General
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• Resembles solitary fibrous tumor but prominent vessels
• 30% recur, 15% metastasize (lung, liver, bone, regional lymph nodes), usually late
• Histology does not predict behavior (Hum Pathol 1982;13:210)

Case reports
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• 66 year old woman with left eye proptosis, ptosis, and blindness (Arch Pathol Lab Med 2002;126:1555)

Micro description
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• Usually encapsulated
• Random pattern of polygonal and rounded cells with ill defined cytoplasm, variable nucleoli
• Staghorn vascular pattern and perivascular collagen, dense pericellular reticulin, occasional mitotic figures
• Must rule out other tumors with this pattern

Micro images
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Small polyhedral cells surround vascular spaces

Vascular channels have a staghorn pattern

Cells are polyhedral and spindled, with mild atypia

Metastatic liver nodule

A-large left orbital mass; B-random pattern of polygonal and rounded cells C-large and small vessels with staghorn pattern; D-reticulin densely surrounds each cell

Positive stains
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• CD34 (focal or weak), dense pericellular reticulin staining, vimentin
• Variable XIIIa

Negative stains
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• EMA, GFAP, S100, keratin, desmin, muscle specific actin, smooth muscle actin

Differential diagnosis
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• Fibrous histiocytoma: predominant storiform pattern; foam cells and giant cells present
• Meningiomas: EMA+, complex interdigitating processes and desmosomes by EM, deletions of #22
• Solitary fibrous tumor: CD34 strongly+

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