Cellular schwannoma of the paranasal sinuses: initial report of a case. (Original Article).

Abstract

Cellular schwannomas are a benign variant of classic schwannomas. Their histologic appearance closely mimics that of malignant peripheral nerve-sheath tumors, which are high-grade sarcomas. In this article, we describe what to our knowledge is the first reported case of a cellular schwannoma of the paranasal sinuses and only the 33rd reported case of any schwannoma at this site. We also discuss the histology and management of cellular schwannomas and review the pertinent literature.

Introduction

Schwannomas are benign tumors that originate in peripheral nerve-sheath cells (i.e., Schwann cells). They are relatively common in the head and neck region; VIIIth cranial nerve schwannomas (i.e., acoustic neuromas) account for a major percentage of these tumors. (1-3) Other common sites are the mediastinum, retroperitoneum, intraspinal space, paraspinal region, sacrum, and cranial cavity. (4) Only 4% of all schwannomas involve the paranasal sinuses, (5) and to date, only 32 cases of schwannoma of the paranasal sinuses have been previously reported. (6)

Cellular schwannomas are a benign variant of classic schwannomas, first described by Woodruff et al in 1981. (7) In this article, we describe a new case of cellular schwannoma, which we believe is the first reported case of this type of tumor occurring in the paranasal sinuses and only the 33rd reported case of any benign schwannoma at this site.

Case report

A 63-year-old man came to our institution in July 1995 with a long-standing history of nasal obstruction and a recent onset of left-sided nasal bleeding. Six years earlier, he had been treated at another hospital in our city for similar complaints. At that time, he underwent a nasal biopsy and a subsequent lateral rhinotomy for excision of a left nasal tumor. The histology in both cases was interpreted as representing "neurofibromatosis." Unfortunately, the pathology material was not available for our review. The patient was lost to follow-up until he came to our hospital.

Findings on our initial physical examination were normal; the patient did have noninsulin-dependent diabetes mellitus and hypertension, but both were kept under control with medication. On otolaryngologic examination, we observed a left-side lateral rhinotomy scar and mild proptosis. The patient's eye movements were normal, and he had no diplopia. Anterior rhinoscopy detected a large, blood-covered, soft-tissue mass in the left nasal cavity; it also showed that the nasal septum was deviated to the right. The postnasal space was normal, and the regional lymph nodes were not palpable.

Computed tomography (CT) demonstrated a fairly homogeneous enhancing lesion in the frontal and ethmoid sinuses on both sides (figure 1). The lesion extended down along the sides of the nasal septum into the nasal cavity. CT also suggested an erosion of the cribriform plate and the lamina papyracea on both sides (moreso on the left), which had caused proptosis.

Magnetic resonance imaging (MRI) of the nose and paranasal sinuses provided confirmation that the soft-tissue mass involved the left ethmoid air cells and extended across the midline to the right side and that it also involved the frontal sinuses, primarily on the left (figure 2). No orbital or intracranial extension of the tumor was observed.

Later in the month, we performed a bilateral external frontoethmoidectomy with a minor modification of the "eagle incision" (8) and with the patient under general anesthesia. The tumor had occupied the ethmoid sinuses on both sides and had extended along the roof of the nasal cavity--that is, along the cribriform plate--but had not eroded it. The floor and part of the anterior walls of the frontal sinuses were removed to provide better access for tumor removal and direct visualization of the posterior wall of the sinuses. The posterior walls of the frontal sinuses were intact. Following removal, the nasal cavity was packed with ribbon gauze soaked in bacitracin ointment, and the incision was closed in two layers. The packs were removed after 72 hours, and the patient was discharged after 7 days.

Histologic examination of the neoplasm revealed a cellular proliferation of spindle cells arranged in interlacing fascicles (figure 3). The cells featured oval vesicular nuclei with small prominent nucleoli, an eosinophilic cytoplasm, and ill-defined borders. No nuclear atypia or necrosis was evident. We did observe 2 to 3 mitoses/10 high-power field (hpf). Immunohistochemical studies demonstrated an intense reactivity for S-100 protein in most of the cells.

