Areas within a lesion that are devoid of any network or other structures, such as globules or regression structures (i.e., scars, peppering, granularity, or blue-white veil over flat areas), are called “structureless areas”. Their size should be at least 10% of the lesions's total surface area. Structureless areas can be hypopigmented, hyperpigmented or regularly pigmented.
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: 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: solar lentigo, flat seborrheic keratosis, pigmented Bowen’s disease, melanocytic nevus of "superficial" or "superficial and deep" congenital type.
- Red + structureless: recent hemorrhage in the stratum corneum. This will become a black structureless lesion as the hemoglobin degrades, before it entirely disappears due to transepidermal elimination.
More than one color
Difficult to decide whether clods or structureless. Clods: well circumscribed and always occur in numbers. Structureless: one large contiguous area.
- Colors of keratin (yellow and orange): keratinizing lesions such as seborrheic keratosis.
- Differential diagnoses: basal cell carcinoma
- Colors of hemoglobin (red and purple): hemorrhage, or hemorrhage in a pre-existing lesion such as a nevus.
- Black zones in structureless lesion: thrombosis.
- Differential diagnoses: black should be attributed to blood when it appears together with red or purple and attributed to melanin when it appears together with brown, blue or gray.
- Symmetrical distribution of melanin: nevus.
- Asymmetrical distribution of melanin: melanoma, melanoma metastasis, seborrheic keratosis.
- Differential diagnosis: pigmented basal cell carcinoma or a dermatofibroma.
A blotch is defined as an area with a size that is at least 10% of the lesion’s surface area and is heavily pigmented. In a blotch the melanin pigment is often present throughout the skin, including the stratum corneum, epidermis, and the dermis . The dark pigment in a blotch visually obscures the ability to discern any underlying structures . Blotches can be regular or irregular.
Regular blotches are defined as those that display symmetry, regular borders,homogenous dark hue, and are located within the center of the lesion. A pigment network often surrounds a regular blotch. Regular blotches are associated with nevi. Regular blotches can be seen in “activated” nevi and are attributed to heavy melanin concentrations in the stratum corneum. Because the pigment is concentrated in the stratum corneum, it can easily be stripped off using a tape-stripping procedure, thereby revealing underlying structures.
Irregular blotches are defined as those that are asymmetric, have irregular contours, are located off center, and/or display multiple dark hues (i.e., heterogenous dark hues). Irregular blotches are associated with melanoma or dysplastic nevus.
Hypopigmented structureless areas have a lighter pigment compared with the rest of the lesion; however, they manifest the same or slightly more pigment compared with the surrounding normal skin (N.B.: structureless areas that are hyperpigmented are called blotches). Focal structureless areas within a lesion are a common finding in nevi.
In contrast, focal tan to light brown structureless areas at the periphery of a melanocytic lesion is commonly associated with melanoma. Peripherally located structureless areas in melanoma tend to have a light brown to fawn color and tend to end abruptly at the edge of a lesion. Histologically, these areas are characterized by flattening of the DEJ (loss of the undulating pattern of rete ridges and dermal papillae) and scattering of atypical melanocytes in suprabasal epidermal layers (i.e., pagetoid cells).
- Yadav et al.: Histopathologic correlates of structures seen on dermoscopy (epiluminescence microscopy). Am J Dermatopathol 1993;15:297-305. PMID: 8214386.
- 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;74:1093-106. PMID: 26896294. DOI.