Module 21: Superficial Spreading Melanoma
1. Learning Objectives
After completing this module, the learner should be able to:
- Define superficial spreading melanoma (SSM) histologically and explain its distinction from other melanoma subtypes, including the requirement that the in situ component extend beyond three rete ridges of the invasive component.
- Recognize and describe the ten major dermoscopic features of SSM -- atypical network, streaks (pseudopods and radial streaming), atypical dots, atypical globules, regression structures, blue-white veil, multiple colors, negative network, peripheral light brown structureless areas, and shiny white lines -- and correlate each with its underlying histopathology.
- Differentiate thin (early) SSM from thick SSM based on dermoscopic feature prevalence and morphologic patterns.
- Apply sensitivity and specificity data for individual SSM dermoscopic features to guide clinical decision-making.
- Identify amelanotic and hypomelanotic SSM variants and describe the dermoscopic features that distinguish them from pigmented SSM and from other amelanotic malignancies.
- Recognize nevus-associated melanoma dermoscopically and explain the significance of features such as negative network, globules, and streaks in this context.
- Describe nested melanoma as a histopathologic variant of SSM and identify its hallmark dermoscopic pattern of atypical globules.
- Construct a differential diagnosis for SSM, distinguishing it from atypical (dysplastic) nevi, Spitz nevi, and pigmented basal cell carcinoma using dermoscopic criteria.
2. Prerequisites
Learners should have completed the following modules before beginning this module:
- Module 01: Introduction and Principles of Dermoscopy -- understanding of polarized vs. nonpolarized dermoscopy, basic equipment operation, and the optical principles underlying shiny white structures.
- Module 02: Histopathologic Correlations of Dermoscopic Structures -- knowledge of how dermoscopic structures (network, globules, dots, streaks, blotches, regression, blue-whitish veil, shiny white structures) correlate with histologic findings.
- Module 03: Pattern Analysis Revised -- familiarity with the basic elements of dermoscopy (lines, dots, clods, circles, pseudopods, structureless areas) and the Chaos and Clues short algorithm.
- Module 06: Chaos and Clues Triage Algorithm -- ability to assess chaos and apply the 8 clues to malignancy in clinical practice.
- Module 07: TADA and Other Triage Algorithms -- working knowledge of the ABCD rule, Menzies method, 7-point checklist, and other scoring systems for melanoma detection.
3. Key Concepts
3.1 Epidemiology
Superficial spreading melanoma (SSM) is the most common histological subtype of cutaneous melanoma, accounting for up to 66% of all cutaneous melanomas. It occurs on trunk and extremities and is the melanoma subtype most amenable to dermoscopic diagnosis due to its rich array of identifiable surface features.
3.2 Histologic Definition
SSM is defined as an invasive melanoma in which the in situ component extends beyond three rete ridges of its invasive component. It is characterized by:
- Pagetoid spread: Invasion of malignant melanocytes both singly and in nests upward within the epidermis.
- Radial junctional spread: Radial proliferation of malignant melanocytes at the dermal-epidermal junction (DEJ).
These two histologic hallmarks directly correlate with the dermoscopic features observed at the edge of a SSM.
3.3 Radial vs. Vertical Growth Phase
- Radial growth phase (RGP): The initial horizontal expansion of melanoma cells within the epidermis and superficial dermis. Dermoscopically manifest as atypical network, streaks, pseudopods, and peripheral structureless areas. Predominates in thin (early) SSM.
- Vertical growth phase (VGP): The subsequent downward invasion into the dermis. Dermoscopically associated with blue-white veil (melanin in mid-dermis with overlying orthokeratosis), shiny white lines (dermal fibrosis), and atypical vascular patterns. Predominates in thick SSM.
3.4 Key Terminology
| Term | Definition |
|---|---|
| SSM | Superficial spreading melanoma |
| DEJ | Dermal-epidermal junction |
| Pagetoid spread | Upward migration of malignant melanocytes through the epidermis |
| Radial growth phase | Horizontal expansion of melanoma cells |
| Vertical growth phase | Downward invasion of melanoma cells into the dermis |
| Breslow thickness | Measurement (in mm) from the granular layer to the deepest invasive melanoma cell |
| Multicomponent pattern | Dermoscopic pattern composed of three or more distinct structures |
| Negative network | Hypopigmented serpiginous lines surrounding elongated curvilinear pigmented globules |
4. Core Content
4.1 SSM as the Most Common Melanoma Subtype
SSM accounts for up to 66% of all cutaneous melanomas and is the subtype most readily identifiable by dermoscopy. The vast majority of pigmented SSMs are easily identified using established dermoscopic criteria. This is in contrast to nodular melanoma, which has fewer specific dermoscopic features. SSMs present on the trunk and extremities and typically display an asymmetric pattern that is often multicolored (scored from tan, dark brown, gray, black, blue, and red).
4.2 Dermoscopic Features of SSM
The following ten features represent the principal dermoscopic structures observed in SSM. Their morphologic definitions are provided in detail in Chapter 7 (Modules 15--20). Each feature is presented with its histopathologic correlation.
