Pigmented Basal Cell Carcinoma

01Blue-grey ovoid nests are the dominant pigmented feature of nonsuperficial BCC. They are large, well-circumscribed pigmented ovoid or elongated structures, not intimately connected to the surrounding tumor. Histologically they correspond to large pigmented basaloid tumor nests with melanin aggregates invading the dermis. Prevalence is 50 percent in nodular BCC and up to 80 percent in pigmented mixed-subtype BCC.

02Multiple blue-grey globules are smaller round to oval pigmented structures, also basaloid nests but localized to the papillary or reticular dermis. They appear in roughly one-third of all BCCs and are not specific for any single histologic subtype. Distinguishing globules from melanocytic globules requires looking at color (blue-grey vs brown), size (often more uniform in BCC), and association with other BCC features.

03Maple leaf-like areas, spoke-wheel areas, and concentric structures are the trio of pigmented structures characteristic of superficial BCC. Maple leaf-like areas are translucent brown to grey-blue peripheral bulbous extensions that do not arise from a network and instead form independent multifocal aggregates. Spoke-wheel areas are well-circumscribed radial projections (usually tan, sometimes blue-grey) meeting at a darker central axis. Concentric structures are early forms of spoke-wheels: small irregular pigmented globules with darker central pigmentation. All three correspond histologically to multifocal pigmented basaloid nests at the dermoepidermal junction.

04The Menzies criteria for pigmented BCC require absence of a pigment network plus at least one of six positive features: large blue-grey ovoid nests, multiple blue-grey globules, maple leaf-like areas, spoke-wheel areas, ulceration, and arborizing telangiectasias. In the original 2000 paper this combination gave 97 percent sensitivity and 92 to 93 percent specificity for differentiating pigmented BCC from melanoma and nevi.

05Differential with melanoma is the central diagnostic challenge. Pigmented BCC lacks a pigment network (the reticular pattern of melanocytic lesions) and instead shows discrete pigmented structures at multiple foci. Melanoma in situ and invasive melanoma show atypical network, irregular streaks, and asymmetric pigmentation. When in doubt, the combined absence of pigment network and presence of arborizing vessels strongly favors pigmented BCC.

06Pigmented BCC in skin of color presents diagnostic challenges. In darker phototypes background pigmentation can mask vessels and shiny white structures. Blue-grey ovoid nests and concentric structures stand out, but maple leaf-like areas can blend with surrounding pigmentation. RCM is particularly useful here: pigmented basaloid nests appear bright on RCM regardless of skin type because of strong melanin contrast.

07Reflectance confocal microscopy of pigmented BCC shows brightly outlined tumor islands or nests with a clearly defined shape, due to the high contrast generated by melanin. Pigmented basaloid nests contain melanophages and dendritic cells that further enhance refractility. In Longo's 2014 study, dendritic cells and melanophages were prominent in pigmented BCC and helped distinguish them from amelanotic variants. The identification of bright tumor islands plus the absence of pagetoid spread excludes melanoma.