The 10 MOST Concerning Dermoscopic Signs of Melanoma

For those who are new to dermoscopy, memorizing the different signs, structures, patterns, and colors can feel overwhelming. Here we focus on the 10 MOST CONCERNING that all clinicians must consider when screening for melanoma.

The significance of pigmented lesions within cutaneous/non-acral skin ("on the body") is that they tend to follow a standard network/reticular pattern. 

Lines and streaks represent lesion growth and can be seen in both melanoma as well as rapidly evolving non-melanoma lesions (such as Spitz Nevi). 

A blue-white veil is an area which looks blue but with a hint of white haze. The blue color is the result of the Tyndall effect, and can represent pigment which may have entered the papillary dermis (therefore making it a potential clue to invasive melanoma). As a standalone sign, having a blue-white veil in one area of the lesion is more concerning than “throughout” (which would be more likely in benign lesions like blue nevi).

Angulated lines are most common in older patients who have sun-damaged skin. Many times they are found within lesions which outwardly appear to simply be a solar lentigo, but upon dermoscopic examination the angulated lines can be appreciated.

Peppering presents as “sprinkles” of black, gray, or blue. Peppering can also be seen in lichen planus-like keratoses (LPLK), so a tip is to look for peppering next to a structureless area (which would be suggestive of melanoma).

Lesions on the face tend to follow a dermoscopic pattern known as a pseudonetwork.

A pseudonetwork is characterized by the presence of pigmented lines and dots that appear to form a network-like structure, however, unlike a true pigment network, the pseudonetwork is formed by the pigmentation around adnexal openings (such as hair follicles and sweat gland ducts). A pseudonetwork can also be seen in non-melanocytic lesions like lentigines and seborrheic keratoses.

The pseudonetwork can be distinguished from a true pigment network by its irregular and interrupted appearance, as the pigmentation is not continuous but rather surrounds the adnexal structures. This pattern is important in dermoscopy for differentiating between various types of pigmented lesions on the face.

Gray circles are considered the most specific dermoscopic sign of early melanoma on the face.

These gray circles represent either free melanin or melanin within macrophages. As the gray dots and granules accumulate around the follicles, they form an annular-granular pattern. 

In benign nevi, follicular openings tend to be evenly spaced throughout the entire lesion. In melanoma, the uniformity and homogeneic appearance of the follicular openings is compromised. That is, blotches of pigment will encroach upon (if not entirely replace) the areas which were previously follicular openings.

Melanocytic lesions on the hands and feet pose a unique challenge due to the unique microanatomy of acral skin.

So before devoting time and energy to recognizing "unusual" patterns, it's worth taking a moment to better understand the "normal" presentation of pigmentation in these areas:

There are two key microanatomical structures unique to acral skin - the rete ridges and the eccrine ducts.

Rete Ridges:

• Crista Limitans: The "furrow."
• Crista Intermedia: The "ridge" (crista superficialis).

Eccrine Ducts:

• The eccrine ducts traverse through the crista intermedia and open on the surface of the ridge.

Pigmentation within the Crista Limitans (the "furrows") presents in 3 main patterns (all of which typically point to a lesion as being benign).

• Parallel furrow pattern is where you see the pigment in the furrows of the acral skin.
• Lattice pattern is characterized by a network of intersecting lines that form a lattice-like structure.
• Fibrillar pattern consists of multiple thin parallel lines oriented obliquely to the dermatoglyphics. These lines appear to cross both the furrows and the ridges of the skin.
  
  NOTE: The unusual appearance of the fibrillar pattern is attributed to the oblique growth of melanin-laden keratinocytes due to pressure/weight-bearing. Therefore, if/when a fibrillar pattern is seen on non-weight bearing areas (e.g., the hand), it should raise suspicion and be further investigated.

In contrast to the above "reassuring" signs, there is one ominous finding that should always be cause for concern when seen within acral pigmented lesions:

The parallel ridge pattern is a dermoscopic clue to acral melanoma. It's characterized by pigmentation that follows the ridges of the skin (rather than the furrows). 

Unfortunately, most of the "classic melanoma signs" in dermoscopy are inherently tied to pigment production (e.g., atypical network or blue-gray veil). With amelanotic lesions, the clues we're provided can be divided into two categories - “white structures” and “pink structures.”

The "white structures" of amelanotic melanoma include:

• Crystalline structures: shiny, white lines that are best seen in polarized light.
• "Scar-like" background: May include shades of red, pink, light brown or gray.
• Atypical vessels: Polymorphous vessels exhibiting both "dotted" and linear patterns.