From dermoscopedia
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 Author(s): Nicoleta Neagu
Description This chapter covers the dermatoscopic features of Melanoma.
Author(s) Nicoleta Neagu
Responsible author N. N.→ send e-mail
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Status update August 25, 2021
Status by Ralph P. Braun


Dermoscopic features

Classical criteria

Atypical pigment network

The atypical network is irregularly meshed with lines that vary in width and degree of pigmentation and with “holes” that are heterogeneous in area and shape. An atypical network shows foci with broader and darker pigmented lines; the network often ends abruptly at the lesion’s periphery. An atypical network within a lesion may also appear perturbed and broken up, a finding referred to as “branched streaks”.

Atypical network31.jpg

An example of an atypical pigment network clinically and dermoscopically:

Atypical network.jpg

On histolopathology, the irregular lines of an atypical network correspond to variation in the width, length, and spacing of the rete ridges due to variation in the size, spacing, and tendency to confluence of melanocytic nests. Rete ridges that are elongated and widened by larger junctional nests of melanocytes would appear as darker and wider lines on dermoscopy [1]. The atypical network is often seen in melanoma and dysplastic nevi [2] .

Angulated lines/ Polygons

Angulated lines are geometrical lines in a zig-zag pattern, which may coalesce forming polygons. These structures are called rhomboids or zig-zag pattern (Kittler et al., 2016a) when observed on the face or neck and are associated with lentigo maligna (LM) (Schiffner et al., 2000; Slutsky and Marghoob, 2010). In other locations, the angulated lines appear to be larger than the rhomboids seen in LM and are highly suspicious of lentiginous melanomas from chronically sun-exposed skin (Jaimes et al., 2015). Histologically, the polygonal nature of these lines is still unknown. However, angulated lines seem to correspond to a flattened dermoepidermal junction (DEJ) with fewer and more blunted rete pegs due to a proliferation of atypical melanocytes at the DEJ together with a focal accumulation of melanophages in the superficial dermis. (Vanden Daelen et al., 2016). [3]

Angulated line pattern.jpg

Irregular blotches
Irregular dots/ globules
Irregular streaks/ pseudopods

Streaks are linear pigmented projections seen at the periphery of lesions.

Streaks schematic 25.jpg

Both pseudopods (streaks with bulbous projections at their tips) and radial streaming (streaks without bulbous projections at their tips) are considered to be streaks. Streaks in melanoma are usually observed only focally and asymmetrically at the lesion’s periphery and reflect the radial growth phase of the tumor. On the other hand, streaks that are distributed symmetrically around the entire perimeter of the lesion are seen mostly in pigmented spindle cell nevi (Spitz or Reed). Histologically, streaks represent confluent junctional nests of melanocytes.

Regression structures
Blue-white veil
Negative network (reticular depigmentation)

The “negative” of the pigmented network (also known as reverse or inverse network) consists of relatively lighter areas comprising the apparent grid of the network and relatively darker areas filling the apparent “holes”. The lighter grid lines tend to be serpiginous and the darker areas, when viewed in isolation, resemble elongated tubular or curved globules. Histopathologically, the negative network appears to correspond to thin elongated rete ridges accompanied by large melanocytic nests within a widened papillary dermis or to bridging of rete ridges. Although the negative network is highly specific for melanoma (95% specific), especially for a melanoma arising in a nevus, it can also be found in some Spitz nevi and rarely in other nevi, such as congenital nevi. In congenital nevi, the negative pigmented network is usually diffuse and symmetrical in its distribution. In contrast, the negative pigmented network seen in melanoma is often focal and asymmetrically distributed.

Crystalline structures
Atypical vascular pattern

Additional criteria

Superficial spreading melanoma

Dermoscopy significantly improves the sensitivity and specificity of clinicians for melanoma diagnosis.[4] The dual benefit of dermoscopy lays on its potential to allow the detection of clinically inconspicuous melanomas, while enabling the recognition of benign lesions that might look clinically worrisome, reducing, thus, the number of unnecessary excisions.[5]

Melanoma becomes clinically recognizable at a certain progression point, after acquiring one or more of the ABCD clinical criteria. At an earlier stage, melanoma is macroscopically undetectable, since it is small in size and symmetric in terms of shape and color. At such an early stage, dermoscopy often uncovers sub-macroscopic morphologic criteria that allow melanoma recognition.

