Rosettes May Be Observed in a Range of Conditions

We have come to appreciate that the rosette structure, depicted as 4 white points arranged as a 4-leaf clover or as leaves radiating out from a central stem, may be seen under polarized dermoscopy in a range of skin lesions.¹ Until recently, rosettes were deemed to be a dermoscopic structure observed only in actinic keratoses (AKs) and squamous cell carcinoma (SCCs), and their presence was thought to support this diagnosis.¹ We assert, instead, that rosettes are not uniquely specific to SCCs (Figure, A, arrows) or AKs. Rather, rosettes can be seen in a variety of neoplasms, including, but not limited to, basal cell carcinomas (Figure, B, arrows) and melanomas (Figure, C, arrows, and Figure, D, arrow). They have also been observed in nonlesional actinically damaged skin.

Rosettes are seen exclusively with polarized dermoscopy and are not visualized under nonpolarized dermoscopy or in nondermoscopic clinical images.¹ We believe that rosettes are probably attributable to an optical effect of the polarized light and its interaction with adnexal openings that are either narrowed or filled with keratin. Indeed, under reflectance confocal microscopy, which images tissue en face (like dermoscopy) and hence allows correlation of dermoscopic structures, rosettes appear as keratin-filled adnexal openings (Figure, E). Rosettes appear to display angular dependence as the dermoscope is rotated around its central axis.² Although rosettes are common and more numerous in AKs and SCCs, we have demonstrated that they can also be seen in melanomas and basal cell carcinomas; therefore, further research is required to determine the predictive value of rosettes for any given diagnosis.