Pathology of the Head and Neck

Nasal Cavity and Paranasal Sinuses Chapter 2 49tendency towards local invasion and recurrence, whichrarely arise in the sinonasal mucosa [96]. They compriseinterlacing fascicles of bland spindle-shaped fibroblasts,in a collagenous or myxoid background. The main differentialdiagnoses are fibrosarcoma and reactive fibrosis.Desmoid fibromatosis of the sinonasal tract showslower recurrence rates than desmoid fibromatoses arisingin other locations.2.10.5 Fibrous HistiocytomaICD-O:8830/0Benign fibrous histiocytoma presents as a yellow-tan noduleor polyp, most commonly causing nasal obstruction orbleeding [201]. It is composed of spindle-shaped cells producinga storiform pattern admixed with histiocytic cellsand multinucleated giant cells. Distinction from other benignsinonasal spindle cell proliferations is largely basedon the immunohistochemical findings. Benign fibroushistiocytomas may recur if incompletely excised.Fig. 2.6. Haemangiopericytoma: interconnected thin-walledblood vessels surrounded by uniform spindle-shaped cells withoval or elongated nuclei2.10.6 LeiomyomaICD-O:8890/0Sinonasal leiomyoma is a rare tumour occurring inadults, preferentially involving the nasal cavities, withnon-specific symptoms of nasal obstruction [91]. Itsmorphologic and immunohistochemical profile is identicalto that of leiomyomas of other sites. It has been postulatedthat they may originate from blood vessel walls.Distinction from sinonasal leiomyosarcoma is basedon the absence of atypia and mitoses. Huang and Antonescuhave proposed separating a category of smoothmuscle tumours of uncertain malignant potential, characterisedby the presence of 1–4 mitotic figures/10 highpower fields, that tend to pursue a more aggressive behaviourthan leiomyomas [119].2.10.7 Schwannoma and NeurofibromaICD-O:9560/0, 9540/0About 4% of schwannomas of the head and neck regionarise in the sinonasal tract [202]. They usually presentas polypoid lesions involving the nasal cavity and/ora paranasal sinus, with non-specific symptoms of obstruction,compression, or extension in the surroundingstructures [202]. Histologically, the tumour is composedof elongated wavy-shaped monomorphic spindle cells,with eosinophilic cytoplasm and oval nucleus. Antonitype A and type B areas usually coexist within the lesion,and nuclear palisading may be present. Focal degenerativenuclear atypia has been described [108], whilemitotic activity is absent to low. A consistently reportedFig. 2.7. Solitary fibrous tumour: fibroblastic proliferation, collagenproduction and dilated blood vessels. Identical features to thepleural counterpartfeature of sinonasal schwannomas is the lack of tumourencapsulation that determines an apparently infiltrativegrowth pattern [36, 108]. Immunohistochemically,sinonasal schwannoma is intensely reactive for S-100protein [108]. The differential diagnosis includes otherspindle cell lesions of the sinonasal mucosa, like juvenileangiofibroma, solitary fibrous tumour and leiomyoma.Particular care should be taken when evaluating cellularschwannomas with a predominance of Antoni typeA areas, which should not be confused with malignantspindle cell neoplasms, like fibrosarcoma, leiomyosarcoma,malignant peripheral nerve sheath tumour, andspindle cell melanoma.Neurofibromas of the sinonasal mucosa are usuallynot associated with the Von Recklinghausen syndrome,and appear as unencapsulated lesions composed of a mixtureof Schwann cells and fibroblasts embedded in a predominantlymyxoid stroma [117, 202]. Due to the overlappingof the histologic features, it may be difficult to differ-