The dermoscopic criteria of melanoma are a result of its asymmetric growth and vary among different subtypes of the disease. The main dermoscopic features seen in superficial spreading melanoma of the trunk and the extremities are: As a rule, dermoscopy of superficial spreading melanoma of the trunk and the extremities reveals asymmetry of shape, more than 2 colors (light brown, dark brown, black, blue, gray, red, white) and asymmetry of structures.[5][6] Furthermore, local dermoscopic features associated with melanoma are the following:

Dermoscopic features associated with melanoma.jpeg

In the real clinical setting, the dermoscopic diagnosis of melanoma is usually straight-forward, based on the immediate recognition of its morphologic asymmetry and/or a combination of the structures described above.[7][8][9] Obviously, the dermoscopic morphology of melanoma is less evident at an initial stage (melanoma in situ/early invasive), where only 1 (or even none) of these features might be present. The most frequent criteria of melanoma in situ are atypical network and regression.[10]

As the tumor progresses, more dermoscopic criteria develop and the diagnosis is usually straight forward, based on the immediate recognition of its morphologic asymmetry and a combination of the structures described above.[7][8][9] However, less morphologically evident melanomas do exist, and in such cases, an analytic approach of the lesion is required. The firstly introduced and more widely adopted method for analysing the morphology of a pigmented lesion is the so-called 2-step algorithm, but also other methods do exist.[5][11][12][13]

Here is one example of some dermoscopic features seen in superficial spreading melanoma:


===== Melanoma on sun damaged skin ===== Identifying melanomas located on chronically sun-damaged skin (CSDS) is challenging because their characteristics often clinically overlap with benign lesions. Dermoscopy has proven useful in detecting and differentiating melanoma from many benign lesions, including solar lentigo and seborrheic keratosis. The dermoscopic attributes associated with melanoma on sun-damaged skin of the face, primarily lentigo maligna are well described (see chapter). These descriptions may be dependent on the specific anatomic structure of the facial skin (ie, absence of rete ridge pattern and presence of pilosebaceous structures and hair follicles). The anatomy of sun damaged skin on other areas is different. This is characterized by atrophy of the epidemis and flattening of the dermoepidermal junction. This is the reason why melanoma on sun damaged skin looks different on non facial skin. Jaimes et al. [14] recently described 3 different dermoscopy patterns for this entity:

Focal islands of pigmentation.jpg

Focal islands of pigmentation The most frequent pattern is called "patchy peripheral pigmented islands’’, which consist of focal islands of pigmentation (network or structure-less areas) located towards the periphery of the lesion. Toward the center focal featureless areas, most often scar-like or hypopigmented, are observed. 13 (7%) of those melanomas had crystalline structures, and 21 (11.3%) revealed vascular blush, most commonly within the focal hypopigmented areas. This pattern was most frequently seen on the back (n = 43; 61.4%) and were rather large with an average size of 10.72 mm

Angulated line pattern.jpg

Angulated line pattern The second most common dermoscopic pattern is called ‘‘angulated line pattern’’; this was composed of angulated lines with or without the presence of granularity or circle within a circle and was most commonly seen on the upper extremities.

Tan structures with granularity.jpg

Tan structureless areas with granularity The third pattern, consisted of lesions with tan structureless areas and granularity. These lesions had the smallest average diameter (7.39 mm) and occurred most frequently on the back.

Non specific pattern.jpg

Non-Specific pattern 21.5% of the lesions in this series did not have one of the 3 pattern describes previously but showed granularity, atypical network, peripheral tan structureless areas, atypical aggregated dots/globules, dotted vessels, milky red areas/vascular blush, serpentine vessels, asymmetric perifollicular hyperpigmentation, angulated lines, crystalline structures, and scar-like areas, negative network, off-centered blotch, and blue-white veil. Melanomas with a nonspecific pattern were more frequently seen on the back.

