Step 2: It’s melanocytic, but is it a nevus or a melanoma?
If, by following Step 1 of the algorithm, the lesion is determined to be of melanocytic origin, then one proceeds to Step 2 to decide whether the growth is a nevus, a suspicious lesion, or a melanoma. For this purpose, several additional algorithms are available.12-17
Benign nevi tend to manifest with 1 of the following 10 patterns: (FIGURE 12)
- diffuse reticular
- patchy reticular
- peripheral reticular with central hypopigmentation
- peripheral reticular with central hyperpigmentation
- peripheral globules/starburst. It has been suggested that lesions that show starburst morphology on dermoscopy require complete excision and follow-up since 13% of Spitzoid-looking symmetric lesions in patients older than 12 years were found to be melanoma in one study.18
- peripheral reticular with central globules
- symmetric multicomponent (this pattern should be interpreted with caution, and a biopsy is probably warranted for dermoscopic novices).
Melanomas tend to deviate from the benign patterns described earlier. Structures in melanomas are often distributed in an asymmetric fashion (which is the basis for diagnosis in many of the other algorithms), and most of them will reveal 1 or more of the melanoma-specific structures (FIGURE 13). The melanomas in FIGURES 14 A-H each show at least 2 melanoma-specific structures. On the face or sun-damaged skin, melanoma may present with grey color, a circle-in-circle pattern, and/or polygonal lines (FIGURE 15). Note that melanoma on the soles or palms may present with a parallel ridge pattern (FIGURE 16).
How to proceed after the evaluation of melanocytic lesions
After evaluating the lesion for benign patterns and melanoma-specific structures, there are 3 possible pathways:
1. The lesion adheres to one of the nevi patterns and does not display a melanoma-specific structure. You can reassure the patient that the lesion is benign.
2. The lesion:
A. Adheres to one nevus pattern, but also displays a melanoma-specific structure.
B. Does not adhere to any of the benign patterns and does not have any melanoma-specific structures.
This is considered a suspicious lesion, and the choices of action include performing a biopsy or short-term monitoring by comparing dermoscopic images over a 3-month interval. (Caveat: Never monitor raised lesions because nodular melanomas can grow quickly and develop a worsened prognosis in a short time. Instead you’ll want to biopsy the lesion that day or very soon thereafter.)
3. The lesion deviates from the benign patterns and has at least 1 melanoma-specific structure. Biopsy the lesion to rule out melanoma.
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