Dermoscopy of facial lesions

INTRODUCTION — Dermoscopy is a noninvasive, in vivo technique used for the examination of skin lesions. It is performed with a handheld instrument called a dermatoscope, which allows the visualization of subsurface skin structures in the epidermis, dermoepidermal junction, and upper dermis that are usually not visible to the naked eye.

For clinicians who have been formally trained, dermoscopy significantly improves the diagnostic accuracy of pigmented and nonpigmented skin lesions [1,2]. However, the dermoscopic diagnosis of lesions located on the face may be challenging due to the unique anatomic and histologic features of facial skin and their progressive changes caused by chronologic and photo-induced aging.

This topic will review the dermoscopic features of benign and malignant facial lesions. The principles of dermoscopy and the dermoscopic evaluation of skin lesions, mucosal lesions, pigmented lesions of palms and soles, nail lesions, and hair and scalp are discussed separately. Dermoscopic algorithms for skin cancer triage are also discussed separately.

●(See "Overview of dermoscopy".)

●(See "Dermoscopic evaluation of skin lesions".)

●(See "Dermoscopy of mucosal lesions".)

●(See "Dermoscopy of pigmented lesions of the palms and soles".)

●(See "Dermoscopy of nail pigmentations".)

●(See "Dermoscopy of nonpigmented nail lesions".)

●(See "Overview of dermoscopy of the hair and scalp".)

●(See "Dermoscopic algorithms for skin cancer triage".)

HISTOLOGIC FEATURES OF FACIAL SKIN — The facial skin is characterized by a thin epidermis with an extremely thin stratum corneum, nearly flat dermoepidermal junction, and a high density of large pilosebaceous units [3,4]. Continuous anatomic changes occur in its anatomy, due to intrinsic (chronologic) and extrinsic (photo-induced) aging [5]. The hallmark of sun-damaged skin is solar elastosis, characterized by the deposition in the upper dermis of a fibrillary material composed of elastin, fibronectin, and glycosaminoglycans. Other changes include epidermal atrophy, thinning of the spinous layer, flattening of the dermoepidermal junction with loss of rete ridges, and decreased collagen content (picture 1). (See "Photoaging".)

DERMOSCOPIC-PATHOLOGIC CORRELATION — While the pigment network is the dermoscopic hallmark of melanocytic pigmented lesions located on the trunk and extremities, a true pigment network is rarely found on adult facial skin. The pigment network corresponds to epidermal melanin (either in melanocytes or keratinocytes) arranged along the elongated rete ridges. Thereby the tips of the rete ridges appear as network holes and the lateral borders as network lines (figure 1) [6,7].

Because of the histologic characteristics of facial skin (ie, flat dermoepidermal junction, absence of rete ridges, and high density of pilosebaceous units), pigmented lesions in this location exhibit distinctive dermoscopic patterns, which include:

●Pseudonetwork – Pigmented keratinocytes or melanocytes along the flattened dermoepidermal junction appear on dermoscopy as structureless diffuse brown pigmentation interrupted by numerous, variably broad and hypopigmented "holes," which correspond to hair follicles and sweat gland openings (figure 1). The combination of diffuse brown pigmentation and nonpigmented adnexal openings results in a distinctive dermoscopic feature known as "pseudonetwork," which is characteristic of facial melanocytic lesions (picture 2).

●Gray circles – Gray circles, also known as asymmetric pigmented hair follicles, correspond to pigmented melanocytes within the hair follicle (figure 2) [8,9]. The gray circles pattern is a unique dermoscopic feature of lentigo maligna (LM) (figure 2 and picture 3A).

●Yellow clods – The presence of keratotic plugs within the follicular structures enlarges the follicular openings and gives rise to variably large, partially confluent white to yellow clods (figure 2). Yellow clods are typically seen in pigmented actinic keratoses (AKs).

Since the pseudonetwork is not specific of facial melanocytic lesions but can be seen also in nonmelanocytic pigmented lesions, additional criteria must be employed to differentiate melanocytic from nonmelanocytic lesions of the face [6,7,10].

BENIGN MELANOCYTIC LESIONS

Common nevus — In adults, the most common facial nevi are intradermal nevi of the Miescher type. They appear clinically as dome-shaped, usually nonpigmented or hypopigmented nodules with a smooth surface (picture 4). Terminal hairs are often present.