Here is an example of a melanoma on sun damaged skin with granularity and patchy peripheral pigmented islands:

Melanoma in situ 69 yo man sun damaged arm dm bp-007.JPG
Amelanotic/ hypomelanotic melanoma

Amelanotic/hypomelanotic melanoma (AHM) represents 2-8% of all melanomas[15], but its real incidence is difficult to estimate because at the beginning it is often misdiagnosed and/or confused with inflammatory diseases, benign tumors and other malignant tumors (i.e. actinic keratosis, Bowen’s disease, basal cell carcinoma, keratoacanthoma, Merkel cell carcinoma, pyogenic granuloma, haemangioma, wart, etc). Definitely, if singly evaluated, the real prevalence of amelanotic melanoma is very low, since many of these tumors present a residual pigmentation that can be seen mostly at the periphery and should be considered hypomelanotic rather than amelanotic. The low or absent melanin production and the presence of regression are the two reasons why melanoma could be amelanotic or hypomelanotic; both these phenomena may even occur within the same lesion.

AHM has been classified in several variants:

  1. True amelanotic melanoma (melanoma not producing any trace of pigment)
  2. Hypomelanotic melanoma (with low production of melanin that may extend to the entire lesion)
  3. Partially pigmented melanoma(with a pigmentation occupying less than 25% of the lesion)
  4. Regressive melanoma (in advanced stages of regression)

AHM often occurs in sun-exposed skin of older people[15][16] and appears as a flat lesion, but more frequently as an elevated tumor, firm on palpation, and typified by rapid growth. This three characteristics (EFG: Elevation, Firmness, Growth) represent a precious clinical guide in melanomas without the classical ABCD clinical criteria[17][18].

By dermoscopy, the diagnostic clues for AHM are the vascular structures, often also difficult to detect because require a minimal pressure of the dermatoscope on the lesion to avoid the compression of the blood vessels[19]. As general rule, six main categories of vascular morphologies can be seen in tumoral lesions[20]: comma vessels (in intradermal nevi); dotted vessels (in melanocytic lesions, especially Spitz nevi and melanoma); linear–irregular vessels (in melanoma and other skin malignancies); arborizing vessels (in basal cell carcinoma); hairpin vessels (in keratinizing tumors, especially if surrounded by a whitish halo, and melanoma); and glomerular vessels (in Bowen’s disease). Moreover, also the following three specific global morphologies can be identified: crown vessels surrounding a white center, strawberry pattern and milky-red areas/globules[21][22][23] [24]. (Fig.1)

Figure 1: The most common vessels in dermoscopy.
Figure 1: The most common vessels in dermoscopy.

The most common vascular structures in AHM are dotted vessels, linear-irregular vessels, hairpin-irregular vessels, serpentine vessels or a combination of them (polymorphic vessels)[19]; also milky-red areas can be frequently visualized[15].Morphology of vessels modifies during tumor growth. In fact, in early stages, the vessels often appear short and homogenous in shape, while in the advanced tumors, they appear longer and irregular. In thin melanoma (less than 0.5 mm Breslow thickness) the vessels are usually point-like with a rather regular arrangement. Tumors of 0.5–2mm thickness show both point-like and hairpin vessels, again with a regular arrangement. When thickness is over 2 mm the hairpin loops are more twisted, splintered and irregularly distributed, while melanomas of more than 3 mm of thickness develop polymorphic vessels. A multicenter retrospective study from Menzies et al. evaluated several amelanotic and hypomelanotic melanomas to determine the diagnostic accuracy of various dermoscopic features[19]. Positive predictors included blue-white veil, scar-like depigmentation, multiple blue-gray dots, irregularly shaped depigmentation, irregular brown dots or globules, 5 to 6 colors within the same lesion and peripheral light brown structureless areas covering more than 10% of the lesion. Among vascular features, the positive predictors were predominant central vessels, milky red-areas, more than one shade of pink, and a combination of dotted and linear irregular vessels. The most significant negative predictors of melanoma were multiple (>3) milia-like cysts, the predominance of comma vessels with a regular arrangement, a symmetrical pigmentation, and regular and multiple blue-gray globules (Fig.2, 3,4,5,6,7).

Figure 2: Nodular hypomelanotic melanoma with hairpin, glomerular, linear irregular vessels (polymorphic vessels) and blue-white veil over a milky-red area.
Figure 2: Nodular hypomelanotic melanoma with hairpin, glomerular, linear irregular vessels (polymorphic vessels) and blue-white veil over a milky-red area.

Figure 3: Early invasive amelanotic melanoma with mainly dotted vessels irregularly distributed over a pinkish background.
Figure 3: Early invasive amelanotic melanoma with mainly dotted vessels irregularly distributed over a pinkish background.