4.2.1 Atypical Pigment Network
Description: A web of lines of varying colors and thicknesses with holes of varying diameters. The color ranges from brown to black or gray, and the network can appear smudged or seemingly out of focus. This "broadened" network shows thickened, irregular lines with variable spacing between them.
Histopathologic correlation: Expansion of malignant melanocytes at the rete ridges.
Distribution: Often found focally at or near the edge of a SSM, rather than in a uniform distribution. Broadened network is usually seen focally rather than uniformly.
Clinical significance: The atypical network is often associated with the in situ component and may be the only specific feature of an early thin SSM. It is probably the most important (most sensitive) feature of early nonregressing SSM.
Reported statistics: Sensitivity 77.1%, Specificity 88.5%, PPV 67%, NPV 88%, OR 9.
4.2.2 Irregular Streaks (Pseudopods and Radial Streaming)
Description: Radial projections at the periphery of the lesion emanating from the tumor and radiating towards the surrounding normal skin. Streaks include both pseudopods (bulbous projections) and radial streaming (linear projections).
Histopathologic correlation: Confluent radial nests of melanoma at the DEJ.
Distribution: Located at the periphery, asymmetrically distributed (segmental rather than circumferential). When streaks are circumferentially distributed, consider Spitz/Reed nevus instead (starburst pattern).
Clinical significance: Streaks correspond to the radial growth phase of either a pigmented Spitz nevus or a SSM. Their presence in a SSM is indicative of active radial growth. In melanoma in situ, atypical streaks may be the predominant feature, with structural asymmetry particularly at the long edge of the lesion.
Reported statistics: Sensitivity 32%, Specificity 98.7%, PPV 76.5%, NPV 86%, OR 5.8.
4.2.3 Atypical Dots
Description: Black or brown round structures measuring less than 0.1 mm in diameter.
Histopathologic correlation:
- Black dots: Malignant melanocytes found at or near the stratum corneum.
- Multiple brown dots: Suprabasal epidermal malignant melanocytes representing pagetoid spread.
Distribution: Tend to be distributed randomly and are often found towards the periphery of the melanoma. They may or may not be associated with a network; if a network is present, it is often atypical.
Clinical significance: Multiple brown dots in a focal distribution are a classic finding representing pagetoid spread, one of the histologic hallmarks of SSM.
4.2.4 Atypical Globules
Description: Round to oval pigmented structures larger than 0.1 mm in diameter, with varying size, shape, and/or colors, distributed in a disorganized fashion within the lesion.
Histopathologic correlation: Nests of melanocytes at the DEJ or dermis. Color depends on location:
- Brown globules: Nests of melanocytes at the DEJ or superficial dermis.
- Blue globules: Nests of melanocytes located deeper in the dermis.
- White globules: Balloon cell changes in melanocytes.
Clinical significance: An atypical globular pattern with globules of different size, shape, and color that are irregularly distributed is the hallmark dermoscopic pattern of nested melanoma (a histopathologic variant of SSM).
Combined dots and globules statistics: Sensitivity 39.6%, Specificity 91.1%, PPV 79%, NPV 86%, OR 4.8.
4.2.5 Regression Structures
Regression structures encompass two distinct morphologic patterns:
A. Scar-like areas (white scar-like depigmentation)
- Description: Porcelain white structureless areas that are lighter than the surrounding normal skin.
- Histopathologic correlation: Dermal fibrosis.
- Reported statistics: Sensitivity 22.9%, Specificity 93.6%, OR 4.4.
B. Peppering (granularity)
- Description: Blue-gray fine dots.
- Histopathologic correlation: Melanophages or free melanin in the papillary dermis.
- Reported statistics: Sensitivity 21.9%, Specificity 92.6%, PPV 78%, NPV 62%, OR 3.5.
Combined significance: When peppering is seen in association with scar-like depigmentation, the combination can manifest a blue-whitish color. This blue-white pattern is usually seen in macular (flat) lesions, as opposed to the blue-white veil which is seen in raised or palpable lesions. Regression is a common occurrence in SSM.
Either regression structure: Sensitivity 41.7%, Specificity 89.2%, OR 7.8.
4.2.6 Blue-White Veil
Description: A confluent blue-white coloration overlying a raised or palpable area of the lesion.
Histopathologic correlation: Melanin in the mid-dermis with overlying epidermal compact orthokeratosis.
Clinical significance: Frequently observed in invasive melanomas. Its presence suggests vertical growth phase with dermal invasion. Blue-white veil is distinct from regression-associated blue-white color, which occurs in flat lesions.
Reported statistics: Sensitivity 11.4%, Specificity 99%, OR 13.
4.2.7 Multiple Colors
Description: Presence of more than one color within the lesion. Colors in SSM are scored from: tan, dark brown, gray, black, blue, and red. The presence of five to six colors is a significant finding.
Histopathologic correlation: Melanin at various levels within the dermis and epidermis. Each color reflects a specific depth and density of melanin or melanocytes:
- Tan/light brown: Melanin in the superficial epidermis.
- Dark brown: Melanin at the DEJ.
- Black: Melanin in the stratum corneum or upper epidermis.
- Gray: Melanin in the papillary dermis (melanophages).
- Blue: Melanin in the deeper dermis.
- Red: Increased vascularity or inflammation.
