ARTICLE
Auteur(s) : Antonio
Torrelo1, Eulalia Baselga2, Eduardo
Nagore3, Antonio Zambrano1, Rudolf
Happle4
1Department of Dermatology, Hospital del Niño Jesús,
Menéndez Pelayo 65 28009-Madrid, Spain
2Department of Dermatology, Hospital Santa Creu i Sant
Pau, Barcelona, Spain
3Department of Dermatology, Instituto Valenciano de
Oncología, Valencia, Spain
4Department of Dermatology, University of Marburg,
Marburg, Germany
accepté le 15 Juillet 2005
Despite the widespread use of the term nevus, there was during the
last century no generally accepted definition [1]. Nevi may be
congenital or acquired, they may show increase or decrease of a
given cellular structure, or they may reflect a functional
disorder. In this situation it is understandable that some authors
ironically stated that every lesion that once was called a nevus
may be considered a nevus [2]. In 1995, a workable definition was
proposed by Happle who put forward the idea that all nevi reflect
mosaicism [1]. He proposed the following definition: “Nevi are
visible, circumscribed, long-lasting lesions of the skin or the
neighboring mucosa, reflecting genetic mosaicism. With the
exception of melanocytic nevi, they do not show neoplastic growth.
They never show malignant neoplasia” [1]. Although this concept has
so far not been proven in every type of nevus, mosaicism has today
indeed been documented in many nevi such as segmental
hypermelanotic lesions [3], segmental hypomelanotic lesions (nevus
depigmentosus) [4], segmental acne (“Munro nevus”) [5],
epidermolytic epidermal nevus [6] and segmental Darier disease
[7].Happle has described five standard patterns of cutaneous
mosaicism in human skin, in the form of the Blaschko-linear,
checkerboard, phylloid, midline patch, and lateralization pattern
[8, 9]. These patterns reflect the arrangement of rather large
lesions and visualize either genomic or epigenetic mosaicism.
However, if the concept of nevi as mosaics holds true, an
explanation should be offered to the fact that most nevi we
regularly see in clinical practice apparently do not follow such
archetypical patterns. Hence, two hypotheses might be put forward:
1) more clinical patterns of mosaicism may exist in human skin, and
2) every nevus follows one of those ‘archetypical’ mosaic patterns
but in small or medium-sized lesions this arrangement cannot be
recognized, although they may display one or more characteristic
shapes. To assess which one of these hypotheses is more likely, we
studied the shapes and patterns of nevi from photographic files. In
this way we recognized that many of such lesions show a highly
repetitive shape or pattern. Defining the specific shape or pattern
of a given nevus would be helpful as a first step to elucidate the
genetic basis of such lesions, since different clinical shapes or
patterns might possibly reflect different genetic mechanisms such
as different mutations or even different moments of appearance of
such mutations (i.e., timing) during embryogenesis or later in
life. Furthermore, a more thorough study of the shapes and patterns
of nevi would help to further delineate the association of
cutaneous nevi with extracutaneous manifestations. Finally, because
some distinct types of nevi may appear simultaneously or in close
apposition, their shapes and patterns may be useful to further
depict this so called twin spotting phenomenon [8].In this article,
we propose a new classification of the shapes and patterns of nevi,
based on a retrospective review of photographic images.
Materials and methods
A photographic review of our image files was carried out. We
reviewed all evaluable and recognizable images of every nevus of
the skin. For the selection of images, we used Happle’s definition
of nevus to consider a lesion eligible (table 1)( Table 1 ). For nevi with conflicting terminology,
we decided arbitrarily to follow a denomination used in a classic
reference textbook [10]. In this way, the conditions listed in
table 1 were chosen for review. Some facts about the choice deserve
further comment. Regarding melanocytic nevi, we decided to include
only congenital melanocytic nevi, disregarding common acquired
ones. Vascular nevoid conditions were troublesome because of
different denominations by different countries or schools; thus,
although in some classifications of vascular skin disorders the
word “nevus” is no longer present [11], we only considered lesions
diagnosed under the terms telangiectatic nevus and nevus flammeus
amenable to our study. Nevi flammei affecting the face and neck
were not used for this review because they will be the subject of
another study. Salmon patches of the newborn were not considered
because they are not included in the definition of nevus we used
for our study [1]. When a picture showed more than one cutaneous
lesion of the same clinical type of nevus, the most conspicuous one
was selected; for example, in cases of giant melanocytic nevus with
smaller “satellites”, only the largest lesion was chosen for
assignment to a pattern.