Figure 4: Early invasive amelanotic melanoma with dotted vessels regularly distributed over a pinkish background (Spitzoid- looking melanoma).
Figure 4: Early invasive amelanotic melanoma with dotted vessels regularly distributed over a pinkish background (Spitzoid- looking melanoma).

Figure 5: More advanced hypomelanotic melanoma with polymorphous vessels. Blue-white veil, and remnants of pigment network and brown globules are also detectable.
Figure 5: More advanced hypomelanotic melanoma with polymorphous vessels. Blue-white veil, and remnants of pigment network and brown globules are also detectable.

Figure 6: Early invasive hypomelanotic melanoma with dotted vessels in the upper part and pigment network in the lower part of the lesion.
Figure 6: Early invasive hypomelanotic melanoma with dotted vessels in the upper part and pigment network in the lower part of the lesion.

Figure 7: Regressive hypomelanotic melanoma with linear-irregular vessels and a peripheral residual pigmentation.
Figure 7: Regressive hypomelanotic melanoma with linear-irregular vessels and a peripheral residual pigmentation.
Desmoplastic melanoma

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Blue-gray globules &dots.jpg
Nodular melanoma

Nodular melanomas (NMs) are defined as invasive melanomas without a radial growth phase. Specifically, they lack an in situ component beyond three rete ridges of the invasive vertical growth phase. While they represent only 14% of invasive melanomas, whereas they represent the majority of thick melanomas (>3 mm Breslow thickness).

Clinically, NMs may lack the “ABCD” features more typical of superficial spreading melanomas (SSMs) since they appear as a symmetric lesion.

The classic melanoma specific criteria are predominantly seen in SSMs but much less frequently in NMs.

Especially the features correlating with the radial growth of melanoma and pagetoid spread (pseudopods, radial streaming) as well as those criteria found in thin melanoma (such as atypical broadened network and the early regression feature of multiple blue-gray fine dots or peppering) are often lacking in NMs.

However, pigmented NMs more frequently have those dermoscopy features associated with thick melanoma[25] :

  • blue-white veil
  • multiple (5–6) colors
  • crystalline structures (seen only with polarized light)
  • atypical vascular patterns

In a more recent publication using multivariate analysis the following criteria were found to be highly significant for nodular melanoma[26]

  • asymmetric pigmentation
  • blue–black pigmented areas
  • homogeneous disorganized pattern
  • combination of polymorphous vessels and milky-red globules/areas
  • combination of polymorphous vessels and red homogeneous areas

Nodular melanoma schematic.jpg

Melanomas tend to have an asymmetric pigmentation pattern under dermoscopy. While most NM are asymmetric, 6% have a symmetric pattern [25] . Nevertheless, the majority of pigmented NMs can be diagnosed using standard dermoscopy criteria.

What is diagnostically problematic is the fact that a significant number (more than a third) of NMs are hypomelanotic or amelanotic. In these cases, atypical vascular patterns may be the only clues for the diagnosis of such lesions [25]. The most significant of these patterns are the combination of linear irregular and dotted vessels or linear irregular vessels as the predominant vessel type, greater than one shade of pink, milky red-pink areas and or globules, and hairpin vessels.

Nodular melanoma schematic 2.jpg

Melanoma on special locations

Melanoma in skin of color

Melanoma occurs less frequently in persons of color but is associated with higher rates of morbidity and mortality. In a systematic review performed by Higgins et al., the following conclusions were made: [27]

  • African Americans have deeper tumors at time of diagnosis in addition to increased rates of regionally advanced and distant disease. Lesions are generally located on the lower extremities and have an increased propensity for ulceration. Acral lentiginous melanoma (ALM) is the most common melanoma subtype found in AA patients.
  • In Hispanics, superficial spreading melanoma is the most common melanoma subtype. Lower extremity lesions are more common relative to Caucasians. Hispanics have the highest rate of oral cavity melanomas across all ethnic groups.
  • In Asians, acral and subungual sites are most common. Specifically, Pacific Islanders have the highest proportion of mucosal melanomas across all ethnic groups.

Local dermoscopic features described for melanoma in general (mostly studied in light skinned populations) are the following:

Current literature on melanoma in SOC:

December 2020, Pubmed search of dermoscopy melanoma “skin of color” comes up with 2 references only:[28][29] Note that none of the lesions were melanomas.

