Histopathological diagnostic features to consider in the evaluation of benign skin adnexal lesions
| Category | Feature description | Common examples |
|---|---|---|
| Location | Intraepidermal | Basaloid epidermal proliferations |
| Pilar sheath acanthoma | ||
| Hidroacanthoma simplex (intraepidermal poroma) | ||
| Dermal with epidermal connection | Trichofolliculoma | |
| Trichilemmoma | ||
| Poroma | ||
| Hidradenoma (rarely) | ||
| Dermal without epidermal connection | Folliculosebaceous cystic hamartoma | |
| Sebaceous tumours | ||
| Pilomatricoma | ||
| Hidradenoma | ||
| Morphology | Nests and/or cords | Syringoma |
| Syringofibradenoma | ||
| Solid sheets, nodular | Hidradenoma | |
| Spiradenoma | ||
| Cylindroma | ||
| Jigsaw puzzle-like pieces | Cylindroma | |
| Ductal-tubular formation | Syringoma | |
| Syringofibradenoma | ||
| Papillary structures | Syringocystadenoma papilliferum | |
| Hidradenoma papilliferum | ||
| Tubulopapillary hidradenoma (papillary eccrine adenoma and tubular apocrine adenoma) | ||
| Partially cystic | Pilomatricoma | |
| Pilar tumour | ||
| Hidradenoma | ||
| Chondroid syringoma | ||
| Fully cystic | Hidrocystoma | |
| Trichilemmal cyst | ||
| Steatocystoma | ||
| Borders | Well-defined, round and lobulated | Pilomatricoma |
| Hidradenoma papilliferum | ||
| Spiradenoma | ||
| Cylindroma | ||
| Pushing | Pilar tumour | |
| Infiltrative | A feature suspicious of malignant transformation | |
| Cellular details | Basaloid | Basaloid follicular hamartoma |
| Basaloid epidermal proliferations | ||
| Sebaceoma | ||
| Pilomatricoma | ||
| Hidradenoma | ||
| Poroma | ||
| Cylindroma | ||
| Spiradenoma | ||
| Epidermoid/squamoid | Hidradenoma papilliferum | |
| Hidradenoma | ||
| Spiradenoma | ||
| Syringocystadenoma papilliferum | ||
| Shadow (ghost) cells | Pilomatricoma | |
| Clear | Trichilemmoma | |
| Hidradenoma | ||
| Poroma | ||
| Spiradenoma | ||
| Syringoma | ||
| Mulberry cells | Lesions with sebaceous differentiation | |
| Presence of more than one population of cells | Spiradenoma | |
| Cylindroma | ||
| Apical snouts | Most lesions with apocrine differentiation | |
| Peripheral palisading | Basaloid follicular hamartoma | |
| Trichoepitheliomas | ||
| Trichoblastoma | ||
| Trichilemmomas | ||
| Sebaceoma | ||
| Pilar tumour | ||
| Evidence of differentiation | Trichilemmal keratinisation(without granular layer) | Pilar tumour |
| Follicular germ and hair shaft formation | Trichoblastoma | |
| Trichoepitheliomas | ||
| Glandular formation | Syringoma | |
| Tubulopapillary hidradenoma | ||
| Syringofibroadenoma | ||
| Hidradenoma papilliferum | ||
| Syringocystadenoma papilliferum | ||
| Sebaceous differentiation | Sebaceous tumours and lesions with sebaceous differentiation | |
| Spindle cell differentiation (rare) | Hidradenoma | |
| Stroma | Stromal desmoplasia | Most adnexal lesions |
| Mucinous change | Trichoblastic fibroma | |
| Chondroid syringoma | ||
| Chondroid change | Chondroid syringoma | |
| Vascular component | Folliculosebaceous cystic hamartoma | |
| Trichodiscoma/fibrofolliculoma | ||
| Poromas | ||
| Syringofibroadenoma | ||
| Spiradenoma | ||
| Neural component | Folliculosebaceous cystic hamartoma | |
| Prominent stromal plasma cell infiltrate | Syringocystadenoma papilliferum | |
| Other morphological associations | Epidermal verrucous hyperplasia | Trichilemmoma |
| Sebaceoma | ||
| Nevus sebaceous of Jadassohn | ||
| Melanocytic hyperplasia | Trichoblastoma | |
| Ulceration | Suspicious feature for malignancy | |
| Dystrophic calcification/ossification | Trichoepitheliomas | |
| Trichoblastoma | ||
| Pilomatricoma | ||
| Pilar tumour | ||
| Hyaline basement membrane | Trichilemmomas | |
| Cylindroma | ||
| Steatocystoma | ||
| Foreign body granuloma | Trichoepithelioma | |
| Pilomatricoma | ||
| Pilar tumour | ||
| Presence of rare Merkel cells | Basaloid epidermal proliferation | |
| Trichofolliculoma | ||
| Trichoepitheliomas | ||
| Trichoblastoma |