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Objective To identify criteria for the diagnosis of squamous cell carcinoma (SCC) and actinic keratosis (AK) by in vivo reflectance confocal microscopy (RCM). Design Prospective RCM imaging of lesions suspected clinically and/or dermoscopically to be SCC or AK, followed by RCM assessment of the biopsy-proven SCCs and AKs. Setting Private skin cancer clinic, Plantation, Florida. Patients A total of 38 lesions in 24 patients were assessed, including 7 AKs, 25 SCCs in situ, 3 invasive SCCs, and 3 keratoacanthomas. Interventions Prior to undergoing biopsy, all lesions were assessed by RCM. Results Mosaic RCM images at the stratum corneum level revealed scale in 29 SCCs (95%) and in all 7 AKs. Polygonal nucleated cells at the stratum corneum were seen in 3 SCCs (10%) and 1 AK (14%). All 38 cases displayed an atypical honeycomb and/or a disarranged pattern of the spinous-granular layer of the epidermis; round nucleated cells were seen in the spinous-granular layer in 20 SCCs (65%) and 1 AK (14%). Round blood vessels in the superficial dermis were seen in 28 SCCs (90%) and 5 AKs (72%). Conclusions An increasing frequency of abnormal RCM features can be observed across the spectrum of keratinocytic neoplasias. The presence of an atypical honeycomb or a disarranged pattern of the spinous-granular layer, round nucleated cells at the spinous-granular layer, and round blood vessels traversing through the dermal papilla are the key RCM features of SCC.

C LINICALLY, CUTANEOUS LYMPHANGIOMA circumscriptum (CLC) (Figure 1A and Figure2A) should be differentiated from other vascular and lymphatic lesions, such as hemangiomas, angiokeratomas, lymphangioendotheliomas, and angiosarcomas, as well as from warts, molluscum contagiosum, condyloma acuminata, and hidrocystoma. The dermoscopic features of CLC demonstrate 2 distinct patterns: (1) yellow lacunae surrounded by pale septa without inclusion of blood (Figure 1B) and (2) yellow to pink lacunae alternating with dark-red or bluish lacunae due to the inclusion of blood (Figure 2B). In pattern 2, the blood cells precipitate, giving rise to 2-tone lacunae.

T HE DERMOSCOPIC FEATURE OF YELLOW LOBUlarlike structures has been described in sebaceous hyperplasia. The dermoscopic appearance of aggregated yellow globules with or without a central puncta and fine, nonarborizing blood vessels (“crown vessels”) is thought to be classic for sebaceous hyperplasia. However, these features are not limited solely to sebaceous hyperplasia (Figure 1). These structures may also be seen in nevus sebaceous of Jadassohn (Figure 2) and sebaceous adenoma (Muir-Torre syndrome) (Figure 3). Histopathologically, yellow lobules correspond to dermal conglomerations of sebaceous glands, a feature shared by these 3 lesions. Dermoscopically, small blood vessels may also be seen at the periphery of the yellow lobularlike structures, representing dermal vessels displaced by lobules of hyperplastic sebaceous glands. Thus, when yellow lobularlike structures are visualized on dermoscopy, the differential diagnosis includes not only sebaceous hyperplasia but also other conditions with sebaceous differentiation such as nevus sebaceous and sebaceous adenoma.