Solitary fibrous tumor of the oral mucosa—morphological and immunohistochemical profile in the differential diagnosis with hemangiopericytoma
Introduction
Solitary fibrous tumors (SFT) are rare spindle cell neoplasms that most often originate from mesothelial-lined surfaces, mainly the pleura and peritoneum. Because of that, it is also known as localized fibrous mesothelioma or submesothelial fibroma [1], [2], [3]. However, SFT has been also described in extrapleural sites, including the lung, mediastinum, peritoneum, renal pelvis, periosteum, spinal cord [4], [5], [6], sinonasal tract, nasopharynx, thyroid [7], [8], [9], orbit [10] and breast [11].
Recent studies have indicated that SFT appears to be a mesenchymal neoplasm, not necessarily restricted to serosal surfaces [2], [4], [12]. A certain specific population of CD34-positive cells is one of possible candidates for the histogenetic origin of SFT [6]. They are primitive mesenchymal cells that exhibit spindle or dendritic shape and show a wide distribution in various organs and tissues [13]. These cells may function as antigen-presenting cells or may play a role in tissue repair.
Involvement of oral cavity has been reported, but it appears to be rare [14], [15], [16], [17]. The mean age of patients with SFTs in the oral cavity is 59 years [15]. The preferential sites are: cheek, posterior trigone and soft palate [15], although there are cases reported in ventral tongue [18], parotid [19], upper lip [14], and sublingual gland [20].
The lesion is usually a slow-growing, painless, well-circunscribed, nontender and mobile submucosal growth of variable size and duration. The color and texture of the overlying mucosa are normal [14], [21]. SFT in the head and neck is usually nonaggressive [2], [7], [8], but there is a rarer malignant counterpart that exhibits high cellularity and mitotic activity.
The diagnosis of SFT is generally difficult, because of its broad range of morphologic characteristics [3], and the fact that many other lesions present similar features. The immunohistochemical profile can be useful in cases of schwannoma, neurofibroma [17], peripheral nerve sheat tumor [15], angioleiomyoma [17] and solitary myofibromas [15], where the morphological differences are not clear. In the cases of fibrous histiocytoma, on the other hand, accurate evaluation on the histological aspects is enough to make the differential diagnosis. Malignant cytologic features also contribute to rule out leiomyosarcoma and fibrosarcoma.
Hemangiopericytoma (HPC) is probably the lesion that is most difficult to distinguish from SFT, due to their morphological similarities [16], [17]. The purpose of this study was to investigate two cases of solitary fibrous tumor emphasizing the differential diagnosis with hemangiopericytoma by means of morphological and immunohistochemical profiles.
Section snippets
Material and methods
Two cases diagnosed as solitary fibrous tumor and one case of hemangiopericytoma were retrieved from the files of Oral Pathology Department of the University of Sao Paulo—Brazil for histological and immunohistochemical investigation. Lesional tissue had been fixed in 10% neutral formalin solution and embedded in paraffin. Five-μm sections were obtained and submitted for routine hematoxylin-eosin and also for toluidine blue and reticulin (counterstained with van Giesson) histochemical stainings.
SFT 1
On microscopic examination, the tumor showed disorganized spindle cell proliferation with alternating cellular nodules and hypocellular areas, presenting distinct morphologic pattern. The cells had fusiform, voluminous, elongated and ovoid nucleus. Most of this nucleus showed internal vacuoles. Inconspicuous nucleoli and undefined cytoplasm were seen. Few mitotic figures were noted. Stroma displayed an advanced degree of collagenization and shown the emergence of numerous small vessels with
Discussion
The cases of SFT reported in this study were unencapsulated and have exhibited different patterns of cell arrangements: nodular, diffuse sclerosing areas, fascicular and neural-type palisading. They were composed of small to medium-sized spindle cells with ill-defined cytoplasmic membrane, pale eosinophilic cytoplasm, uniform spindle or ovoid vesicular nuclei with finely dispersed chromatin, and inconspicuous nucleoli. These are features often atributted to SFT [15]. Scattered giant nuclei
Acknowledgements
We thank Edna Toddai and Elisa dos Santos for technical assistance. Supported by FAPESP grant 99/05383-6 and CNPq grant 46111/00-0.
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The first two authors have collaborated equally to this paper.