Schwannoma of the sinonasal tract: A clinicopathologic and immunohistochemical study of 5 cases

Archives of Pathology & Laboratory Medicine, Sep 2003 by Buob, David, Wacrenier, Agnes, Chevalier, Dominique, Aubert, Sebastien, Et al

* Context.-Peripheral nerve sheath tumors are soft tissue neoplasms rarely encountered in the nasal cavity and paranasal sinuses.

Objective.-To describe the clinicopathologic and immunohistochemical features of a series of schwannomas of the sinonasal tract.

Design.-Surgical pathology files were searched for the diagnosis "sinonasal schwannoma." All histologic documents and clinical data were reviewed, Immunohistochemistry was performed on paraffin-embedded tissue with antibodies to S100 protein, epithelial membrane antigen, CD34, and MIB-1.

Results.-Five cases of sinonasal schwannoma were retrieved; patients included 3 women and 2 men, aged 20 to 56 years. Three cases were located in the ethmoid sinus. Clinical symptoms were nonspecific (nasal obstruction, epistaxis, and anosmia). All tumors were treated with conservative surgical resection. Pathologic examination showed a spindle cell proliferation without encapsulation in all cases. No cytologic atypia was seen, and the mitotic activity was low (

Conclusions.-Schwannoma is a very unusual tumor of the sinonasal tract and is associated with nonspecific symptoms. Histologically, sinonasal schwannomas differ from schwannomas of other locations by their lack of a peripheral capsule and possible ulceration of the epithelial covering. Sinonasal schwannomas are treated with conservative surgical resection and have an excellent prognosis.

Sinonasal tract tumors are usually of epithelial origin, such as papilloma, salivary gland tumors, or carcinoma. Soft tissue tumors of the sinonasal tract are rare and are predominantly vascular and fibrohistiocytic lesions. Neural tumors are unusual in this location. Among them, schwannomas of the sinonasal tract are very infrequent, representing less than 4% of the schwannomas of the head and neck. Fewer than 100 cases, mainly isolated tumors, have been described in the literature to date.

We present a clinicopathologic and immunohistochemical study of 5 cases of schwannomas of the paranasal sinuses encountered at our institution.

MATERIALS AND METHODS

Five cases of schwannomas of the sinonasal region were retrieved from the files of the Department of Pathology at Lille University Hospitals (Lille, France) between 1976 and 2001. The specimens were fixed in formalin and embedded in paraffin. Four-micrometer-thick sections were routinely stained with hematoxylin-eosin and saffron. All histologic slides were reviewed independently by 2 pathologists (D.B. and X.L.). Clinical data and follow-up information were obtained from patients' charts and referring clinicians in all cases. Immunohistochemistry was performed using an avidin-biotin-peroxidase complex method on an automated immunostainer (ES, Ventana, Strasbourg, France). Primary antibodies used were S100 protein (polyclonal, dilution 1: 300; Dako, Trappes, France), CD34 (QBend/10, dilution 1:100; Immunotech, Marseille, France), epithelial membrane antigen (monoclonal, dilution 1:25, Dako), and MIB-1 (Ki-67, dilution 1: 50, Immunotech). Appropriate negative and positive controls were added to each run.

The assessment of MIB-1 positively stained nuclei was performed in the areas of greatest labeling density of each tumor on high-power fields (HPF; x 400).

RESULTS

Clinical Findings

Patient ages ranged from 20 to 56 years (median, 44 years). Three patients were women, and 2 were men. None of these patients had a significant past medical history; in particular, none reported neurofibromatosis.

Clinical symptoms contributing to the diagnosis were varied and nonspecific, including epistaxis (1 case), partial anosmia (1 case), clear rhinorrhea (1 case), unilateral nasal obstruction (2 cases), and posterior ethmoiditis symptomatology (1 case). Endoscopic exploration revealed a mass in the sinonasal tract in all cases.

Tumors were located in the ethmoid sinus in 3 cases, the maxillary sinus in 1 case, and in the nasal cavity in 1 case. Conservative surgical treatment was performed in all cases.

Patient follow-up ranged from 7 months to 22 years (median, 6 years). All patients were alive without evidence of recurrence or metastatic spread.

Pathologic Findings

Grossly, the tumors were described as pediculated and polypoid, encephaloid, white to yellowish, friable, and nonencapsulated masses measuring 2 to 4 cm. Evidence of hemorrhage was noted in 1 case. The paranasal sinus mucosa did not present abnormality. The nerve of origin of the tumor was never individualized during the surgical procedures. No osteolytic lesions were observed.

Microscopically, tumor encapsulation was absent in all cases. The tumor cells were mainly composed of elongated spindle cells arranged in fascicles. The tumor cells had a wavy shape, poorly defined cytoplasm, and oval nuclei with tapering ends (Figure 1). Nuclei were focally palisading without atypia. In 2 cases, numerous images of juxtaposed palisades, typical of Verocay bodies, were seen (Figure 2). Frequently, Antoni A and B patterns were associated within the same tumor. No epithelioid cells were observed. Mitotic activity was low (1-3 mitotic figures/10 HPF). No abnormal mitosis or necrosis was observed. The background was richly vascularized in every case, with some thickened hyalinized vessels. No evidence of vascular thrombosis was observed. In 2 cases, the proliferation reached the epithelial surface, without fibrous interposition, leading sometimes to epithelial ulceration (Figure 3). In 1 case, inflammatory changes were observed, with numerous histiocytes, lymphocytes, polymorphonuclear leukocytes, and hemosiderin deposits.