Solitary fibrous tumor of the parotid region. Report of a case and review of the Literature

SUÁREZ-ROA ML, RUÍZ-GODOY-RIVERA LM, MENESES GARCÍA A, GRANADOS-GARCÍA M, MOSQUEDA-TAYLOR A. SOLITARY FIBROUS TUMOR OF THE PAROTID REGION. REPORT OF A CASE AND REVIEW OF THE LITERATURE. MED ORAL 2003;9:82-8

SUMMARY

Solitary fibrous tumor is a well-recognized entity that most commonly involves the pleura; however, it has been recently described in other locations including the head and neck region, where it occurs as a slowly growing and well-circumscribed lesion. Due to its low frequency it may be confused with other neoplasms, and for this reason microscopic, ultrastructural and immunohistochemical features are necessary to establish its diagnosis. Prognosis of this tumor depends on its location and size. We present a 20-year-old woman with a well circumscribed, rapidly enlarging solitary fibrous tumor located in the parotid region, which protruded into the oral cavity, measured 10 x 8.5 x 5.5 cm and exhibited benign histological features and positive immunoreactivity to CD34.

Key words: Fibrous tumor, parotid.

INTRODUCTION

Solitary fibrous tumor (SFT) is a rare neoplasm, first described by Klemperer and Rabin in 1931 in the pleura, which usually tends to be located in serosal surfaces (1). At present, there are numerous reports of cases of SFT located in extra pleural sites, such as mediastinum, pericardium, retroperitoneum, lung and liver. In the head and neck it has been described in sites unrelated to serosal cavities, such as meninges, infratemporal fossa, orbit, nasal cavity, paranasal sinuses, nasopharynx, oral cavity, salivary glands, thyroid, perithyroid soft tissue, pharynx, parapharyngeal space and epiglottis (1,2). SFT occurs more frequently around the third to the sixth decades of life, with no gender predilection (1,3-6). Histogenesis of SFT is not well established, and although it was initially considered by Stout (1950) a mesothelial neoplasm, ultrastructural and immunohistochemical studies suggest a mesenchymal origin, as this tumor express high reactivity for this phenotype and shows negative results for epithelial antigens (1-3,7). Some authors consider that prognosis is dependent on location, size and histological features of the tumor, as an increase in cellularity, presence of pleomorphism, high mitotic index, necrosis and hemorrhage are considered parameters of malignancy (1,2,5).

In this article we describe a case of extrapleural SFT located in the head and neck region of a young woman, in which diagnostic difficulty, histopathologic and immunohistochemical patterns and biologic behavior are discussed.

CASE REPORT

A 20-year-old woman presented with a one-year history of an asymptomatic subcutaneous nodule located in the right retro auricular region, which she referred to have been surgically excised six months before admission without having performed a histopathological analysis. On admission, the patient presented with an asymptomatic tumoral growth located in the right parotid region, which was approximately 6 cm in diameter and protruded into the oral cavity. CAT disclosed a mass that was located on the right pterigomaxillary fossa region, which compressed and displaced the parapharyngeal space on its medial and posterior areas. The lesion appeared well circumscribed, extending into the hard palate and infratemporal fossa and partially obliterated the maxillary sinus, with no evidence of bony erosion (Fig. 1). On fine needle aspiration biopsy there were numerous cells with scant cytoplasm, regular elongated nuclei with fine chromatin, which were scattered individually and in small groups over a myxoid background, and for this reason it was considered as compatible with a pleomorphic adenoma (Fig. 2).

Right superficial parotidectomy and tumor resection from the infratemporal fossa was performed. Surgical specimen consisted in two nodules, the largest of which was white, ovoidal, firm in consistency and measured 10 x 8.5 x 5.5 cm. On section it appeared solid and fibrous, alternating with mucoid areas and peripheral hemorrhagic zones. The smaller nodule measured 1.8 cm in diameter and showed features similar to those described for the larger one (Fig. 3). The resected parotid gland showed no macroscopic changes suggestive of lesion.

