Pathology of the Head and Neck

148 S. Di Palma · R.H.W. Simpson · A. Skalova · I. Leivo5Fig. 5.32. Adenoid cystic carcinoma, cribriform variant: multiplecribriform spaces composed of basaloid cells, with hyalinised materialsurrounded by small hyperchromatic cellsFig. 5.34. Adenoid cystic carcinoma, solid variant. This is composedof multiple solid nodules, some displaying central comedolikenecrosis. The tumour can be seen to infiltrate boneFig. 5.33. Adenoid cystic carcinoma, cribriform variant. Diffusehyalinisation with compression of tumour cells. Nuclear pleomorphismmay be difficult to appreciate, leading to a false diagnosis ofpleomorphic adenomaFig. 5.35. Adenoid cystic carcinoma, solid variant. Tumour islandscontain small ducts lined with a layer of epithelial cells. Inthe absence of characteristic cribriform structures, the latter featureis diagnosticdant; the MIB1 proliferation index exceeds 10% [201].The contents of the spaces can be loose and basophilicor dense and eosinophilic. Hyalinisation is commonin adenoid cystic carcinoma and may be extreme. Inthose cases with excessive deposition of hyalinised material,the spaces are distended with loss of the cribriformpattern. Tumour cells may be sparse and bland,and thus the lesions may mimic a pleomorphic adenoma(Figs. 5.32, 5.33).Tubular: this is composed of small tubules lined withone or two cell types, luminal and abluminal withoutsignificant cytological atypia. Because of this bland cytologicalappearance it may be mistaken for basal celladenoma, except for the presence of infiltration.Solid (basaloid): this is dominated by large solid sheetsof tumour cells, sometimes with comedo-like centralnecrosis. Within the solid masses of tumour cells, thereare small duct-like spaces surrounded by a definite layerof epithelial cells (Figs. 5.34, 5.35). This latter findingdistinguishes solid variant AdCC from (relatively lowgrade)basal cell adenocarcinoma and the aggressive basaloidsquamous cell carcinoma, which in addition oftenshows intraepithelial dysplastic changes.A rare finding in all types of AdCC is squamousmetaplasia, either as single cells or with keratin pearlformation [62].A system of three grades based on the presence oftubular, cribriform and solid pattern [171] has shown