Module 16: Acquired Melanocytic Nevi

Melanocytic nevi are the most common skin lesions encountered during total body skin examinations and represent the primary differential diagnosis of early presentations of cutaneous melanoma. Their accurate recognition is critical for efficient skin cancer detection. Most nevi can be correctly identified after careful clinical and dermatoscopic evaluation combined with integration of patient- and lesion-related factors such as age, anatomic location, skin color, and clinical history.

Symmetry in dermatoscopy refers to the regular distribution of colors and structures within the lesion, evaluated across two axes. Critically, the border, shape, silhouette, and size of the lesion do not factor into this determination. Therefore:

• A lesion with an irregular silhouette but a regular distribution of uniformly brown pigment network is clinically asymmetric but dermatoscopically symmetric.
• A lesion with a regular silhouette but an eccentric pigment blotch or atypical network is clinically symmetric but dermatoscopically asymmetric.

This distinction is fundamental: dermatoscopic symmetry is a more reliable diagnostic feature than clinical border regularity/irregularity.

Melanocytic nevi exist along a histopathologic spectrum based on the location of nevus cell nests:

Nevus Type	Location of Melanocytes	Typical Pattern
Junctional nevus	Epidermis (rete ridges/DEJ)	Reticular (pigment network)
Compound nevus	Epidermis + dermis	Mixed patterns (reticular + globular)
Intradermal (dermal) nevus	Dermis only	Globular, cobblestone, homogeneous; comma vessels

Two classical subtypes of intradermal nevi, named after their original describers:

• Miescher nevus: Dome-shaped papule found predominantly on the face (91% of Miescher nevi are facial). Nevus cells extend endophytically in a wedge pattern, often reaching the deep reticular dermis. Diameter typically 4--6 mm. Dermoscopically: homogeneous pattern with comma vessels, golden-brown halo. Brown to skin-colored. Stable over lifetime. No reports in the literature of melanoma arising in a Miescher nevus.

• Unna nevus (papillomatous nevus): Sessile to pedunculated papule found predominantly on the trunk. Strikingly exophytic, with a papillomatous surface resembling a fibroepithelial polyp. Nevus cell nests do not reach the reticular dermis (in contrast to Miescher type). Dermoscopically: homogeneous, globular, or cobblestone pattern; comma vessels stereotypic; keratin-filled invaginations resembling comedo-like openings; deep sulci. Almost one-third of Caucasians have at least one Unna nevus.

Most individuals have nevi that resemble each other -- a phenomenon described as "moles breed true" or the signature nevus concept. Each patient has a characteristic dermoscopic "signature" that their nevi share. This observation enables:

• Identification of morphologic outliers: A lesion that does not match the patient's signature pattern is an "ugly duckling" and should be viewed with suspicion.
• The ugly duckling sign: A major factor of efficiency in melanoma detection. Lesions that differ from the predominant nevus pattern in a given individual warrant closer scrutiny or biopsy.

Term	Definition
Pigment network (lines, reticular)	Grid-like pattern of interconnecting pigmented lines surrounding hypopigmented holes; corresponds to pigmented melanocytes along epidermal rete ridges
Negative pigment network	Serpiginous interconnecting broadened hypopigmented lines surrounding elongated and curvilinear globules; seen in Spitz/"spitzoid" nevi and melanoma
Globules (clods, brown, round/oval)	Round to oval brown structures with minimal variability in color, size, and shape; represent dermal nests of melanocytes
Cobblestone globules	Larger, closely aggregated, somewhat angulated brown-gray structures; represent large nevomelanocytic nests in upper and deeper dermis
Regular blotch	Central structureless hyperpigmented zone surrounded by typical pigment network
Black lamella	Regular blotch composed of melanized stratum corneum that can be removed by tape-stripping
Comma vessels	Linear, curved, short vessels characteristic of dermal nevi
Streaks (starburst)	Radial linear extensions at the lesion edge; composed of radial streaming or pseudopods
Pseudopods	Bulbous, often kinked projections at the lesion edge associated with a network or solid tumor border
Peripheral globules	Single rim of small brown globules surrounding a central pattern; marker of nevus growth
Target dots / target network	Dots located in the center of hypopigmented spaces between reticular lines; suggestive of congenital origin
Targetoid vessels	Red dots (vessels) in the center of hypopigmented spaces between reticular lines
Wobble sign	Horizontal back-and-forth motion of dermatoscope causes intradermal nevi to wobble (vs. flat lesions that slide)

