Solitary fibrous tumor

Solitary fibrous tumor (SFT) is the most common mesenchymal tumor of the orbit in adults. The superonasal orbit is a common site. The tumor most commonly presents in the fifth decade of life, but there is a wide age range. Most patients present with an orbital mass causing a combination of signs and symptoms, including proptosis, pain, diplopia, blurred vision, and epiphora.

Figure 14-11 Orbital lymphatic malformation (lymphangioma). A, Clinical photograph shows an inferior orbital lesion extending anteriorly and nasally below the left lower eyelid of a young boy. B, CT scan (axial view) depicts a multilobulated mass (white circles) within the left orbit. C, Photomicrograph shows numerous vascular channels with lymphoid follicles (arrows) in between the vessels.D, Higher magnification demonstrates endothelium-lined vascular channels (asterisks), a lymphoid follicle (arrow), and scattered lymphocytes and plasma cells within the fibrous walls.

(Parts A and B courtesy of Sander Dubovy, MD; parts C and D courtesy of Heather Potter, MD.)

Several studies have demonstrated that other soft-tissue tumors, such as hemangiopericytomas, fibrous histiocytomas, and giant cell angiofibromas of the orbit, share common histologic and immunophenotypic characteristics and may be more accurately classified as subtypes of orbital SFTs. Two commonalities among all these tumors are that (1) they are collagen rich and contain proliferating CD34-positive fibroblast-like cells; and (2) they often demonstrate strong nuclear STAT6 expression on IHC studies.

Classically, the presence of staghorn sinusoidal blood vessels (Fig 14-13) was used to distinguish hemangiopericytoma from other tumors; fibrous histiocytoma was differentiated by spindle-shaped, plump histiocyte-like cells with a focal storiform architecture (Fig 14-14); and giant cell angiofibroma was distinguished by the presence of multinucleated floret-type giant cells and ectatic vascular spaces. However, these findings overlap. For example, 87% of all fibrous tumors show staghorn vessels. Other shared histologic features may include mild hemorrhage, osteoclast-type cells, stromal myxoid change, mature adipocytes, and mineralization. The presence of overlapping features is the reason that the nomenclature of SFT is preferred to define all of these tumors.

Figure 14-12 Orbital cavernous hemangioma. A, CT scan (axial view) shows a well-circumscribed retrobulbar intraconal mass (asterisk).B, Low-magnification photomicrograph demonstrates large blood-filled spaces that are separated by relatively thin septa. C, Higher-magnification photomicrograph shows the large, irregular venous channels lined with flat endothelial cells and containing red blood cells. The collagenous capsule can be seen on the left side of the image.

(Part A courtesy of Sander Dubovy, MD; part B courtesy of Hans E. Grossniklaus, MD; part C courtesy of Nasreen A. Syed, MD.)

Figure 14-13 Solitary fibrous tumor (hemangiopericytoma-like). A, Photomicrograph demonstrates a cellular tumor with a characteristic slitlike and branching vascular (staghorn) pattern. B, Photomicrograph demonstrates closely packed cells with oval to spindle-shaped vesicular nuclei.

(Part A courtesy of Nasreen A. Syed, MD; part B courtesy of Ben J. Glasgow, MD.)

Figure 14-14 Fibrous histiocytoma. Photomicrograph illustrates the storiform (whorled and matlike) growth pattern.

(Courtesy of Nasreen A. Syed, MD.)

Most SFTs are benign, although they do have a propensity for local recurrence. Marked cytologic atypia and increased mitotic activity, accentuated by strong IHC staining for Ki-67 and/or p53, support the designation of borderline or low-grade malignant behavior in these tumors.

Other primary tumors of fibrous connective tissue that may occur in rare cases in the orbit include nodular fasciitis, fibroma, and fibrosarcoma.

• Demicco EG, Harms PW, Patel RM, et al. Extensive survey of STAT6 expression in a large series of mesenchymal tumors. Am J Clin Pathol. 2015;143(5):672–682.

• Furusato E, Valenzuela IA, Fanburg-Smith JC, et al. Orbital solitary fibrous tumor: encompassing terminology for hemangiopericytoma, giant cell angiofibroma, and fibrous histiocytoma of the orbit: reappraisal of 41 cases. Hum Pathol. 2011;42(1):120–128.

Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.