Pigment Network and variants
Definition
The pigment network, a key feature in dermoscopic analysis, is characterized by a reticular pattern of intersecting brown lines resembling a grid. These lines are not random; they are histologically tied to the increased presence of melanin within the skin's keratinocytes or melanocytes, typically along the lengthened structures known as rete ridges. The spaces within this grid, often referred to as the "holes" of the network, correspond to thinner skin areas known as suprapapillary plates.
This pattern is not universally present across the skin. On the face, the reticular pattern is often absent, giving way to a pseudo-network due to the different skin architecture in this region. Similarly, the palms and soles exhibit a parallel pattern reflective of their unique dermatoglyphics.
Clinicians distinguish between a 'typical' pigment network, which denotes a regular, homogeneous pattern that corresponds with benignity, and an 'atypical' pigment network, where irregularities in color, shape, or distribution can signal potential malignancy. Recognizing these patterns is crucial as they provide invaluable insights into the nature of cutaneous lesions.
Typical network
A typical, or regular, pigment network in dermoscopic evaluations is marked by the uniformity of its lines—both in width and color—and is often observed in benign melanocytic nevi. Interestingly, this pattern can also manifest in a range of non-melanocytic lesions, such as ink spot lentigo, dermatofibromas, or even accessory nipples, indicating its broader diagnostic relevance (Scope et al., 2006; Zaballos et al., 2008). From a histological perspective, the pigment network's brown lines correlate with rete ridges that are evenly spaced and consistent in structure (Woltsche et al., 2017). Understanding this pattern's characteristics is crucial for clinicians, as it aids in distinguishing between benign lesions and those that may require further investigation.
An example of a typical pigment network clinically and dermoscopically:
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 [1].
Atypical network
An atypical pigment network in dermoscopy is a red flag, often associated with dysplastic nevi and melanomas, such as the superficial spreading type. This pattern deviates from the norm, presenting lines that are inconsistent in size, color, thickness, and distribution. These variances are not random; histopathologically, they reflect a disruption in the skin's architecture, specifically an irregularity in the rete ridges, clustering of melanocyte nests, and uneven melanin spread within the epithelium, which may indicate cellular atypia (Russo et al., 2017).
Moreover, the atypical network may present as "branched streaks" within the lesion, where the pattern appears disrupted and fragmented. The identification of these streaks is clinically significant as they can be indicative of malignancy within the lesion, warranting a more aggressive approach to diagnosis and management.
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 [2]. The atypical network is often seen in melanoma and dysplastic nevi [3] .
Pseudonetwork
In facial dermoscopy, the typical reticular pattern seen in non-facial skin, known as the pigment network, often gives way to what is termed a pseudonetwork. This is due to the flatter architecture of the facial skin's rete ridges. Instead of the expected pigmentation pattern, one observes the pseudonetwork, where the apparent "holes" are not gaps in pigmentation but rather represent the histological presence of facial adnexal structures—such as sebaceous glands, hair follicles, and sweat glands. Recognizing a pseudonetwork is crucial as it prevents the misinterpretation of normal facial anatomy as pathological changes, ensuring accurate dermoscopic assessment. A pseudonetwork sketch:
Clinical and dermoscopic images of pseudonetwork:
Histologically, adnexal openings are responsible for the "holes" in the pigment reticulation:
Negative network
The negative pigment network, previously referred to as the inverse network, is identified in dermoscopy by its characteristic pattern of pale, serpiginous lines that intertwine with darker, often curvilinear globules. This pattern is not merely a visual cue but corresponds histologically to slender, lightly pigmented rete ridges that encircle larger melanocytic nests within the dermis's expanded papillary layer (Marghoob and Braun, 2012). Notably, this network is a specific marker for melanoma, particularly when it develops from an existing nevus, and although less common, it may also appear in Spitz nevi and, on rare occasions, in congenital nevi (Pizzichetta et al., 2014; Shitara et al., 2015). Recognizing this pattern is clinically vital as it assists dermatologists in identifying melanomas at an earlier stage, which is crucial for a favorable prognosis.
- ↑ 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.