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The majority of melanocytic nevi reveal symmetry of colors and structures across two axes and can be categorized into easily recognizable, reproducible patterns based on color and distribution of structures. The literature identifies the following principal patterns:

1. Reticular / patchy reticular
2. Globular (including cobblestone variant)
3. Peripheral reticular with central globules
4. Homogeneous
5. Starburst
6. Peripheral globular
7. Two-component
8. Multicomponent

4.2.1 Histopathologic Basis

The lines of the pigment network represent pigmented melanocytes/nevus cells and melanized keratinocytes in or along the epidermal rete ridges. The holes of the network are created by the relative paucity of pigment in the suprapapillary epidermal plate overlying the dermal papillae. Histopathologically, reticular nevi have prominent junctional or lentiginous components.

4.2.2 Variants

• Diffuse reticular pattern: Network distributed evenly throughout the entire lesion. Minimal variability in the width and color of network lines and in the sizes of hypopigmented holes. Characteristically, the network fades into the surrounding skin at the periphery.
• Patchy reticular pattern: Network scattered in patches throughout the lesion. Network with broken lines and incomplete connections is often present (sometimes referred to as "branched streaks").
• Peripheral reticular with central hypopigmentation: Common in fair-skinned individuals. Network lines are tan to light brown, with a central structureless hypopigmented area.
• Peripheral reticular with central hyperpigmentation: Common in darker-skinned individuals. Network lines are dark brown to black, with a central structureless hyperpigmented area (regular pigment blotch). Occasionally, this hyperpigmented area is melanized stratum corneum ("black lamella") that can be removed by tape-stripping, revealing the underlying regular network.

4.2.3 Skin Phenotype Influence

• Fair skin: Network lines are tan to light brown; central hypopigmentation is common.
• Dark skin: Network lines are dark brown to black; central hyperpigmentation is common.

4.2.4 Anatomic and Demographic Distribution

Reticular patterned nevi can be found anywhere on the trunk and extremities with no anatomic site predilection. They are the most prevalent nevi pattern in adults.

Check Your Understanding

What are the main dermoscopic patterns seen in acquired melanocytic nevi?

The main patterns include reticular (pigment network), globular (aggregated round structures), homogeneous (uniform structureless pigmentation), starburst (symmetrical radial projections), and combinations thereof. The specific pattern correlates with the histologic architecture and maturation of the nevus.

Clinical Scenario

A 32-year-old woman presents for a skin check. She has numerous nevi on her trunk, most showing a regular reticular pattern with thin brown lines fading at the periphery. One 7 mm lesion on her left shoulder shows a homogeneous blue-gray pattern that differs markedly from all her other nevi.

What concept guides management, and what is the likely diagnosis of the outlier?

Ugly Duckling Sign -- Blue Nevus vs. Melanoma

The patient's "signature nevus" pattern is reticular, so a homogeneous blue-gray lesion is a dermoscopic outlier (ugly duckling sign). The differential diagnosis includes blue nevus (benign, homogeneous blue structureless pattern) and nodular melanoma. The ugly duckling sign warrants closer evaluation: a stable, symmetric, structureless blue lesion may be monitored, but any asymmetry, regression structures, or atypical features should prompt biopsy.