Clinical significance: Multiple (five to six) colors can be found even in relatively thin melanoma. Five to six colors is a highly significant positive feature in partially pigmented lesions.
4.2.8 Negative Network
Description: Hypopigmented serpiginous interconnecting lines that surround irregularly shaped pigmented structures resembling elongated curvilinear globules.
Histopathologic correlation: Bridging or elongation of rete ridges in association with large melanocytic nests in the papillary dermis.
Differential significance: Negative network can be seen in melanoma, Spitz nevi, dysplastic nevi, or melanomas arising in association with nevi. It is a particularly common structure observed in nevus-associated melanomas (OR 9.9 in one series).
Reported statistics: Sensitivity 34.6%, Specificity 95%, OR 1.8.
4.2.9 Peripheral Light Brown Structureless Areas
Description: Homogeneous light brown areas of variable size and shape, located at the periphery of the lesion and occupying more than 10% of its surface.
Histopathologic correlation: Relative flattening of the rete ridges in combination with a preponderance of single-cell pagetoid melanoma cells and pigmented keratinocytes rather than the formation of nests in the epidermis.
Clinical significance: A highly specific and sensitive indicator. Widespread peripheral light brown structureless areas are commonly observed in SSM and are important in differentiating atypical melanocytic nevi from thin melanomas.
Reported statistics: Sensitivity 62.5%, Specificity 96.1%, PPV 93.8%, NPV 73.1%, OR 27.9.
4.2.10 Shiny White Lines (Crystalline Structures / Chrysalis)
Description: Short, bright, white lines that are usually oriented parallel or orthogonal to each other. These structures can only be seen with polarized light dermoscopy.
Histopathologic correlation: Stromal alteration and dermal fibrosis.
Clinical significance: Shiny white lines correlate with an altered stromal matrix and are suggestive of invasion. Their detection requires polarized dermoscopy; they are invisible under nonpolarized dermoscopy.
Reported statistics: Sensitivity 9.7% (low sensitivity but high significance when present).
Check Your Understanding
What are the key dermoscopic features of early (thin) superficial spreading melanoma?
Early SSM shows an atypical pigment network (irregular meshes with thickened lines and variably sized holes), irregular dots and globules distributed asymmetrically, and asymmetry of structure and color. Regression structures (blue-white veil, peppering, scar-like depigmentation) may also be present even in thin melanomas.
Key Takeaways
- Superficial spreading melanoma (SSM) is characterized by an atypical pigment network with irregular line thickness, variable color (including gray), and abrupt peripheral termination.
- The atypical network reflects disorganized rete ridges with irregular melanocytic nests and pagetoid spread, distinguishing it from the regular network of benign nevi.
- Gray network lines indicate deeper melanin location (dermis) and suggest dermal invasion or regression, representing a more advanced stage than brown network.
Clinical Scenario
A 45-year-old man presents with a 9 mm asymmetric brown-black macule on his upper back. Dermoscopy reveals an atypical pigment network with broadened, irregular lines of variable color (brown to gray), irregular streaks (pseudopods) distributed asymmetrically at one edge, and scattered atypical brown-black dots of varying sizes.
What is the most likely diagnosis, and which features indicate early vs. advanced disease?
Superficial Spreading Melanoma (SSM)
The triad of atypical network, asymmetric streaks, and atypical dots is classic for SSM. The atypical network with gray coloration suggests some dermal invasion, while the asymmetric streaks indicate active radial growth at the periphery. The broadened network may be the only specific feature of early thin SSM. The absence of blue-white veil and regression structures suggests the melanoma is still relatively thin (radial growth phase predominant). Excisional biopsy is mandatory.
4.3 The Multicomponent Pattern
SSM characteristically manifests an asymmetric pattern that may be multicolored. When a lesion displays three or more distinct dermoscopic structures (e.g., atypical network + blue-white veil + regression + streaks), it is described as having a multicomponent pattern. This pattern is one of the strongest indicators of melanoma and serves as a criterion in multiple diagnostic algorithms (see Modules 06 and 07).
In SSM, the multicomponent pattern reflects the complex biology of the tumor: simultaneous radial and vertical growth, regression phenomena, and melanin production at multiple epidermal and dermal levels.
4.4 Thin Melanoma (In Situ and Early Invasive)
Thin SSM (in situ through approximately 1.0 mm Breslow thickness) presents with more subtle dermoscopic features. Key observations from the literature case series:
Features of thin SSM:
- Atypical (broadened) network may be the sole specific feature in the earliest lesions. It is the most sensitive feature of early nonregressing SSM.
- Subtle radial streaming and pseudopods -- often very subtle and easily overlooked.
- Multiple brown dots in a classical focal distribution representing pagetoid spread.
- Peripheral light brown structureless areas occupying more than 10% of the lesion surface.
- Regression structures (scar-like depigmentation and granularity) may be the predominant finding in regressing thin SSM.
- Five to six colors can be found even in relatively thin melanoma (Breslow thickness as low as 0.5--0.55 mm).
- Pin-point (dotted) vessels in hypomelanotic areas indicate melanocytic origin rather than melanoma-specific features, but their presence in a melanocytic lesion does not exclude melanoma.
- Negative network asymmetrically distributed, particularly in collision tumors (e.g., melanoma in situ with seborrheic keratosis).
