The pigment network consists of intersecting brown lines forming a grid-like reticular pattern (Kittler et al., 2016a). Histologically, the lines correspond to increased pigmentation (melanin within the keratinocytes or the melanocytes) along elongated rete ridges (table 3). The "holes" of the network correspond to the suprapapillary plates (figure 2) (Massi et al., 2001b). The pigment network is usually absent in the face, palms, and soles and is replaced by a pseudo-network (face) and a parallel pigment pattern on acral skin (see below). The pigmented network can be described as typical or atypical.
The typical or regular pigment network is characterized by uniform lines (in width and color) and is common in melanocytic nevi, but can be present in non-melanocytic lesions such as ink spot lentigo, dermatofibromas or accessory nipples (table 4) (Scope et al., 2006; Zaballos et al., 2008). Histologically, the brown lines of the typical network correspond to equidistant and uniform rete ridges. (Woltsche et al., 2017)
An example of a typical pigment network clinically and dermoscopically:
On histopathology, the lines of the typical network correspond to the pigment in the rete ridges, that are relatively uniform in width and equidistant from each other.
The typical network usually corresponds to the junctional component of a nevus. However, reticulation can also be seen in darkly pigmented normal skin and heavily pigmented rete ridges as encountered in dermatofibromas, ink spot lentigo or accessory nipples .
Atypical pigment network is irregularly meshed with lines varying in size, color, thickness, or distribution and is often seen in dysplastic nevi and superficial spreading melanoma (Kittler et al., 2016a). On histopathology, the atypical pigment network corresponds to disarrangement of the rete ridges, a tendency to confluence of nests of melanocytes, and changes in melanin distribution within the epithelium (Russo et al., 2017). An atypical network within a lesion may also appear perturbed and broken up; a finding referred to as "branched streaks".
An example of an atypical pigment network clinically and dermoscopically:
On histolopathology, the irregular lines of an atypical network correspond to variation in the width, length, and spacing of the rete ridges due to variation in the size, spacing, and tendency to confluence of melanocytic nests. Rete ridges that are elongated and widened by larger junctional nests of melanocytes would appear as darker and wider lines on dermoscopy . The atypical network is often seen in melanoma and dysplastic nevi  .
The anatomy of the rete ridge pattern of the face differs from that of non-facial skin and is usually flatter. Accordingly, the pigment network is usually absent in these locations and is replaced by a pseudonetwork pattern. The "holes" in the pigmented epidermis correspond histologically to adnexal openings, such as sebaceous glands, hair follicles or sweat glands.
A pseudonetwork sketch:
Clinical and dermoscopic images of pseudonetwork:
Histologically, adnexal openings are responsible for the "holes" in the pigment reticulation:
- Scope et al.: Nonmelanocytic lesions defying the two-step dermoscopy algorithm. Dermatol Surg 2006;32:1398-406. PMID: 17083595. DOI.
- Russo et al.: Dermoscopy pathology correlation in melanoma. J. Dermatol. 2017;44:507-514. PMID: 28447355. DOI.
- Kittler et al.: Standardization of terminology in dermoscopy/dermatoscopy: Results of the third consensus conference of the International Society of Dermoscopy. J. Am. Acad. Dermatol. 2016;74:1093-106. PMID: 26896294. DOI.