4.3.1 Description and Histopathologic Basis

The globular pattern presents with round to oval, brown globules representing dermal nests of melanocytes. The most common presentation is globules diffusely and evenly present throughout the lesion, with minimal variability in color, size, and shape (diffuse globular pattern).

4.3.2 Cobblestone Variant

Cobblestone globules are a variant characterized by larger, closely aggregated, somewhat angulated brown-gray structures reminiscent of cobblestones. Histopathologically, these large globules correspond to large nests of nevomelanocytes in the upper and deeper parts of the dermis (dermal nevi or small congenital nevi). It is not uncommon to see both regular globules and cobblestone globules in the same lesion.

4.3.3 Anatomic and Demographic Distribution

Globular patterned nevi are most commonly found on the trunk, particularly the upper trunk. They are one of the most common nevi patterns in children but can be seen at any age.

4.3.4 Dermal Nevi (Unna/Miescher Types) -- Dermoscopic Challenges

Variants of globular and cobblestone nevi are clinically recognized as dermal nevi, Unna or Miescher types. These nevi can be diagnostically challenging because they often reveal:

• Asymmetry of colors and structures
• Irregularly distributed globules or brown-gray structureless areas

Helpful recognizing features include:

• Typical background brown to flesh-colored appearance
• Presence of comma-like vessels (linear, curved, short vessels)
• Arborizing vessels that appear out of focus and dull red (in contrast to the bright red, sharply focused arborizing vessels of basal cell carcinoma)
• Comedo-like openings, milia-like cysts, and terminal hairs

Wobble sign: Placing a dermatoscope on the lesion and applying horizontal pressure in a back-and-forth motion will show that an intradermal nevus wobbles, whereas lesions without a dermal component will slide. This is a useful diagnostic maneuver.

Key Takeaways

• Reticular (network) pattern nevi show a regular pigment network of uniform brown lines fading at the periphery, corresponding to melanocytes along regular rete ridges.
• Globular pattern nevi feature round brown clods distributed symmetrically, representing dermal melanocytic nests; this pattern is common in children and indicates growth.
• Homogeneous pattern nevi show diffuse brown structureless pigmentation without network or globules, typically seen in dermal or combined nevi.

This nevus type consists of a central portion showing a globular pattern (which may be elevated, representing a dermal component) surrounded by a peripheral flat portion composed of reticular pigment network.

• Clinically, some of these lesions correspond to the "fried egg" nevus type (see eclipse nevi below for the intradermal nevus variant of this morphology).
• These nevi are often large and more frequently encountered on the trunk or scalp than on the extremities.

Check Your Understanding

What is the 'ugly duckling sign' in dermoscopy, and why is it clinically important?

The ugly duckling sign refers to a nevus that looks different from the patient's other nevi -- the dermoscopic 'outlier.' Most of a patient's nevi share a similar dermoscopic pattern (the patient's 'signature pattern'). A lesion that deviates significantly from this pattern warrants closer evaluation because melanoma tends to lack the organized pattern seen in an individual's benign nevi.

4.5.1 Description

The homogeneous pattern is characterized by a paucity or total lack of discernible structures. Color can be tan, light brown, pink, or blue.

4.5.2 Color-Specific Associations

• Homogeneous blue pattern: Corresponds to a blue nevus.
• Homogeneous tan, light brown, or pink pattern: Most frequently encountered in fair-skinned individuals.

4.5.3 Diagnostic Challenges

Homogeneous nevi can be a significant diagnostic challenge because they may simulate:

• Spitz nevi
• Hypomelanocytic/amelanotic melanoma

Worrisome features in a homogeneous lesion include: vascular blush/erythema, dotted vessels alone or in combination with comma/linear/serpentine vessels, or nonspecific shades of structureless brown pigmentation.

4.5.4 Clinical Context Is Essential

Evaluation must always be performed in the individual's clinical context:

• A solitary homogeneous pink lesion in a darker-skinned individual should be viewed with caution.
• Numerous homogeneous pink lesions with polymorphous vessels in a red-haired patient may be a normal finding (signature nevus pattern).