A similar search on “dermoscopy melanoma African” added this article:[30] performed in Brazil, 100 clinically suspicious cases, 79 were Clark naevi, 15 seborrhoeic keratoses, four blue naevi, one dermatofibroma and one melanoma. Darker pigmentation of the skin did not impede the identification of single dermoscopic features. With only one melanoma, it is hard to draw conclusions about sensitivity of the features described originally in lighter skin.

A similar search on “dermoscopy melanoma Asian” found 13 articles including some relating to Hispanic skin. Most of these articles dealt with ALM. The Asian population is clearly the most studied group among all types of skin of color for dermoscopy of melanoma. We will address the details under the ALM section.

False negative diagnosis

In situ melanoma. Main false negative diagnosis: Clark nevus The morphologic overlap between early melanomas and “atypical” nevi is also discussed in the chapter “false positive diagnosis”. It should be underlined that the majority of the known melanoma-specific dermoscopic criteria are usually absent in melanoma in situ.[31] Therefore, it might be possible that a melanoma in situ might be dermoscopically assessed as a nevus. To minimize this risk, management rules based on the overall patient’s context have been suggested.[9] Furthermore, 3 new predictors of melanoma in situ have been recently introduced: dark, irregularly-shaped small structures (DISSS), prominent skin markings and angulated lines (polygons), the latter 2 mainly seen on sun-damaged skin.

Nevoid melanoma. Main false negative diagnosis: Dermal nevus Nevoid melanoma represents a rare melanoma subtype that clinically and histopathologically mimics a nevus. Dermoscopy might improve the recognition of nevoid melanomas, since some of them display a multicomponent pattern, which is considered suggestive of melanoma.[32] A proportion of nevoid melanomas, however, mimic dermoscopically a dermal nevus, displaying a relatively symmetric globular pattern. A possible clue might be the presence of polymorphic vessels instead of the “comma” vessels that would be expected in a dermal nevus.

Spitzoid melanoma. Main false negative diagnosis: Spitz/Reed nevus The potential of spitzoid melanoma to perfectly mimic a Spitz or Reed nevus has been extensively reported in the literature. Due to this significant morphologic overlap, specific strategies and guidelines on the management of spitzoid-looking tumors have been released by the International Dermoscopy Society.[33]

Verrucous melanoma. Main false negative diagnosis: Seborrheic keratosis Occasionally, melanoma might have a verroucous surface, because of hyperkeratosis and epidermal hyperplasia, acquiring an overall aspect similar to a seborrheic keratosis. A recent study highlighted that the majority of seborrheic keratosis-like melanomas can be uncovered by dermoscopy, since they display one or more of the following melanoma specific criteria: blue-white veil, pseudopods, streaks, atypical network and the blue-black sign.[34] However, approximately 20% of melanomas displayed dermoscopic features suggestive of seborrheic keratosis (false negative). The multivariate analysis revealed than only the blue-black sign remained a potent melanoma-predictor.

Reggressive melanoma. Main false negative diagnosis: Lichen planus-like keratosis (LPLK) Regression structures (white scar-like depigmentation and blue/gray granules/peppering) are included among the classic melanoma-specific criteria. However, in fact they represent criteria suggestive of the regression process, since very similar features are seen in regressive nevi and regressive seborrheic keratoses/solar lentiggines (LPLK). The feasibility to accurately classify a regressive lesion depends on the stage (extension) or regression. When the regression is partial and parts of the initial tumor are still present, then the diagnosis might be possible. If, in contrast, the regression is so extensive that no remnants of the primary tumor are evident, a safe diagnosis is impossible. The only safe strategy to address this problem is to perform a biopsy/exciosion of any fully regressive lesion.[35]

Amelanotic melanoma. Main false negative diagnosis: Pyogenic granuloma, inflammatory nodules et al. Amelanotic melanoma represents the most important trap for clinicians. In fact melanotic melanoma is usually featureless, but very rarely acquires a pattern highly suggestive of a benign tumor. Strategies on how to approach non-pigmented tumors can be found in other chapters. The main false negative diagnosis of melanotic melanoma is pyogenic granuloma, which led experts to suggest that the diagnosis pyogenic granulomas should be histopathologically confirmed in all (if possible) cases.