For our review, two observers from different departments of
dermatology (A.T. and E.B.) independently evaluated the selected
conditions from their image files. Then, an agreement was reached
regarding conceptual shapes or patterns of the skin lesions. In our
evaluation process, no attention was paid to the cellular origin of
the nevus, although this is the most usual way to refer to any of
such nevi. We only assigned the nevi to one or other pattern by
their shape, outlines, and distribution, regardless of features
such as color, size, depth of involvement, association with other
nevi or extracutaneous abnormalities, or supposed cellular
components of the lesions.
After discussion and training, a second review of all of the
selected cases was carried out, and all images were assigned to one
of the shapes or patterns designed. In a third step, all images
with conflicting assignment were reassessed, and every doubtful
case was ultimately categorized by agreement after reasoning.
Table 1 List of nevi chosen for review
|
• Epidermal nevus (without further specification)
|
|
• Sebaceous nevus
|
|
• Comedo nevus
|
|
• Linear porokeratosis
|
|
• Porokeratotic eccrine ostial and dermal duct nevus
|
|
• Congenital triangular alopecia
|
|
• Becker’s nevus
|
|
• Collagen nevi
|
|
• Juvenile elastoma
|
|
• Nevus anelasticus
|
|
• Congenital smooth-muscle hamartoma
|
|
• Telangiectatic nevi (including nevus flammeus)
|
|
• Nevus anemicus
|
|
• Cutis marmorata telangiectatica congenita
|
|
• Segmental venous malformations
|
|
• Angiokeratoma
|
|
• Congenital melanocytic nevus
|
|
• Nevus spilus (syn. speckled nevus)
|
|
• Ota nevus
|
|
• Aberrant blue spot (dermal melanocytosis)
|
|
• Congenital blue nevus
|
|
• Nevus depigmentosus
|
|
• Hyperchromic nevus
|
Results
A total of 1,188 images were selected for the study. Only images
where the whole lesion could be photographed were chosen but, for
very extensive lesions, a set of images from a single patient was
accepted to clarify the distribution and extent of the nevus. By
observation of images of nevi, we were able to define three
distinct shapes as well as two so far undescribed patterns, in
addition to the well-established Blaschko-linear, block/flag-like
and garment-like patterns, to which all lesions could be allocated.
A single case was only assigned to one single shape or pattern. The
configurations identified and the number of entities assigned to
such shapes or patterns are shown in table 2( Table 2 ). In brief, the configurations were
described and named as follows:
Assignment to three distinct shapes
Round or oval shape
Typically, a round or oval patch, papule or plaque, usually of
small size, with regular borders is present at any part of the skin
surface. In our review, this was the most frequently occurring
shape of all nevi, and corresponded mostly to small or medium-sized
congenital melanocytic nevi (table 2). Other examples of nevi with
this common shape include nevus depigmentosus, small sebaceous
nevi, and small patches of dermal melanocytosis (aberrant blue
spots) ( (figure
1) ).
Table 2 Assignment of nevi to the different shapes or
patterns
|
TYPE OF NEVUS
|
Round or oval
|
Patch with indented borders
|
Teardrop / triangular
|
Agminated
|
Blaschkolinear
|
Blocks or flags
|
Diffuse patchy
|
Garment-like
|
TOTAL
|
|
Epidermal nevus (without further specification)
|
3
|
|
|
1
|
128
|
|
|
|
132
|
|
Sebaceous nevus
|
74
|
|
4
|
|
37
|
|
|
|
115
|
|
Comedo nevus
|
|
|
|
|
16
|
|
|
|
16
|
|
Linear porokeratosis
|
|
|
|
|
15
|
|
|
|
15
|
|
PEODDN a
|
|
|
|
|
3
|
|
|
|
3
|
|
Triangular alopecia
|
|
|
15
|
|
|
|
|
|
15
|
|
Becker’s nevus
|
|
58
|
|
|
|
|
|
|
58
|
|
Collagen nevi
|
|
17
|
|
9
|
|
|
|
|
26
|
|
Juvenile elastoma
|
|
10
|
|
5
|
|
|
|
|
15
|
|
Nevus anelasticus
|
|
|
1
|
|
|
|
|
|
1
|
|
Congenital smooth-muscle hamartoma
|
35
|
4
|
1
|
|
|
2
|
|
|
42
|
|
Telangiectatic nevus (without further specification)
b
|
5
|
38
|
|
|
|
31
|
14
|
|
88
|
|
Nevus anemicus
|
|
12
|
|
|
|
|
|
|
12
|
|
Cutis marmorata telangiectatica congenita
|
|
|
|
|
|
43
|
|
|
43
|
|
Congenital melanocytic nevus
|
148
|
3
|
4
|
6
|
|
1
|
|
70
|
232
|
|
Nevus spilus (speckled nevus)
|
38
|
|
|
1
|
|
13
|
|
|
52
|
|
Ota nevus
|
|
9
|
|
|
|
|
|
|
9
|
|
Aberrant blue spot (aberrant Mongolian spot, dermal
melanocytosis)
|
36
|
4
|
|
|
|
1
|
37
|
|
78
|
|
Congenital blue nevus
|
7
|
5
|
2
|
|
|
|
|
|
14
|
|
Nevus depigmentosus
|
67
|
15
|
3
|
|
52
|
8
|
|
|
145
|
|
Hyperchromic nevus c
|
37
|
18
|
|
|
18
|
1
|
|
3
|
77
|
|
TOTAL
|
450
|
193
|
30
|
22
|
269
|
100
|
51
|
73
|
1188
|
aPEODDN: porokeratotic eccrine ostial and
dermal duct nevus.