Our patient returned for regular follow-up, and at each visit we performed rigid endoscopy (0[degrees] and 30[degrees]) to examine the nasal cavity. Thus far, he remains disease-free, a finding that is confirmed by follow-up CT (figure 4).

Discussion

Classic schwannoma is marked by two different histologic patterns: Antoni type A and Antoni type B. Type A areas are cellular and are made up of spindle cells that are often arranged in a palisading fashion (Verocay bodies). In type B areas, the tumor cells are separated by abundant myxoid stroma that can form cystic spaces.

In their original description of cellular schwannomas, Woodruff et al reported a series of 14 cases that were characterized by high cellularity, frequent mitotic activity, moderate nuclear atypia, and a lack of organized nuclear palisades of Verocay bodies. (7) Six of these cases were misdiagnosed as either fibrous histiocytoma, leiomyoma, malignant peripheral nerve-sheath tumor, or an undetermined type of sarcoma. Four of these 14 tumors (29%) were located in the head and neck region--one in the pterygoid area at the level of the maxillary tuberosity, one under the carotid bifurcation, one beneath the strap muscles, and one in the supraclavicular area.

In 1987, Fletcher et al provided further support for the existence of cellular schwannomas in their report of 18 cases. (9) They found that the most common sites of origin were the mediastinum (33%) and the retroperitoneum (22%). It is interesting that another two cases (11%) originated in the VIIIth cranial nerve.

In 1990, White et al published a review of 58 cellular schwannomas in 57 patients who had been evaluated between 1974 and l989. (10) They found that the most common sites of origin were the retroperitoneum (32%) and mediastinum (23%). In most of these cases, the identification of a tumor as a cellular schwannoma was based on microscopic examination alone. Bone erosion was either identified radiologically or visualized by the surgeon. White et al warned that radiologic or visual evidence of bone erosion or the presence of a local recurrence (probably as a result of an incomplete removal) can be misinterpreted by the radiologist as a malignant tumor. Finally, they preferred complete surgical excision as their treatment of choice.

As White et al pointed out, microscopic examination is usually sufficient to identify a cellular schwannoma, even though these tumors have certain features in common with classic schwannomas, such as Antoni B areas, hyalinized and thick-walled blood vessels, and collections of foamy macrophages. Nonetheless, cellular schwannomas differ from the classic variety in that they manifest greater cellularity and a lack of Verocay bodies. Spindle cells in both the cellular and classic forms are similar, but the former are more compactly arranged and are often hyperchromatic and pleomorphic. Mitoses are infrequent in cellular schwannomas, and when they do occur, they are usually of the typical variety. Support for a microscopic diagnosis of cellular schwannoma can be obtained by immunohistochemical staining and ultrastructural examination. The cells are usually diffusely and strongly reactive for S-100 protein and Leu-7. Ultrastructurally, they show a "schwannian" differentiation with complex, entangled cytoplasmic pr ocesses, and they are surrounded by a continuous basal lamina.

The pathologist-aware of this clinical picture and faced with a tumor of probable nerve origin that possesses atypical histologic features, such as increased cellularity, hyperchromatism, nuclear pleomorphism, and mitotic activity--should be aware of a common pitfall: misdiagnosing a cellular schwannoma as a malignant peripheral nerve-sheath tumor. Malignant peripheral nerve-sheath tumors are usually high-grade sarcomas. Approximately two-thirds of them arise in a neurofibroma or in a patient with von Recklinghausen's disease; the remainder arise de novo. Malignant peripheral nerve-sheath tumors are more cellular, their cells exhibit frank anaplasia, they feature numerous mitotic figures (usually >10/10 hpf), and they are less differentiated than cellular schwannomas.Although they show Schwann cell differentiation, the cell processes are less numerous, and the basal lamina tends to be discontinuous or focal. Moreover, their immunohistochemical reactivity for S-100 protein and Leu-7 is patchy or focal in most cases.