4.6.1 Definition

The starburst pattern is specific to Spitz and Reed nevi. It manifests in two forms:

1. Peripheral tiered globules: Globules stacked one on top of the other at the lesion edge.
2. Circumferential streaks: Radial streaming or pseudopods around the entire perimeter.

4.6.2 Diagnostic Caution

Although the starburst pattern with peripheral tiered globules is commonly seen in Spitz nevi, it can also be seen in atypical/dysplastic nevi with spitzoid features. Critical caution: Lesions with a starburst pattern presenting in adolescents or adults, even when completely symmetric, should be viewed cautiously because melanoma can present with this pattern.

Check Your Understanding

How does the dermoscopic pattern of acquired nevi change with anatomic site?

Nevi on different body sites display characteristic patterns: trunk and proximal extremities favor reticular patterns; face shows a pseudo-network pattern; palms and soles show parallel furrow, lattice-like, or fibrillar patterns; and nail matrix nevi produce longitudinal melanonychia with regular brown lines. These site-specific patterns must be recognized to avoid misdiagnosis.

A single rim of small, brown peripheral globules surrounding a reticular, homogeneous, or globular center is characteristic of growing nevi. Histopathologically, these peripheral globules correspond to small junctional nests of melanocytes at the tips of rete ridges, present at the edge of junctional or compound nevi.

4.7.1 Age-Related Significance

• Adolescents and young adults: This pattern is common, particularly among individuals with increased total body nevus counts. Typically benign.
• Adults: This pattern is rare. A lesion with a peripheral globular pattern in an adult, especially if solitary, should be examined with caution and biopsy considered to rule out melanoma.
• Key principle: The likelihood of a lesion with a peripheral globular pattern being melanoma increases with age.

4.7.2 Always Examine the Central Component

One must always carefully examine the central component of a lesion with a peripheral rim of globules for melanoma-specific structures. If present, biopsy should be strongly considered regardless of patient age.

4.7.3 Natural History -- Growth and Senescence

Longitudinal studies have revealed that growing nevi with a peripheral rim of small brown globules show symmetric enlargement over years until senescence, at which point the peripheral rim of globules is no longer visible. This progression from active growth to quiescence is a normal biological pattern.

Key Takeaways

• Combined pattern nevi (e.g., reticular center with globular periphery) are common and benign; symmetry is the key reassuring feature.
• Nevus patterns vary predictably by anatomic site: reticular on trunk, globular on face and scalp in children, starburst on extremities (Spitz), and parallel furrow on acral skin.
• Special site nevi (genital, breast, scalp, acral) may show features that mimic melanoma in other locations; site-specific criteria must be applied.

Clinical Scenario

A 16-year-old boy presents with a 6 mm brown lesion on his upper back that has been slowly and symmetrically enlarging over the past year. Dermoscopy shows a central reticular pattern with a single rim of small brown globules at the periphery. There is no atypical network, regression, or blue-white veil.

What is the diagnosis, and does this lesion require biopsy?

Growing Compound Nevus with Peripheral Globular Pattern

A peripheral rim of small brown globules surrounding a reticular center is characteristic of a growing nevus. In an adolescent, this is a common and typically benign finding, especially when symmetric with no melanoma-specific structures. Monitoring is appropriate. However, the same pattern in an adult (especially over age 40) would be rare and suspicious, warranting biopsy. The key principle: the likelihood of a peripheral globular pattern representing melanoma increases with age.

Two-component nevi reveal two different structures arranged in two halves of the lesion:

• Reticular-globular
• Reticular-homogeneous
• Globular-homogeneous

This can represent a collision of two different nevi, usually in individuals with many lesions. However, the possibility of malignant transformation (melanoma) should also be considered when confronted with lesions manifesting two distinctly different structures.

Check Your Understanding

What dermoscopic changes in an acquired nevus are considered 'benign evolution' versus 'worrisome change'?