bExcluding nevi flammei of the face and
neck.
cA hyperchromic, usually congenital
macule, as counterpart of nevus depigmentosus (i.e., hyperchromic
mosaic patches), excluding café-au-lait macules of NF1.
Patchy indented shape
This shape is characterized by irregular, usually serrated or
indented borders, and it may be round, oval or rhomboidal. The size
of the nevus may range from a small lesion to a larger one even
measuring some centimeters in diameter. Nevi displaying this shape
may appear on any part of the body, and some of them may ignore the
midline ( (figure
2) ).
This shape was exhibited by some hyperpigmented epidermal
macules or hyperchromic nevi (café-au-lait macules of NF1 and
lentigines excluded), nevus anemicus, and aberrant blue spots,
among others. Lesions adopting this shape may show areas of normal
tissue within the patch, intermingled with involved areas, leading
to a somewhat reticular pattern with preserved irregular borders.
This was noted in cases of Becker’s nevus or connective tissue
nevus.
Teardrop or triangular shape
This peculiar configuration is characterized by comma shaped
lesions, with a sharply, angled end. Their size is rather variable,
and the lesions do not extend in a Blaschko-linear distribution.
This shape may resemble some lesions of the phylloid pattern, but
we are describing isolated lesions here. Remarkably, a significant
portion of skin lesions in our review adopting this teardrop shape
consist of nevi of absent or decreased tissue, such as nevus
anelasticus or congenital triangular alopecia, but other lesions
such as small sebaceous nevus, melanocytic nevus, and nevus
depigmentosus may also show this outline ( (figure 3) ).
Assignment to seven distinct archetypical patterns
Agminated or cannonball pattern
The Latin term ‘agminated’ means clustered. Under this term we
include small patches or papules being grouped in a circumscribed
area of the skin, with sparing of the normal skin between the
individual lesions. These clusters are mostly solitary, and they
may appear in every part of the skin. It is a rarely occurring
pattern, and in our series, the most common skin lesions following
this pattern were agminated melanocytic nevi and collagen nevi (
(figure 4) ).
Diffuse patchy pattern
This pattern consists of disseminated lesions, usually affecting a
large portion of the trunk, which appear as multiple, discrete or
confluent, patchy macules, showing no tendency to respect the
midline. Such extensive patches leave areas of uninvolved skin. In
our series, only two types of nevi, extensive aberrant blue spots
and some extensive telangiectatic nevi were assigned to this
pattern ( (figure
5) ).
Blaschko-linear pattern
Today this is the best known pattern of nevi or nevoid disorders.
It is generally accepted that Blaschko lines are the lines of
embryonic development of the skin, and that every Blaschko line is
derived from a single cell forming a clone [12]. Dermatoses
following these lines are indeed mosaic states of the disease, as
has been demonstrated for epidermal nevi, systematized nevus
depigmentosus, segmental hypermelanosis, segmental Darier disease,
segmental Hailey-Hailey disease and linear lesions of child nevus.
