Seborrheic keratoses and trichostasis spinulosa.

In 54 of 325 seborrheic keratoses, trichostasis spinulosa was found within the keratinous cysts and between papillomatous surface keratin, in addition to being present in contiguous hair follicles. Trichostasis in seborrheic keratoses and trichostasis spinulosa are both more frequent in older age groups. Trichostasis spinulosa represents a marker of vellus hair follicles and indicates that some seborrheic keratoses incorporate and may be partially derived from the cells of the infundibular portion of the follicle.