Correlation of keratinizing tumors
White circles
White circles are bright white circles around a yellow/orange keratin plug (Rosendahl et al., 2012a). Histopathologically, they reveal acanthosis and hypergranulosis of the infundibular epidermis and are highly suggestive of keratoacanthomas and well-differentiated SCC (table 2) (Rosendahl et al., 2012a).
Dark dots/globules or round circles in linear arrangement
Dark brown/gray dots/globules arranged linearly are frequently found in pigmented SCC in situ/pigmented Bowen disease (Cameron et al., 2010). Histologically, they correspond to aggregates of atypical basal pigmented keratinocytes.
Strawberry pattern
The strawberry pattern is a reddish pseudonetwork interrupted by prominent follicular openings (Kittler et al., 2016a). Histologically, it corresponds to a localized increase in vasculature. The strawberry pattern is highly suggestive of non-pigmented actinic keratosis (Zalaudek et al., 2006).
Rosettes
Rosettes or four-clod dots are seen as four bright white dots or clods arranged together as a 4-leaf clover (or as a square). Histologically, they reveal hyperkeratosis of the follicular openings alternating with normal stratum corneum (Liebman et al., 2012, 2011). A recent study using ex-vivo dermoscopy and transverse histological sections with polarization showed that smaller rosettes correspond to polarization of concentric horn material in adnexal openings (follicular or eccrine ducts), and larger rosettes to concentric perifollicular fibrosis (M. Haspeslagh et al., 2016). Rosettes are associated with keratinizing tumors, but can be seen in BCC, inflammatory dermatosis (M. Haspeslagh et al., 2016) and are rarely seen in melanoma (González-Álvarez et al., 2014).
Scale
Scales are homogenous opaque yellow/brown structures. Histologically, they reveal hyperkeratosis and parakeratosis (Tan et al., 2016; Wolner et al., 2017). Scale is common in AKs, SCC, and inflammatory dermatosis.
Gray circles or inner gray halo
Gray circles or an inner gray halo are a subtle homogeneous gray or brown halos that surround follicular openings (as an internal ring). Histologically, they correlate to pigmentation of the basal keratinocytes surrounding the hair follicle, and are observed in pigmented AKs (Nascimento et al., 2014).