False positive diagnosis

Reticular SK and solar lentigo (SL). Main false positive diagnosis: melanoma Comparing to the network of melanocytic tumors, the network of reticular SK and SL is characterized by thinner lines and larger holes and ends abruptly at the periphery without fading out.

This solar lentigo has areas of network with some heterogeneity in the network. Such a lesion could be confused for an early melanoma.

Melanoacanthoma. Main false positive diagnosis: melanoma Melanoakanthoma is a heavily pigmented variant of SK, which is often “false positive” dermoscopically, mainly because the presence of intense pigmentation does not allow the visualization of SK-related dermoscopic features (5).

Melanoacanthoma is a heavily pigmented seborrheic keratosis

Irritated SK. Main false positive diagnosis: SCC, melanoma Irritated SK lacks the typical SK-related dermoscopic features (comedo-like openings, milia-like cysts etc) and is typified by vessels of various morphologies (hairpin, glomerular, tortuous) which are usually surrounded by whitish halos. The presence of perivascular whitish halos is known to represent a sign of keratinization which might be seen in several keratinizing tumors including squamous cell carcinoma, common warts and SK. Some clues to discriminate between SCC and irritated SK do exist: irritated SK is usually characterized by a symmetric distribution of structures (vessels surrounded by halos), in contrast to the more uneven arrangement of features in SCC. Furthermore, SCC rarely displays multiple white halos surrounding vessels as the only dermoscopic feature. If present, usually white halos in SCC are combined with white circles surrounding hair follicles or structureless whitish areas.

Irritated seborrheic keratosis with numerous vessels. The presence of keratin and vessels may lead to the incorrect diagnosis of squamous cell carcinoma.

Clonal SK. Main false positive diagnosis: BCC, melanoma This peculiar SK variant dermoscopically displays globular structures of brown or blue-gray color, which might be misinterpreted as irregular globules of a melanoma or blue-gray ovoid nests of a basal cell carcinoma (4-6). The sharp demarcation of the lesion at the periphery or the co-existence of SK-specific structures (ex. milia-like cysts) might help to recognize SK.

This is a clonal linear epidermal nevus / seborrheic keratosis
Clonal seborrheic keratosis that could be mistaken for a BCC
This clonal seborrheic keratosis has features overlapping with melanoma and basal cell carcinoma

Lichen planus-like keratosis (LPLK). Main false positive diagnosis: Melanoma LPLK is a term used to describe a SK/SL undergoing regression. LPLK dermoscopically displays the usual features associated to the regression process, namely blue-gray granules and white color. The clinically relevant problem is that precisely the same features typify also regressive nevi and melanomas. In early stages of regression of a LPLK, the typical features of SK/SL might still be present in some parts of the lesion, allowing its recognition. However, the presence of extensive regression usually does not allow a safe recognition of the pre-existing lesion. Therefore, lesions displaying extensive regression should always be histopathologically examined.

lichen plans like keratosis like features suggestive of an amelanotic melanoma or basal cell carcinoma
This lichen planes like keratosis has shiny white lines. This lesion has overlapping features with amelanotic melanoma and superficial basal cell carcinoma.

Targetoid hemosiderotic hemangioma (THH). Main false positive diagnosis: Melanoma, Kaposi sarcoma. THH is a peculiar lymphatic malformation usually with a targeted appearance. Dermoscopically, the majority of THH are typified by the presence of central red and/or dark lacunae and a peripheral red-brownish homogeneous area

Thrombosed angioma. Main false positive diagnosis: Melanoma Occasional thrombosis might occur in any angioma and is often combined with bleeding. Thrombosed blood is black-colored dermoscopically and might be restricted within the lacunas or be more diffuse.

Angiokeratoma. Main false positive diagnosis: Melanoma, BCC Dark lacunae, red lacunae and whitish veil are the most frequent dermoscopic criteria of angiokeratomas. Dark lacunae represent the most useful feature, having a sensitivity of 93.8% and a specificity of 99.1% for the diagnosis of angiokeratoma when compared with several other benign and malignant tumors.

Angiokeratoma can sometimes mimic a melanoma or basal cell carcinoma

Atypical dermatofibrmas. Main false positive diagnosis: Melanoma In addition to the aforementioned “typical” dermoscopic criteria, several other dermoscopic patterns have may be seen in DF: central white network and peripheral network, central homogenous pigmentation and peripheral network, central white patch and peripheral homogeneous pigmentation, white network throughout the lesion etc.

