Melanoma patterns and structures
Melanomas will usually manifest a disorganized distribution of structures and colors making their identification quite easy. These lesions will reveal at least one, but usually more than one, of the melanoma specific structures listed below. On rare occasions melanomas will present with a symmetric and organized pattern but these tumors will almost always reveal one of the following features: starburst pattern, negative network, blue-black or gray color, shiny white structures, vessels or ulceration.
A few melanoma patterns deserve special mention.
- Featureless or structureless (non-specific or feature poor) lesions are lesions that have no dermoscopic structures or do have dermoscopic structures but the structures present cannot be used to differentiate benign from malignant. If such lesions are non-palpable then they can be digitally monitored or can be biopsied. If such a lesion is palpable then digital monitoring is contraindicated and the lesion should be biopsied.
- Melanoma should be in the differential diagnosis for any blue-black nodule.
- Melanoma in situ can manifest a pattern comprised of small foci of hyperpigmentation. The hyperpigmented areas differ from blotches in that they are small (cover <10% surface area), multiple and do not obscure the ability to see underlying structures. These melanomas will also often reveal prominent skin markings.
- Melanoma on sun damaged non-facial skin (lentigo maligna) is associated with the following patterns: patches of peripheral network islands, tan structureless areas with granularity, and a lesion with angulated lines.
Melanoma specific structures:
Almost all melanomas will reveal at least one of the following structures/features:
- Atypical network
Typical network consists of brown lines with minimal variability in their color and thickness. The holes of the network are of similar size. Atypical network consists of lines with increased variability in color and thickness. The atypical lines are often broadened, smudgy in appearance and often have a grayish color.
- Angulated lines
- Negative network
- Atypical streaks
Typical streaks consist of streaks arranged symmetrically around the entire perimeter of the lesion as seen in Reed’s nevi.
Atypical streaks consist of streaks that are only focally present at the periphery.
- Atypical dots and globules
Typical dots consist of dots that are centrally located within an otherwise organized lesion or dots associated with a typical network. The typical dots associated with a typical network are located on the network lines or in the holes of the network. Any other manifestation of dots is considered atypical.
Atypical dots are distributed asymmetrically, are not clustered in the center and are associated with an atypical network. Typical globules are those found in nevi described in step-1 of this algorithm. Globules of similar shape, size and color distributed throughout the lesion (including cobblestone), at the periphery of an otherwise reticular nevus, or in the center of an otherwise reticular pattern nevus are considered typical.
Any other manifestation of globules would be considered atypical.
- Peripheral tan structureless areas
- Atypical blotches
Typical blotch consists of one round to oval homogeneous blotch in the center of an otherwise reticular pattern nevus.
Atypical blotch consists of an off center blotch or the presence of multiple blotches. The blotches can have irregular shapes and hues.
- Multiple small hyperpigmented areas of irregular shape
- Accentuated skin markings
- Blue-white veil over raised areas
- Regression structures (flat, non-palpable areas)
- Granularity / peppering
- Scar like depigmentation
- Blue-white veil over flat area
- Shiny white lines
- Comma vessels in flat lesions (not IDN)
- Dotted vessels
- Serpentine or linear vessels
- Milky red areas and globules
- Polymorphous pattern - The most common pattern is one with both dotted and serpentine vessels
- Corkscrew vessels