Pathology of the Head and Neck

164 S. Di Palma · R.H.W. Simpson · A. Skalova · I. Leivo5Mucosa-associated lymphoid tissue lymphomas usuallypresent clinically as parotid enlargement, sometimesbilateral [217]. There is often a history of Sjögren’ssyndrome, but not always. Cases have been reported inpost-transplant patients [101]. General lymphadenopathyand bone marrow involvement are unusual in MALTlymphoma, and such a presentation favours a diagnosisof nodal lymphoma.The histopathology of MALT lymphoma is intimatelylinked with that of LESA from which it develops– the risk of lymphoma in LESA has been estimatedat approximately 4–7% [91]. Histological criteriaalone cannot identify exactly when a clonal B-cell populationemerges in LESA, and in practice the processcan be considered not so much a sharp change fromone (benign) entity to another (malignant) one, butrather as a spectrum of lymphoma gradually evolvingfrom a purely inflammatory process (Table 5.5) [165].It can be considered that MALT lymphoma begins asan antigen-driven lymphoid proliferation that progressesfirst to monoclonality and then, with the acquisitionof secondary genetic changes, to MALT lymphoma[105].The microscopic picture evolves with time [105]; theearliest morphologically recognisable feature of malignancyis the proliferation of marginal zone B-cells toform a distinct halo-like zone around the LELs of LESA.As the lymphoma evolves in a background of LESA marginalzones B cells expand, displace and then replace thefollicles. Alternatively, they may colonise the germinalcentres assuming a follicular-like architecture (pseudofollicles)[106]. In addition, there may be foci of sclerosis,and infiltration by epithelioid histiocytes, which canform small granulomas.Mucosa-associated lymphoid tissue lymphoma restrictedto the salivary glands is a relatively indolentdisease that is often curable with local treatment. Prognosisremains favourable even in the presence of otherextranodal sites, including bone marrow [108].Other primary non-MALT extranodal salivary lymphomasare rare, and are mainly T-cell neoplasms[29].Nodal non-Hodgkin’s lymphomas can involve theintra-salivary and adjacent lymph nodes, and theyshould be classified using the appropriate scheme [104,108].5.15 Other TumoursA variety of soft tissue and other non-salivary neoplasmsmay rarely present as tumours of the salivaryglands. These include solitary fibrous tumour, granularcell tumour, follicular dendritic cell sarcoma, inflammatorypseudotumour (inflammatory myofibroblastictumour), primary malignant melanoma, primitive neuroectodermaltumour (PNET) and teratoma.5.16 Unclassified TumoursThe revised WHO classification defines this group asbenign or malignant tumours that cannot be placed inany of the categories [171]. This designation may be unavoidableif only a small quantity of tissue is availablefor study.References1. Albeck H, Bentzen J, Ockelmann HH, Nielsen NH, Bretlau P,Hansen HS (1993) Familial clusters of nasopharyngeal carcinomaand salivary gland carcinomas in Greenland natives.Cancer 72:196–2002. Alós LL, Cardesa A, Bombí JA, Mallofré C, Cuchi A, TraserraJ (1996) Myoepithelial tumors of salivary glands: a clinicopathologic,immunohistochemical and flow-cytometricstudy. Semin Diagn Pathol 13:138–1473. 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