Microscopically, the tumor was composed by oval epithelioid cells with pale cytoplasm and elongated hyperchromatic nuclei, which were scattered in a slightly myxoid stroma, alternating with hypercellular areas containing hyperchromatic fusiform cells with vesiculous nuclei that exhibited marked atypia and occasional small nucleoli. These areas alternated with hyalinized areas showing a vascular pattern with hemangiopericytoid aspect (Fig. 4). Immunohistochemical study showed intense cytoplasmic positivity for CD34 (Fig. 5) and vimentin. S-100 protein, cytokeratin, desmin and p53 were negative. These findings confirmed the diagnosis of SFT. The patient received 65 Gy of postoperative radiotherapy to the affected zone, and after one year she is alive without evidence of tumoral activity.

DISCUSSION

SFT of the head and neck region is a rare, slowly growing and well-circumscribed neoplasm that possesses a low rate of recurrence. Age of occurrence ranges from 30 to 70 years with no gender predilection. Symptoms are usually related to the site of location and size of the lesion, and these tend to resolve with its surgical excision (1,8,9). This lesion is particularly important when located in the head and neck, as in its early stage it does not compromise any important structure and therefore may not be clinically evident until it reaches a considerable size or invades adjacent structures, which sometimes makes difficult its complete removal. Table 1 shows the salient clinical features of the previously reported SFT of the oral and maxillofacial regions.

Table 1. Clinical features of reported cases of SFT of the oral and maxillofacia regions
Based on references 1, 3, 4, 5, 7, 9, 12, 13, 14, 15, 18
* NR: Not referred

The present case reached 10 cm in size and caused pain due to compression. Previously reported cases arising in the oral cavity have been smaller, which may be explained because of the normal dimensions of the oral cavity and the early symptomatology consequent to the interference with the normal functions of that anatomic region, which differs from other regions of the head and neck, such as nasal cavity, where there have been cases measuring up to 7 cm, in which the main symptoms are nasal obstruction and rhinorrea (9). These large sizes are commonly seen in malignant neoplasms of the head and neck and also in some long-standing benign lesions. Invasion to adjacent structures is important because this situation may produce incomplete removal of the tumor. As our case was well circumscribed in both nodules, surgical excision was complete.

One of the most important aspects of SFT is its differential diagnosis, both clinical and histopathologic. In the present case the first clinical diagnostic possibility was a pleomorphic adenoma or malignant mixed tumor, which was considered because of the location of the lesion in the parotid region, the six-month evolution time and the antecedent of a previous surgical excision of a lesion in the same area. These diagnostic possibilities were supported by the fine needle aspiration biopsy (FNAB) results, which were compatible with a pleomorphic adenoma. In this respect, there are only few SFT cases studied by FNAB that have been reported in the literature, and most of them have occurred in the pleura. In a report of six cases presented by Clayton et al (10), which included one extrapleural and two malignant lesions, these authors described the following cytological features: mild hemorrhagic background with scant inflammatory cells, polygonal and fusiform cells with oval to round nuclei, fine cytoplasm, uniform and finely granular and uniform chromatin. This description is very similar to that found for pleomorphic adenoma in FNAB (11). In these cases it is very difficult to establish the diagnosis of FST based solely on FNAB, as its cytological variety and its parotid location very often lead to diagnose a pleomorphic adenoma or any of the lesions that share cytological features in other locations (4,5,10,12). Clayton et al (10), as well as other authors emphasize the importance of histopathology for definitive diagnosis.

Macroscopically, SFT has been described as a firm, non-encapsulated but well circumscribed neoformation, with smooth white surface and translucent areas, as it occurred in the present case (1-3,12,13), but also it may share macroscopic features of a pleomorphic adenoma, although this neoplasm develops from salivary gland tissue and may be multinodular. In the present case the two nodules were immersed into the soft tissues and were not related to glandular tissue.

