Analytic approach
The analytic approach refers to algorithmic method for the diagnosis of pigmented lesions using dermoscopy.
The essence of pattern analysis is a structured description formulated using a clearly defined algorithmic method. The diagnostic method is structured in such a way that one starts by describing the most general of features, then proceeds progressively to finish with the most specific features.
The algorithm always takes the general form: Pattern + Color + Clues = Diagnosis
Using patterns, colors and clues, the number of potential diagnoses is progressively minimized. Pattern is a method by which algorithms are constructed.
It has the following subchapters:
- Introduction to the analytic approach
- Lines
- Dots
- Clods
- Circles
- Pseudopods
- Structureless
- Combination of pattern
Introduction
The analytic approach is a dermoscopic algorithmic method for the diagnosis of pigmented lesions that is based on 5 basic geometric elements.
The essence of pattern analysis is a structured description formulated using a clearly defined algorithmic method. The diagnostic method is structured in such a way that one starts by describing the most general of features, then proceeds progressively to finish with the most specific features.
The algorithm always takes the general form:
Pattern + Color + Clues = Diagnosis
Using patterns, colors and clues, the number of potential diagnoses is progressively minimized.
Elements and patterns
The analytic approach builds on 5 Basic elements:
Lines: structures with parallel edges, with their length much greater than their breadth
Dots: circumscribed, small, round, indivisible pigmented structures with no length or breadth
Clods: solid, circumscribed, diversely formed pigmented or unpigmented structures larger than dots, with length and breadth
Circles: lines or collection of pigmented dots arranged sensibly equidistant from a common focal point that constitutes the center
Pseudopods: short pigmented lines with a bulbous end
A pattern is formed by an aggregation of one of the five basic elements: lines, pseudopods, circles, clods and dots. Multiple repetitions of the same single basic element are required to constitute a pattern. This collection of basic elements should comprise a significant portion of the pigmented lesion (~ 25%). There are lesions with only one pattern and lesions with a combination of patterns.
When basic elements are not seen or there are too few basic elements to constitute a pattern, the "pattern" is termed structureless.
Single Pattern
A minority of pigmented lesions present with only one pattern. The different patterns can be grouped based on the geometric elements comprising them:
Lines
Lines may form six different patterns, depending on their shape and arrangement: reticular, branched, angulated, parallel, radial, and curved.
Reticular lines
Straight lines crossing each other at an angle of 90° forming a greed are termed reticular lines. Lesions with reticular lines are not always melanocytic. In most cases the histological correlate of reticular lines is hyperpigmentation of basal keratinocytes, which may or may not be created by an increase in the numbers of melanocytes.
Color
- Usually light-brown or dark-brown, due to melanin in the epidermis.
- If the pigment is very dense, the lines are black.
- Rarely, they can appear gray.
Not every shade of brown is to be interpreted as a separate color. One or two black lines do not render the lesion multicolored. The normal hypopigmentation around follicular openings does not create an extra color. Nearly all pigmented lesions are somewhat lighter at the periphery compared to their center.
Light-brown + thin reticular lines
Junctional Clark nevus or solar lentigo.
A Clark nevus is round or oval and the pigmentation does not end abruptly at the periphery. The border of a solar lentigo is usually sharply demarcated and scalloped.
Differential diagnoses: a variant of dermatofibroma with only reticular lines and urticaria pigmentosa, a type of mastocytosis.
Brown + thick reticular lines
Clark nevus or superficial congenital nevus.
Differential Diagnoses: Solar lentigo, seborrheic keratosis.
Black (very dark-brown) reticular lines
Ink-spot lentigo. No differential diagnosis needs to be considered. Very rarely a Reed nevus may demonstrate this pattern and color combination, but without the additional clues to "ink-spot lentigo"
More than one color + reticular lines
Solar lentigo or seborrheic keratosis.
- Clues to solar lentigo: well-demarcated, scalloped border.
- Clues to seborrheic keratosis: white dots or clods, orange or yellow clods, well-demarcated border, circles, thick curved lines, vessels as loops or coils.
- Differential diagnoses: Clark nevus, superficial or superficial and deep congenital nevus, and melanoma in situ.
