Etiology
- Arises from mesenchymal cells in fascia, muscle, or other soft tissues
- Orbit is the most commonly affected periocular structure
- Conjunctiva and eyelids can also be involved.
Epidemiology
- Three main subtypes. based on clinical behavior
- Benign 63%
- Locally aggressive 26%
- Malignant 11%
- A rare tumor, however the most common mesenchymal tumor of the orbit
- Most common in adults 30–60 years old
- 3%–10% occur in pediatric population; can occur following external beam radiation for retinoblastoma (Shields, Ophthal Plast Reconstr Surg. 2001)
- Male = female
- Some authors have suggested that fibrous histiocytoma refers specifically to fibroblastic spindle cell tumors of the orbit with aggressive behavior and have advocated re-classifying more superficial, benign lesions as dermatofibromas (Tieger, Ophthal Plast Reconstr Surg. 2019).
History
- Decreased vision
- Progressive proptosis
- Diplopia
- Previous history of FH
Clinical features
- Proptosis
- Dystopia
- Lid swelling
- Loss of vision
- Afferent pupillary defect due to compressive optic neuropathy
- Decreased motility
- Ptosis
- Chemosis
- Ephiphora and dacryocystitis if there is extension into the lacrimal sac (Stefanyszyn, Ophthal Plast Reconstr Surg. 1994)
- Most commonly occur supranasally, however can occur anywhere in the orbit and periorbital sctructures
- FH reportedly can occur in the lacrimal gland (Bajaj, Ophthal Plast Reconstr Surg. 2007)
Testing
Evaluation of motility, vision, pupils, Hertel exophthalmometry
Computed tomography
- Typically well circumscribed, but can be irregular
- Similar in appearance to schwannomas or cavernous hemangiomas
- Bone erosion is rare, but can be seen in recurrences or malignant lesions.
Magnetic resonance imaging
- T1
- Heterogenous
- Isointesnse to slightly hyperintense to muscle, hypointense to fat
- T2: Collagenous regions appear hypointense, whereas cellular areas are hyperintense.
- Heterogenous enhancement with gadolinium
Positron emission tomography
- Useful in detecting metastases as well as deciphering a recurrence from post-surgical changes (Char, Orbit. 2000)
Histopathology
- Benign:
- Poorly defined margins
- Spindle-shaped fibroblasts with a storiform pattern
- Can have vascular areas that are indistinguishable from hemangiopericytomas
- Locally aggressive
- Infiltrative margins
- Hypercellular
- Mitotic figures
- Malignant
- Infiltrative margins
- Nuclear pleomorphisms
- Atypia
- Necrosis
- Multinucleated giant cells
- Immunohistochemical staining
- Vimentin
- Alpha-antitrypsin
- Factor XIIIA
- Smooth muscle actin
- CD68

Figure 1. Completely excised fibrous histiocytoma.
Risk factors