Miscellaneous Mesenchymal Tumors

Tumors of fibrous connective tissue, cartilage, and bone are uncommon lesions that may involve the orbit. It is likely that a number of these mesenchymal tumors were classified incorrectly before the availability of immunohistochemical staining, which has allowed them to be differentiated accurately.

Fibrous histiocytoma is the most common of these tumors. Characteristically, it is very firm and displaces normal structures. Both fibroblastic and histiocytic cells in a storiform (matlike) pattern are found in these locally aggressive tumors. Less than 10% have metastatic potential. This tumor is sometimes difficult to distinguish, clinically and histologically, from a solitary fibrous tumor.

A solitary fibrous tumor (Fig 5-14) is composed of spindle-shaped cells that are strongly positive for CD34 and STAT 6 on immunohistochemical studies. These lesions, some of which were previously termed hemangiopericytomas, are uncommon, encapsulated, hypervascular, and hypercellular; they often appear in midlife. They can occur anywhere in the orbit; and they may recur, undergo malignant degeneration, or metastasize if incompletely excised. They may resemble cavernous hemangiomas on both CT and MRI, but they appear bluish intraoperatively. On histologic examination, these tumors are unique in that microscopically “benign” lesions may recur and metastasize, whereas microscopically “malignant” lesions may remain localized. Treatment consists of complete excision.

Fibrous dysplasia (Fig 5-15) is a benign developmental disorder of bone that may involve a single region or be polyostotic. CT shows hyperostotic bone, and MRI shows the lack of dural enhancement that distinguishes this condition from meningioma. When associated with cutaneous pigmentation and endocrine disorders, the condition is known as Albright syndrome. Resection or debulking is performed when the lesion causes disfigurement or vision loss due to stricture of the optic canal.

Osteomas (Fig 5-16) are benign tumors that can involve any of the periorbital sinuses. CT scans show dense hyperostosis with well-defined margins. The lesions can produce proptosis, compressive optic neuropathy, and orbital cellulitis secondary to obstructive sinusitis. Most are incidental, slow-growing lesions that require no treatment. Complete excision is advised when the tumor is symptomatic.

Figure 5-14 Solitary fibrous tumor. A, Solitary fibrous tumor (arrows) producing hypoglobus. B, T1-weighted, gadolinium-enhanced MRI shows superolateral enhancing lesion (arrows).C, Intraoperative appearance demonstrates high vascularity of the tumor. D, Spindle cell neoplasm with myxoid background in a “patternless pattern” with extensive vasculature (original magnification ×200, hematoxylin-eosin [H&E] stain). E, Predominant STAT-6 immunostaining positivity (original magnification ×200). Brown areas represent STAT-6 immunohistochemical positivity.

(Courtesy of Julian D. Perry, MD, and Alexander D. Blandford, MD.)

Figure 5-15 Fibrous dysplasia. A, Facial asymmetry. B, CT scan shows characteristic hyperostosis of involved facial bones.

(Courtesy of Jerry Popham, MD.)

Figure 5-16 Osteoma. A, External photograph shows a firm, immobile lesion along the superior orbit (arrow).B, Intraoperative view shows osteoma arising from the frontal bone.

(Courtesy of Julian D. Perry, MD, and Alexander D. Blandford, MD.)

Malignant mesenchymal tumors such as liposarcoma, fibrosarcoma, chondrosarcoma, and osteosarcoma rarely appear in the orbit. When chondrosarcomas and osteosarcomas are present, they usually destroy normal bone and demonstrate characteristic calcifications in radiographs and CT scans. Children with a history of bilateral retinoblastoma are at higher risk for osteosarcoma, chondrosarcoma, or fibrosarcoma, even if they have not been treated with therapeutic radiation.

• Katz BJ, Nerad JA. Ophthalmic manifestations of fibrous dysplasia: a disease of children and adults. Ophthalmology. 1998;105(12):2207–2215.

Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.