Case examples from the text:
- In situ SSM: Broadened atypical network as the sole positive feature, with subtle pseudopods and radial streaming.
- Breslow 0.3 mm: Regression (scar-like depigmentation and multiple blue-gray dots) as the predominant features.
- Breslow 0.35 mm: Focal broadened network, sometimes with contiguous compound nevus.
- Breslow 0.4 mm: Atypical brown globules with peripheral light brown structureless areas and atypical vessels.
- Breslow 0.45 mm: Multiple brown dots, radial streaming, pseudopods, focal broadened network, blue-white veil, and five to six colors.
Check Your Understanding
How does the dermoscopic pattern of SSM change as the lesion progresses from thin to thick?
As SSM thickens, the atypical network progressively disappears (replaced by structureless areas), blue-white veil becomes more prominent (indicating dermal invasion), irregular blotches enlarge, and atypical vessels (dotted, linear-irregular) appear. In advanced lesions, the original network pattern may be entirely replaced by a multicomponent pattern with multiple colors.
4.5 Thick Melanoma Features
As SSM increases in Breslow thickness, additional features become more prominent:
- Blue-white veil becomes more prominent (reflecting deeper dermal melanin with overlying orthokeratosis).
- Shiny white lines (visible only under polarized dermoscopy) increase, correlating with dermal fibrosis from invasion.
- Multiple (five to six) colors become increasingly common.
- Peripheral black dots and globules are more frequently observed.
- Combination of dotted and serpentine/linear vessels within the same lesion is highly suggestive of melanoma.
- Linear irregular vessels become more prominent, especially in hypomelanotic areas.
- Extensive regression with widespread scar-like depigmentation.
- Pin-point (dotted) vessels combined with linear irregular vessels in the same lesion is predictive of melanoma.
Case examples from the text:
- Breslow 0.7 mm: Negative pigment network, scar-like depigmentation, blue-white veil, dotted vessels with linear irregular vessels.
- Breslow 0.8 mm: Broadened network, blue-white veil, peripheral black dots/globules, pseudopods, five to six colors.
- Breslow 1.1 mm: Scar-like depigmentation, blue-white veil, extensive dotted vessels in amelanotic component, peripheral light brown structureless areas.
- Breslow 1.2 mm: Multiple brown dots, blue-white veil, extensive negative pigment network, with associated compound nevus.
- Breslow 1.4 mm: Blue-white veil, peripheral black dots/globules, five to six colors, peripheral light brown structureless areas.
Key Takeaways
- Regression structures in SSM include white scar-like depigmentation (fibrosis) and blue-gray peppering/granularity (melanophages), often found together in melanomas with immune response.
- Irregular dots and globules distributed asymmetrically at the periphery of a lesion are a key feature of SSM, indicating irregular melanocytic nesting and pagetoid spread.
- Blue-white veil over raised areas of SSM corresponds to acanthotic epidermis with orthokeratosis overlying heavily pigmented dermal melanocytes and is strongly associated with melanoma.
4.6 SSM on Different Body Sites
SSM occurs predominantly on the trunk and extremities. While the dermoscopic features described above are generally applicable across body sites, certain considerations apply:
- On sun-damaged skin of the head and neck, lentigo maligna melanoma (a distinct subtype) is more common than SSM (see Module 23).
- On acral sites, acrolentiginous melanoma has distinct features (see Module 24).
- When a SSM presents on any body site, the general dermoscopic criteria outlined above remain the primary diagnostic framework.
Check Your Understanding
What dermoscopic features distinguish melanoma regression from complete regression of a benign lesion?
Melanoma regression shows a combination of blue-gray peppering (granularity), scar-like white areas, and often an asymmetric distribution within the lesion. Complete regression of a benign lesion (such as in halo nevi) tends to be more symmetric and uniform. The coexistence of regression with residual atypical structures (network, streaks) in other areas is more suggestive of melanoma.
Clinical Scenario
A 52-year-old woman presents with a 7 mm flat lesion on her right thigh showing five colors (tan, dark brown, black, blue, and gray). Dermoscopy reveals a multicomponent pattern with atypical network peripherally, a central blue-white veil, regression (peppering and scar-like white areas), and irregular brown-black globules.
What does the combination of regression and blue-white veil indicate about tumor thickness?
SSM with Both Radial and Vertical Growth Phase Features
The atypical network and regression reflect the radial growth phase and regressive changes, while the blue-white veil indicates vertical growth with melanocytes deep in the dermis overlaid by orthokeratosis. This combination suggests a thicker melanoma than one showing only network features. The five colors further support melanoma (SSMs are characteristically multicolored). The multicomponent pattern (>3 distinct structures) is one of the strongest indicators of melanoma across all diagnostic algorithms.
4.7 SSM Arising in a Nevus (Nevus-Associated Melanoma)
Nevus-associated melanomas have been described in one-third to half of patients with melanoma, particularly those with multiple nevi. Up to 42% of these cases are associated with a SSM.
Key dermoscopic findings in nevus-associated SSM:
- Negative network: Odds ratio 9.9 -- the most significant dermoscopic feature in nevus-associated melanomas.
- Globules: Odds ratio 2.4.