Dark-brown or black and light-brown areas: variegate color distribution
- Differential diagnosis: Clark nevus, superficial / superficial and deep congenital nevus, or melanoma in situ
- Only 5 of the 8 clues to melanoma are seen in reticular pattern lesions:
- gray dots, clods, circles or lines;
- radial lines or pseudopods seen only in some segments of the periphery;
- black dots or clods at the periphery;
- thick reticular lines and angulated lines (polygons). When one of these clues is present, the diagnosis of melanoma should be seriously considered;
- Eccentric hyperpigmentation ,i.e. the more heavily pigmented area is not in the center but the periphery- can be seen in Clark nevi and melanomas in situ, rarely in congenital nevi.
Differential diagnosis: Invasive melanoma. When no clue to melanoma is present, a Clark nevus is the most likely diagnosis.
Branched lines
Branched lines and reticular lines are closely related and often occur together. Unlike reticular lines that cross each other at a 90° angle, branched lines are straight lines crossing each other in different angles. Lesions that are exclusively composed of branched lines are either black or brown, and they are all benign.
Brown branched lines: Clark nevus or superficial / superficial and deep congenital nevus.
Black (or very dark-brown) branched lines: ink-spot" lentigo.
Angulated lines
Angulated lines are pigmented lines that form angles.
- May appear on facial skin and on non-facial skin.
- Are the hallmark of flat melanomas on chronic sun-damaged skin.
- Most melanomas with angulated lines are not invasive (in situ).
- They are usually brown or grey.
Parallel lines
Parallel lines are straight lines that don't cross each other.
- Typical pigment pattern of acral skin.
- They may be arranged in one of three ways; on the ridges (ridge pattern), in the furrows (furrow pattern), or crossing ridges (crossing pattern).
- Acral lesions that only show a pattern of furrows or a crossing pattern may be safely considered to be benign.
- Assessment of a lesion showing the ridge pattern proceeds by evaluating color.
- If it is brown, in situ melanoma must be considered. Black, red or purple parallel lines on the ridges indicate either hemorrhage or exogenous pigmentation. Satellite clods are a strong clue to the diagnosis of hemorrhage.
Radial lines
Radial lines are staright lines that converge to the center of a lesion or to a central dot or clod.
- They always occur in combination with another pattern.
Curved lines
Curved lines are lines that bend and are not straight.
- They usually occur in combination with other patterns.
- can be seen in seborrheic keratosis and solar lentigo.
Pseudopods
Pseudopods are short pigmented lines with a bulbous end and are often kinked. They are seen at the lesion edge, either directly associated with a network or solid tumor border.
- They occur only in combination with other patterns.
Circles
It is the pattern of facial skin, but also not unusual at other locations on the body.
On the face, they are formed by melanin pigment arranged either around the openings of the crater-like infundibula or in infundibular epithelium. The center of the infundibulum appears hypopigmented. If infundibula contain keratinized material the hypopigmented center is seen as a yellow or orange clod. Circles may be brown, gray or black.
Brown circles
Are found solar lentigo or flat seborrheic keratosis.
Gray circles on facial lesions
Are found in melanoma in situ. Differential diagnoses: lichen planus-like keratosis, pigmented actinic keratosis.
Circles On the trunk or the extremities
This pattern of circles may be a variant of the reticular pattern. Differential diagnoses: junctional Clark nevus, solar lentigo, and dermatofibroma.
Clods
After reticular lines, the pattern of clods is the second most common.
Clods can be classified based on the predominant color/ colors.It is necessary to distinguish between the colors of melanin and the colors of other pigments. Clods whose pigmentation is due to melanin are either brown, blue or gray.
Clods with one predominant color:
White and/or yellow clods
Are often found in seborrheic keratosis and represent dilated infundibula and inclusion cysts ("milia") filled with keratin. If they are accompanies by radial vessels that do not cross the center of the lesion sebaceous gland hyperplasia should be considered.
