Streaks
Streaks are lineal pigmented projections at the periphery of a melanocytic lesion and include radial streaming (linear streaks) and pseudopods (bulbous projections). Histologically, streaks reveal the radial growth phase of a melanocytic tumor characterized by confluent junctional nests of pigmented melanocytes at the periphery of the lesion (figure) (Massi et al., 2001b). Symmetrical distribution of streaks along the periphery of the entire melanocytic lesion favors the diagnosis of a spindle cell nevus (Spitz/Reed nevus), whereas if the distribution is asymmetrical, a superficial spreading melanoma should be excluded (Braun et al., 2005)
Needless to say, the statistical probability of this happening is very low unless of course the pathologist uses dermoscopy at the grossing table to orient and oversee the step sectioning process. On occasion, peripheral globules and pseudopods can look similar to each other at first glance. However, with peripheral globules one will observe a small clear space separating the globule from the main tumor mass. These peripheral globules are presumed to correspond to junctional melanocytic nests at the tips of rete ridges and they are usually associated with growing/enlarging nevi. In contrast, pseudopods emanate from, and are directly connected to, the main tumor mass through a stalk. Radial streaming appears as radial parallel linear extensions at the periphery of the lesion. On histopathology, radial streaming also correlates with confluent junctional nests of pigmented melanocytes.