- Streaks: Odds ratio 2.4.
Clinical clue: When a melanoma arises within a pre-existing nevus, the benign nevus component may be visible as a contiguous structure (compound nevus, dermal nevus) adjacent to or underlying the melanoma. The dermoscopic pattern will show asymmetry where melanoma features (atypical network, blue-white veil, regression) abruptly transition from the organized benign nevus pattern.
4.8 Variants
4.8.1 Amelanotic and Hypomelanotic SSM
While the vast majority of pigmented SSMs are easily identified dermoscopically, amelanotic or hypomelanotic variants present a greater diagnostic challenge. These can be due to:
- Widespread regression -- diagnosis is less difficult due to positive specific features of scar-like depigmentation with or without multiple blue-gray fine dots (melanophages).
- True amelanotic or hypomelanotic SSM -- more diagnostically challenging.
In the largest published series (where more than 80% were SSMs), the most significant positive predictive nonregressing features were (in order):
- Blue-white veil
- Irregularly shaped depigmentation
- Irregularly distributed and shaped brown dots/globules
- Five to six colors (in partially pigmented lesions)
- Predominant central vessels
- Peripheral light brown structureless areas
- Asymmetrical pigmentation pattern
- Milky red-pink areas
- Greater than one shade of pink
- Asymmetrical shape
- Dotted and linear irregular vessels in combination
- Linear irregular vessels as the predominant vessel type
Features that were uncommon in amelanotic/hypomelanotic melanomas (and therefore argue against the diagnosis):
- Multiple (>3) milia-like cysts (1%)
- Regularly distributed comma vessels (1%)
- Comma vessels as the predominant vessel type (2.9%)
- Blue-gray globules of irregular size or distribution (1.9%)
- Arborizing small-diameter vessels (6.7%)
- Arborizing vessels as the predominant vessel type (8.6%)
- Symmetrical pigmentation pattern (7.6%)
Clinical pearl: Because there is overlap between amelanotic melanoma and other malignant amelanotic lesions, it is relatively easier to distinguish all malignant amelanotic/hypomelanotic lesions from all benign lesions (rather than to attempt to discriminate melanoma from other malignant lesions such as BCC). This underscores the importance of biopsy prior to any nonsurgical treatment of amelanotic lesions.
4.8.2 Nested Melanoma
Nested melanoma is a histopathologic variant of SSM characterized by:
- Large intraepidermal nests
- Sharp lateral circumscription
- Focal areas of lentiginous proliferation of melanocytes at the DEJ
Clinical presentation: Usually pigmented flat lesions with irregular borders on the trunk and extremities of patients older than 60 years. Less frequently, nested melanomas can present as exophytic papillomatous nodules with little junctional component.
Hallmark dermoscopic finding: Atypical globules of different size, shape, and color that are irregularly distributed -- the most common dermoscopic finding in this variant.
Key Takeaways
- Irregular streaks or pseudopods at the periphery of SSM represent the radial growth phase with confluent junctional nests extending beyond the lesion border.
- Negative network in SSM appears as serpiginous hypopigmented lines and corresponds to broadened rete ridges with melanocytic nests; its asymmetric distribution distinguishes it from Spitz nevi.
- Early SSM may show only subtle features: slight network irregularity, a single eccentric structureless area, or focal gray dots, making serial dermoscopy critical for detection.
4.9 Vascular Patterns in SSM
Vascular patterns play an important role in SSM diagnosis, particularly in hypomelanotic variants:
- Pin-point (dotted) vessels: Commonly found in thin SSM, particularly in hypomelanotic areas. These indicate melanocytic origin.
- Linear irregular vessels: More common in thicker lesions and amelanotic/hypomelanotic SSM.
- Combination of dotted and serpentine/linear vessels: Within the same lesion, this combination is highly suggestive of melanoma.
- Arborizing (tree-like) vessels: Can be seen in amelanotic SSM but their presence also raises the differential of BCC. This overlap illustrates the difficulty in distinguishing amelanotic melanoma from BCC.
4.10 Differential Diagnosis
SSM vs. Atypical (Dysplastic) Nevus
| Feature | SSM | Atypical Nevus |
|---|---|---|
| Pattern symmetry | Asymmetric pattern over every axis | May show some asymmetry but usually symmetry over at least one axis |
| Network | Atypical/broadened, focal, variable color and thickness | Regular or mildly atypical, more uniform |
| Peripheral structureless areas | Light brown, occupying >10% of surface | Absent or limited |
| Colors | Multiple (3--6 colors common) | Usually 1--2 colors (brown shades) |
| Regression | Scar-like areas, peppering common | Absent or minimal |
| Blue-white veil | Present in invasive SSM | Absent |
| Streaks/pseudopods | Asymmetric, focal | Absent |
SSM vs. Spitz Nevus
| Feature | SSM | Spitz Nevus |
|---|---|---|
| Streaks | Asymmetric, segmental distribution | Symmetric, circumferential (starburst pattern) |
| Globules | Atypical, variable size/color, disorganized | Regular, symmetric peripheral distribution |
| Negative network | Present (asymmetric) | May be present (symmetric) |
| Overall symmetry | Asymmetric | Typically symmetric |
| Blue-white veil | Suggestive of melanoma | Not typical |
| Patient age | Any age; more common in adults | More common in children and young adults |
SSM vs. Pigmented BCC
| Feature | SSM | Pigmented BCC |
|---|---|---|
| Arborizing vessels | Uncommon; if present, small diameter | Classic feature, large-diameter branching |
| Blue-gray ovoid nests | Absent | Present |
| Leaf-like areas | Absent | Present |
| Spoke-wheel structures | Absent | Present |
| Pigment network | Atypical network present | Network absent (nonmelanocytic) |
| Ulceration | Uncommon in thin SSM | Common |
Key Takeaways
- The presence of three or more dermoscopic colors in a melanocytic lesion significantly raises melanoma probability and is incorporated into multiple scoring algorithms.