Orange clods
Can be seen in seborrheic keratosis, or basal cell carcinoma (orange clods due to ulceration (serum crust)). Whereas multiple orange clods are seen in seborrheic keratosis, in basal cell carcinoma one usually finds one or two orange clods with traces of red due to red blood cells in the serum crust. A further clue to the diagnosis is the pattern of vessels: in basal cell carcinoma the vessels are serpentine, often branched; in seborrheic keratosis the vessels are looped or coiled (or rarely serpentine).
Red or purple clods
Are found in hemangioma or vascular malformations.
Black clods
Represent thrombosed vessels
Red clods
Represent hemorrhage
Large, polygonal skin-colored clods
Are seen in exophytic congenital nevi with papillomatous surface (Unna nevus or Miescher nevus), or verrucous seborrheic keratosis.
Brown clods
Are seen in various types of melanocytic nevi.
Large, polygonal light-brown clods
Are seen in Unna nevus or Miescher nevus
Small to medium-sized, round and oval brown clods
Small congenital nevi of superficial and superficial and deep types. Central hyperpigmentation is common in pigmented Spitz nevi, and peripheral clods are usually smaller than those in the center.
Blue clods
Are seen in pigmented basal cell carcinoma.Differential diagnoses: melanoma and combined congenital nevus.
Clods with more than one predominant color:
White, yellow or orange clods
Keratin with (orange) or without (white or yellow) inclusions of melanin. Orange clods may also result from ulceration (serum crust).
White or yellow clods
Are mainly found in seborrheic keratoses and less often in Unna nevi. Orange clods also indicate a seborrheic keratosis or less often an Unna nevus.
Combination of red, purple or black clods
Hemangioma, vascular malformation or hemorrhage.
Melanin colors (brown, blue or gray) clods with symmetrical color distribution
Melanocytic nevi, i.e. superficial and deep congenital nevi, combined congenital nevi, Unna nevi and pigmented Spitz nevi
Melanin colors (brown, blue or gray) clods with asymmetrical color distribution
Pigmented basal cell carcinoma and melanoma.
Dots
Dots, like the rest of the elements, are grouped based on their color. Dots usually occur in combination with other patterns. Only gray or brown dots are found in lesions without another pattern. Only red dots: are found in non-pigmented lesion, i.e. vessels as dots.
Gray dots
Are found in lichen planus-like keratosis, pigmented actinic keratosis, pigmented Bowen’s disease and melanoma.
- Lichen planus-like keratosis: curved lines or typical sharply defined and scalloped border. On chronic UV-exposed sites (face or the dorsum of the hand).
- Pigmented actinic keratoses: on the face. Usually seen as gray circles
- Pigmented Bowen’s disease: on the trunk and extremities. It may mimic other lesions, but the clues of coiled vessels and dots arranged as lines lead to the correct diagnosis.
- In situ melanomas: gray dots mixed with brown dots. Random distribution, arranged as circles around the openings of the infundibula (face), or lines arranged as polygons (trunk or extremities)
Brown and small gray dots
Are found in clark nevus, or rarely in solar lentigo and pigmented Bowen’s disease.
Brown and red dots
Are found in inflammatory skin diseases with extravasation of red blood cells, e.g. pigmented purpuric dermatosis.
Structureless
Definition: no basic elements, too few to constitute a pattern, or the visible structures cannot be assigned to one of the five basic elements.
Lesions that only have a structureless pattern are difficult to diagnose using dermatoscopy and often require histopathology.
One color predominates over all others
Black + structureless
Usually represents the presence of hemoglobin (not melanin) and its degradation products, e.g. hemorrhagic crusts, hemorrhages in the epidermis and thrombosed vessels. Differential diagnoses: heavily pigmented melanocytic lesions, e.g. Reed nevus, Clark nevus or melanoma.
Blue + structureless
"Blue nevi" of all types. Differential diagnoses: melanomas, melanoma metastases, structureless blue pigmented basal cell carcinomas.
Brown + structureless
Can be seen in solar lentigo, flat seborrheic keratosis, pigmented Bowen’s disease, and melanocytic nevus of superficial or superficial and deep congenital type.
Red + structureless
This pattern represents recent hemorrhage in the stratum corneum. It will become a black structureless lesion as the hemoglobin degrades, before it entirely disappears due to transepidermal elimination.
