Fibrous histiocytomas are soft tissue tumours and may be benign or malignant, the benign variety being the most common.1
They are usually found on the extremities, but can occur in any part of the body, including orbital tissues. Fibrous histiocytomas account for 1% of all orbital tumours, and are the most common primary mesenchymal tumour of the orbit.2
Benign fibrous histiocytomas have been reported in the orbit,3
Symptoms and signs depend on the site, but may include decreased vision, pain, restricted eye movements, diplopia, and disc swelling. To date, there are only 18 cases of fibrous histiocytoma arising from the corneoscleral limbus reported in the literature1,6
; 11 of these were classified as benign. They usually present as painless masses and can develop at any age, but most commonly between the ages of 20–40 years. Their gross appearance is of a circumscribed yellow or white mass, and they may have focal areas of haemorrhage, which can make them appear brown or black in colour.
The histopathological appearance of a benign fibrous histiocytoma includes a mixture of fibroblastic and histiocytic cells that are often arranged in a cartwheel or storiform pattern, and accompanied by varying numbers of inflammatory cells, including foam cells and siderophages. No atypical nuclei or mitotic figures are present. Although some authors regard these tumours as reactive proliferations of fibroblasts, others do not accept this view because the lesions tend not to regress spontaneously. Recurrence is rare, with less than 5% of cutaneous benign fibrous histiocytomas recurring after local excision.7
In contrast, malignant fibrous histiocytomas of the corneoscleral limbus characteristically appear in later life, between the ages of 50–70 years, with an equal distribution of males to females.1
They are highly aggressive tumours, and have been reported to have a local recurrence rate of 100% if a limited excision is performed.8
Recurrence can occur within a few months of excision. There are seven reported cases of corneoscleral malignant fibrous histiocytoma. Two of the cases had an enucleation and two cases underwent orbital exenteration. Follow up of these patients ranged from 18 months to 5 years and all were free from recurrence. The other three patients had a local excision. One patient developed local scleral recurrence 2 months later. (It is not evident from the literature if the borders of excision were clear of tumour.) He was found to have a metastasis in the “parotid gland” 4 months later, and even after a parotidectomy and radical neck dissection, the patient developed multiple pulmonary metastases and died within 1 year.9
One of the patients was lost to follow up. The third patient who had a local excision went on to develop two recurrences, which subsequently needed excision and cryotherapy.6
However, after 1 year he was free of any recurrence. Malignant fibrous histiocytomas have a broad range of histological appearances; storiform-pleomorphic, myxoid, giant cell, and inflammatory.10
The storiform-pleomorphic type is the most common. The cells are predominantly plump pleomorphic spindle-shaped with occasional large, ovoid histiocyte-like cells. Modest amounts of inflammatory cells, such as lymphocytes and plasma cells may be present. The differential diagnosis of a malignant fibrous histiocytoma includes pleomorphic carcinoma, malignant melanoma, and other sarcomas.
For those limbal fibrous histiocytomas with a benign histopathological appearance, the management should be local surgical excision. Malignant fibrous histiocytomas need to be managed cautiously, preferably by wide local excision and cryotherapy at the earliest opportunity. If necessary, enucleation should be considered to fully excise a limbal malignant fibrous histiocytoma.