- SSM must be differentiated from severely dysplastic nevi, which may show similar features but with greater overall structural organization and symmetry.
- Any melanocytic lesion with a multicomponent pattern (three or more distinct dermoscopic areas) that cannot be confidently diagnosed as benign warrants excision.
5. SSM Criteria Reference Table
The following table summarizes the major dermoscopic features of SSM with their reported sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and odds ratios (OR). Data are adapted from Menzies et al. and derived from both in situ and thin invasive melanoma.
| # | Feature | Description | Sensitivity (%) | Specificity (%) | PPV (%) | NPV (%) | OR |
|---|---|---|---|---|---|---|---|
| 1 | Atypical network | Web of lines of varying colors/thicknesses with holes of varying diameters; smudged or out of focus; brown to black or gray | 77.1 | 88.5 | 67 | 88 | 9.0 |
| 2 | Streaks (pseudopods and/or radial streaming) | Radial projections at the periphery emanating from the tumor towards surrounding normal skin | 32.0 | 98.7 | 76.5 | 86 | 5.8 |
| 3 | Atypical dots and/or globules | Dots <0.1 mm (black/brown); globules >0.1 mm (brown/blue/white); variable size, shape, color; disorganized | 39.6 | 91.1 | 79 | 86 | 4.8 |
| 4a | Regression -- Granularity (peppering) | Blue-gray fine dots representing melanophages or free melanin in papillary dermis | 21.9 | 92.6 | 78 | 62 | 3.5 |
| 4b | Regression -- Scar-like areas | Porcelain white structureless areas lighter than surrounding normal skin; dermal fibrosis | 22.9 | 93.6 | -- | -- | 4.4 |
| 4c | Regression -- Either | Presence of granularity and/or scar-like areas | 41.7 | 89.2 | -- | -- | 7.8 |
| 5 | Blue-white veil | Confluent blue-white coloration over raised area; melanin in mid-dermis with overlying orthokeratosis | 11.4 | 99.0 | -- | -- | 13.0 |
| 6 | Negative network | Hypopigmented serpiginous lines surrounding elongated curvilinear globules; bridging/elongation of rete ridges | 34.6 | 95.0 | -- | -- | 1.8 |
| 7 | Brown peripheral structureless areas | Homogeneous light brown areas at periphery occupying >10% of lesion surface | 62.5 | 96.1 | 93.8 | 73.1 | 27.9 |
| 8 | Shiny white lines (crystalline structures) | Short bright white lines, parallel or orthogonal; visible only with polarized light; stromal alteration and fibrosis | 9.7 | -- | -- | -- | -- |
| 9 | Multiple colors | Three to six colors scored from tan, dark brown, gray, black, blue, red | -- | -- | -- | -- | -- |
| 10 | Multiple brown dots (pagetoid) | Focal brown dots representing suprabasal pagetoid melanocytes | -- | -- | -- | -- | -- |
Note: Highest reported values shown. OR = odds ratio. Data were derived from both in situ and thin invasive melanoma.
6. Thin vs. Thick SSM Comparison Table
| Parameter | Thin SSM (in situ to ~1.0 mm) | Thick SSM (>1.0 mm) |
|---|---|---|
| Pattern | Asymmetric, may be subtle | Asymmetric, usually obvious multicomponent |
| Atypical network | Often the only specific feature; focal broadened network | May be present but often disrupted or replaced by structureless areas |
| Streaks/pseudopods | Subtle, may be very subtle and easily overlooked | More prominent when present |
| Brown dots | Classical focal distribution (pagetoid spread) | May be present; often overshadowed by other features |
| Globules | Small atypical globules possible | Larger atypical globules, peripheral black dots/globules |
| Regression | Scar-like depigmentation and granularity may dominate in regressing thin SSM | Extensive regression possible |
| Blue-white veil | Small areas possible; absent in many thin SSMs | Frequently observed and prominent |
| Colors | May have 5--6 colors even in thin lesions (>=0.5 mm) | 5--6 colors very common |
| Shiny white lines | Less common | More common (correlates with dermal fibrosis from invasion) |
| Vascular patterns | Pin-point (dotted) vessels in hypomelanotic areas | Dotted + serpentine/linear irregular vessels in combination |
| Peripheral structureless areas | Light brown structureless areas occupying >10% | May be present but often replaced by other features |
| Negative network | May be present, especially in nevus-associated cases | May be present |
| Key diagnostic challenge | Subtle features; may mimic atypical nevus | May mimic nodular melanoma or other tumors |
7. Clinical Pearls
Broadened atypical network is the sentinel feature of early SSM. It is the most sensitive dermoscopic feature in nonregressing thin SSM and may be the sole positive finding in melanoma in situ. Always scrutinize the edges of a lesion for focal areas of broadened network, even when the center appears benign.
