Reflectance confocal microscopy: hallmarks of keratinocyte cancer and its precursors.

Actinic keratosis is a common result of severe sun damage and is usually present on sun-exposed skin. Reflectance confocal microscopy is a non-invasive clinical imaging modality that results in quasi-histological, en face skin images. In this chapter, we review the available literature and distill the common features of actinic keratosis, as seen by reflectance confocal microscopy. Finally, several examples are discussed in the context of matching clinical, histopathological and reflectance confocal microscopy images. Of all of the morphological features of actinic keratoses, the epidermal honeycomb pattern is the most telling when viewing the lesions using reflectance confocal microscopy. In the near future, we expect the definition of consensus criteria for diagnosing actinic keratoses and differentiating this precursor lesion.