Foundations of Dermoscopy

01Dermoscopy uses optical magnification, typically tenfold, to visualize features below the stratum corneum that are not appreciable to the naked eye. The technique can be performed with non-polarized contact instruments (which require an immersion fluid such as alcohol or ultrasound gel and rely on the contact interface to suppress surface reflection) or with polarized devices, which use cross-polarized light to eliminate glare without skin contact. Non-polarized contact dermoscopy emphasizes superficial structures (milia-like cysts, comedo-like openings, the pigment network at the dermo-epidermal junction). Polarized dermoscopy enhances visualization of deeper dermal structures, including vessels and crystalline structures (chrysalis or shiny white streaks) that are not readily visible with non-polarized light.

02The standardized terminology for pigmented skin lesions was refined at the 2000 Consensus Net Meeting on Dermoscopy (CNMD), in which 40 international experts evaluated 108 lesions and reached consensus on definitions, reproducibility, and validity of dermoscopic criteria. The CNMD established a two-step procedure as the morphologic backbone of dermoscopic diagnosis: step one differentiates melanocytic from non-melanocytic lesions; step two differentiates benign melanocytic lesions from melanoma. Although interobserver agreement on individual criteria was often only fair, agreement on the overall diagnosis was good, reflecting the role of pattern gestalt.

03Step-one melanocytic clues include pigment network or pseudonetwork on facial skin, aggregated globules, streaks (combining pseudopods and radial streaming), homogeneous blue pigmentation, and the parallel pattern on volar or mucosal sites. The presence of any one of these features classifies the lesion as melanocytic and triggers step-two analysis. Importantly, in the absence of all the listed criteria, a flat pigmented lesion is also handled as melanocytic by default to avoid missing featureless melanoma.

04Step-one non-melanocytic clues are equally specific. Seborrheic keratosis is suggested by multiple milia-like cysts, comedo-like openings, light-brown fingerprint-like structures, and a cerebriform brain-like surface pattern. Basal cell carcinoma is recognized by arborizing telangiectases, leaf-like areas, large blue-gray ovoid nests, multiple blue-gray globules, spoke-wheel structures, and ulceration when no clear trauma history exists. Vascular lesions show red-blue lacunas or homogeneous reddish-black areas. Three exceptions deserve attention: pigment network can rarely appear in solar lentigo, seborrheic keratosis, dermatofibroma, and accessory nipple; homogeneous blue pigmentation can appear in some hemangiomas, basal cell carcinomas, and dermal metastases; ulceration also occurs in invasive melanoma.

05Within melanocytic lesions, eight global patterns describe how pigment is distributed: reticular (network covering most of the lesion), globular, cobblestone (large angulated globules), homogeneous, starburst (radial streaks at the edge), parallel (acral and mucosal), multicomponent (three or more patterns combined), and nonspecific. The multicomponent pattern carried the highest odds ratio for melanoma in the CNMD (4.3), while globular, cobblestone, homogeneous, and starburst patterns were most predictive of benign nevi. Local features include pigment network, dots and globules, streaks, blue-whitish veil, regression structures, hypopigmentation, blotches, and vascular structures, each scored as typical (regular) or atypical (irregular) based on symmetry of color, thickness, and distribution.

06Vascular morphology is a major diagnostic axis, especially for amelanotic and partially pigmented tumors. Comma-like vessels point to dermal nevus. Hairpin vessels, when uniformly distributed, suggest seborrheic keratosis; when irregular, melanoma must be considered. Dotted vessels, linear irregular vessels, and milky-red areas or globules favor melanoma. A polymorphous vascular pattern (combining several vessel morphologies) is highly suspicious for malignant tumors including amelanotic melanoma and porocarcinoma. Vessels seen within regression areas are an additional melanoma clue.

07Color reflects the depth and quantity of melanin: black corresponds to melanin in the stratum corneum or upper epidermis; dark brown to the dermo-epidermal junction; light brown to deeper junctional pigment or a thinner network; gray to dermal melanophages or regression; blue to deep dermal melanin (Tyndall effect); white to scar-like fibrosis or regression; and red to vascular structures. The presence of five or six colors carries an odds ratio of 5.0 for melanoma in CNMD-validated ABCD scoring.

08Site-related patterns must be known to avoid misclassification. Facial skin shows a pseudonetwork interrupted by adnexal openings; melanoma on chronically sun-damaged facial skin progresses through annular-granular structures, gray pseudonetwork, rhomboidal structures, and asymmetric pigmented follicles. Volar skin (palms and soles) shows benign parallel-furrow, lattice-like, or fibrillar patterns; the parallel-ridge pattern (pigmentation on the ridges rather than the furrows) is the dermoscopic hallmark of acral melanoma. Mucosal lesions follow analogous parallel patterns, with structureless or multicomponent patterns favoring melanoma.