Sinonasal schwannoma with new bone formation expressing bone morphogenic protein

Abstract

Schwannoma is a benign tumor that arises from the sheath of myelinated nerve fibers and may occur in any part of the body. Osteogenesis in schwannoma is extremely rare and, to date, new bone formation in sinonasal schwannoma has not yet been reported. Here, we describe the first reported case of sinonasal schwannoma with new bone formation. The tumor was successfully treated by endoscopic sinus surgery, and the patient showed no evidence of recurrence 24 months postoperatively. Immunohistochemically, the tumor expressed bone morphogenic protein 4, indicating a possible role of this protein in the new bone formation in schwannomas.

Figure 1

Horizontal (a) and axial (b) enhanced computed tomography (CT) showed an inhomogeneously enhancing mass that filled the left nasal cavity. A low-density lesion with metal-dense spots in the left maxillary sinus, indicating mycetoma, was also observed. Bone window images ((c), (d)) also showed a new bone formation in the tumor. Black arrows indicate a new bone formation.

Figure 2

Horizontal (a) and axial (b) magnetic resonance imaging (MRI) showed a nasal tumor in the left nasal cavity with a hypointense signal on T1-weighted images, and a moderately hyperintense signals on T2-weighted images. This signal was different from that of the left maxillary sinus lesions.

Figure 3

Macroscopic (a) and microscopic (x100 magnification) (b) features of the excised tumor. The spindle cells are arranged in a patternless fashion, and new bone formation consisting of randomly organized trabeculae lined by osteoblasts was observed in the tumor. black arrows and *asterisk: bone tissue.

Figure 4

Immunohistochemistry for bone morphogenic protein (BMP; x100 magnification). (a) BMP-2, (b) BMP-4, and (c) BMP-7. The tumor cells stained positive for BMP-4 and negative for BMP-2 and BMP-7. *asterisk: bone tissue.

Figure 5

Western blot analysis for BMP. The tumor tissue expressed BMP-4 but not BMP-2 and -7.