On dermoscopy, Miescher nevi typically reveal comma-shaped or curved vessels and a structureless skin-colored to light brown background pigmentation. At times, residual brown globules (clods) or brown thick circles, mainly located around the hair follicles, can be seen (picture 5) [11,12].

In children, common facial nevi usually appear as flat, pigmented macules or papules, characterized dermoscopically by structureless, brown to brown-gray pigmentation and small globules, and histologically correspond to compound nevi in most cases. The age-related difference in the morphologic appearance of facial nevi between children and adults has led to the concept that facial nevi may initially present as flat and pigmented macules and over time acquire the typical appearance of the intradermal nevus of Miescher [11,13].

Blue nevus — Blue nevi have a predilection for the head/neck area, especially the scalp. They appear clinically as bluish macules or papules (picture 6A-B). The dermoscopic hallmark of blue nevus is a structureless blue pigmentation, although structureless color variegations of blue and white (white-blue nevus) or blue and brown (brown-blue nevus) can be sometimes observed (picture 7). (See "Acquired melanocytic nevi (moles)", section on 'Blue nevi'.)

It is important to remember that structureless blue color may also be seen in nodular melanoma, melanoma metastases, or heavily pigmented basal cell carcinoma (BCC). However, in contrast with the stable history of blue nevi, malignant tumors are generally associated with recent onset, rapid growth, and other clinical signs, such as erosions or ulceration. In the absence of a reliable history, blue lesions should be biopsied and sent for histopathologic examination.

The so-called "blue-black rule" has been proposed as an additional dermoscopic clue to differentiate blue nevus from nodular melanoma [14]. This rule states that the combined presence of blue and black colors (either structureless or in the form of blotches or dots) should always raise the suspicion of nodular melanoma. Lesions with structureless blue and black color on dermoscopy should be biopsied.

Spitz nevus — Spitz nevus is a benign, indolent melanocyte proliferation that most commonly develops in children, adolescents, and young adults. There are two main clinical variants of Spitz nevus, the nonpigmented (classic Spitz nevus) and the pigmented, Reed-like Spitz nevus. Nonpigmented Spitz nevus typically presents as a rapidly growing pink nodule on the cheek of a child (picture 8). On dermoscopic examination, it often exhibits coiled vessels and a white network (also called reticular depigmentation or negative network) over a pink to reddish background (picture 9). Additionally, the regularly distributed dotted vessels represent a common dermoscopic pattern of flat nonpigmented variant of Spitz nevus (picture 10). (See "Spitz nevus and atypical Spitz tumors".)

Pigmented Spitz/Reed nevus typically appears as a heavily pigmented, growing papule (picture 11). On dermoscopy, it reveals a structureless, black to gray color intermingled with hypopigmented follicular openings and irregular peripheral streaks, pseudopods, or globules lines (picture 12). It should be noted that a starburst pattern is rarely seen in facial Reed nevus (picture 13).

The challenges and controversies in clinical identification, biologic behavior, and management strategies arise from lesions displaying a Spitzoid appearance. Adding to the complexity is the presence of tumors defying precise histopathologic classification. To address these complexities, the International Dermoscopy Society has introduced a consensus-driven algorithm [15]. This algorithm suggests excising dermoscopically asymmetrical Spitzoid lesions (whether flat or raised), nodular lesions, and flat symmetric Spitzoid lesions in individuals aged 12 years and above.

Solar lentigo — Solar lentigines are associated with ultraviolet (UV) exposure and skin aging and appear as multiple brownish spots a few millimeters to >5 mm in diameter that range in color from light brown to dark brown (picture 14). Histologically, they show increased deposition of melanin in keratinocytes and an increased number of melanocytes arranged in a linear fashion at the dermoepidermal junction. (See "Benign pigmented skin lesions other than melanocytic nevi (moles)", section on 'Solar lentigo'.)

Dermoscopy may show faint pigmented fingerprint structures or a structureless pattern. Frequently, a delicate, light brown pseudonetwork with well-defined borders and a "moth-eaten" edge is recognizable (picture 15) [16].

LENTIGO MALIGNA AND LENTIGO MALIGNA MELANOMA — The terms lentigo maligna (LM) and lentigo maligna melanoma (LMM) refer to in situ and invasive melanoma, respectively, arising on chronically sun-damaged skin. (See "Lentigo maligna: Clinical manifestations, diagnosis, and management" and "Melanoma: Clinical features and diagnosis", section on 'Lentigo maligna melanoma'.)