More than one color
It can be difficult to differentiate between clods or structureless. Clods: are well circumscribed and always occur in numbers while Structureless is one large contiguous area.
Colors of keratin (yellow and orange)
Are seen in keratinizing lesions such as seborrheic keratosis. Differential diagnoses: basal cell carcinoma.
Colors of hemoglobin (red and purple)
Represent hemorrhage that can also occur in a pre-existing lesion such as a nevus.
Black zones in structureless lesion
Black color should be attributed to blood (thrombosis) when it appears together with red or purple and attributed to melanin when it appears together with brown, blue or gray.
Colors of melanin (black, brown, blue)
- Symmetrical distribution of melanin: nevus.
- Asymmetrical distribution of melanin: melanoma, melanoma metastasis, seborrheic keratosis.
- Differential diagnosis: pigmented basal cell carcinoma or a dermatofibroma.
Multiple patterns
The majority of pigmented lesions have more than one pattern. The diagnostic algorithm for pigmented lesions with multiple patterns depends on the type of patterns that are present in the lesion. First, if "lines" are present - the algorithm of "lines" should be followed. If "lines" are not present, the investigator should look next for "pesudopods" and follow their algorithm. This process continues sequentially through "circles", "clods" and finally "dots".
Structural symmetry
The combination of patterns should be assessed for symmetry. Symmetry is judged based on the distribution of patterns and colors within the lesion. The more patterns, the less symmetric the lesion is. There are two ways in which two patterns can be combined symmetrically:
- One pattern is in the center and the other at the periphery
- The basic elements of one pattern (e.g. dots) are regularly spread over a second pattern (e.g. reticular lines).
All other combinations of two patterns are, by definition, considered asymmetrical.
Lines
Reticular and/or branched lines
Reticular lines are much more common than branched lines.
Sharply demarcated patterns
- Sharply demarcated scalloped border + curved lines: solar lentigo or lichen planus-like keratosis.
- Sharply demarcated border, white dots or clods, yellow or orange clods + thick curved lines: seborrheic keratosis.
Symmetrical patterns
- Clods in the center + reticular lines at the periphery: superficial or superficial and deep congenital nevus, Clark nevi.
- Reticular lines in the center + clods (or dots) peripherally: Clark nevus in phase of growth, or growing superficial or superficial and deep congenital nevus.
- Reticular lines + uniformly distributed clods (or dots): Clark nevi or superficial or superficial and deep congenital nevi.
- Symmetrical combination of pseudopods (i.e. the pseudopods are seen occupying the entire circumference): Reed nevus.
- Symmetrical combination of peripheral radial lines: Reed nevus, or Clark nevus.
- Symmetrical combinations of three patterns, e.g. structureless in the center and reticular lines and dots or clods at the periphery: superficial and superficial and deep congenital nevi
Symmetrical color
- Skin-colored: raised and papillomatous. Most commonly in superficial and deep congenital nevus, less frequently in Clark nevus.
- Dark-brown or black: Clark nevus, or rarely Reed nevus.
- Blue: combined congenital nevus, or less often Reed nevus.
- White: dermatofibroma.
Asymmetrical patterns
- Asymmetrical combination of patterns: usually exclusively brown and likely to be a nevus (Clark nevus or superficial or superficial and deep congenital nevus).
- Asymmetrical lesions with more than one pattern (most lesions) should be assessed for clues to melanoma.
Parallel lines
Commonly seen in acral pigmented lesions. They may appear on the ridges, in the furrows, or crossing ridges and furrows.
Ridge pattern
- It takes precedence if more than one parallel line pattern is seen.
- If pigmentation on the ridges is in the colors of melanin, the diagnosis of melanoma must be considered. Hemorrhage or exogenous pigmentation are the likely diagnoses when colors other than those of melanin are seen.\
Pattern of furrows or crossing pattern
Distinction between symmetrical and asymmetrical is necessary.
- Symmetrical combinations: classic acral nevi and other nevi, e.g. Reed nevi or superficial and superficial and deep congenital nevi.
- Asymmetrical combinations: clues to melanoma.
Radial lines
Always occur in combination with other patterns.
