Pathology of the Head and Neck

Major and Minor Salivary Glands Chapter 5 147Fig. 5.29. Mucoepidermoid carcinoma: clear, intermediate andmucus-secreting cellsFig. 5.31. High-grade mucoepidermoid carcinoma: “epidermoid”cells arranged in a solid pattern also show nuclear pleomorphism.Mucus-secreting cells may be scarcepredict outcome to some degree, and MECs should begiven one of three microscopic grades, based on the extentof the cystic component, neural invasion, necrosis,cytological pleomorphism and mitotic activity. Thisassessment has considerable prognostic significance,with death rates due to disease of 3.3, 9.7 and 46.3%for grades 1, 2 and 3 respectively [62]. Recently, a newgrading system has been proposed, but it is still underevaluation [22]. Assessment of the MIB1 proliferationindex has also been shown to be of value [196].5.9.3 Adenoid Cystic CarcinomaFig. 5.30. Low-grade mucoepidermoid carcinoma: typical cysticand solid patternance (Figs. 5.29–5.31). In fact, keratinisation is veryrare in MEC, and indeed is much commoner as partof squamous metaplasia in pleomorphic adenoma ormalignant myoepithelioma, and in metastatic squamouscarcinoma from the skin or upper aerodigestivetract. Epidermoid cells may be sparse in MECs, andhigh molecular weight cytokeratin stains (e.g. LP34)and p63 can help identify them. Intermediate cells aresmall with dark-staining nuclei and they often formthe stratified lining of cysts beneath the mucous cells.Clear cell change may be seen in either the squamousor intermediate cells and MEC may take the form of aclear cell carcinoma [182]. Similarly, oncocytes can beplentiful [109]. All MECs are malignant with a metastaticpotential, regardless of their microscopic appearance.Nevertheless, histological features can be used toICD-O:8200/3Adenoid cystic carcinoma (AdCC) is a malignant tumourwith no particular age or sex predilection. It canoccur in any gland, but most often in the submandibularor minor salivary glands, particularly the palate. However,in spite of often apparently slow growth, outcomeover the long term is poor. AdCC is an extensively infiltrativetumour with characteristic perineural invasion,and this is partly responsible for the clinical presentationof late, but repeated local recurrences. Unlike othersalivary gland malignancies, when AdCC metastasises,it tends to involve distant organs (lung, bone) ratherthan local lymph nodes [117].Histologically, AdCC is a generally solid tumour inwhich the cribriform pattern is easily recognised on microscopy,but tubular and solid structures can also bepresent. The commonest growth patterns are:Cribriform: this is the most characteristic microscopicfeature, dominated by multiple cribriform structures,composed of epithelial and basal/myoepithelial cells.The nuclei are usually dark, hyperchromatic and angulated.Mitotic figures are easy to find and may be abun-