4 курс / Дерматовенерология / Дерматоскопия (3)

3.2.7 Combinations of patterns

A pigmented lesion may be composed of one or more patterns. In the latter case the combination of patterns may be symmetrical or asymmetrical. Symmetry exists when the lesion’s pattern can be mirrored in any conceivable axis. Asymmetry exists when this is not the case. Symmetry is independent of the shape of the lesion; it is assessed on pattern. When assessing symmetry or asymmetry, one must remember that Nature does not make its designs on a drawing board; symmetry is only approximate and not exact.

When a lesion consists of two patterns there are three possible symmetrical combinations: a) one pattern at the center and the other at the periphery, or b) vice versa, or c) the elements of one pattern (usually dots or clods) are regularly distributed within the other pattern (3.17). All other combinations are, by definition, asymmetrical.

The number of possible asymmetrical combinations of patterns is, of course, infinite.

A pigmented lesion with three patterns is only symmetrical when the patterns are arranged concentrically. The more numerous the patterns, the greater is the likelihood of their being asymmetrical.

3.3 Colors

3.3.1 Melanin

A pigmented lesion is characterized not only by its pattern but also by its color (3.18). Melanin is the most important pigment. Depending on the layer of skin in which melanin is located, it may appear black (when located in the stratum corneum), brown (when located in the basal layers of the epidermis), gray (when located in the papillary dermis) or blue (when located in the reticular dermis).

Furthermore, the observed color depends on the density of melanin and the thickness of the epidermis. A dense accumulation of melanin in the basal layer of the epidermis may appear dark-brown or nearly black, a less dense accumulation would be light-brown. When the epidermis is thickened due to acanthosis (e.g. some seborrheic keratoses) melanin in the epidermis may appear blue.

It is often useful to divide pigmented lesions into those where melanin is the dominant pigment, and those where other pigments dominate.

3.3.2 Other pigments

Hemoglobin is the next most important pigment. Depending on the level of oxygen saturation, hemoglobin in vessels ranges from bright red to blue. When a massive

extravasation of red blood cells occurs (i.e. hemorrhage), the entire coagulated blood is dark red, or may be black when it is in the stratum corneum (corneal bleeding). In the dermis, fresh blood may again be red to blue, but degradation of hemoglobin may give rise to various shades of color ranging from green to brown. In cases of ulcerated lesions, serum exudes from the surface, dries, and forms a crust. The serum is often mixed with red blood cells and is therefore orange. Keratin is white or yellow (when the stratum corneum is not pigmented it appears yellow). Mixture of the white or yellow of keratin with the brown of melanin gives rise to colors in the range orange to yellow which are characteristic of pigmented seborrheic keratoses. Fibrosis or sclerosis of the dermis also appears white. Pus, sebum and sebaceous glands also appear white

in dermatoscopy. In contrast to keratin and fibrosis, which are shiny white, pus, sebum and sebaceous glands appear dull white (3.19).

3.3.3 Color combinations

A pigmented lesion may be composed of one or several colors. As is true for patterns, colors may be arranged symmetrically or asymmetrically. With the exception of brown, variations in shade should not be interpreted as a separate color. It is diagnostically meaningful to distinguish between light-brown and dark-brown, but only in clear-cut cases and particularly when the transition between the two shades of brown is abrupt. It is very common to see lighter pigmentation at the periphery of a lesion, or around follicular openings; such lesions should still be classified as one color. The number of colors and the presence of specific colors are of immense importance in dermatoscopy. When evaluating colors (as patterns), the investigator should know when the observation should be very accurate and when it may be less exact. The color of normal skin varies from person to person, and even according to location on the body. While this normal skin color is not counted as a separate color, it is used as a reference to define “white”; white structures must be clearly lighter in color than surrounding normal skin (3.20).

Distribution of color in lesions with a purely reticular pattern

It is usually sufficient to distinguish between symmetrical and asymmetrical arrangements of more than one color. Pigmented lesions that consist exclusively of a reticular pattern are, however, a special case, as three further specific arrangements are diagnostically significant. When a darker shade is seen in the center and a lighter one at the periphery, so that symmetry is retained, the lesion is considered to be centrally hyperpigmented. If the darker shade is seen at the periphery the lesion is called eccentrically hyperpigmented. If the colors within the lesions are distributed in such a way that areas of dark pigmentation alternate with areas of light pigmentation, the lesion is termed speckled or variegated (3.21).

This can involve two shades of the single color brown (a single color because the transition is gradual), or two shades of brown plus black.

3.4 Descriptions of pigmented lesions on the basis of patterns and colors

Formulating a description of pattern(s) and color(s) is always the first step towards diagnosis. One first looks at the lesion from a distance. A pattern should

occupy a significant portion of the pigmented lesion; everything else may be initially ignored. Beginners tend to become immediately absorbed in details. However, at least at the initial step, single dots or single clods are of no importance. If necessary, these details can be incorporated later in the analysis.

Examples of pigmented lesions with a single pattern Figures 3.22 and 3.23 show pigmented lesions with just one pattern.1 Usually it is simple to decide which pattern is present. Occasionally it may be difficult to distinguish between reticular lines and branched lines, in which case one should prefer the more common reticular pattern.

In almost all cases, it is pigment that defines structure. A few examples will show how potential confusion can be avoided by keeping this principle in mind. The less pigmented areas between reticular lines are not a separate pattern, i.e. they are not clods. Hypopigmented areas between dots, clods, circles and all other lines should not be viewed as structureless areas. A circle of hypopigmentation around a hair follicle is not a structure, only an interruption to the pattern of the lesion. The few exceptions to pigment defining structure – mainly white structures – will be addressed in detail later.

For a zone to constitute the structureless pattern it must

– as for patterns composed of basic elements – occupy a significant portion of the lesion. On the other hand, a sufficiently large zone does not have to be entirely devoid of pigmented structures to be considered structureless. Areas with visible structures which cannot be definitively classified as one of the basic elements are still correctly termed structureless, as are areas which

1As this chapter is mainly focused on a description of patterns and colors rather than diagnosis, only the dermatoscopic images are shown here. Clinical and dermatoscopic appearances are shown simultaneously in most of the remaining chapters.

contain basic elements, but too few to constitute a pattern. In other words, not all pigment is structure, some is noise.

Examples of pigmented lesions with more than one pattern

Figure 3.24 shows pigmented lesions with more than one pattern. When assessing a lesion consisting of more than one pattern, the first question one should ask is whether the patterns are combined symmetrically or asymmetrically. When assessing symmetry one should exercise latitude, as symmetry in biology never reaches geometrical perfection. A beginner tends to over-inter- pret in favor of asymmetry. The examples in figure 3.24 will help the reader to develop a feeling for biological symmetry and asymmetry. The vast majority of lesions can be unequivocally classified as either symmetrical or asymmetrical. When (very rarely!) this cannot be done with certainty, one “investigates” in both directions, as we will see later.

3.5 Clues

Sometimes pigmented lesions can be unequivocally diagnosed on the basis of pattern(s) and color(s) alone. More often, assessment of pattern and color leads to a small differential diagnosis. In this case, one looks for clues. A clue is simply a feature which favors one possible diagnosis over another possible diagnosis. Sometimes a pattern may also constitute a clue, for example a structureless eccentric zone is both a pattern, and (in some contexts) a clue to the diagnosis of melanoma. Usually however, clues are features too localized to constitute a pattern, but nonetheless favoring one diagnosis over another. Clues include a special arrangement of basic elements, a typical color, a special combination of pattern and color, a characteristic pattern