Step 1: Melanocytic vs non-melanocytic
Step 1 of the 2-step algorithm requires the observer to determine whether the lesion is melanocytic (ie, originates from melanocytes and, therefore, could be a melanoma) or nonmelanocytic in origin.
A melanocytic lesion usually will display at least 1 of the following structures:
- pigment network (FIGURE 3A) (This can include angulated lines.)
- negative network (FIGURE 3B) (hypopigmented lines connecting pigmented structures in a serpiginous fashion)
- streaks (FIGURE 3C)
- homogeneous blue pigmentation (FIGURE 3D)
- globules (aggregated or as a peripheral rim) (FIGURE 3E)
- pseudonetwork (facial skin) (FIGURE 3F)
- parallel pigment pattern (acral lesions) (FIGURE 3G).
Exceptions. Sometimes, nonmelanocytic lesions will present with pigment network. Dermatofibromas, for example, are one exception in which the pattern trumps the network. Two other exceptions are solar lentigo and supernumerary or accessory nipple.
If the lesion does not display any structure, it is considered structureless. In these cases, proceed to the second step to rule out a melanoma.
Doesn’t meet criteria for a melanocytic lesion?
If the lesion does not reveal any of the criteria for a melanocytic lesion, then look for structures seen in nonmelanocytic lesions: dermatofibromas; seborrheic keratosis; angiomas and angiokeratomas; sebaceous hyperplasia; clear-cell acanthomas; basal cell carcinomas (BCCs); and squamous cell carcinomas (SCCs).
Continue to: Benign nonmelanocytic lesions