Asymmetry of pattern is the overarching principle. SSM lacks symmetry of pattern over every axis through the center of the lesion. If a lesion shows structural asymmetry plus one or more melanoma-specific features, it should be biopsied regardless of how few features are present.
Streaks in SSM are segmental, not circumferential. If radial streaks or pseudopods are distributed symmetrically around the entire periphery (starburst pattern), the diagnosis is more likely Spitz/Reed nevus. In SSM, streaks are asymmetric and focal.
Dotted vessels plus linear irregular vessels in the same lesion = melanoma. This combination of vessel morphologies is highly suggestive of melanoma. Pin-point (dotted) vessels alone indicate melanocytic origin but are not melanoma-specific.
Blue-white veil vs. blue-white regression color. Blue-white veil is seen in raised/palpable areas (reflecting mid-dermal melanin with overlying orthokeratosis). Blue-white color from regression is seen in flat/macular areas (reflecting peppering + scar-like changes). Both are significant but have different histologic correlates.
Negative network is the key to nevus-associated melanoma. With an odds ratio of 9.9, negative network is the strongest dermoscopic predictor of melanoma arising in a pre-existing nevus. When you see negative network in an otherwise bland-appearing lesion, look carefully for additional asymmetric features.
Peripheral light brown structureless areas have the highest odds ratio (27.9). This frequently overlooked feature -- homogeneous light brown areas at the periphery occupying more than 10% of the lesion surface -- is both sensitive and highly specific for melanoma, making it an excellent discriminator between atypical nevi and thin melanoma.
Shiny white lines require polarized dermoscopy. These crystalline structures are invisible under nonpolarized dermoscopy. If you use a nonpolarized or hybrid dermatoscope, always toggle to polarized mode to check for shiny white lines, which are suggestive of dermal invasion.
Amelanotic SSM: think "malignant vs. benign" rather than "melanoma vs. BCC." Because amelanotic melanoma and other amelanotic malignancies (especially BCC) share overlapping vascular features, the practical clinical approach is to distinguish all malignant amelanotic lesions from benign ones -- and then biopsy. Never treat an amelanotic lesion with a nonsurgical modality without first performing a biopsy.
Five to six colors can occur in thin melanomas. Do not assume that the presence of multiple colors necessarily indicates a thick lesion. Multiple colors have been reported in SSM with Breslow thickness as low as 0.5 mm.
Clinical Vignettes
Clinical Scenario A 47-year-old woman presents with an 8 mm flat pigmented lesion on the left upper back that she noticed 6 months ago. Dermoscopy reveals an asymmetric pattern with a broadened, irregular pigment network (thickened brown lines with irregular spacing) along the superior and lateral edges. The inferior portion shows a regular thin brown network that fades at the periphery. No blue-white veil, regression structures, or vessels are visible. The lesion has five colors: light brown, dark brown, tan, black, and gray.
What is the most likely diagnosis?
Diagnosis: Superficial spreading melanoma (thin/early).
Broadened atypical network is the sentinel feature of early SSM (Clinical Pearl 1) and may be the sole positive finding in melanoma in situ. Here it is found focally at the lesion edge, illustrating why scrutinizing the periphery is critical. The asymmetry of pattern -- atypical network superiorly versus regular network inferiorly -- is the overarching principle of SSM diagnosis (Clinical Pearl 2). The presence of five colors does not necessarily indicate a thick lesion (Clinical Pearl 10); multiple colors have been reported in SSM as thin as 0.5 mm Breslow thickness. This case also demonstrates that the absence of "classic" features like blue-white veil and regression does not exclude melanoma -- focal broadened network with structural asymmetry is sufficient indication for biopsy.
Clinical Scenario A 58-year-old man presents with an 11 mm pigmented lesion on the right calf that his wife noticed had changed. Dermoscopy reveals an asymmetric multicomponent pattern with irregular brown-black dots and globules in the northern half, a flat blue-white area (peppering) in the southeast quadrant, and asymmetric streaks (pseudopods) at the 2 and 3 o'clock positions. A central area of negative network is present. Polarized dermoscopy reveals shiny white lines crossing the lesion.
What is the most likely diagnosis?
Diagnosis: Superficial spreading melanoma with regression.
This lesion displays multiple melanoma-specific structures distributed asymmetrically. The flat blue-white area represents regression (Clinical Pearl 5: blue-white color from regression is seen in flat areas, reflecting peppering + scar-like changes, different from blue-white veil in raised areas). The asymmetric streaks/pseudopods are segmental rather than circumferential, consistent with SSM rather than Spitz/Reed nevus (Clinical Pearl 3). Negative network has the highest odds ratio (9.9) for melanoma arising in a pre-existing nevus (Clinical Pearl 6). Shiny white lines require polarized dermoscopy and are suggestive of dermal invasion (Clinical Pearl 8). The combination of dotted features plus linear structures in the same lesion strongly supports melanoma (Clinical Pearl 4).