Benign evolution includes symmetric, uniform growth and gradual overall lightening (global change). Worrisome changes include focal darkening, new asymmetric structures (streaks, irregular dots, regression), and emergence of blue-white structures or new colors not previously present. The key distinction is global/symmetric versus focal/asymmetric change.

Multicomponent nevi have three or more structures present, including network, globules, and structureless areas. The structureless areas may include hypopigmented areas (but not white scarlike areas) or hyperpigmented areas (such as blotches).

4.9.1 Symmetric Multicomponent Pattern

If structures are distributed symmetrically in at least one axis and in an organized manner, the lesion will usually prove to be a dysplastic nevus upon histopathological examination.

4.9.2 Asymmetric Multicomponent Pattern

If structures are distributed asymmetrically in a disorganized manner, or if melanoma-specific structures are present, the diagnosis of melanoma must be considered.

4.10.1 Acquired Nevi: Banal and Atypical/Dysplastic

Banal (common) nevus: Clinically symmetric, uniformly pigmented (usually brown), flat, slightly elevated, or raised, with regular borders and a round or oval shape.

Atypical/dysplastic nevus: Acquired nevi with:

• Diameter >5 mm
• Prominent macular component
• Variable asymmetry, notched/irregular/ill-defined borders, and variegated colors

Some authors have proposed replacing the term "atypical/dysplastic nevus" with "large acquired melanocytic nevus" to more accurately reflect the etiology, morphology, and biology of this lesion.

4.10.2 Clinical Significance of Atypical/Dysplastic Nevi

1. Their presence is associated with melanoma risk in a dose-response manner, greatest in individuals with a family history of cutaneous melanoma.
2. Their morphology can resemble early presentations of melanoma on naked-eye examination, leading to unnecessary biopsies.
3. Critical point: The risk of melanoma arising in association with atypical/dysplastic nevi is exceedingly low. Prophylactic removal to prevent melanoma development is not effective, warranted, or recommended.
4. Although up to 30% of melanomas are histopathologically associated with a nevus, the associated nevus can be banal, atypical/dysplastic, or congenital.

4.10.3 Dermoscopic Patterns of Atypical/Dysplastic Nevi

No study has documented a dermoscopic structure or pattern specific to atypical/dysplastic nevi. Both banal and atypical/dysplastic nevi can display any of the principal dermoscopic patterns. As a result, the dermatoscopist recognizes the vast majority of atypical/dysplastic nevi as benign lesions that do not require biopsy.

However, a subset of indeterminate atypical/dysplastic nevi will be difficult or impossible to differentiate from melanoma. These often have:

• A multicomponent pattern
• One or more melanoma-specific structures

4.10.4 Melanoma-Specific Structures That Prompt Biopsy

The following structures are unusual in nevi and should generally prompt consideration of biopsy:

• Atypical streaks
• Shiny white structures
• Blue-white veil over raised areas
• Scarlike depigmentation
• Polymorphous vessels (specifically the combination of dotted and serpentine vessels)

Any melanoma-specific structure in a nevus should be viewed with caution, prompting consideration of monitoring, biopsy, or another diagnostic procedure (e.g., reflectance confocal microscopy).

Clinically, a growing nevus is a lesion increasing in surface area over time. Digital dermatoscopic imaging revealed that nevi with a peripheral rim of small brown globules frequently increase in size -- but not all growing nevi display this pattern.

The central component of nevi with a peripheral rim of globules may be reticular, homogeneous, or globular. Histopathologically, peripheral globules correspond to small junctional nests of melanocytes at the tips of rete ridges.

Clinical significance by age:

• Common in adolescence and young adulthood, particularly in individuals with increased total body nevus counts.
• Rare in adults. A peripheral globular pattern in an adult (especially if solitary) warrants caution; biopsy must be considered.
• The likelihood of melanoma increases with age for lesions displaying this pattern.

