Infundibular keratosis--a prototype of benign infundibular tumours.

Three cases of a benign follicular tumour of infundibular origin are reported. The neoplasms were solitary, verrucous, slowly-growing papules or nodules on the face, which were diagnosed clinically as verruca vulgaris or seborrhoeic keratoses. Histologically, several epithelial lobules were seen, mainly above the level of the surface of the surrounding skin, with characteristic funnel-shaped invaginations. The tumours occasionally contained vellus hairs or were connected with sebaceous glands and/or hair follicles at their bases, indicating their follicular origin. The tumour masses consisted of peripherally arranged basaloid and inner squamoid cells. The latter cells contained more glycogen and appeared paler with haematoxylin and eosin (H&E) stains than the normal inter-follicular squamous cells. Neither clear cells nor squamous eddies were observed. Palisading of the basaloid cells was not a prominent feature. The name 'infundibular keratosis' is proposed for such tumours, which probably represent the prototype of infundibular tumours of the hair follicle.