Schwannoma commonly occurs in the head and neck region but rarely in the nasal cavity and sinuses [1
]. In addition, new bone formation accompanying schwannoma is extremely rare, with only a few cases of schwannoma with calcification in the internal auditory canal, lacrimal gland, spine, and other softtissues having been reported [4
]. To date, sinonasal schwannoma with new bone formation has not been reported. Here, we present the first case of sinonasal schwannoma with new bone formation and its clinical management.
There have been three reported cases of bone formation in nasal polyps [10
]. In addition, four cases of the association of inverted papillomas and new bone formation have been reported recently [11
]. However, the mechanism of osteogenesis in these inflammatory and tumor tissues remains unclear. Calcifications may be classified as entrapped bone structures or as primary tumoral calcifications. Essentially, entrapped bone is the bone fragment, which is enclosed within the tumor and erodes due to pressure atrophy whereas primary tumorous calcification is calcification created by the tumor itself; both may appear as calcifications on CT [13
]. The histopathologic examination revealed no entrapped bone or primary tumor calcification in the current bone structure. The examination showed new bone formation consisting of randomly organized trabeculae lined by osteoblasts. These randomly organized trabeculae were divided with prominent capillaries and mesenchymal cells. In general, however, the entrapped bone should be in a lamellar structure, but in our case, the bone trabeculae were woven and represented active osteoblast production of newly formed bone. In addition, intraoperative findings showed that the newly generated bone in the tumor was independent of normal anatomical bone structure. Thus, the current case was diagnosed as schwannoma with new bone formation.
Clinically, schwannoma with accompanying new bone formation might appear to behave no differently from common schwannoma, and its features might be similar. The treatment of choice for sinonasal schwannoma is surgery. To date, less than 100 cases of sinonasal schwannoma have been reported [1
], and different approaches, including lateral rhinotomy with external ethmoidectomy, the Caldwell-Luc approach, midfacial degloving, or ESS, have been employed in relation to tumor extension [3
]. ESS is now widely accepted and commonly performed in cases requiring nose or paranasal sinus surgery. ESS provides excellent magnification, illumination, and angled visualization, thereby allowing the surgeon to isolate the base of the tumor and accurately define the extent of disease. Long-term followup of our patient will reveal the optimal clinical management of sinonasal schwannoma with new bone formation.
Another important finding in this paper is the demonstration of BMP expression in the tumor. This is the first paper showing BMP expression in schwannomas. BMPs are multifunctional growth factors belonging to transforming growth factor beta superfamily. It has been demonstrated that BMPs had been involved in the regulation of cell proliferation, survival, differentiation, and apoptosis [15
]. However, their hallmark ability is that play a pivotal role in inducing bone, cartilage, ligament, and tendon formation at both heterotopic and orthotopic sites. Extensive studies demonstrate that BMPs are important factors regulating chondrogenesis and skeletogenesis during normal embryonic development [16
]. The BMPs with greatest osteogenic capacity are BMP-2, -4, -5, -6, -7, and -9. BMP-2 acts as a disulfide-linked homodimer and induces bone and cartilage formation. It is candidate as a retinoid mediator and plays a key role in osteoblast differentiation. BMP-4 regulates the formation of teeth, limbs, and bone from mesoderm and also plays a role in fracture repair. BMP-7 plays a key role in osteoblast differentiation [15
]. Expression of BMPs in tumor tissues has also been reported [17
]. BMP 2/4 was localized predominantly to the cytoplasm of malignant cells with primitive mesenchymal features; no or little BMP is detected in the more differentiated elements of bone and softtissue sarcomas [17
]. Different levels of BMP 2/4 expressions in bone and soft tissue sarcomas have been considered to be associated with the stage of mesenchymal differentiation. In the current case, the schwannoma cells expressed BMP-4 inhomogenously. Although the detail of role of BMP remains unclear in the pathogenesis in the current tumor, this indicates possible role of BMP-4 for new bone formation in schwannomas.
In conclusion, we have described the first reported case of sinonasal schwannoma with new bone formation. ESS could be successfully used to achieve complete removal of the tumor. BMP-4 might be associated with new bone formation in the tumor.