Pathology of the Head and Neck

Nasal Cavity and Paranasal Sinuses Chapter 2 43This lesion is differentiated from the very rare sinonasalteratoma by the limited variety of tissue types andthe absence of endodermal components [100]. Epidermalinclusion cysts do not contain adnexa. Dermoidcysts of the nose should also be distinguished from encephalocele.We are unaware of hairy polyps occurringin the nose.2.5 Pseudotumours2.5.1 MucoceleMucocele is a cyst filled with mucus that develops withina sinus cavity as the result of occlusion of the ostium.Most commonly it is due to infection, but may also resultfrom trauma or be congenital [109]. Retained secretionscause expansion of the sinus and bone erosion. Themost common sites of occurrence are the frontal and thesphenoidal sinuses. The cyst is lined by respiratory epitheliumthat shows prominent goblet-cell hyperplasia[158, 184]. Expansion of the cyst may cause atrophy andmetaplasia of the epithelium.2.5.2 Organising HaematomaOrganising haematoma, also known as “ cholesterolgranuloma” or “rhinitis caseosa”, is in most cases the resultof occult submucosal haemorrhage in the maxillarysinus due to external trauma or tooth extraction [147].Resolution of the haematoma produces the formation ofcholesterol granulomas and fibrosis, simulating a foreignbody reaction.2.5.4 MyospherulosisMyospherulosis is characterised by the presence of cystlikespaces lined by flattened histiocytes and containingclusters of brownish spherules resembling fungi [198,217, 230]. They lie loosely or within sacs formed by thinrefractile membranes. The brownish spherules do notstain with PAS or Gomori methanamine silver and theirmorphology does not correspond to any known fungus[228]. They are found within fibrous granulation tissue,which may show a foreign body reaction. The lesion isusually found in patients who have had previous operations[145]. It is now recognised that the spherules areextravasated red cells that have been altered by interactionwith traumatised fat or petrolatum-based ointmentsand gauzes used in surgical procedures.2.5.5 Eosinophilic Angiocentric FibrosisEosinophilic angiocentric fibrosis is a rare, chronic, benign,idiopathic condition of the upper respiratory tractoccurring predominantly in adult women [214, 248].Initially, the histologic picture is characterised by nonnecrotisingeosinophilic vasculitis involving capillariesand venules of the sinonasal mucosa, accompanied by aninflammatory infiltrate with lymphocytes, plasma cells,histiocytes and occasional neutrophils [214]. In late lesionsthere is a characteristic obliterative perivascularonion-skin fibrosis, while the inflammatory infiltrate isless dense and eosinophils predominate [214]. The differentialdiagnosis includes reactive processes of the sinonasalmucosa, like Wegener’s granulomatosis, Churg-Strauss syndrome, Kimura disease, and angiolymphoidhyperplasia with eosinophilia.2.5.3 AmyloidosisIsolated amyloid deposition in the sinonasal mucosa isa rare event, with about 20 cases reported in the English-languageliterature [180, 258]. Grossly, the lesionappears as a friable tumour-like mass, with a tendencyto bleed. Histologically, there is a deposition of intenselyeosinophilic material in the stroma, around blood vesselsand around ducts of the mucoserous glands, whichis often associated with diffuse chronic inflammationand foreign body granulomatous reaction. Amyloidstains orange with Congo red, and showed apple greenbirefringence under polarised light examination. Immunohistochemistrymay help to identify the type ofamyloid deposition.2.5.6 Heterotopic Brain TissueThis lesion mostly occurs in young children, usually theresult of a congenital abnormality related to a variant ofmeningoencephalocele [136, 196]. Commonly used synonymsare glial heterotopia and nasal glioma, althoughthe latter is a misnomer. The lesion mainly arises at thebase of the nose or in the upper part of the nasal cavity,and grossly may be polypoid. Histologically, it is mostlycomposed of a mixture of astrocytes, glial fibres andfibrous connective tissue. Multinucleated glial cells arefrequently found. Some glial cells can have large nucleiresembling nerve cells. Immunostaining for glial fibrillaryacidic protein is a helpful diagnostic adjunct. A fewtrue nerve cells or even ependymal elements can rarelybe identified. Mitoses are not found.