Congenital melanocytic nevi (CMN) are determined in utero. Although most are present at birth, some are not apparent until the first 2 years of life (tardive CMN). Principal dermoscopic patterns include: reticular, globular, peripheral reticular with central globular, structureless/homogeneous brown, and multicomponent.

Dermoscopic clues suggesting congenital origin:

• Reticular network composed of thick linear network fragments resembling hyphal elements
• Cobblestone globules
• Target dots or target globules (dots or globules within the holes of pigment network)
• Milia-like cysts
• Hypertrichosis, often with perifollicular hyperpigmentation or hypopigmentation
• Dotted vessels in the hole of pigment network ("targetoid vessels" / "target network with vessels")

Key Takeaways

• Atypical nevi show reticular pattern with irregular network, eccentric hyperpigmentation, or regression-like areas but maintain overall structural organization.
• The multicomponent pattern (three or more distinct dermoscopic patterns in one lesion) raises concern for melanoma and warrants close monitoring or biopsy.
• Serial digital dermoscopy is the most effective tool for monitoring atypical nevi; any significant change at short-term follow-up (3 months) warrants excision.

4.13.1 Eclipse Nevi (Fried Egg Nevi)

The eclipse nevus is a compound nevus with a central portion resembling an intradermal nevus surrounded by a junctional component. Clinically, the tan elevated center and brown peripheral rim create the characteristic appearance.

Dermoscopic features:

• Elevated central part: Light brown to skin-colored with papillomatous surface forming a cobblestone pattern; short curved vessels (comma vessels) are often present.
• Pigmented periphery: Brown shades with reticular or homogeneous pattern.
• Rarely, the peripheral pigmentation is disrupted or shows streaks, creating a stellate appearance.

Location: Preferred anatomic site is the scalp, especially in children.

Management: The typical eclipse nevus is a benign melanocytic nevus that does not need to be excised. Somewhat irregular eclipse nevi can be monitored via digital dermoscopy. There is evidence that eclipse nevi can transform into pure intradermal nevi over time.

4.13.2 Cockade Nevi (Targetoid Nevi)

Cockade nevi reveal a targetoid pattern characterized by:

• A central pink to brown papule or macule
• An inner hypopigmented rim
• An outer pigmented rim

Dermoscopic features:

• Targetoid appearance with a darker central globular or homogeneous pattern
• Surrounded by a hypopigmented homogeneous structureless inner rim
• And a peripheral darker reticular outer rim

Location: Often found on the scalp of children and adolescents.

Histology: Central portion corresponds to a compound nevus; peripheral portion shows a nonpigmented junctional nevus pattern.

4.13.3 Halo Nevi (Sutton Nevi)

Halo nevi, also known as Sutton's nevi or leukoderma acquisitum centrifugum, are nevi surrounded by a rim of depigmentation that undergo progressive involution with eventual total disappearance. They represent a T-cell immune-mediated process of nevus involution.

Epidemiology: Most commonly found on the trunk (particularly the back) of younger individuals, with or without a history of atopic dermatitis or autoimmune disorders (e.g., vitiligo). Halo nevi persist an average of 8 years before re-pigmentation occurs.

Dermoscopic patterns (from Chapter 7b and 7f):

• Most common: homogeneous-globular (42%)
• Followed by: homogeneous (23%)
• Then: globular (17%)
• Reticular patterns are uncommon (7%) -- melanoma should be ruled out in halo nevi with reticular patterns.

Dermoscopic characteristics:

• Symmetric white structureless area surrounding central dots/globules, homogeneous tan pigmentation, and/or gray dots/granules
• After complete involution of the nevus, a pink central area can be observed

Caution: The presence of a white halo surrounding a melanocytic lesion is not necessarily reassuring, as halo melanomas can occur. In melanoma, the halo tends to be irregular with asymmetry and unevenness in its distribution, and the central lesion shows a multicomponent pattern with one or more melanoma-specific structures.

