologic features with other mesenchymal tumors, which may contribute to its misdiagnosis. However, advanced immunohistochemical techniques have facilitated a clear distinction.

Imaging modalities such as ultrasonography, CT scan, magnetic resonance imaging (MRI), and magnetic resonance angiography have been described for SFT and can be useful adjuncts in diagnosis although there are no specific diagnostic features.[1112] Ultrasonography shows SFTs to have low reflectivity with moderate sound attenuation.[11] CT scan typically reveals a mild to moderately enhancing, well-circumscribed mass with or without local bony remodeling.[12] MRI reveals an intermediate intensity mass on pregadolinium T1-weighted images with moderate enhancement postgadolinium. T2-weighted images are less consistent and less useful.[12] Angiography shows the tumor to be hypervascular with homogenous staining in the venous phase resembling an angioma.[12]

The basic histopathologic feature consists of a “patternless” growth pattern, wherein fibroblast-like, spindle cells form a disorderly or random arrangement. The cells are often densely arranged in a fasicular and storiform pattern with numerous vascular channels that may occasionally form branching or stag horn-like channels.[3-613] Cellularity can be variable depending on the amount of collagen. The degree of collagen can range from very little to extensive keloid-like fibrosis.[613] The tumor can be divided as benign or malignant based on cellular atypia, mitotic figures, pleomorphism, necrosis, compression of vascular spaces, and infiltrative margins.[3-6] Histologic features suggestive of aggressive behaviors include high mitotic rate of >4 per 10 HPF, necrosis, hypercellularity, nuclear pleomorphism, and high MIB-1 labeling.[14]

Immunohistochemical studies show SFT to have strong and diffuse positivity to CD 34, vimentin and BCL-2, and nonspecific reactivity to CD99. SFTs are negative to desmin, cytokeratin, factor VIII-related antigen, S-100, SMA, and muscle-specific actin.[3-15] Among the spindle-cell tumors, differentiating SFT from hemangioperictyoma is mandatory because hemangiopericytomas are known for aggressive behaviors, frequent recurrences, and metastasis as against the usually benign nature of SFT. Strong and consistent positivity to CD 34 is an important diagnostic clue favoring SFT. Hemangiopericytoma shows inconsistent and weak positivity to CD 34.[3-15] In one of the largest studies by Furosato et al,[15] (n = 41), CD 34 positivity was seen in all cases, CD99 in 67.5%, and BCL-2 in 47.5% of the cases.

Recently, Furusato et al,[15] published a reappraisal of 41 cases of orbital tumors previously designated as hemangiopericytoma, fibrous histiocytoma, and giant cell angiofibroma. They like many others found all these tumors to have overlapping morphologic and immunohistochemical features and suggested SFT to be used as an encompassing terminology. However, there probably exists a small cohort of cases where using the terms hemangiopericytoma or malignant fibrous histiocytoma as a diagnosis is acceptable.

Orbital SFTs are largely benign tumors with few instances of recurrence.[4-69] Most reported cases behave in a nonaggressive fashion, similar to SFT in other sites in the head and neck region. Bernardini et al,[5] reported 8 recurrences of the 42 cases. Malignant SFT and malignant transformation of a recurrent SFT are uncommon but have been reported.[569] There is increasing evidence that supports the notion that aggressive tumor behavior does not necessarily correlate with the histologic grade, and the most important predictor of tumor recurrence is subtotal resection.[610] Although en bloc surgical excision with complete tumor removal is the treatment of choice, it may not always be possible to achieve this. This could be partly explained by its less cohesive nature when compared with other orbital tumors, making it prone to fractures during removal. Residual tumor needs close follow-up and possibly further surgery.[6910] There is no conclusive evidence supporting any benefit of adjunctive radiotherapy or chemotherapy.[8] As recurrences have been reported following surgical removal, a regular follow-up is ideal in these patients.

Although rare, orbital SFT should be included in the differential diagnosis of a well-circumscribed enhancing mass. Clinical features along with immunohistochemistry findings help significantly in differentiating orbital SFT from other spindle-cell tumors of the orbit.