Clinical Scenario A 63-year-old woman presents with a 9 mm slightly elevated pink lesion on the left forearm. It has been slowly growing for 8 months. Dermoscopy reveals a milky-pink background with polymorphous vessels (dotted and serpentine), focal areas of light brown structureless pigment at the periphery, and faint remnants of what appears to be pigment network in one corner. No blue-white veil or ulceration is present.
What is the most likely diagnosis?
Diagnosis: Amelanotic/hypomelanotic superficial spreading melanoma.
This case illustrates Clinical Pearl 9: for amelanotic SSM, think "malignant vs. benign" rather than trying to determine the specific diagnosis. The polymorphous vessels (dotted + serpentine) in a pink lesion are concerning for malignancy. The focal peripheral light brown structureless areas are a critical clue -- with an odds ratio of 27.9, peripheral light brown structureless areas have the highest specificity for melanoma (Clinical Pearl 7). The faint remnants of pigment network in one corner provide a hint of melanocytic origin. Never treat an amelanotic lesion with a nonsurgical modality without first performing a biopsy. The practical approach is to distinguish this from benign amelanotic lesions -- and then excise.
9. Cross-References
| Topic | Chapter/Section | Pages |
|---|---|---|
| SSM dermoscopic features and case series | Chapter 8a | 180--186 |
| Sensitivity/specificity of SSM features | Chapter 8a | 185 |
| Morphologic definitions of dermoscopic structures | Chapter 7 | 150--190 |
| Histopathologic correlations of dermoscopic structures | Chapter 3 | 20--52 |
| Hypomelanotic melanoma details | Chapter 8e | 213--220 |
| Chaos and Clues algorithm application | Chapter 5a | 81--91 |
| Menzies method and other algorithms | Chapters 5b--5c | 92--100 |
| Nodular melanoma (comparison with SSM) | Chapter 8b | 198--200 |
| Atypical nevi (differential diagnosis) | Chapter 7b | 157--167 |
| Spitz and Reed nevi (differential diagnosis) | Chapter 7e | 180--186 |
| BCC (differential diagnosis) | Chapter 6b | 108--112 |
Key References from Chapter 8a
- Annessi G, et al. Sensitivity, specificity, and diagnostic accuracy of three dermoscopic algorithmic methods. J Am Acad Dermatol. 2007;56(5):759--67.
- Argenziano G, et al. Dermoscopy of pigmented skin lesions: results of a consensus meeting via the Internet. J Am Acad Dermatol. 2003;48(5):679--93.
- Balagula Y, et al. The significance of crystalline/chrysalis structures in the diagnosis of melanocytic and nonmelanocytic lesions. J Am Acad Dermatol. 2012;67(2):194.e1--8.
- Menzies SW, et al. Frequency and morphologic characteristics of invasive melanomas lacking specific surface microscopic features. Arch Dermatol. 1996;132(10):1178--82.
- Menzies SW, Ingvar C, McCarthy WH. A sensitivity and specificity analysis of the surface microscopy features of invasive melanoma. Melanoma Res. 1996;6(1):55--62.
- Menzies SW, et al. Dermoscopic evaluation of amelanotic and hypomelanotic melanoma. Arch Dermatol. 2008;144(9):1120--7.
- Pizzichetta MA, et al. Negative pigment network: an additional dermoscopic feature for the diagnosis of melanoma. J Am Acad Dermatol. 2013;68(4):552--9.
- Shitara D, et al. Dermoscopy of naevus-associated melanomas. Acta Derm Venereol. 2015;95(6):671--5.
10. Related Modules
| Module | Title | Relationship |
|---|---|---|
| Module 01 | Introduction and Principles of Dermoscopy | Prerequisite: polarized vs. nonpolarized dermoscopy (essential for shiny white lines) |
| Module 02 | Histopathologic Correlations | Prerequisite: understanding the histologic basis of all dermoscopic structures |
| Module 03 | Pattern Analysis Revised | Prerequisite: basic pattern elements and chaos recognition |
| Module 06 | Chaos and Clues Triage Algorithm | Prerequisite: systematic approach to melanoma detection |
| Module 07 | TADA and Other Triage Algorithms | Prerequisite: scoring systems for melanoma |
| Module 16 | Acquired Melanocytic Nevi | Differential diagnosis: atypical/dysplastic nevi vs. SSM |
| Module 19 | Spitz and Reed Nevi | Differential diagnosis: starburst pattern vs. asymmetric streaks |
| Module 22 | Nodular Melanoma | Follow-on: features distinguishing NM from SSM |
| Module 25 | Other Melanoma Subtypes | Follow-on: nested melanoma, nevoid melanoma, and rare variants |
| Module 26 | Amelanotic and Hypomelanotic Melanoma | Follow-on: detailed coverage of amelanotic/hypomelanotic features |
| Module 27 | Differentiation -- Pattern Analysis and Melanoma-Specific Criteria | Application: using SSM features in algorithmic melanoma differentiation |
| Module 28 | Improving Sensitivity and Specificity in Melanoma Diagnosis | Application: statistical performance of SSM criteria in clinical practice |
Part of the Dermoscopy Educational Course.