4 курс / Дерматовенерология / Дерматоскопия (3)

pigment defines structure and acknowledging that gray structures are less densely pigmented than blue structures, one should not interpret such gray regions as a separate pattern.

Correlation between dermatoscopy and dermatopathology

Dermal melanocytes filled with melanin appear as a blue or gray structureless zone. When the melanocytes contain little or no melanin the structureless area appears light gray or even skin colored.

Unna and Miescher nevi

Both these nevi are primarily dermal proliferations of melanocytes. Although they appear after birth, histopathologically they are marked by a congenital growth pattern. For both Unna and Miescher nevus, the diagnosis is usually based on clinical appearance, with dermatoscopy providing little extra information. The typical dermatoscopic appearance of Unna nevus is of large polygonal skin-colored or light-brown clods (3.69). Between these clods there may be orange clods, and white dots and/or clods may be seen through the lesion. In such cases, the dermatoscopic appearance may resemble seborrheic keratosis. If skin-colored clods are poorly demarcated, the impression of a structureless pattern may be created.

The best clue to Unna nevus is short, thick and curved vessels in the center of skin-colored or light brown clods. Occasionally one may find brown dots or small brown clods. Very rarely there may be reticular brown lines at the periphery of the Unna nevus, which represent a junctional component.

Miescher nevus only occurs on the face. Features at dermatoscopy are similar to Unna nevus. Due to the anatomy of the facial skin and its prominent hair follicles, heavily pigmented types may have circles instead of clods. A strong clue to the diagnosis of Miescher nevus is excess numbers of terminal hairs, which also underlines the congenital nature of this nevus.

Correlation between dermatoscopy and dermatopathology

Polygonal clods correspond to widened dermal papillae filled with melanocytes, which cause the epidermis to protrude outward. In the invaginations between these epidermal protrusions there may be accumulations of keratinous material (orange clods) while exophytic growth may lead to the formation of epidermal inclusion cysts (milia), which appear as white dots. The curved vessels are located in the widened dermal papillae.

3.7.2 Melanoma

The dermatoscopy of melanoma is unique in that any pattern and any color may be seen (3.70–3.76). The more patterns and the more colors a lesion has, the more likely it is to be a melanoma. The question of the minimal features ever seen in melanoma is more about the limitations of dermatoscopy rather than the biology of the lesion. Melanomas can be diagnosed dermatoscopically at a stage when they have only one pattern, but by the time they have a specific clue to melanoma they will normally have more than one color. Melanomas can only be diagnosed earlier than this by monitoring for change (or by luck!). More advanced melanomas generally have two or more patterns which are nearly always arranged asymmetrically. In revised pattern analysis, the diagnosis of melanoma requires either more than one pattern or more than one color (chaos) and at least one clue to melanoma. This is a similar schema to the algorithm for the diagnosis of melanoma proposed by Menzies.

However, the clues used are somewhat different, and pattern analysis can be used regardless of lesion location; i.e. it may also be used to diagnose facial and acral melanomas.

Revised pattern analysis defines nine primary clues to melanoma:

1.Eccentric structureless zones of any color (except skin color)

2.Gray circles, lines, dots or clods

3.Black dots or clods at the periphery

4.Pseudopods or radial lines at the periphery, which do not occupy the entire circumference

5.White lines

6.Thick reticular lines

7.Polymorphous vessels

8.Parallel lines on the ridges

9.Angulated lines (polygons)

Clues to melanoma are shown in figures 3.70 to 3.76 and described in the figure legends. As mentioned in chapter 2, in this book we make no distinction between the types of melanoma, namely nodular, superficial spreading, acral lentiginous and lentigo maligna melanoma, because this classification is illogical and inconsistent. The nine clues to melanoma apply regardless of the histopathological growth type, size, and intensity of pigmentation.

Due to the specific anatomy of rete ridges on acral skin, the clue “parallel lines on ridges” refers only to acral melanomas. However, all other clues to melanoma are also clues to acral melanomas. While parallel lines on the ridges is the commonest clue to acral melanoma, it is not necessary to make the diagnosis.