Benign
- Pilomatrixoma
- Tricoepithelioma
- Apocrine Gland Tumours
- Sebaceous Gland Tumours
Malignant Skin Appendage Tumours

Benign

Pilomatrixoma

“Calcifying epithelioma of Malherbe”
- Benign appendageal tumour with differentiation toward hair cells
Incidence
- Relatively infrequent (e.g. 1/500 histological specimens)
- More common in children; but does occur in adults → 2 peaks: 5-15yrs & 50-65yrs
- Most reported in white people
- Slight female preponderance (1.5:1)
Aetiology
- Genetic pathogenesis: Faulty suppression of apoptosis
- Rare association with Myotonic Dystrophy
Clinical
- Solitary, asymptomatic firm/stony nodule, colour of normal skin
- Often stretch the overlying skin
- 50% occur on head & neck
- 0.5-3cm, but can be up to 15cm
Pathology
- Lower dermis and subcutaneous fat: Irregular islands of cells ± Ca2+ deposits
DDx:
- Pilomatrix carcinoma (rare)
Investigations
- Often calcified on x-ray
- USS: Ovoid complex mass at the junction of dermis and subcutaneous fat, with focal thinning of the overlying dermis
Management
- Excision with wide margin (1-2cm) to avoid local recurrence
Prognosis / Natural Hx:
- Slowly grows over months or years
- Do not spontaneously regress
- No association with mortality
- Incomplete excisions → Local recurrence

Solitary nodule
Face
Adults
Familial form
- Multiple
Histology
- Resembles BCC
- Contains keratin horn cysts
- May rupture
- Get foreign body reaction & focal calcification

1-2cm diameter
Vulva, perianal skin
Females - external genitalia
Histology
- Papillary processes in cystic cavity
- Lined by double layer epithelial cells and myoepithelial cells

Malignant hair follicle tumours
- Extremely rare
Apocrine carcinoma
- Rare
- Axilla, areola of nipple, vulva
- Can be associated with extramammary Paget’s
Eccrine carcinoma
- De novo or in pre-existing lesions
- Mets common (2/3 cases)
Sebaceous carcinoma
- Rare
- Eyelids
- Mets 20%