Pathology of the Head and Neck

290 M.R. Canninga-Van DijkFig. 10.9. Intraepithelial component of a sebaceous adenocarcinoma:intraepithelial pagetoid spread of tumour cells may be misinterpretedas dysplasia; positive staining for EMA can be veryhelpful (EMA immunostaining)Fig. 10.11. Sebaceous adenocarcinoma: detail of the clear cells,showing sebaceous differentiation10like EMA and CAM 5.2 can help in differentiating thisaggressive tumour from a squamous cell carcinoma(Figs. 10.09–10.11). Treatment of choice is wide excision,which can cure patients at an early stage of thelesion. However, the mortality rate from metastases is25%, and even higher in a poorly differentiated tumourwith angioinvasive growth.10.2.6.2 Melanocytic10.2.6.2.1 NaevusFig. 10.10. Sebaceous adenocarcinoma: basaloid epithelial nestswith a clear cell component10.2.6.1.5 Sebaceous AdenocarcinomaICD-O:8410/3This lesion is important because it can be a pitfall forboth the clinician and the pathologist. The tumourpresents as a solitary nodule, that can clinically be misdiagnosedas a basal cell carcinoma or even as a chalazionor blepharoconjunctivitis [1, 36, 81]. Histologically,the tumour is composed of epithelial nests withvarying sebaceous differentiation. The well-differentiatedsebaceous carcinomas are not very hard to recognise,but the poorly differentiated ones can be easilymissed. The intraepithelial pagetoid spread of tumourcells (which is frequently present) may be misinterpretedas dysplasia. Immunohistochemical stainingsICD-O:8720/0The most common melanocytic lesion of the conjunctivais the compound naevus. Other types of naevi thatcan be found in the conjunctiva are intraepithelial,subepithelial, Spitz and blue naevi. Their histology issimilar to melanocytic skin lesions. The naevus mostlyarises in the first or second decade as a nodule in thebulbar conjunctiva. A band of melanocytes in the basallayer of the epithelium represents the intraepithelialcomponent. These melanocytes can be melanin-containing,but can also present as clear cells. Melanocytescan also be found in the epithelium of the inclusioncysts, which are almost invariably present. These large,mucin-containing cysts are formed by incarceratedepithelial nests and can give an erroneous clinical impressionof growth. The stromal component is formedby nests of mature cells with maturation to smaller cellsin the deeper parts of the lesion (Fig. 10.12). Especiallyat a young age, a considerable variation in cell size canbe seen; these active lesions are easily overdiagnosed asmalignant melanomas.