About 4% of schwannomas of the head and neck region arise in the sinonasal tract . They usually present as polypoid lesions involving the nasal cavity and/or a paranasal sinus, with non-specific symptoms of obstruction, compression, or extension in the surrounding structures . Histologically, the tumour is composed of elongated wavy-shaped monomorphic spindle cells, with eosinophilic cytoplasm and oval nucleus. Antoni type A and type B areas usually coexist within the lesion, and nuclear palisading may be present. Focal degenerative nuclear atypia has been described , while mitotic activity is absent to low. A consistently reported
feature of sinonasal schwannomas is the lack of tumour encapsulation that determines an apparently infiltra-tive growth pattern [36, 108]. Immunohistochemically, sinonasal schwannoma is intensely reactive for S-100 protein . The differential diagnosis includes other spindle cell lesions of the sinonasal mucosa, like juvenile angiofibroma, solitary fibrous tumour and leiomyoma. Particular care should be taken when evaluating cellular schwannomas with a predominance of Antoni type A areas, which should not be confused with malignant spindle cell neoplasms, like fibrosarcoma, leiomyosar-coma, malignant peripheral nerve sheath tumour, and spindle cell melanoma.
Neurofibromas of the sinonasal mucosa are usually not associated with the Von Recklinghausen syndrome, and appear as unencapsulated lesions composed of a mixture of Schwann cells and fibroblasts embedded in a predominantly myxoid stroma [117, 202]. Due to the overlapping of the histologic features, it may be difficult to differ-
Fig. 2.8. Juvenile angiofibroma. a Polypoid mass of white-red cut surface and rubbery consistency. b Vascular elements embedded in fibrous tissue showing intravascular microembolisation, a treatment modality prior to surgery sinuses. Histologically, they are similar to paragangliomas elsewhere [12, 98, 187].
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