Dermoscopic features — LM and LMM exhibit a range of dermoscopic features that differ from those of melanoma arising on the trunk or extremities. These features are either related to the follicular openings or to the interfollicular skin. One or more of the following dermoscopic structures are commonly seen in LM and LMM [8,9,16-22]:

●Follicular structures

•Asymmetric pigmented follicular openings – They appear as gray circles within the follicular opening (picture 16).

•"Circle-within-a-circle" – This feature consists of an inner small gray circle within the follicular opening, surrounded by a larger, outer gray to gray-brown circle or lines (picture 17).

•Target-like pattern, also called "dot-within-a-circle" – This feature refers to a gray dot or clod in the center of a hair follicle that is surrounded by a gray circle (picture 18).

•Obliterated hair follicles – This feature refers to large gray to bluish blotches within follicular openings. They are a sign of invasive LMM (picture 19).

•Irregularly distributed brown dots/globules – Light to dark brown dots/globules irregularly distributed throughout the lesion.

●Interfollicular structures

•Annular-granular pattern – This feature refers to densely aggregated, partially confluent grey dots or clods that are located in the interfollicular space (picture 20).

•Zig-zag pattern – This feature refers to brownish-gray dots and lines arranged in an angulated, linear pattern representing incompletely formed, rhomboidal structures, forming a zig-zag appearance (picture 21) [23].

•Pigmented rhomboidal structures – This pattern consists of brown to grayish, angulated lines located in the interfollicular space that form rhomboids (picture 22).

•Red rhomboidal structures – This pattern consists of linear vessels that are seen in the interfollicular space around the follicular openings (picture 23).

•Increased density of the vascular network – The vascular network appears of higher density within the lesion than in the surrounding peripheral skin (picture 24).

●Colors

•White scar-like areas – White to gray structureless areas in-between the follicular openings.

•Gray color – Presence of shades of gray color within the lesion.

•Darkening at dermoscopic examination – Presence of a color that is invisible to the naked eye and appears on dermoscopy darker than all clinically observable shades of brown or gray in the lesion.

Progression model for lentigo maligna — Based upon dermoscopic criteria, a four-step progression model of LM has been proposed [24]. According to this model, asymmetric pigmented follicular openings, also called gray circles, gray dots within the follicular opening, and/or circles within circles represent the earliest features of LM (picture 16).

These structures subsequently evolve to a so-called annular-granular pattern (picture 20), which consists of aggregated fine gray dots, gray globules, and streaks around the follicle. With further progression of the lesion, these streaks become longer and intersect with neighboring streaks, finally forming angulated lines between hair follicles called rhomboidal structures (picture 22). Further progression and invasion is represented by the development of obliterated hair follicles filled with black or blue-gray blotches (picture 19) and structureless blue areas, white scar-like, and milky-red areas [9].

BENIGN NONMELANOCYTIC LESIONS

Sebaceous hyperplasia — A benign hyperplasia of the sebaceous glands or sebaceous hyperplasia is commonly seen on the forehead, nose, and cheeks of middle-aged or older patients (picture 25) [25]. Lesions are usually multiple and do not exceed the size of a few millimeters. (See "Cutaneous adnexal tumors", section on 'Sebaceous hyperplasia'.)

Dermoscopically, the lesions are characterized by a structureless yellow to whitish center surrounded by short linear vessels (picture 26). These vessels are also called "crown vessels" because they embrace but do not cross the central parts of the lesion. In contrast, the arborizing vessels of nodular basal cell carcinoma (BCC) are typically bright red in color, sharply focused, and branch all over the tumor's surface (picture 27).

Lichen planus-like keratosis — Lichen planus-like keratosis (LPLK) or lichenoid keratosis is considered a regressing solar lentigo or seborrheic keratosis. Clinically, it appears as a solitary, gray to brown papule or plaque; on dermoscopy, LPLK shows a coarse or fine, gray to blue, granular pigmentation covering most of the lesion (picture 28). Fully or nearly fully regressed LPLK is characterized by diffuse brownish gray granules, which may coalescence to form globules, streaks, or even structures similar to rhomboids [26-28].

Because lentigo maligna (LM) may exhibit the same features as LPLK, a lesion dermoscopically characterized by signs of evident regression should always be biopsied and sent for histopathologic examination.

Seborrheic keratosis — Seborrheic keratoses are common benign tumors that are dermoscopically characterized by one or more of the following patterns [29-31] (see "Seborrheic keratosis"):

●Moth-eaten borders – The borders of the lesion show invaginations that result in a moth-eaten appearance (picture 29).

