Transarterial Onyx Embolization of an Orbital Solitary Fibrous Tumor

This case report describes the first documented use of transarterial Onyx embolization in an orbital solitary fibrous tumor (SFT), including histopathologic findings of the embolization material within the resected specimen. The study was published in Ocular Oncology and Pathology in 2015.

Background

Solitary fibrous tumor (SFT) is an uncommon mesenchymal neoplasm that can arise in the orbit, most typically in the superior orbit. These tumors present with unilateral proptosis that progresses over months to years. While often benign, orbital SFTs can exhibit aggressive behavior and borderline malignant features.

Historically, SFTs have been underdiagnosed, sometimes mistaken for hemangiopericytoma, fibrous histiocytoma, or giant cell angiofibroma. There is ongoing debate in the pathology community about the classification of tumors previously designated as hemangiopericytoma, which are now generally grouped under the SFT category.

A key surgical challenge with orbital SFTs is their vascularity. Highly vascular orbital tumors carry significant hemorrhagic risk during resection. Preoperative embolization—blocking the tumor's blood supply before surgery—can reduce intraoperative bleeding and improve surgical outcomes.

The Patient

A 55-year-old woman presented with:

• Right eye pain and proptosis (bulging of the eye)
• Eyelid swelling
• Limited eye movement (abduction limitation)
• Symptoms progressive over several months

Diagnostic Imaging

Orbital imaging with CT, MRI, and angiography revealed:

• A well-circumscribed, highly vascular mass with multiple large flow voids
• The mass was adjacent to the optic nerve, displacing the globe laterally and downward
• Blood supply came from both long and short ciliary arteries off the right ophthalmic artery
• A large draining vein extended to the superior ophthalmic vein, draining into the cavernous sinus
• No supply from the external carotid territory

Method: Transarterial Onyx Embolization

The embolization procedure was performed by an interventional neuroradiologist using the following approach:

1. Right femoral percutaneous access was used to reach the orbital vasculature
2. Dyna CT examination with contrast injection into the right internal carotid artery mapped the blood supply
3. Selective catheterization of the right ophthalmic artery was performed
4. Polyvinyl alcohol particles (45 µm) were first used for initial devascularization
5. Onyx liquid embolic agent (ethylene vinyl alcohol copolymer) was instilled at the entrance of tumor vessels

Why Onyx?

Onyx is an ideal embolization material for orbital tumors because its slow precipitation properties allow deep penetration into smaller vessels within the tumor. This produces diffuse infiltration and minimizes the need for repeated catheterizations. Embolization can be performed transarterially (as in this case) or via direct percutaneous tumor puncture.

Result of Embolization

Post-treatment imaging showed complete devascularization of the tumor with stasis of contrast in the proximal ophthalmic artery. No choroidal blush was identified, confirming that the tumor's blood supply had been fully eliminated.

Surgical Resection

Immediately following embolization, orbitotomy was performed. The surgeons removed a partially shrunken 2.7 x 2.0 x 1.5 cm irregularly shaped lesion with a glistening, micronodular, and hypervascular surface. Post-resection angiography confirmed complete surgical removal with no residual tumor vascularity.

Histopathology Findings

Microscopic examination revealed several important findings:

Tumor Characteristics

• Well-circumscribed, encapsulated neoplasm with a focal area of capsular invasion
• Patternless sheets of oval to spindled cells—the classic SFT morphology
• Staghorn-type blood vessels—large, branching vessels characteristic of tumors with hemangiopericytoma-like features
• Immunohistochemistry: diffuse CD34 and BCL-2 positivity, consistent with SFT

Malignancy Assessment

• Ki-67 (MIB-1) proliferation index of 5–10%—elevated, suggesting borderline malignant potential
• Increased cellularity and focal capsular invasion
• Diagnosis: Orbital SFT with borderline malignant potential

Embolization Material in Tissue

This was the novel finding of the study. The Onyx embolization material was identified in prominent vessels penetrating the fibrous capsule of the tumor:

• Appeared as eosinophilic hyaline admixed with small polarizable granular black pigment (tantalum powder)
• Under polarized light microscopy, the tantalum powder component was the polarizable element
• No necrotic or inflammatory changes were seen in tumor tissue adjacent to the embolized vessels

Clinical Significance

This case demonstrates several important points for the management of vascular orbital tumors:

• Preoperative Onyx embolization is safe and effective for orbital SFTs with high arterial flow
• The Onyx material can be identified histopathologically, which is important for pathologists evaluating post-embolization specimens
• Immediate post-embolization resection is a viable strategy, producing a partially shrunken tumor that is easier to remove
• Borderline malignant SFTs require close follow-up after resection due to potential for recurrence

Potential Complications

While no complications occurred in this case, rare potential complications of preoperative Onyx embolization include:

• Skin and soft tissue necrosis
• Stroke
• Intracerebral hemorrhage
• Cranial nerve palsy

These risks underscore the importance of having an experienced interventional neuroradiologist perform the procedure.

Citation

Hashemi N, Ling JD, Soparkar C, Sami M, Ellezam B, Klucznik R, Lee AG, Chévez-Barrios P. Transarterial Onyx embolization of an orbital solitary fibrous tumor. Ocul Oncol Pathol. 2015;1(2):98-102.

References