In 1997 Chan (2) proposed as essential criteria for diagnosis of SFT: to be circumscribed, the presence of hypercellular areas alternating with hypocellular sclerotic foci, bland appearance, short spindly or plump cells with poorly defined scant cytoplasm, few mitotic figures (<4/10 high power fields) and haphazard, storiform or fascicular arrangement of spindle cells intimately intermingled with collagen fibrils, which is in accordance with the findings described by other authors (1,2,11-16). As secondary findings, there may be calcification, psammoma bodies and focal areas of myxoid changes (2,17). Immunohistochemical studies help to establish the diagnosis. Epithelioid-like plump cells do not express S-100 protein, desmin, cytokeratin or EMA. CD 34 antibody is intensely positive in most of the reported studies, and for Chan (2) it is one of the essential criteria for diagnosis of SFT. Despite some other authors do not consider it a necessary finding; CD 34 positivity is helpful for diagnosis of SFT in extrapleural sites (3,7,12,15,18).

The presence of sarcomatoid areas (hypercellularity, nuclear atypia, pleomorphism and more than 4 mitotic figures/10 HPF) within a typical SFT, or development of a sarcoma in the same site where a SFT occurred before are two conditions that satisfies the criteria of malignancy; however, some authors disagree with this, and they consider SFT as malignant when there is recurrence and distant metastasis (2,7,16). Malignancy has been reported in 23% of pleural cases, but this feature in extrapleural tumors is rare (9-11). Our case showed both clinical benign and malignant features, such as nuclear atypia and pleomorphism, relatively rapid growth and large size, but it was well circumscribed and there were no mitotic figures.

In a study of 10 cases by Yakoi et al (16), these authors found that malignant SFT may occur de novo or as malignant transformation of a previously benign or low-grade lesion, and that it may be associated with p53 mutation, and that in spite CD34 is the usual immunohistochemical marker for this tumor, its expression does not persist in high grade tumors, as these authors found that this protein was positive only in low and intermediate grade malignant SFT but was negative in the high grade neoplasms. In a study of 29 cases reported by Hanau and Miettinen (7), these authors found three cases of malignancy, positive for CD34, but they did not specified their grade. Our case showed strong positivity for CD34 and was negative for p53 and therefore, on the basis of the findings previously reported, led us to consider it as a low grade malignant neoplasm (7,16).

Differential diagnosis of SFT of the head and neck includes fibrosarcoma, malignant or benign fibrous histiocytoma, metastatic malignant mesothelioma, hemangiopericytoma and benign and malignant nerve sheath tumors (2,8,11,15,18). However, in most of the cases the morphologic pattern and the immunohistochemical findings allow to exclude these neoplasms. Hence, fibrous histiocytoma exhibits a storiform pattern and marked cellular pleomorphism with positivity for S-100 protein, which is also positive for benign and malignant nerve sheath tumors, in which there may be also myxoid areas (2,17,18).

The treatment of choice for SFT is complete surgical resection. Some authors have reported favorable results with postoperative chemotherapy and radiotherapy after surgery in cases whith incomplete resection (9,15). SFT may recur after several years, and therefore complete resection is the most important prognostic factor (8,11). The biologic behavior of SFT is unpredictable, as 23% of pleural tumors have been aggressive (1,15,18). Some authors consider that invasion, recurrence and distant metastases may be related to tumor size, hypercellularity, increased number of mitosis, pleomorphism and history of hemorrhage (8).

CONCLUSION

In spite of being an infrequent tumor in the oral and maxillofacial regions, SFT has to be included in the differential diagnosis of those lesions that share similar clinical and histopathological features, from which it has to differentiate by means of immunohistochemical studies.

Prognosis of SFT of the head and neck is reserved, due to the small number of cases reported to date, and it has to be based in the location and the size of the neoplasm. Rapid growth, recurrence and metastasis are determinant factors to consider it as malignant.

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