Abstract

Cutaneous adnexal tumours derived from outer root sheath of hair follicles demonstrating a trichilemmal variety of keratinzation commonly manifest as trichilemmal cysts, proliferating trichilemmal cysts and malignant proliferating trichilemmal tumours. Proliferating trichilemmal tumour (PTT) is enunciated as an exceptional, benign, cutaneous adnexal neoplasm originating from outer root sheath of the hair follicle and is additionally nomenclated as proliferating trichilemmal cyst or pilar tumour of the scalp. Malignant proliferating trichilemmal tumour was initially described by Wilson Jones as a “proliferating epidermoid cyst” in 1966 and further segregated from proliferating epidermoid cyst in 1995 [1]. Although contemplated as a biologically benign lesion, proliferating trichilemmal tumour can emerge as an aggressive, locally infiltrative tumefaction, exceptionally delineating malignant transformation as evidenced with concurring regional or distant metastasis. Terminology of malignant proliferating trichilemmal cyst for describing a proliferating trichilemmal cyst exemplifying malignant transformation was proposed by Headington [1,2].