Hemosiderotic and aneurysmal DF. Main false positive diagnosis: Melanoma The main dermoscopic features of hemosiderotic and aneurysmal DF are a central homogenous bluish to red-brownish area with white linear structures and a peripheral delicate pigment network with vessels of various morphologic types.

Sweat gland tumors. Main false positive diagnosis: BCC, melanoma, SCC Eccrine poroma is the most well-studied sweat gland tumor and has been suggested to display a great dermoscopic variability, potentially mimicking all known malignant tumors.

Clark nevus (dysplastic nevus). Main false positive diagnosis: melanoma The clinical, dermoscopic and histopathologic overlap between some Clark nevi and early melanoma is very well-known. Clark nevi may display one or more of melanoma-specific criteria, such as asymmetry of colours and/or structures, atypical netwok, irregular globules, regression etc. This problem is particularly relevant in patients with the so-called atypical mole syndrome. The most efficient (and safe) strategy to reduce the number of excisions of nevi is the application of the comparative approach, which is based on the notion that the majority of an individuals’ nevi are morphologically similar among them, while melanoma deviates this “signature pattern”. Therefore, the comparative approach suggests that, in individuals with multiple atypical moles, instead of trying to measure the degree of each mole’s atypic, one should search for the morphologically different lesion (“ugly duckling”).

Spitz and Reed nevus. Main false positive diagnosis: melanoma Three dermoscopic patterns of Spitz and Reed nevi have been thoroughly studied. Reed nevi are typified by the so-called “starburst” pattern, consisting of a dark brown/black/blue centre and symmetrically distributed peripheral streaks or pseudopods. Pigmented Spitz nevi are characterised by the presence of symmetrically distributed globules and white spaces among them (inverse network or reticular depigmentation). Non-pigmented Spitz nevi are typified by the presence of symmetrically distributed vessels (usually dotted) and white spaces among them (inverse network). All the aforementioned patterns are characterised by a symmetric distribution of structures. The same structures (streaks, pseudopods, vessels, inverse network), if not symmetrically distributed, represent melanoma criteria (irregular streaks, irregular pseudopods, atypical vessels etc). Therefore, the morphologic overlap between Spitz/Reed nevi and melanoma is obvious, since any Spitz/Reed nevus deviating the perfect symmetry is, by definition, looking like melanoma. The problem of how to manage a spitzoid-looking lesion gets even more complicated by the fact that spitzoid melanomas perfectly mimicking a symmetric Spitz/Reed nevus do also exist. To address this problem, the International Dermoscopy Society has recently released management guidelines (see “Management of Spitz nevi”).

Combined nevus. Main false positive diagnosis: melanoma The co-existence of 2 different melanocytes proliferations within the same nevus results in a peculiar, asymmetric dermoscopic pattern, often resulting in a false positive diagnosis of melanoma. The most frequent combination (blue nevus plus compound/dermal nevus) is dermoscopically characterized by peripheral network or globules and a central homogenous blue area. Of note, the blue area is often rather eccentric than central.

Reccurent nevus. Main false positive diagnosis: melanoma The safest way to classify a recurrent pigmentation within/on a scar is to re-evaluate the histopathologic report of the primary tutor (if available). If not, the differential diagnosis between recurrent nevi and recurrent melanoma is based on the time of recurrence and the precise distribution of the pigmentation. Specifically, nevi typically recur quickly (up to 6 months after excision) and the recurring pigmentation is restricted within the scar of the previous excision. In contrast, melanoma usually recurs several months to years after excision and tends to expand beyond the borders of the scar onto the normal skin.

Sclerosing nevi with pseudomelanomatous features. Main false positive diagnosis: melanoma This peculiar nevus subtype might clinically and histopathologically mimic regressive melanoma. Dermoscopically, nevi with regression-like fibrosis display both white and blue/gray (peppering) regression structures that usually extend on 10% to 50% of lesion’s surface), without any other melanoma specific criteria. Typically the regression area is located in the centre of the nevus.

Dermatopathological correlation

Podcasts, videos


This chapter is based on the previous Melanoma chapter which can be found here:

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