Clinical history: 50 year old male lesion on forehead.
What is the diagnosis, the main differential, and pathological features that help to distinguish between them?
The dermis shows solar elastosis, and at low power there is acanthosis with a cutaneous horn.
There are some features suggestive of verrucous vulgaris such as papilla, alterating areas of hyper and hypo-granulosis with concomitant overlying eosinophilic horn with para and ortho-keratosis,
however the cytologic atypia is too severe for this entity. Parts of the horn are more disorganized and the epidermis in these areas show marked atypia, leading to the diagnosis of actinic keratosis.
Also in the differential is keratoacanthoma, and although there is lipping at one side of the lesion the other edge is less well defined and the atypia is not full thickness.
This is one of the common lesions that can give rise to prominent hyperkeratosis (cutaneous horn).