Symmetrical patterns
Radial lines occupy the entire circumference of the lesion.
- Structureless center + white: dermatofibroma.
- Structureless center + brown, black or gray: Reed nevus.
Asymmetrical patterns
Peripheral radial lines do not occupy the entire circumference of the lesion but are present only in some segments. The primary differential diagnosis includes melanoma versus basal cell carcinoma. In basal cell carcinoma arrangements of radial lines usually have a common base. The radial lines are not only seen at the periphery but also within the lesion.
Curved lines
The least specific pattern. Lesions are almost always asymmetrical.
- Brown color: solar lentigo, seborrheic keratosis.
- Colors of melanin (gray, blue or black): melanoma, seborrheic keratosis, lichen planus-like keratosis.
Pseudopods
Psueodopods are only seen in combination with another pattern. Most commonly pseudopods are at the periphery with other pattern in the center of the lesion: structureless, clods, or reticular lines.
Symmetrical pattern
Regularly distributed pseudopods in the periphery, e.g. Reed nevus.
Asymmetrical pattern
Melanoma must be considered. Patient’s age, skin type, number of nevi, distribution of pseudopods, clinical appearance and history of change are relevant to the diagnosis.
Circles
This is a typical pattern of facial skin.
Symmetrical pattern
Peripheral brown circles combined with a structureless zone (or less often white lines) centrally, e.g. dermatofibroma.
Asymmetrical pattern
Pattern of circles with no lines. The color of the circles becomes more important than assessment of symmetry:
- Brown: solar lentigo, seborrheic keratosis, superficial or superficial and deep congenital nevus, Clark nevus, Miescher nevus.
- Gray or black: melanoma, lichen planus-like keratosis and pigmented actinic keratosis.
Clods
Clods + structureless: combined symmetrically or asymmetrically:
Symmetrical pattern
Structureless zone in the center of the lesion and clods at the periphery.
- Skin-colored center: Superficial and deep congenital nevus, Spitz nevus.
- Brown or black center: Growing superficial and deep congenital nevus (commonly in children), pigmented Spitz nevus.
- Blue structureless center: Combined congenital nevus.
Asymmetrical pattern
Contains clods but no lines, Pseudopods or circles. These lesions are analyzed depending on whether the colors are predominantly those of melanin, or of another pigment:
(a) Lesions with melanin pigment are predominantly black, brown, gray or blue
- Black pigmentation: coagulated blood or melanin. The interpretation depends on what other colors are present.
- Brown, blue or gray: melanin in the stratum corneum.
- Red or purple: coagulated blood.
When melanin is the predominant pigment, the color of the whole lesion should be assessed:
- Brown color: superficial and deep congenital nevus or a Spitz nevus.
- Other colors: basal cell carcinoma, melanoma, seborrheic keratosis and its variants.
(b) Lesions with no pigment, or with pigments other than melanin are assessed based on the color of the clods:
- White or yellow clods: seborrheic keratosis.
- Orange clods: seborrheic keratosis, basal cell carcinoma.
- Red or purple clods: hemangioma, vascular malformation, melanoma or melanoma metastasis.
Dots
Dots and structureless
The algorithm for "dots and structureless" differs only slightly from the algorithm for "dots":
- Gray dots: melanoma, lichen planus-like keratosis, pigmented superficial squamous cell carcinoma (actinic keratosis or Bowen’s disease), basal cell carcinoma.
- Blue dots: basal cell carcinoma.
- Black dots: uncommon; exclude melanoma.
- Brown dots: solar lentigo, pigmented Bowen’s disease, Clark nevus.
References:
- Kittler. Dermatoscopy: introduction of a new algorithmic method based on pattern analysis for diagnosis of pigmented skin lesions. Dermatopathology: Practical & Conceptual, 2007
- Kittler et al. Standardization of terminology in dermoscopy/dermatoscopy: Results of the third consensus conference of the International Society of Dermoscopy. J Am Acad Dermatol. 2016 June ; 74(6): 1093–1106.
- Kittler et al. Revised version of pattern analysis. In Marghoob et al. Atlas of Dermoscopy, Second Edition. Informa healthcare, London, 2012.