Cellular schwannomas must be distinguished from other spindle-cell neoplasms, as well. These other tumors include fibrosarcomas, synovial leiomyosarcomas, and meningiomas. Differentiation can usually be accomplished on the basis of immunohistochemical studies and/or electron microscopy.

Misinterpretation of a cellular schwannoma might lead the surgeon to perform a far more aggressive resection than is warranted for a benign tumor. It could also lead to the unnecessary administration of radiation therapy.

The primary treatment for cellular schwannoma is a complete surgical excision. The approach to the tumor is obviously dictated by its site and extension. Nasal tumors can be approached either externally or with a rigid sinus endoscope, depending on the available surgical expertise and personal preference. For a tumor that involves only one side of the nasal cavity, a lateral rhinotomy approach provides good access to the nose and sinuses. For a tumor that involves the frontal sinuses, ethmoids, and the cribriform plate (i.e., the anterior skull base), an eagle incision offers easy access and direct visualization; moreover, the resultant scarring is minimal and partially hidden in the eyebrow. For a tumor that is located primarily in the skull base and intracranially, a bicoronal incision is suitable, although it allows only limited access to the ethmoid area. Midfacial degloving is a good option for sinonasal tumors but not for tumors that extend into the frontal sinuses and anterior skull base.

In our case, the patient had already undergone removal of one nasal tumor 6 years earlier. After relevant investigations, we were convinced that the new tumor was confined to the ethmoids, frontal sinuses, and the roof of the anterior part of the nasal cavity. We opted for a modified eagle incision, and we were able to remove the tumor under direct vision.

References

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(3.) Wilson JA, McLaren K, McIntyre MA, et al, Nerve-sheath tumors of the head and neck. Ear Nose Throat J 1988;67:103-7, 110.

(4.) Casadei GP, Scheithauer BW, Hirose T, et al. Cellular schwannoma. A clinicopathologic, DNA flow cytometric, and proliferation marker study of 70 patients. Cancer 1995;75:1109-19.

(5.) Shugar JM, Som PM, Biller HF, et al. Peripheral nerve sheath tumors of the paranasal sinuses. Head Neck Surg 1981;4:72-6.

(6.) Donnelly MJ, at-Sader MH, Blayney AW. Benign nasal schwannoma. J Laryngol Otol 1992;106:l011-5.

(7.) Woodruff JM, Godwin TA, Erlandson RA, et al. Cellular schwannoma: A variety of schwannoma sometimes mistaken for a malignant tumor. Am J Surg Pathol 1981;5:733-44.

(8.) Beasley NJ, Jones NS. A modification to the brow incision for access to the anterior skull base and paranasal sinuses. J Laryngol Otol 1995;109:134-6.

(9.) Fletcher CD, Davies SE, McKee PH. Cellular schwannoma: A distinct pseudosarcomatous entity. Histopathology 1987;11:21-35.

(10.) White W, Shiu MH, Rosenblum MK, et al. Cellular schwannoma. A clinicopathologic study of 57 patients and 58 tumors. Cancer 1990;66: 1266-75.

From the Department of Otolaryngology--Head and Neck Surgery and Communication Sciences (Dr. Al-Otieschan, Dr. Manohar, and Dr. Gangopadhyay) and the Department of Pathology (Dr. Tulbah), King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia.

Reprint requests: Kunal Gangopadhyay, MS, Department of Otolaryngology--Head and Neck Surgery and Communication Sciences, King Faisal Specialist Hospital and Research Centre, MBC 47, P.O. Box 3354, Riyadh 11211, Saudi Arabia. Phone: [phone]; fax: [phone]; e-mail: [e-mail]