| 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 |