4.13.4 Recurrent Nevi (Pseudomelanoma)

Recurrent nevi are proliferations of nevomelanocytes occurring after the partial surgical or traumatic removal of a melanocytic nevus. They most commonly occur on the back of young adults and often develop within the first 3 to 8 months after incomplete removal.

Dermoscopic characteristics:

• Pigmentation is usually confined to the scar and follows a centrifugal growth pattern
• Radial lines that are symmetric
• Pigment does not traverse from the scar into the surrounding normal skin
• Pigmented structures are arranged contiguously and centrifugally

Differentiating recurrent nevi from recurrent melanoma:

Feature	Recurrent Nevi	Recurrent Melanoma
Age	Younger patients	Older patients
Location	Torso	Head and neck
Average time to recurrence	8 months	25 months
Pigment	Confined to scar; contiguous	Traverses scar's edge; noncontiguous
Growth pattern	Centrifugal	Chaotic

4.13.5 Traumatized Nevi

Trauma most frequently occurs in papular or sessile melanocytic nevi and intradermal nevi, due to scratching, shaving, or clothing. After trauma, these nevi may display clinical and dermoscopic features worrisome for melanoma, including a dermoscopic appearance similar to that seen in recurrent nevi -- specifically, central brown streaks confined to the lesion in a predominantly structureless background.

4.13.6 Combined Nevi

A combined nevus is a melanocytic nevus showing histological characteristics of two or more nevus subtypes. The most common combination is a common blue nevus in association with a dermal and/or compound nevus.

Clinical and dermoscopic features:

• Asymmetry in shape and/or color, mimicking melanoma
• Dermoscopy shows both patterns intermingled
• Most frequently: structureless blue central area with peripheral pigmented network
• However, any combination of patterns can occur

4.13.7 Balloon Cell Nevi

A rare variant in which part of the cell population is composed of "balloon" cells, formed by vacuolization of melanocytes due to enlargement and disintegration of melanosomes. Typically appear on the head and neck in the first three decades of life.

Dermoscopic features:

• White globules (three or more aggregated white-to-yellow globules), corresponding to balloon cell clusters
• In contrast to milia-like cysts (more conspicuous with nonpolarized light), white globules in balloon cell nevi can be visualized equally well with polarized and nonpolarized light

4.13.8 Ultraviolet Radiation-Related Changes in Nevi

Melanocytic nevi can undergo morphological changes after exposure to ultraviolet radiation (natural or artificial):

• Increase in surface area and pigmentation
• Increase in quantity and size of dots/globules
• Blurring of pigment network lines
• Thicker pigment lines
• Scaling, erythema, dotted vessels
• Bluish-gray regression structures

Melanocytic nevi undergo predictable changes across the lifespan:

1. Childhood/Adolescence: Globular patterned nevi are common. Growing nevi with peripheral globules are frequently seen, particularly in individuals with high nevus counts.
2. Young Adulthood: Active growth continues. Reticular patterns become increasingly prevalent. Peripheral globular patterns remain common but begin to diminish.
3. Adulthood: Reticular patterned nevi are the most prevalent. Peripheral globular growth patterns become rare -- their presence in an adult should raise suspicion.
4. Senescence: Previously growing nevi enter quiescence. The peripheral rim of globules disappears. Dermal nevi may become more prominent. Some nevi involute completely (particularly halo nevi).

