Streaks are basically nothing but brownish-black linear structures of variable thickness, not clearly combined with pigment network lines. Streaks are regular or irregular, more or less converging, linear structures that may be observed throughout a lesion, but are more apparent when situated at the periphery. The term streaks includes radial streaming, radial streaks and pseudopods that, in our opinion, morphologically are just variations on the theme of streaks and, moreover, are basically similar from a histopathological standpoint.
Streaks correlate with discrete nests of more or less heavily pigmented junctional nests of melanocytes independently of the cytomorphologic characteristics of the melanocytes within these nests. The longish, linear shape of the streaks gives evidence to the fact that these pigmented junctional nests of melanocytes form tubules parallel to the skin surface. However, three-dimensional reconstruction will be needed to confirm this assumption.
Although streaks are found in benign and malignant melanocytic skin lesions, the presence of irregular streaks strongly indicates malignancy, especially when the streaks are distributed unevenly throughout a given melanocytic lesion. However, a symmetric, radial arrangement over an entire lesion is particularly found in the pigmented spindle cell nevus of Reed. So, the architectural arrangement of streaks rather than the morphology of a single streak is crucial for diagnosis.