Other skin lesions following Blaschko lines still await genetic
confirmation of its mosaic state. Blaschko lines originate from the
dorsal midline, and have a fountain-like, V or S shape on the
trunk, and a longitudinal shape on the limbs. Blaschko lines on the
face and scalp have been recently addressed [13]. Examples of
lesions following this well known pattern in our study were
sebaceous nevus, epidermal nevus (without further specification),
nevus depigmentosus, linear hyperchromic nevus (linear
hyperpigmentation), porokeratotic eccrine nevus, nevus comedonicus,
and linear porokeratosis ( (figure 6) ).
Block or flag-like pattern
Under the synonymic designation “checkerboard pattern” this
arrangement was also depicted by Happle as an archetypical
manifestation of mosaicism. Extensive areas of mutant tissue take
the form of blocks or flags involving large areas of the skin,
mostly located on the trunk. Typically, these blocks stop at the
midline, and they may affect one side or both sides of the body; in
this latter instance, alternating mutant blocks may give rise to a
true ‘checkerboard pattern’, but if the same areas of both sides of
the body are affected, the checkered appearance is blurred. On the
limbs the checkers are more difficult to recognize because, instead
of squares or rectangles they appear as broad ribbons or as an
involvement of the whole extremity extending from the girdle, where
the lesion usually has straight upper and medial margins. In many
instances, patients with this pattern have been described with
rather loose words such as “dermatomal”, “segmental”, “zosteriform”
or others. The most common lesions following this pattern in our
study were vascular nevi such as cutis marmorata telangiectatica
congenita or nevus flammeus, but speckled nevus as well as hyper-
or hypopigmented macules sometimes were likewise assigned to this
pattern ( (figure
7) ).
Paradoxically, however, Becker’s nevus that was presented by
Happle as exemplifying the flag-like or checkerboard pattern,
failed to show this arrangement in our series of 58 cases. This may
be explained by the fact that the Becker nevi included in our study
tended to be rather small lesions ( (figure 8) ).
Extensive garment-like pattern
This pattern is almost exclusively described for pigmented lesions.
It shows a typical involvement of large areas of the skin covering
the trunk or limbs. The mutant tissue does not stop at the midline,
and usually involves partially or completely, the trunk or a limb,
in the form of a shirt, a bathing suit or a cuff. In general the
extension of the lesion is wider on the back than on the abdomen,
and the lesion may not embrace the whole circumference of the
trunk, leaving abdominal areas uninvolved. In our series, this
pattern was almost restricted to giant melanocytic nevi, but some
hypermelanotic macules were likewise extensive enough to be
included in this group ( (figure 9) ).
Failure to observe other patterns
We did not observe any clinical image consistent with a phylloid
pattern of mosaicism or a lateralization pattern [15].
Discussion
In this study we have tried to specify the shapes and patterns that
nevi may exhibit. According to our working definition of a nevus
[1], all nevi reflect mosaicism. At least two other mosaic patterns
exist, namely the phylloid and the lateralization patterns [8, 9],
but we did not identify in our files any patient whose nevi
followed such configurations. On the other hand, we are proposing
two so far undescribed mosaic patterns in the form of the
“agminated” and the “diffuse patchy” patterns. It is important to
realize that we assigned a given case to one single shape or
pattern only, although a limited number of cases might have been
allocated to more than one category. In such instances, the most
conspicuous configuration was chosen by agreement between both
observers.
We are using the term “shape” for the configuration of an
individual skin lesion that is usually small or medium-sized,
whereas the term “pattern” denotes an archetypical arrangement of
usually larger lesions that, in a given case, may or may not show a
systematized distribution. For example, a small Becker’s nevus is
assigned to the “patchy indented” shape, whereas a large Becker’s
nevus, although likewise being both patchy and indented, can be
assigned to the block/flag-like pattern. Hence, it should be noted
that the categories of “shape” and “pattern” are not mutually
exclusive.
We emphasize that the three newly described shapes in the form
of round/oval, patchy indented, and teardrop/triangular
configurations are categories that apply to small or medium-sized
nevi. When the same types of nevi are of larger size or show a
systematized arrangement, they may adopt an “archetypical” pattern.
For example, in cases of non-organoid or organoid epithelial nevi
we often observed a round or oval shape, and sometimes even a
teardrop shape, but they never showed a patchy indented shape. From
this we conclude that a round/oval or a teardrop-shaped patch
indeed represents, at least in some types of nevi, a “point” on a
Blaschko line. On the other hand, in the group of vascular nevi
that often show a block or flag-like pattern, we find that smaller
lesions may show a “patchy indented” shape. Similarly, large Becker
nevi are patches with indented margins arranged in a block or
flag-like pattern, whereas small lesions can only be assigned to
the “patchy indented” shape (table 2). Thus, we infer that, at
least for some types of nevi, a patch with indented borders is,
indeed, a small part or “forme fruste” of a block or flag-like
pattern.