The decision to biopsy should integrate dermoscopic findings with clinical context. Biopsy should be considered when:

1. Melanoma-specific structures are present in a nevus:

• Atypical streaks (asymmetric radial extensions)
• Shiny white structures
• Blue-white veil over raised areas
• Scarlike depigmentation
• Polymorphous vessels (dotted + serpentine combination)
• Peppering/granularity in a disorganized distribution
• Eccentric blotch
• Negative pigment network

1. Asymmetric multicomponent pattern -- disorganized distribution of three or more structures

2. Peripheral globular pattern in an adult -- especially if solitary; likelihood of melanoma increases with age

3. Starburst pattern in an adolescent or adult -- even if symmetric, melanoma can present with this pattern

4. Ugly duckling sign -- a lesion that differs from the patient's signature nevus pattern

5. Halo nevus with reticular pattern -- reticular patterns are uncommon in halo nevi (only 7%) and warrant melanoma exclusion

6. Central component of a growing nevus contains melanoma-specific structures -- regardless of patient age

7. New or changing lesion in a patient with known melanoma risk factors

The most critical differential diagnosis in dermoscopy is distinguishing an indeterminate atypical/dysplastic nevus from early melanoma. Key differentiating principles:

Feature	Atypical/Dysplastic Nevus	Early Melanoma
Dermatoscopic symmetry	Symmetric distribution of colors/structures (at least in one axis)	Asymmetric distribution of colors/structures
Pattern organization	Organized multicomponent	Disorganized multicomponent
Pigment network	Regular or mildly atypical (uniform thickening)	Atypical (focal, irregular thickening/thinning)
Structureless areas	Hypopigmented areas without scarlike quality	Scarlike depigmentation, blue-white veil, regression
Streaks	Absent or symmetric	Asymmetric, segmental
Vessels	Absent or monomorphous	Polymorphous (dotted + serpentine)
Evolution	Stable or slowly changing in an organized manner	Changing with increasing disorganization
Context	Matches patient's signature pattern; multiple similar lesions	Ugly duckling; outlier among patient's nevi

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Key Takeaways

• A nevus showing symmetric structure, uniform pattern, and gradual peripheral fading can be confidently diagnosed as benign regardless of clinical appearance.
• The ugly duckling sign (a nevus that looks different from the patient's other nevi) is a powerful clinical adjunct to dermoscopy for identifying melanoma.
• Patients with dysplastic nevus syndrome require total body photography combined with sequential digital dermoscopy for effective long-term surveillance.

• Diameter >5 mm
• Prominent macular component
• Variable display of: asymmetry, notched/irregular/ill-defined borders, variegated colors

No dermoscopic structure or pattern is specific to atypical/dysplastic nevi. Both banal and atypical nevi can display identical dermoscopic patterns. The dermatoscopist's goal is not to classify a nevus as "atypical" per se, but to determine whether it is benign or suspicious for melanoma.

• Symmetric distribution of colors and structures in two axes
• Regular pigment network (uniform line thickness and hole size)
• Uniform globules (minimal variability in size, shape, and color)
• Network fading at periphery into normal skin
• Pattern consistent with patient's signature nevi
• Homogeneous brown/tan in a patient with multiple similar lesions

Structure	Significance
Atypical (asymmetric) streaks	Segmental radial projections suggestive of peripheral melanoma growth
Shiny white structures	Altered collagen associated with melanoma (and BCC, dermatofibroma)
Blue-white veil over raised areas	Orthokeratosis overlying dermal melanin; suggestive of invasive melanoma
Scarlike depigmentation (regression)	White structureless areas suggesting melanoma regression
Polymorphous vessels	Combination of dotted + serpentine vessels; highly concerning
Negative pigment network	Serpiginous hypopigmented lines; seen in Spitz nevi and melanoma
Eccentric blotch	Asymmetrically placed area of structureless hyperpigmentation
Peppering/granularity	Blue-gray dots suggesting dermal melanophages (regression)

Indeterminate lesion identified
 |
 v
Are melanoma-specific structures present?
 |
 Yes -+-> Consider biopsy (or RCM if available)
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 No --+-> Is the lesion an ugly duckling?
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 Yes -+-> Consider biopsy or short-term monitoring (3 months)
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 No --+-> Does it match the patient's signature pattern?
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 Yes -+-> Routine monitoring (6-12 months)
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 No --+-> Short-term monitoring (3 months) or biopsy

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