Pattern analysis
Created 2008.
Learning objectives
- Describe dermoscopic diagnosis of melanocytic lesions using pattern analysis
Introduction
In dermoscopy, the first step algorithm identifies whether a lesion is melanocytic or nonmelanocytic. Pattern analysis is the method preferred by many expert dermoscopists to diagnose melanocytic lesions and to differentiate benign melanocytic lesions from malignant melanoma. Pattern analysis refers to the simultaneous assessment of the diagnostic value of all dermoscopy features shown by the lesion.
In general terms, benign lesions have few colours, a regular structure and are symmetrical in pattern. Malignant tumours often have several colours (especially melanoma), disordered structure and asymmetry of pattern.
If conventional or morphological pattern analysis appears too complicated, use modified pattern analysis, or the 3-point checklist to identify malignant pigmented lesions.
Benign melanocytic lesions
Global pattern
- Reticular pattern (diffuse or patchy network)
- Globular pattern (globules in shades of brown)
- Homogeneous pattern (diffuse colour)
- Starburst pattern (uniform peripheral radial streaks, dots or globules)
- Parallel pattern (along furrows; palms and soles only)
- Complex pattern (2 patterns within a single lesion, usually symmetrically or regularly distributed)
- Multicomponent pattern (3 patterns, usually concentric)
Non-concentric multicomponent pattern is highly suspicious of malignancy, but is occasionally seen in benign lesions, eg collision tumours, recurrent naevus, congenital melanocytic naevus.
Local features
- Pigment network, evenly spaced, fading out
- Dots/globules distributed regularly
- Streaks distributed regularly
- Central hypopigmentation
- Symmetrical blotches
- Comma-like regular vasculature
- On face: regular pseudonetwork
- On palms/soles: Parallel furrow, lattice-like or fibrillar pattern
Melanoma
Global pattern
- Multicomponent pattern (3 or more patterns)
- Unspecific pattern (mainly structureless or 2 patterns, irregular)
- Parallel pattern (along ridges; palms and soles only)
Local features
- Atypical pigment network (branched, broken-up, thickened, asymmetrical)
- Dots/globules distributed irregularly and of different sizes and shapes
- Asymmetrical blotches (featureless colours)
- Focal irregular streaking or peripheral linear projections (radial streaming and pseudopods)
- Five or six colours (black, brown, tan, grey, blue, red, white)
- Blue-white veil over part of the lesion
- White scar-like depigmentation
- Blue pepper-like granules
- Irregular linear or dotted vessels, or polymorphous vascular pattern especially with milky-red areas
- On face: grey dots, pseudonetwork, rhomboidal structures, asymmetrical pigmented follicles, annular-granular structures
- On palms/soles: parallel ridge, irregular
Modified pattern analysis
Modified or revised pattern analysis is the descriptive system described by Kittler et al, now widely adopted. Terminology is much simpler in this system than in tranditional metaphoric dermoscopic pattern recognition. It is a single step system. Describe the lesion and decide if it should be excised or not. Lesions with asymmetry of structural elements and patterns are suspicious of malignancy.
Dermoscopic features are broken down into elements: lines and rounded structures. The absence of a defined structure is described as structureless.
- Lines may be reticular, branched, parallel, radial or curved
- Rounded structures may be circles, dots, clods, pseudopods (radial line + clod) or structureless zones
- Colours are black, blue, red, light and dark brown, grey, yellow, orange, white, purple and skin coloured
Global dermoscopic patterns for melanocytic lesions are described using these terms.
- Reticular pattern: intersecting lines
- Radial line pattern: radial lines
- Parallel line pattern: lines in furrows or on ridges
- Clod pattern: aggregated clods
- Dotted pattern: diffuse, scattered, central or peripheral
- Structureless pattern: no lines or rounded structures
- Mixed patterns: lines + dots, lines + circles, lines + clods, structureless + lines or dots or clods
Non-melanocytic lesions are made up of the same elements.
- Seborrhoeic keratosis: white / yellow clods, brown / black clods, blue / grey clods, thin or thick curved lines (fingerprinting in solar lentigo or ridges in seborrhoeic keratosis). Solar lentigo can also show reticular or structureless pattern. In addition, note sharp lesion margin. Facial lesions may have brown circles.
- Lichen-planus like keratosis is made up of grey dots.
- Pigmented basal cell carcinoma (BCC): no brown lines, brown and blue-grey dots/clods, sometimes with small or larger segmental peripheral radial lines. Pigmented and non-pigmented BCC: branched red lines, short white shiny lines, yellow/red structureless zones or clods (ulceration)
- Vascular lesions: red/blue/purple clods (angioma) or structureless zones (pyogenic granuloma). Haemorrhage is structureless, usually several colours, with a sharp border and satellite clods. Acral subcorneal haemorrhage has parallel ridge pattern.
- Dermatofibroma: structureless or intersecting fine brown or red lines in peripheral zone, often with white structureless centre, may have white shiny areas centrally. Appearance may be bland
Chaos and clues
Chaos means the lesion shows more than one pattern, and asymmetry of structure and/or colour on dermatoscopy. This is true for melanoma, basal cell carcinomas and squamous cell carcinomas. Consider excising the lesion if it has one or more dermoscopic clues to malignancy:
- Eccentric structureless area (any colour)
- Grey or blue structures
- Peripheral black dots or clods
- Segmental radial lines or pseudopods
- Polymorphous vessels
- White lines
- Thick lines – reticular or branched
- Parallel lines on ridges (palms and soles only)
All the melanocytic lesions illustrated in the figures below show chaos. Similar chaos and clues can be observed in the basal cell carcinomas illustrated above.
Clues to malignancy in chaotic lesions (melanoma)
Activity
Practice pattern analysis by identifying global and local features in melanocytic lesions. Do the same using modified pattern analysis terminology.
Previous ChapterReferences
- Dermoscopy of pigmented skin lesions: results of a consensus meeting via the Internet. J Am Acad Dermatol. 2003 May;48(5):679-93. Medline.
- Braun RP, Rabinovitz HS, Oliviero M, Kopf AW, Saurat JH. Pattern analysis: a two-step procedure for the dermoscopic diagnosis of melanoma.Clin Dermatol. 2002 May-Jun;20(3):236-9. Medline.
- Carli P, Quercioli E, Sestini S, Stante M, Ricci L, Brunasso G, De Giorgi V. Pattern analysis, not simplified algorithms, is the most reliable method for teaching dermoscopy for melanoma diagnosis to residents in dermatology. Br J Dermatol. 2003 May;148(5):981-4. Medline.
- Dermatoscopy. A Method Algorithmic for Diagnosis Accurate by Harald Kittler, M.D. and Philipp Tschandl, M.D., Derm101.com
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