Paediatric cutaneous adnexal tumours: a study of 559 cases.

Cutaneous adnexal tumours encompass a wide group of lesions with apocrine, eccrine, follicular, sebaceous and mixed differentiation. The large majority are benign and represent sporadic lesions, though malignant forms are occasionally encountered and some cases develop in the setting of inherited tumour syndromes. Accurate histological classification can be difficult as there are numerous histological appearances, many of which are individually uncommon, and complex, overlapping and historically variable nomenclature is typical. The aim of this study was to review and classify the spectrum of cutaneous adnexal tumours seen in patients 18 years of age and under in two major tertiary centres over a 20 year period. A total of 559 cases were included, with 60% occurring in female patients. The large majority (87%) occurred in the head and neck region and were benign. Only one (0.2%) was malignant. The original diagnosis was supported by histological review in 99% of cases of pilomatricoma reviewed, but in only 71% of non-pilomatricoma cases reviewed. The most common lineage was follicular (97%), with pilomatricoma accounting for the large majority of lesions. Predominant glandular/ductal differentiation was seen in 3% of cases, with no tumours showing predominant sebaceous differentiation.