4 курс / Дерматовенерология / Дерматоскопия (3)

Structureless

1 color

Black

Blue

Brown

Red

Hemorrhage Hemangioma, thrombosed

Reed nevus or Clark nevus (rarely) Melanoma (rarely)

Blue nevus

Apocrine hidrocystoma Exogenous pigmentation

Melanoma or melanoma metastasis (rarely)

Solar Lentigo/seborrheic keratosis Pigmented Bowen’s disease Congenital nevus

Clark nevus

Hemorrhage

in the stratum corneum. This will become a black structureless lesion as the hemoglobin degrades, before it entirely disappears due to transepidermal elimination.

More than one color

Sometimes for lesions with more than one color it is difficult to decide whether the pattern is one of clods or structureless. The difference is that clods are well circumscribed, and always occur in numbers. When

only one large contiguous area is seen, the lesion should be interpreted as structureless and not as a large clod. Skin color and white are not regarded as pigment. Lesions consisting only of these two “colors” are discussed in chapter 6 as non-pigmented lesions. When the colors of keratin, namely yellow and orange are predominant, one should first consider keratinizing lesions such as seborrheic keratosis. Structureless lesions that are only yellow or orange are rare. Occasionally a

basal cell carcinoma may have a large, orange structureless area, corresponding to an erosion. When the colors of hemoglobin, namely red and purple predominate, the only diagnoses to consider are hemorrhage, or hemorrhage in a pre-existing lesion such as a nevus. Structureless lesions whose pigmentation is primarily due to melanin may have black, brown, gray or blue areas (5.36). Black zones in a structureless lesion can also result from thrombosis. As a rule of thumb, black should be attributed to blood when it appears together with red or purple and attributed to melanin when it appears together with brown, blue or gray.

When the colors of melanin are symmetrically distributed in a structureless lesion, this is most likely a nevus but it could be practically any type of nevus. A specific classification is usually not possible by dermatoscopy. When the colors of melanin are distributed asymmetrically in a structureless lesion, one should consider melanoma, a metastasis of a melanoma, and seborrheic keratosis. The distinction is made on the basis of specific clues. In nodular structureless lesions that are blue and black a melanoma should be ruled out (16). The color black, which usually indicates melanin in the stratum corneum, is not expected in blue nevi. Exceptionally, a pigmented basal cell carcinoma or a dermatofibroma may show a structureless pattern with blue, brown, or grey areas.

5.2 More than one pattern

Although it is true that the majority of pigmented lesions have more than one pattern, beginners tend to classify far too many lesions as having more than

one pattern. To constitute a pattern, multiple repetitions of a given basic element must be found, in an area occupying a significant part of a lesion. Two or more such areas must be found before a lesion can be classified as having more than one pattern. A few isolated lines, dots, clods, circles or pseudopods in a pattern of another basic element does not mean there is more than one pattern, and such isolated basic elements should be ignored at this stage. When appropriate, they can be taken into account when one is weighing clues.

The exact number of patterns is unimportant; no more diagnostic accuracy is achieved by counting patterns than by simply distinguishing between one and more than one pattern. Requiring only this simple judgment improves agreement between observers.

As lesions become more complex, it becomes increasingly likely that more than one interpretation could reasonably be considered by the investigator. In part this reflects the skill of the investigator, but it also reflects (often poorly understood) variations in basic perception between observers. Two features of the algorithm reduce errors in diagnosis due to differing interpretations. Firstly, as will be detailed below, descriptions are generated in a defined stepwise fashion. Secondly, the algorithm is constructed in such a way that various interpretations, as long as they are plausible, lead to the same diagnosis. The result is that the algorithmic method generally leads to the same conclusion regardless of which algorithmic pathway is followed. Of course, this redundancy in the algorithm is not infallible, so when the investiga-

tor is uncertain which pathway to follow, it is good practice to follow all the plausible pathways and consider all the differential diagnoses that the different pathways offer.