●Milia-like cysts – These are round, whitish or yellowish clods that correspond to small intraepidermal, keratin-filled cysts (picture 30A-B). They may also be seen in some congenital nevi and in papillomatous melanocytic nevi.

●Comedo-like openings (pseudofollicular openings) – Comedo-like openings are keratin-filled invaginations of the epidermis that correspond histopathologically to comedo-like structures (picture 31); they are mainly seen in seborrheic keratosis or papillomatous melanocytic nevi.

●Sharp demarcation – Abrupt cutoff of pigmentation at the border (picture 32).

●Ring-like structures and fat fingers – These are brown ring-like structures that are densely aligned to one another. Sometimes they might be oval and elongated, resulting in a feature described as "fat fingers," which are typically seen in flat, reticulated seborrheic keratoses (picture 33)[29].

●Fissures and ridges – These are irregular, linear, keratin-filled depressions that might result in a brain-like appearance to the lesion (picture 34).

●Fingerprinting – Describes a network-like structure that is light brown and delicate, with the pattern of a fingerprint (picture 35).

●Hairpin blood vessels – Vascular loops resembling a hairpin. This typical vascular architecture is predominantly seen in irritated seborrheic keratosis (picture 36).

KERATINOCYTE SKIN CANCER — The term "keratinocyte skin cancer" includes actinic keratosis (AK), intraepidermal carcinoma (including Bowen disease), and invasive squamous cell carcinoma (SCC).

Actinic keratosis — AK, also known as solar keratosis or keratinocytic intraepidermal neoplasia, is a common lesion that represents the earliest stage on a continuum with SCC. (See "Actinic keratosis: Epidemiology, clinical features, and diagnosis".)

AKs can be clinically subdivided into three grades, which correspond to distinctive dermoscopic patterns [32,33]:

●Grade 1, slightly palpable AK – Grade 1 AKs are dermoscopically characterized by a red pseudonetwork pattern and discrete white scales (picture 37).

●Grade 2, moderately thick AK – Grade 2 AKs show an erythematous background intermingled by white to yellow, keratotic, and enlarged follicular openings. These features are similar to the surface of a strawberry, hence the name "strawberry pattern" (picture 38A).

●Grade 3, very thick, hyperkeratotic AK – Grade 3 AKs exhibit either enlarged follicular openings filled with keratotic plugs over a scaly and white-yellow appearing background, or marked hyperkeratosis seen as white-yellow structureless areas (picture 38B) [33,34].

Pigmented actinic keratosis — Pigmented AK clinically resembles a darkly pigmented solar lentigo. Pigmented AK may be misdiagnosed as lentigo maligna (LM) and vice versa because, with the exception of gray circles, it may exhibit all the criteria of LM (picture 3A-B) [22,35]. (See 'Lentigo maligna and lentigo maligna melanoma' above.)

Cutaneous squamous cell carcinoma in situ (intraepidermal carcinoma) — Cutaneous squamous cell carcinoma (cSCC) in situ, also called intraepidermal carcinoma or Bowen disease, is characterized by the presence of dotted and/or glomerular vessels, white to yellowish surface scales, and a red-yellowish background color (picture 39). Glomerular vessels represent a variation of dotted vessels but are larger in size and characterized by tortuous capillaries. Both dotted and glomerular vessels often appear within the same lesion and are distributed in small, densely packed clusters or groups.

Pigmented squamous cell carcinoma in situ — The most common appearance of pigmented cSCC in situ is a structureless brown pattern, brown circles, as well as an asymmetric combination of structureless areas and brown dots. The structureless zone is usually hypopigmented (skin-colored, white, or pink) and often eccentrically located. An important clue for the diagnosis of pigmented cSCC in situ is the presence of brown dots, which are arranged as radial lines in the periphery (picture 40) [36,37].

Invasive cutaneous squamous cell carcinoma — The most important dermoscopic features of invasive forms of cSCC are white circles, white structureless areas, masses of keratin (picture 41), and radially arranged hairpin and linear vessels surrounded by a white halo.

Pigmented invasive squamous cell carcinoma — Pigmented cSCCs are rare. Dermoscopy features include blue structureless areas and polymorphic vessels [38].

