Chapter 5b Actinic keratosis, Bowen’s disease, keratoacanthoma, and squamous cell carcinoma

On nonfacial skin, AK usually exhibits (Zalaudek et al., 2012) nonspecifi c patterns with features, such as surface scale and keratin, and sometimes dotted vessels (Fig. 5b.3). An additional clue to the diagnosis of AK is the rosette sign, which can only be seen with polarized light (Cuellar et al., 2009).The rosette sign consists of a white four-leaf clover-shaped structure (Fig. 5b.4). It probably represents an optical effect of polarized light interacting with follicular openings that contain orthokeratosis and parakeratosis. Although the rosette sign can be seen in actinic damaged skin and in tumors such as basal cell carcinoma (BCC) (Fig. 5a.14c) and melanoma, they are more commonly encountered in AK and thin SCCs (Cuellar et al., 2009).