In contrast to lesions with only one pattern, for which all patterns are regarded as being equally important, the algorithm for pigmented lesions with more than one pattern is constructed in a hierarchical manner. If there is more than one pattern, one looks for the individual patterns in a stepwise manner, following a sequence established on the basis of pattern specificity (5.37). The sequence starts with the pattern of lines, the most specific pattern in dermatoscopy, and ends with the structureless pattern, which is the least specific. Thus the description begins not with the most prominent pattern present, but with the most specific.

When a lesion consists of more than one pattern the investigator first determines whether a pattern of lines is present or not. When a pattern of lines is present, one follows the algorithm for patterns of lines. When no pattern of lines is present, one looks next for pseudopods, then for circles, then clods, and finally for dots. When none of these patterns of basic elements are seen, the lesion logically must consist of only one pattern, namely structureless, and the analysis is performed in accordance with the known rules for this pattern.

The most important decision in the analysis of pigmented lesions with more than one pattern is the presence or absence of structural symmetry. Symmetry in lesions with one pattern is judged on the distribution of colors within the lesion. In lesions with more than one pattern, the distribution of color is not assessed,

and symmetry is judged purely on arrangement of patterns. The more patterns there are, the less is the likelihood of symmetry.

Structural symmetry has been defined in chapter 3. In theory there are an infinite number of ways that two patterns can combine symmetrically. In practice, there are only three symmetrical arrangements of two patterns in pigmented skin lesions: a) One pattern is in the center and the other at the periphery, b) the opposite is the case, and c) the basic elements of one pattern (e.g. dots) are regularly spread over a second pattern (e.g. reticular lines). All other combinations of two patterns are, by definition, considered asymmetrical.

When assessing symmetry we should keep in mind that we are dealing with biological structures. Assessment of symmetry is therefore a matter of judgment as to the type and degree of variation that is expected in nature, rather than a strict application of the propositions of geometry. At times there will be uncertainty as to whether a lesion should be judged symmetrical or asymmetrical.

This is an important role of experience in dermatoscopy; experts can confidently call more lesions symmetrical than beginners, reducing the need for exhaustive assessment to exclude malignancy. In cases of uncertainty, it is prudent to consider all the differential diagnoses at the ends of both applicable branches of the algorithm. Considering all applicable branches of the algorithm is appropriate in any situation when one reaches a decision point and is uncertain of the correct pathway. This ensures that no potential diagnosis is discarded prematurely.

5.2.1 Lines

When analyzing a lesion with more than one pattern, lines are the first of the basic elements the investigator should look for. When a pattern of lines is found, again one proceeds in a stepwise manner (in order of specificity of pattern) through the various types of lines: first look for a reticular or branched pattern of lines, then a pattern of angulated lines, then a parallel line pattern, followed by a radial and finally a curved pattern of lines (5.38).

Reticular and/or branched lines

As in lesions with one pattern, it is sometimes difficult to distinguish between reticular and branched lines. Unlike lesions with one pattern, this distinction has no diagnostic significance when assessing lesions with more than one pattern and so is not assessed. When a lesion contains both these patterns of lines, they are interpreted jointly as one pattern. Reticular lines are much more common than branched lines.

The first step in assessing lesions with reticular or branched lines is to rule out unequivocal cases of solar lentigo, seborrheic keratosis and their regressing variant, the lichen planus-like keratosis. The exclusion of these diagnoses is made on the basis of clues, such as a sharply demarcated scalloped border and curved lines in cases of solar lentigo or lichen planus-like keratosis; or a sharply demarcated border, white dots or clods, yellow or orange clods, and thick curved lines and a few circles in cases of seborrheic

keratosis. When enough of these clues are present to make an unequivocal diagnosis, the analysis stops. When there are no such clues, or too few to make an unequivocal diagnosis, the analysis proceeds.

Once these unequivocally benign lesions have been ruled out, the next step is to assess symmetry. If the patterns are arranged symmetrically the investigator will usually be able to establish a specific diagnosis, depending on the type of combination.