Progression model for squamous cell carcinoma — A dermoscopic progression model of facial AK developing into cSCC in situ and invasive cSCC has been proposed [33]. AKs with increasing atypia tend to display dotted vessels around follicles. As the lesion evolves to cSCC in situ, the dotted vessels become larger, more convoluted (glomerular vessels), and clustered (picture 39). Hair follicles in this area become smaller and then disappear. Keratotic follicles eventually form the discrete whitish, opaque, scaly areas typically seen in cSCC in situ.

With progression of cSCC in situ to invasive cSCC, the lesion becomes thicker and shows on dermoscopy hairpin and/or linear-irregular vessels. Along with these vascular changes, a central mass of keratin is formed, and ulceration may occur. The so-called "red starburst pattern" (ie, peripheral red lines surrounding a central strawberry pattern) may be seen in evolving lesions (picture 42). Specifically, the red starburst pattern may be a sign of rapid growth of AK, intraepidermal carcinoma, or invasive SCC [33].

BASAL CELL CARCINOMA — The clinical and dermoscopic aspects of basal cell carcinoma (BCC) are influenced by several factors, including histopathologic subtype, location, sex, and skin type. Nodular BCC is the most common type and typically presents on the face as a pink or flesh-colored papule (picture 43). Superficial BCCs most commonly occur on the trunk, and typically present as slightly scaly, nonfirm macules, patches, or thin plaques light red to pink in color (picture 44). (See "Basal cell carcinoma: Epidemiology, pathogenesis, clinical features, and diagnosis".)

Nodular basal cell carcinoma — On dermoscopy, the hallmark of nonpigmented nodular-cystic BCC are focused, bright red, and branching arborizing vessels (picture 27). Yellow-white globules, defined as aggregated, white-yellow structures, are restricted to nonpigmented, mainly nodular type of BCC, located on the head and neck region (picture 45) [39,40]. In addition to arborizing vessels, pigmented nodular BCCs typically exhibit loosely arranged blue-gray globules or dots that differ in size and number (picture 46).

Superficial basal cell carcinoma — The most classic features of nonpigmented superficial BCC are shiny white to red, translucent or opaque structureless areas and multiple small erosions (picture 47). This subtype lacks the classic arborizing vessels, but may reveal short, focused fine telangiectasias with relatively few ramifications. The pigmented variant of superficial BCC may display translucent light brown to grayish concentric structures, spoke-wheel areas, and peripheral finger-like projections (leaf-like structures) (picture 48A-B) [41].

MERKEL CELL CARCINOMA — Merkel cell carcinoma (MCC) is a rare, aggressive cutaneous malignancy that predominantly affects older adults with light skin types. MCC is most often located in the head and neck region. Clinically, MCC presents as a rapidly growing, firm, shiny, flesh-colored or bluish-red, intracutaneous nodule (picture 49A-B). Dermoscopy shows a nonspecific polymorphous vascular pattern composed by linear vessels over a pink background (picture 50) [42].

DIFFERENTIAL DIAGNOSIS OF FACIAL LESIONS

Flat lesions

Pigmented — The differential diagnosis of flat pigmented facial lesions includes lentigo maligna (LM), solar lentigo, pigmented actinic keratosis (AK), and lichen planus-like keratosis (LPLK). The clinical recognition of these lesions is challenging, even if coupled with dermoscopy, and requires the consideration of additional clinical criteria, such as number and location of lesions and lesion surface, topography, and color.

●The lesion color is the single most important dermoscopic criterion to differentiate solar lentigo from LM. The latter often shows a combination of brown and gray color (ie, gray circles, gray dots, gray lines), whereas solar lentigo usually exhibits only brown color [6,10,16,18,24].

●Surface scales; background erythema; white circles; and enlarged, white, follicular openings are an important clue for the diagnosis of grade 2 nonpigmented AK. However, the same pattern can also be seen in pigmented AK and represents an important clue for the diagnosis. Although gray color is the strongest clue for LM, it can also be seen in LPLK and pigmented AK. In the latter, evident follicular openings and erythema might represent important additional diagnostic clues.

●In flat, pigmented facial lesions lacking specific melanocytic dermoscopic features, the presence of irregularly distributed, brown dots/globules is more often associated with LM than with flat, nonmelanocytic skin neoplasms, such as pigmented AK, solar lentigo, flat seborrheic keratosis, or LPLK [43].

●In flat lesions, patterns of gray circles are highly suspicious for facial melanoma, but other patterns do not exclude it. Regardless of pattern, the presence of gray color is a clue to malignancy.

