First step algorithm: The seven-level criterion ladder

Level 1: Melanocytic lesions criteria. a) Pigment network (exception: dermatofibroma); b) Negative network; c) Angulated lines; d) Streaks; e) Aggregated globules; f) Peripheral globules; g) Homogeneous blue pigmentation; h) Pseudonetwork (facial skin); i) Parallel pigment pattern (palms and soles).
Level 2: Basal cell carcinoma criteria. a) Arborizing blood vessels; b) Spoke wheel-like structures; c) Leaf-like areas; d) Large blue-gray ovoid nests; e) Multiple nonaggregated blue-gray globules; f) Ulceration; g) Shiny white blotches and strands.
Level 3: Squamous cell carcinoma criteria. a) Focal glomerular vessels; b) Rosettes; c) Keratin pearls (white circles); d) Yellow scale; e) Brown dots aligned radially at the periphery.
Level 4: Seborrheic keratosis criteria. a) Multiple (three or more) milia-like cysts; b) Comedo-like openings; c) Gyri and sulci (fissures and ridges); d) Fingerprint-like structures; e) Moth-eaten borders.
Level 5: Hemangioma/angioma/angiokeratoma. a) Red lacunae; b) Blue lacunae; c) Black lacunae.
Level 6: Blood vessels as seen in nonmelanocytic tumors. a) Arborizing vessels; b) Glomerular vessels; c) Hairpin vessels with white halo; d) Crown vessels; e) Serpiginous or string of pearls; f) "Strawberry" pattern.
Level 7: Blood vessels as seen in melanocytic tumors. a) Comma-shaped vessels; b) Dotted vessels; c) Serpentine vessels (or linear irregular); d) Corkscrew vessels; e) Polymorphous vessels; f) Milky-red areas and milky-red globules.
Level 8: Structureless/featureless lesions or lesions with nonspecific/nondiagnostic features. No vessels noted.