I was caught out today by a particularly large relatively well circumscribed basaloid neoplasm of the dermis for which my first thought was that it was likely to be an adnexal tumour. However basal cell carcinoma should always be a top differential when considering basaloid neoplasms of the skin and when in doubt there should be a low threshold for requesting a Berep4.
- Poorly differentiated SCC
- Benign Adnexal Tumours
- Rarely malignant counterparts of Adnexal tumours
Basaloid – Benign Adnexal Tumours
- Hair follicle tumors – Trichoepithelioma, Trichoblastoma, Tricholemmoma, Pilomatrixioma
- Sebaceous tumours – Sebaceoma
- Apocrine tumours – Cylindroma & Spiradenoma
- Eccrine tumours – Syringoma & Eccrine Poroma
BCC – Basaloid proliferation with peripheral palisading, retraction artefact and mucin deposits with mitoses and apoptosis at high power. Subtypes include nodular, superficial & morpheic/infiltrative.
Hair Follicle Tumours
Trichofolliculoma – Maybe seen as a tuft of fine hairs protruding from a central umbilication. Small follicles with variable maturity radiate from a larger central follicle.
Trichoepithelioma – Multiple nests of basaloid cells some showing abortive hair follicle differentiation often with peripheral palisading.
Desmoplastic Trichoepithelioma – Small cords and islands of basaloid cells set in a fibrous stroma.
Trichoblastoma – Benign tumour of the hair germ cell with trichogenic differentiation and stromal induction.
Pilar sheath acanthoma – Benign tumour found almost exclusively on the upper lip of older individuals. Tumour lobules composed of outer root sheath epithelium radiate from a central depression.
Inverted follicular keratosis – Endophytic lesions with basaloid cells at the periphery and larger keratinizing cells toward the center with characteristic squamous eddies.
Tricholemmoma – Seen in Cowden’s disease (PTEN mutation). Sharply demarcated basaloid lesion which may be in continuity with the epidermis with squamous cells showing glycogen vacuolation (PAS positive & diastase resistant). There is peripheral palisading and the appearances of an underlying basement membrane.
Pilomatrixoma – Nests of basaloid cells with shadow cells, the lesion may be partially cystic.
Sebaceous Hyperplasia – Lobules of enlarged, mature sebaceous glands are attached to a central hair follicle
Sebaceous Adenoma – Multiple sharply demarcated sebaceous lobules separated by compressed connective tissue septae with a peripheral layer of smaller basaloid cells. Assoc with Muir Torre Syndrome.
Sebaceoma – Multiple nests of basaloid cells with a rippled pattern with a random admixture of mature sebaceocytes. Care not to mistake holocrine secretions for keratin.
Other tumours may have areas of sebaceous differentiation.
Syringocystadenoma papilliferum – Irregular papillary projections protrude into the invaginations of the surface epithelium. The stroma contains numerous plasma cells.
Hidradenoma papilliferum – With papillary and glandular areas.
Tubular apocrine adenoma – There are multiple tubular structures lined by apocrine type epithelium.
Apocrine hidradenoma – see images. Uniform cells with uniform nuclei and eosinophilic cytoplasm.
Cylindroma – Basaloid cells are arranged in irregularly shaped islands surrounded by a thin band of hyaline material.
Spiradenoma – Basaloid lesion which is partly cystic and haemorrhagic.
Eccrine Tumours (Sweat gland)
Syringoma – Multiple small ductal structures lined by two layers of cuboidal epithelium are present in a fibrous stroma.
Eccrine poroma – Cords of basaloid cells extending into the dermis
Hidroacanthoma simplex – Well circumscribed nests of basaloid cells are present in the epidermis.
Weedon’s Skin Pathology. 3rd Ed.