Reflectance confocal microscopy patterns and structures of clinically dark lesions are described. Because many of the dark lesions have melanin in superficial skin layers these lesions show great semiology by confocal. Limitations and pitfalls of reflectance confocal microscopy in clinically dark lesions are also detailed.
Key points
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Black color in melanoma is associated with melanin in upper epidermis.
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Under reflectance confocal microscopy (RCM), multiple bright atypical pagetoid cells or atypical cobblestone are visible in upper layers of the epidermis.
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Blue color in dermoscopy corresponds with pigment deep in the dermis.
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Blue color may correspond with bright nests or sheets of atypical cells in melanoma, spindle cells in blue nevus, or a tumor island wrapped by dendrites in pigmented basal cell carcinomas.
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Exogenous pigmentation can also be evaluated by RCM.
Introduction
In vivo reflectance confocal microscopy (RCM) is a noninvasive imaging technique that provides images of the superficial layers of the skin at nearly histologic resolution generated thanks to backscatter of light by several structures. Melanosomes, which are highly reflective, are among the structures that generate white images in RCM. Thus, clinically dark lesions are easily visible by RCM because of melanin. In the RCM, light penetrates to a subsurface focus of the laser and reflects back from that focus out of the skin and into a detector in the microscope. Light that reflects superficial to the focus is eliminated, so if the focus is too deep, there will be no signal. For the same reason, if much melanin exists in superficial layers, like in black lamella ( Fig. 1 ), no signal is generated from the deep epidermis or dermoepidermal layer. RCM can also detect pagetoid melanocytes in the epidermis, which correlate with black dots or dark blotches in dermoscopy. The depth penetration of RCM is limited to 100 to 200 μm in human skin at the 830 nm laser wavelength used in the commercial system. The variability in the imaging penetration depth also depends on natural variations in the concentration of other reflective components comprising skin, such as keratin or collagen in addition to melanin. RCM criteria found in more superficial anatomic layers may be more readily identified, because there is decay in laser light intensity with increasing imaging depth and hence decrease in optical resolution. Because of the limitation in the penetration, those dark blue lesions, in which melanin is deep in dermis, are not always visible by RCM. Finally, some lesions can be clinically dark owing to substances or structures other than melanin structures, such us hemoglobin or exogenous materials. According to the reflective properties of the material, the images generated will be different. In the present article, the RCM criteria of several dark lesions are reviewed ( Table 1 ).
| Melanocytic | Non Melanocytic | |
|---|---|---|
| Benign | Black nevus Blue nevus Spitz | Seborrheic keratosis Ink spot lentigo Angioma Angiokeratoma Pilomatricoma Ocronosis, argiria Tattoos |
| Malignant | Melanoma Seborrhoeic-like melanoma Malignant blue nevus Blue nevus like cutaneous metastasis | Basal cell carcinoma |
Introduction
In vivo reflectance confocal microscopy (RCM) is a noninvasive imaging technique that provides images of the superficial layers of the skin at nearly histologic resolution generated thanks to backscatter of light by several structures. Melanosomes, which are highly reflective, are among the structures that generate white images in RCM. Thus, clinically dark lesions are easily visible by RCM because of melanin. In the RCM, light penetrates to a subsurface focus of the laser and reflects back from that focus out of the skin and into a detector in the microscope. Light that reflects superficial to the focus is eliminated, so if the focus is too deep, there will be no signal. For the same reason, if much melanin exists in superficial layers, like in black lamella ( Fig. 1 ), no signal is generated from the deep epidermis or dermoepidermal layer. RCM can also detect pagetoid melanocytes in the epidermis, which correlate with black dots or dark blotches in dermoscopy. The depth penetration of RCM is limited to 100 to 200 μm in human skin at the 830 nm laser wavelength used in the commercial system. The variability in the imaging penetration depth also depends on natural variations in the concentration of other reflective components comprising skin, such as keratin or collagen in addition to melanin. RCM criteria found in more superficial anatomic layers may be more readily identified, because there is decay in laser light intensity with increasing imaging depth and hence decrease in optical resolution. Because of the limitation in the penetration, those dark blue lesions, in which melanin is deep in dermis, are not always visible by RCM. Finally, some lesions can be clinically dark owing to substances or structures other than melanin structures, such us hemoglobin or exogenous materials. According to the reflective properties of the material, the images generated will be different. In the present article, the RCM criteria of several dark lesions are reviewed ( Table 1 ).
| Melanocytic | Non Melanocytic | |
|---|---|---|
| Benign | Black nevus Blue nevus Spitz | Seborrheic keratosis Ink spot lentigo Angioma Angiokeratoma Pilomatricoma Ocronosis, argiria Tattoos |
| Malignant | Melanoma Seborrhoeic-like melanoma Malignant blue nevus Blue nevus like cutaneous metastasis | Basal cell carcinoma |
Dark melanocytic lesions
Even though most melanocytic lesions are brown, from light brown in fair skin to dark brown in dark skin, the presence of black color is less frequent and associated to specific diagnosis: melanoma, pigmented Spitz/Reed nevus, and black nevus (nevus with black lamella in dark skinned patients or after exposure to ultraviolet light). We also consider dark color the presence of dark blue, again, in the context of melanocytic lesions associated to few diagnosis, melanoma and blue nevus.
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Black color in melanoma: The presence of black color in melanoma is associated to the presence of melanin in upper epidermis, under RCM multiple bright atypical pagetoid cells ( Figs. 2 and 3 ) are visible in upper layers of the epidermis. Occasionally, in lesions with hyperkeratosis and transepidermal elimination of pigment in keratinocytes, a bright cobblestone is visible obscuring the dermoepidermal layers (see Fig. 3 ). If melanin is in atypical melanocytes in upper epidermis, then atypical cobblestone is present (with larger cells and the presence of large nuclei; Fig. 4 ), but if melanin is only present in keratinocytes of the upper layers of the epidermis, typical cobblestone can be present (see Fig. 1 ), obscuring deeper layers of the epidermis. In those cases, if we cannot see the dermoepidermal junction, melanoma cannot be ruled out by RCM.
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