Lesions with gray colors should be biopsied and sent for histopathologic examination [44]. However, the histopathologic diagnosis of early LM may also be difficult, since early lesions may lack significant cytologic atypia or architectural disarrangement [45]. (See "Lentigo maligna: Clinical manifestations, diagnosis, and management".)

Nonpigmented — The differential diagnosis between grade 1 and 2 AKs and fully developed squamous cell carcinoma (SCC) is mainly based upon the presence of vascular patterns [33]. Dotted or glomerular vessels, hairpin vessels, and linear-irregular vessels are most frequently seen in SCC. Additional criteria that are significantly associated with SCC include targetoid hair follicles, white structureless areas, a central mass of keratin, and ulceration.

Raised lesions — The differential diagnosis of raised or nodular lesions on the face, which includes dermal nevus and nodular basal cell carcinoma (BCC), is mainly based upon the presence of vascular patterns [46,47]. Vessels in intradermal nevi are usually blurred, curved, and show few ramifications. In contrast, nodular BCC displays dull red, sharply focused, arborizing vessels that reveal multiple ramifications into finest capillaries.

BENEFITS AND LIMITATIONS OF DERMOSCOPY — Dermoscopy may improve the diagnostic accuracy of formally trained clinicians for most nodular skin lesions occurring on the face. However, the dermoscopic diagnosis of flat, pigmented lesions remains challenging even for the experienced clinician [44]. Since the dermoscopic criteria to differentiate benign from malignant lesions have not been adequately evaluated in large studies, it is important to maintain a low threshold of clinical suspicion to perform a biopsy for histopathologic examination. For large lesions located on cosmetically sensitive areas that require a partial biopsy, dermoscopy may be especially useful to determine the most suspicious areas to be biopsied [48].

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Dermoscopy".)

SUMMARY AND RECOMMENDATIONS

●Histology of facial skin and associated dermoscopic patterns – The dermoscopic diagnosis of lesions located on the face may be challenging due to the unique anatomic and histologic features of facial skin (figure 1) and their continuous changes caused by chronologic aging and photoaging. While the pigment network is the dermoscopic hallmark of melanocytic pigmented lesions located on the trunk and extremities, a true pigment network is rarely seen on adult facial skin. Distinctive dermoscopic patterns found in facial pigmented lesions include the pseudonetwork (picture 2), gray circles, and yellow clods (picture 3A). (See 'Histologic features of facial skin' above and 'Dermoscopic-pathologic correlation' above.)

●Benign melanocytic lesions – Facial melanocytic lesions are characterized by a variety of dermoscopic patterns. Intradermal nevi typically show comma-shaped or curved vessels and a structureless skin-colored to light brown background pigmentation (picture 5), blue nevi show a structureless blue/brown pigmentation (picture 7), and Spitz nevi reveal coiled vessels and a white network background (picture 9). (See 'Benign melanocytic lesions' above.)

●Lentigo maligna and lentigo maligna melanoma – Lentigo maligna (LM) and lentigo maligna melanoma (LMM) exhibit a range of dermoscopic features that differ from those of melanoma arising on the trunk or extremities, including follicular and interfollicular structures: asymmetric pigmented follicular openings (picture 16), "circle-within-a-circle" structures (picture 17), target-like pattern (picture 18), obliterated hair follicles (picture 19), and pigmented rhomboidal structures (picture 22). (See 'Lentigo maligna and lentigo maligna melanoma' above.)

●Keratinocytic skin cancers

•Actinic keratosis and cutaneous squamous cell carcinoma – The so-called "strawberry pattern" and white-yellow structureless areas are characteristic of actinic keratosis (AK) (picture 38A-B). However, pigmented AKs may be difficult to differentiate from LM because, with the exception of gray circles, they may exhibit all the criteria of LM (picture 3A-B). White circles, white structureless areas, masses of keratin, and hairpin and linear-irregular vessels are the main features of cutaneous squamous cell carcinoma (cSCC) (picture 41). (See 'Keratinocyte skin cancer' above.)

•Basal cell carcinoma – Bright red arborizing vessels are the dermoscopic hallmark of nodular basal cell carcinoma (BCC) (picture 27). Blue gray globules or dots can be seen in pigmented tumors (picture 46). Superficial BCCs show white to red structureless areas, small erosions, and fine telangiectasias (picture 47). Pigmented variants may show brown to grayish concentric structures, spoke-wheel areas, or peripheral finger-like projections (picture 48A). (See 'Basal cell carcinoma' above.)