The patterns of lesions diagnosed as nevus depigmentosus support
this view. Accordingly, a nevus depigmentosus, when very
widespread, may be arranged in “archetypical” patterns such as
Blaschko’s lines or the flag-like pattern, whereas smaller lesions
show a round/oval or triangular shape (representing a “point” or a
short piece of a Blaschko line), or a patchy indented shape
(representing rather small “blocks” or “flags”).
It should be noted that some types of nevi which commonly appear
as a round or oval patches, never or virtually never follow the
lines of Blaschko, as is the case for congenital melanocytic nevi,
speckled nevi or aberrant blue spots. From this we conclude that a
round/oval lesion may also represent, in principle, a rather small
block/flag or garment-like lesion.
Other patterns we have described here, such as the “agminated”
and the “diffuse patchy” patterns, need further comment. It seems
conceivable that some agminated lesions, particularly the agminated
melanocytic nevi, may represent in principle a small counterpart of
garment-like lesions showing further modification by tissue
expansion or other unknown factors. In such cases, “agminated”
would perhaps be better taken as a shape rather than as a pattern.
On the other hand, we tentatively introduced a pattern we have
called “diffuse patchy” because we felt that this pattern differs
from the garment-like arrangement. We do so far not know whether
this is a new archetypical pattern of mosaicism or merely
represents a variation of the garment-like pattern. Notably,
lesions that were assigned to this pattern (extensive
telangiectatic nevi and extensive aberrant blue spots) tend to
appear as round/oval lesions or as patches with indented borders
when lesions are smaller.
The fact that some types of nevi virtually always show an
identical, repetitive shape or pattern from patient to patient
suggests that a similar mutational event is responsible for such
configurations. On the other hand, different types of nevi may
exhibit identical shapes or patterns, suggesting that they
originate from some common genetic pathomechanism. As a hypothesis,
if mosaicism is responsible for a single nevus showing various
configurations, we may hypothesize that postzygotic mutations are
occurring at different states of embryonic development, or during
extra-uterine life [14]. Thus, we infer that if a mutation occurs
after the migration of skin components has been completed, a
round/oval or patchy indented shape is expected, whereas
“archetypical” patterns such as Blaschkolinear or flag-like
arrangements would originate from a mutation occurring before the
embryonic development of the skin components has been completed. So
far, postzygotic mutations have been demonstrated to be involved in
some, mostly Blaschkolinear, nevi, but demonstration of mosaicism
in all types of nevi is still lacking [3-7]. However, the striking
and usually under-recognized tendency of lesions with different
clinical shapes or patterns to appear associated in the form of
twin spotting or didymosis is yet another piece of indirect
evidence of the mosaic nature of nevi [15]. The concept of
mosaicism will help to further elucidate the pathogenesis of nevi,
and will also permit us to avoid inappropriate terms such as
“dermatomal” or “zosteriform”, and to develop a more accurate
classification of the various shapes and patterns of nevi.
The classification of different archetypical patterns may yield
some insight into the embryonic development of human skin. Although
our morphological analysis was not designed as an epidemiological
study on the prevalence of nevi, it is clear from our photographic
files that certain nevi derived from embryonic ectodermal tissue
such as non-organoid epidermal nevus, comedo nevus, linear
porokeratosis, and others show a tendency to be arranged in a
Blaschko-linear pattern, whereas pigmentary nevi, that are likewise
derived from the ectodermal layer, may also show a block/flag-like,
diffuse patchy or garment-like pattern, in addition to the
Blaschklo-linear arrangement. On the other hand, the
Blaschko-linear pattern is only rarely followed by nevi of
mesodermal origin, such as vascular or collagen nevi. Such lesions
show a preference for the block/flag-like arrangement and the
diffuse patchy pattern. We should like to emphasize, however, that
mesodermal lesions can likewise follow the lines of Blaschko, as is
the case in focal dermal hypoplasia or linear atrophoderma of
Moulin. Hence, the Blaschko lines can be visualized by cell types
other than those derived from the ectoderm. Melanocytic nevi show
an array of various patterns, but remarkably the garment-like
pattern is almost completely restricted to them. We observed the
indented shape in melanocytic nevi as well as in nevi of vascular
origin. On the other hand, the teardrop shape and the agminated
pattern were not assigned to any type of vascular nevus in the
present study.
