Benign fibroushistiocytoma of the gingiva.

Benign fibroushistiocytoma is a benign connective tissue tumor rarely seen affecting the head and neck region. These tumors were believed to be of histiocytic origin as they are comprised of cells, which showed spindled morphology and cells with a round histiocytic appearance. The current concept consents that the lesional cells rather represent a fibroblastic differentiation. Diagnosis of these tumors proves to be challenging even with the use of immunohistochemistry due to lack of any specific markers. Here, we describe a case which presented in the gingiva mimicking a reactive lesion, which in fact was a tumor.

Benign fibrous histiocytoma is a benign connective tissue tumor comprising of cells resembling both fibroblasts and histiocytes occurring in both cutaneous and non-cutaneous soft-tissues. These tumors represent fibrohistiocytic differentiation, which describes the nature of the tumor and not the cell of origin.[1]

The most common sites affected by benign fibrous histiocytoma are the soft-tissues of the lower extremities, less frequently in the upper extremities, retroperitoneum and orbit.

The occurrence in the head and neck is rare and has been seen within the nasal cavity, temporomandibular joint, the submandibular and parotid glands, larynx, trachea, paranasal sinuses,[2] external auditory canal[3] and a single case occurring within the condyle.[4]

Oral cavity being an uncommon site, but when seen, occurs predominantly in the buccal mucosa and vestibule.[5] This tumor has also been seen on gingival or alveolar ridges, soft palate, floor of mouth, lips and tongue.[6]

The earliest concept that these tumors showed fibrohistiocytic differentiation was based on the biphasic cell population of fibroblasts and histiocytes seen in these tumors. The lesional cell also exhibited phagocytic activity and amoeboid extensions in cell culture, which further supported the fibrohistiocytic pattern. This concept is now understood to be incorrect and that the histiocyte like cells did not show immunoreactivity with CD68 usually taken by macrophages with lysomal activity and the cells tend to express immunoreactivity favoring a fibroblastic differentiation. The name fibrohistiocytic tumors is still ascribed to this tumor for the presence of cells, which resemble fibroblast and histiocytes.[7]

Case Report

A 23-year-old male patient reported with a chief complaint of a growth on the gums of the lower front teeth region for past 1 month. The growth was small when he noticed it and gradually increased in size. Clinical examination revealed two small growths, on both the buccal and lingual aspect of the interdental papillae of 32 and 33. The surface of these growths appeared reddish pink in color measuring around 1 cm × 1 cm in size. On palpation, the growth was firm in consistency and non-tender [Figures 1 and 2].

Figure 1

(a) Growth on the buccal aspect of the gingiva of 32 and 33, (b) growth on the lingual aspect of the gingiva of 32 and 33

Figure 2

OPG - showing no resorption of bone in 32 and 33 region

An excisional biopsy was carried out and both the buccal and lingual growth were submitted separately for histopathological investigations. The section made from the buccal growth showed a connective tissue mass devoid of epithelium. The connective tissue showed budding capillaries toward the center with dense infiltrate of chronic inflammatory cells. The periphery of the mass appeared to be covered by a pseudomembranous layer.

The lingual growth showed a highly cellular connective tissue mass covered by a proliferating epithelium. The lesional cells were plump spindle shaped cells, which in certain areas showed the crisscross pattern or storiform arrangement. The connective tissue had also shown numerous round histiocytic cells and blood vessels.

The sections were sent for immunohistochemistry to detect the expression of Vimentin, smooth muscle actin (SMA), desmin, S-100 protein and CD34. The sections showed strong positivity for vimentin and negative expression for vascular, muscular or neural markers [Figure 3].

Figure 3

(a) Highly cellular connective with plump spindle shaped cells showing storiform arrangement (×40) (b) immunohistochemistry - positive for vimentin marker

Based on the histopathological features and immunohistochemistry findings, a diagnosis of benign fibroushistiocytoma was given.

Discussion

The diagnosis of benign fibrous histiocytoma can prove to be challenging in light microscopy even with the use of immunohistochemistry as these tumors lack any specific markers and are primarily diagnosed based on the absence of marker expression.

Histologically, these tumors show lesional tissue comprising of highly cellular connective tissue comprising of spindle cells. Thus, tumors showing similar histological appearance have to be considered in the differential diagnosis and ruled out by immunohistochemistry for other spindle cell lesions. The panel of markers most commonly employed for spindle cell lesions are SMA, vimentin, S-100 protein, Desmin, cytokeratin, HMB 45, CD34, CD31.[8] Review of literature show that benign fibroushistiocytoma exhibit strong immunoreactivity for vimentin, focal expression of CD68 while no expression for other markers as was observed in the present case.

The histopathology of these tumors shows a submucosal mass, consisting of fibroblasts and histiocytes in rotating or fasciculated bundles, inflammatory cells, multinucleated giant cells and foam cells. The hallmark of these tumors is the characteristic “storiform” or “cartwheel” arrangement of the lesional cells.[9] In the present case, two sections were prepared, one from the nodular mass seen on the interdental papillae of 32 and 33 on the buccal aspect and the other section from the lingual aspect. The section from the buccal aspect showed the histologic appearance of pyogenic granuloma while the lingual mass showed a benign fibrohistiocytic tumor mass with overlying proliferating epithelium. A similar case on the tongue was reported by Syed et al.[6] where primary biopsy report of pyogenic granuloma was given. On recurrence, a deeper biopsy was carried out, which showed fibrohistiocytic appearance confirmed with immunohistochemistry, which showed strong positive expression for vimentin and CD68.

The other diseases to be considered as differential diagnosis include spindle cell lesions as nodular fasciitis, oral inflammatory myofibroblastic tumor, solitary fibrous tumor, neurofibroma, dermatofibroma, leiomyosarcoma and other neurogenic tumors are discussed in Table 1. The malignant counterpart of benign fibrous histiocytoma, a low grade tumor, should also be considered in differential diagnosis, as small specimens (not large enough for an accurate pathological diagnosis) appear benign can be encountered in head and neck region.[11]

Table 1

Differential diagnosis for spindle cell lesions

The current choice of treatment for benign fibrous histiocytoma of the head and neck as well other parts of the body is complete resection and recurrence rate is found to be nil.[235] In conclusion, the tumors occur very rarely in the oral cavity and should be considered in the differential diagnosis.