Table 2 Morphological patterns and useful observations in evaluating skin adnexal tumours.
| Pattern | Examples | Comments |
|---|---|---|
| Tumours with sebaceous elements | Sebaceous hyperplasia, sebaceous adenoma and sebaceoma | Sebaceous differentiation is indicated by “mulberry” cells with coarsely vacuolated cytoplasm and starry nuclei |
| Sebaceous carcinoma | EMA is positive in sebaceous cells | |
| Basal cell carcinoma with sebaceous differentiation | ||
| Trichoblastoma with sebaceous differentiation | ||
| A variety of tumours of the “pilosebaceous‐apocrine” unit | ||
| Sebaceous hyperplasia, sebaceous adenoma and sebaceoma | ||
| Sebaceous carcinoma | ||
| Basal cell carcinoma with sebaceous differentiation | ||
| Trichoblastoma with sebaceous differentiation | ||
| A variety of tumours of the “pilosebaceous‐apocrine” unit | ||
| Tumours with elements of follicular differentiation | Trichoepithelioma | Proliferation of basaloid bulbar follicular germinative cells (with peripheral palisading) or lesions with matrical cells |
| Tumours with elements of follicular differentiation | Trichoblastoma | |
| Trichofolliculoma pilomatricoma | ||
| Tumours with clear cell change | Trichilemmoma | Clear cell change is indicative of trichilemmal differentiation in follicular lesions |
| Poroma and porocarcinoma | Clear cells are glycogen rich and PAS positive | |
| Hidradenoma | Clear cell change is indicative of trichilemmal differentiation in follicular lesions. Clear cells are glycogen rich and PAS positive | |
| Tumours with ductal/tubuloglandular elements | Syringoma poroma and porocarcinoma | Mostly in eccrine/apocrine lesions |
| Syringoma | Ducts have a dense eosinophilic cuticle, and may contain amorphous material. PAS and CEA are usually positive | |
| Cylindroma | Mostly in eccrine/apocrine lesions. Ducts have a dense eosinophilic cuticle, and may contain amorphous material. PAS and CEA are usually positive | |
| Hidradenoma | ||
| Microcystic adnexal carcinoma | ||
| Tumours with small keratin cysts | Desmoplastic trichoepithelioma | Mostly in lesions with follicular differentiation |
| Trichoblastoma | Cysts lack a cuticle, do not stain with PAS or CEA, and may contain keratin | |
| Trichoadenoma | Mostly in lesions with follicular differentiation. Cysts lack a cuticle, do not stain with PAS or CEA, and may contain keratin | |
| Microcystic adnexal carcinoma | ||
| Tumours with predominant small/basaloid elements | Trichoblastoma/trichoepithelioma | This pattern should be interpreted in conjunction with other features such as sebaceous or follicular differentiation, the presence of cysts/ductal elements or clear cell change, etc |
| Pilomatricoma | ||
| Sebaceous tumours | ||
| Poroma | ||
| Spiradenoma | ||
| Acrospiroma | ||
| Cylindroma |
CEA, carcinoembryonic antigen; EMA, epithelial membrane antigen; PAS, periodic acid Schiff.