Lines may form six different patterns, depending on their shape and arrangement: reticular, branched, angulated, parallel, radial, and curved.
Lesions with reticular lines are not always melanocytic. In most cases the histological correlate of reticular lines is hyperpigmentation of basal keratinocytes, which may or may not be created by an increase in the numbers of melanocytes.
Color of lines
- Usually light-brown or dark-brown, due to melanin in the epidermis.
- If the pigment is very dense, the lines are black.
- Rarely, they can appear gray.
Not every shade of brown is to be interpreted as a separate color. One or two black lines do not render the lesion multicolored. The normal hypopigmentation around follicular openings does not create an extra color. Nearly all pigmented lesions are somewhat lighter at the periphery than in the center.
Light-brown + thin reticular lines:
are usually seen in junctional Clark nevus or solar lentigo
A Clark nevus is round or oval and the pigmentation does not end abruptly at the periphery. The border of a solar lentigo is usually sharply demarcated and scalloped.
Differential diagnoses: a variant of dermatofibroma with reticular lines only and urticaria pigmentosa, a type of mastocytosis.
Brown reticular lines + thick:
Can be seen in Clark nevus or superficial congenital nevus'
Differential Diagnoses: Solar lentigo, seborrheic keratosis.
Black (very dark-brown) reticular lines:
No differential diagnosis needs to be considered. Very rarely a Reed nevus may demonstrate this pattern and color combination, but without the additional clues to "ink-spot lentigo"
More than one color + reticular lines:
solar lentigo or seborrheic keratosis
- Clues to solar lentigo: well-demarcated, scalloped border.
- Clues to seborrheic keratosis: white dots or clods, orange or yellow clods, well-demarcated border, circles, thick curved lines, vessels as loops or coils.
- Differential diagnoses: Clark nevus, "superficial" or "superficial and deep" congenital nevus, and in situ melanoma
Dark-brown or black and light-brown areas:
variegate color distribution
- Differential diagnosis: Clark nevus, "superficial" or "superficial and deep" congenital nevus, or in situ melanoma
- Only 5 of the 8 clues to melanoma are seen in reticular pattern lesions:
- gray dots, clods, circles or lines;
- radial lines or pseudopods seen only in some segments of the periphery;
- black dots or clods at the periphery
- thick reticular lines and e) angulated lines (polygons). When one of these clues is present, the diagnosis of melanoma should be seriously considered.
- Eccentric hyperpigmentation ,i.e. the more heavily pigmented area is not in the center but the periphery: Clark nevi and in situ melanomas, rarely in congenital nevi.
Differential diagnosis: Melanoma. When no clue to melanoma is present, a Clark nevus is the most likely diagnosis.
Branched lines and reticular lines are closely related and often occur together. Lesions that are exclusively composed of branched lines are either black or brown, and they are all benign.
Brown branched lines:
Clark nevus or "superficial" or "superficial and deep" congenital nevus
Black (or very dark-brown) branched lines:
- May appear on facial skin and on non-facial skin.
- They are the hallmark of flat melanomas on chronic sun-damaged skin.
- Most melanomas with angulated lines are not invasive (in situ).
- They are usually brown or grey.
- Typical pigment pattern of acral skin.
- They may be arranged in one of three ways; on the ridges (ridge pattern), in the furrows (furrow pattern), or crossing ridges (crossing pattern).
- Acral lesions that only show a pattern of furrows or a crossing pattern may be safely considered to be benign.
- Assessment of a lesion showing the ridge pattern proceeds by evaluating color.
- If it is brown, in situ melanoma must be considered. Black, red or purple parallel lines on the ridges indicate either hemorrhage or exogenous pigmentation. Satellite clods are a strong clue to the diagnosis of hemorrhage.