Some methodological aspects of our work deserve further
explanations. Firstly, the lesions studied here do not reflect the
true prevalence of skin nevi, because this was a retrospective
analysis of photographic files, and it is conceivable that not all
common lesions are photographed in the daily clinic. More
importantly, we have defined shapes and patterns to include all
photographic images in our files, but the configurations we chose
were arbitrarily selected, and some minor differences may be
difficult to recognize. Hence, theoretically it could be
problematic to obtain a high inter- observer agreement when
evaluating cutaneous nevi. However, both observers involved in the
present study reached an almost complete agreement in the
assignment of configurations, but we must acknowledge that the
statistical reliability of these shapes and patterns has not been
studied. In fact, the assessment of the inter-observer agreement
was not a purpose of this study. Hence, further investigations
specifically aimed at this matter are warranted. Nonetheless, it is
our feeling that a high degree of agreement can be achieved with
minimal training. It is still possible that some lesions are very
difficult to assign and may defy our classification of shapes and
patterns, and that other configurations may exist. Thus, some
refinement of the shapes and patterns we have proposed is
acceptable. Finally, regarding the nevi selected for our study, we
acknowledge that some lesions we call nevi may be considered by
others as “malformations” [11]. However, because such lesions tend
to show consistent shapes or patterns, we think that the term
“nevus” is more appropriate.
Another semantic problem may lie in the fact that proliferative
lesions such as hemangiomas, that are definitely not nevi, may
sometimes show a segmental arrangement [16]. In fact, many other
neoplastic lesions can be arranged in a “nevoid” pattern, such as
segmental nevoid basal cell carcinomas, segmental neurofibromas,
linear multiple trichoepithelioma or syringoma, or segmental
leiomyomas [14]. Such cases should be categorized as examples of
“nevoid” arrangement reflecting mosaicism, rather than as
representing true nevi.
The value of a new classification of the shapes and patterns of
nevi might be questioned by those who think that the currently
existing “archetypical” patterns described by one of the co-workers
of this study are sufficient. In our opinion, the present
delineation of shapes and patterns may be valuable for several
reasons: 1) the proposed new shapes in the form of “round or oval”,
“patchy indented” and “teardrop/triangular” configurations can be
considered to reflect mosaicism, thus expanding our view of nevi as
mosaic disorders; 2) this new classification reinforces the
patterns initially described by Happle [8] and highlights the idea
that nevi displaying these “archetypical” patterns may also appear
as small lesions that can only be categorized by their shape; 3)
there is a good correlation between different types of nevi and the
shapes or patterns they assume; 4) new more complex mosaic
configurations are proposed in the form of the agminated pattern
and the diffuse patchy pattern; 5) all nevi reviewed could be
assigned to one of these shapes or patterns; and 6) the concept
that all nevi are mosaic lesions with a recognizable pattern may
lead to a better understanding of the origin and nature of possibly
associated extracutaneous anomalies.
Conclusion
In an attempt to better understand the mosaic nature of nevi, we
have assigned such lesions to a new classification of shapes and
patterns. From this study we conclude that the different patterns
are “archetypical” in a way that they are the perfect or ideal
model of certain types of nevi, whereas the newly delineated shapes
are subordinated to these patterns and can be taken as
“non-archetypical”. We emphasize that nevi derived from a
particular cell type may become manifest in many different shapes
and patterns. For example, nevi originating from the pigmentary
cell line may show a round/oval, patchy indented, or teardrop
shape, whereas larger lesions may be arranged in a Blaschko-linear,
block/flag-like, phylloid, garment-like, agminated, or diffuse
patchy pattern.
From a heuristic point of view, it seems worthwhile to assign a
given dermatological entity to one “archetypical” pattern. For
example, giant melanocytic nevi may then be assigned to the
garment-like pattern, whereas nevus sebaceus would be categorized
as belonging to the Blaschko-linear pattern.
Our work gives more consistency to the idea that nevi reflect
mosaicism, because they have been shown to follow a repetitive,
mosaic pattern, which can be archetypical or not. It is possible,
and even likely, that some other distinct shapes or patterns of
nevi will be delineated in the future. For the time being, however,
it seems appropriate to assign a given nevus to the shapes and
patterns as presented in this article. Most probably, further
molecular studies performed in various nevi will provide additional
evidence that all of these lesions reflect mosaicism.
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