Melanoma: Pattern Analysis & Diagnosis

01Superficial spreading melanoma (SSM) is the archetype that anchors most dermoscopic teaching. Junctional features (atypical network, irregular dots, irregular globules, irregular streaks/pseudopods, irregular blotches) reflect heterogeneous melanocytic nests at the dermoepidermal junction. Mixed junctional-dermal features (regression structures, negative network, white shiny streaks) reflect the regression process and dermal fibrosis. Dermal features (blue-white veil, atypical vessels) signal invasion. Most early SSMs display a multicomponent global pattern, but a subset of in situ tumors still show a reticular or globular pattern with subtle asymmetry.

02Nodular melanoma lacks the junctional vocabulary because the tumor invades the dermis from the outset. Three criteria carry the diagnosis: blue-black coloration (simultaneous blue and black within a single lesion not explained by comedo-like openings or vascular lacunas), atypical vascular pattern (linear-irregular vessels, polymorphic vessels, or more than two vessel types), and milky-red structureless pink. Any nodular lesion that cannot be confidently classified should be excised; nodular melanoma kills disproportionately because diagnosis is delayed.

03Lentigo maligna and acral lentiginous melanoma require site-specific frameworks because the dermoepidermal junction is anatomically flattened (face) or elaborated into ridges and furrows (palms and soles). Network is rarely seen on the face; instead, lentigo maligna features develop around the follicular openings (asymmetric pigmented follicles, gray dots, gray circles, rhomboidal structures, target-like patterns). On acral skin, the parallel ridge pattern (pigment on ridges) discriminates from the parallel furrow pattern (pigment in furrows) of nevi.

04Atypical pigment network is heterogeneous in line thickness, hole size, and color across the lesion. It corresponds to irregular and broadened rete ridges with uneven nest distribution. The thin and uniform network of benign nevi contrasts with the broadened and abruptly ending network of melanoma. Atypical network was the most frequent SSM feature historically, but recent in-situ data suggest that irregular hyperpigmented areas and prominent skin markings may be more sensitive in early lesions.

05Blue-white veil is an irregularly shaped blotch of blue color with overlying white ground-glass haze. Histopathologically it represents acanthotic epidermis with focal hypergranulosis above sheets of heavily pigmented dermal melanocytes. With non-polarized dermoscopy the veil appears as a confluent blue-white area; with polarized light the same anatomy presents as blue structureless color plus white shiny strands. Blue-white veil signals dermal invasion and correlates with tumor thickness over 0.8 mm.

06Regression structures take two forms. Blue-gray peppering (free melanin and melanophages in the upper dermis) marks active regression and can occur in melanoma, regressing nevi, and lichen planus-like keratosis. Scar-like white depigmentation (dermal fibrosis) marks completed regression and is unusual in benign lesions outside dermatofibromas. Extensive regression occupying more than half a lesion is suggestive but not pathognomonic; the regression-with-melanoma-features rule (regression plus any other melanoma criterion) reliably triggers excision.

07Atypical vessels in melanoma are polymorphic. The most informative are linear-irregular vessels (vessels with multiple kinks and bends), corkscrew vessels (looped vessels twisted around an axis), and the combination of dotted plus short linear vessels in flat amelanotic lesions. The presence of more than one vessel morphology in a solitary lesion is itself a melanoma cue. Milky-red areas (structureless pink) often coexist with atypical vessels and signal angiogenesis in vertical-growth-phase tumors.

08Amelanotic and hypomelanotic melanoma lacks pigment-based criteria, forcing reliance on vessel morphology. Polymorphic vessels (multiple morphologies in one lesion), milky-red areas, white shiny structures, and residual pink-red coloration on a lesion arising in light skin warrant excision. Roughly 10% of melanomas are amelanotic or hypomelanotic, and these account for a disproportionate share of missed diagnoses.

09Sequential dermoscopy and the evolution criterion (E in ABCDE) capture melanomas that lack baseline diagnostic features. Argenziano's monitoring data showed that 7 of 12 melanomas detected during follow-up appeared after 8 to 54 months, supporting both short-term (3-month) monitoring for highly suspicious lesions and long-term annual monitoring for slow-growing tumors. Any change in size, color, or structure on a flat melanocytic lesion in an adult is a hard indication for excision.