Adnexal Tumours Overview

Diagnosing adnexal lesions is a pain. You basically want to know if benign or malignant.
You then want to put a name to it. 

Benign - Cytologically bland, few mitoses, smooth border and vertically orientated

Malignant - Cytologically atypical, many mitoses, Infiltrative edges, Horizontally orientated and lymphovascular invasion.

What makes something an Adnexal Tumour?  You can see features of hair follicles, sweat glands or arrector pili muscle proliferating.  ie You see ducts in eccrine tumours or secreting cells eccrine or apocrine. You see proliferating cells of the various layers of the hair follicle.(so you need to know the normal histology of a hair follicle) . You see muscle cells from the arrector pili muscles.You see sebaceous cell proliferations from clear sebacous glands

Proliferations downward from the epidermis - Fibroepithelioma of Pinkus, Fibrofolliculoma, Inverted follicular keratosis, Poroma, Reticulated Seb k, Trichilemmoma, Tumour of Follicular infundibulum.

Pores - Dilated pore of Winer, Pilar sheath acanthoma, Trichofolliculoma,


Lined spaces - Apocrine hydrocystoma, Auricular pseudocyst, Cutaneous ciliated cyst, Branchial cleft cyst, Dermoid cyst, Epidermal inclusion cyst, Pilar cyst, Steatocystoma, (Cutaneous endometriosis)

Cords and tubules -  Syringomas, Desmoplastic syringomas, Desmoplastic trichoepithelioma, Microcystic adnexal carcinoma, Breast cancer metastases, Morphoeic BCC,

Dermal tumour with a papillary growth pattern. Hidradenoma papilliferum,  Florid nipple papillomatosis nipple, Papillary eccrine adenoma, Syringocystadenoma papilliferum, Tubular appocrine adenoma.

Circular dermal islands of cells  Micronodular BCC, Cylindroma, Adenoid cystic carcinoma, Trichoadenoma, Spiradenoma,

You can start with just statistical knowledge of what are the common tumours. Malignancy only occurs in 5% of excised adnexal tumours.

Benign -Syringoma,  Hidradenoma, Spiradenoma, Cylindroma, Poroma, Pilomatricoma, Proliferating trichilemmal cyst, Syringocystadenoma papilliferum, Hidrocystomas,

Malignant - Malignant eccrine Spiradenoma, Adenoid cystic carcinoma, Microcystic adnexal carcinoma, Extramammary Paget's disease. Pilomatrix carcinoma,


You also need to be able to confidently recognise any common tumour that may be a skin marker of internal malignancy associated with certain named syndromes.

Trichoepithelioma, Trichilemmoma, Sebaceous adenoma, Sebaceous carcinoma,

Many adnexal tumours have Clear cell and Desmoplastic variants. Desmoplastic trichoepithelioma,  Chondroid syringoma,

Other commonly biopsied adnexal lesions include Sebaceous hyperplasia, Nevus sebaceous, Angiofibroma,

In learning about adnexal tumours we will concentrate on these statistically significant tumours, look at any malignant variants and look at the common differential diagnoses for these commoner tumours. This approach should make learning about adnexal tumours manageable and clinically appropriate.