There are three combinations of the reticular (or branched) pattern with dots or clods that are symmetrical (5.39, 5.40): The first combination is clods in the center and reticular lines at the periphery. Most of these lesions are “superficial” or “superficial and deep” congenital nevus, some are Clark nevi. As mentioned earlier, many dermatopathologists (regrettably) make no distinction between the two entities and refer to both as “dysplastic” or “compound” nevi. The second combination is reticular lines in the center and clods (or dots) peripherally. These lesions are usually a Clark nevus in its phase of growth, or a growing superficial or superficial and deep congenital nevus. Peripheral brown dots or clods are seen in growing melanocytic nevi of all types. The third combination is reticular lines with uniformly distributed clods (or dots). These are equally likely to be Clark nevi or “superficial” or “superficial and deep” congenital nevi.

In practice, only one symmetrical combination of reticular or branched lines and a structureless zone is seen, with the lines seen peripherally and the struc-

tureless zone centrally (5.41). The central structureless zone may be skin-colored or light brown. If the central structureless zone is skin-colored and raised or papillomatous, the diagnosis is most commonly a “superficial and deep” congenital nevus (5.42). If the central structureless zone is light brown and flat it could be a superficial or superficial and deep congenital nevus or a Clark nevus (5.43). An accessory nipple may also have this pattern.

If the central structureless area is black, the diagnosis is nearly always Clark nevus, or rarely a Reed nevus

(5.43). One should not be misled by the histopathological finding of a “dysplastic junctional nevus” because this is just a different name for Clark nevus. When the center is structureless blue, this is usually a combined congenital nevus (5.44). If the center is white, i.e. lighter than the surrounding skin, and the adjacent reticular lines are light-brown and thin, the most likely diagnosis is dermatofibroma (5.45).

A symmetrical combination of pseudopods and/or radial lines with the reticular pattern (i.e. the pseudopods/radial lines are seen occupying the entire

circumference) indicates a Reed nevus. A symmetrical combination of peripheral radial lines with a reticular pattern in the center is also rarely seen with a Clark nevus. In practice, when any of these patterns are seen it is difficult to reliably exclude melanoma, so such lesions (in adults at least) should be submitted for histopathology.

Symmetrical combinations of three patterns are seen, though less often than symmetrical combinations of two patterns. One example would be structureless in the center and a combination of reticular lines and dots or clods at the periphery. These three-fold combinations are usually found in “superficial” and “superficial and deep” congenital nevi.

Any lesion with an asymmetrical combination of patterns that includes reticular or branched lines

needs careful assessment and should specifically be assessed for clues to melanoma (5.46). As a general rule when assessing a lesion for clues, a clue is only considered to be present when it is clearly present. Imagination and fantasy have no place in the search for clues. The diagnosis is nevus (Clark nevus, combined congenital nevus, “superficial” or “superficial and deep” congenital nevus) only when there are no clues to melanoma (5.47). The diagnosis is melanoma when (by these standards) at least one clue to melanoma is present (5.48).

Angulated lines

The main differential diagnosis of lesions with angulated lines is flat melanoma on chronic sun-damaged skin (including facial and non-facial skin). Many

Clue to melanoma

Asymmetric

No clue to melanoma

Melanoma

Clark nevus

Congenital nevus, "superficial" or "superficial and deep" Combined congenital nevus

flat melanomas on chronic sun-damaged non-facial skin have a lentigo-like reticular pattern and will be assessed according to the algorithm for lesions with a reticular pattern. Some flat melanomas, however, have angulated lines but no reticular lines (5.49). On facial skin reticular lines are rare and therefore facial flat melanomas usually have other combination of patterns including combinations with angulated lines. A lesion with angulated lines on facial skin could also be a pigmented actinic keratosis, which is the main differential diagnosis of facial lesions with angulated lines (5.50).

Parallel lines

Parallel lines are commonly seen in acral pigmented lesions with more than one pattern. Assessment proceeds as for one pattern lesions; first one determines whether the lines are on the ridges, in the furrows, or crossing ridges and furrows (5.51). The ridge pattern takes precedence if more than one parallel line pattern is seen.

Further assessment of the ridge pattern is also similar to that for one pattern lesions, with the color of the ridge pigmentation taking precedence over the symmetry of pattern combination. If pigmentation on