The Dermoscopic Patterns of Melanoma and Non-Melanoma Skin Cancer

Introduction

Dermoscopy (also known as epiluminescence microscopy or dermoscopy) is a method of using a handheld microscope to examine skin lesions. It is an in-vivo, non-invasive technique that permits clinicians to better visualize cellular structures in the epidermis, dermoepidermal junction, and dermis; in contrast to naked-eye inspection, where clinicians may only detect the gross morphological features of the lesions, such as size, shape, colors, elevations or ulcerations. The development of dermoscopy has led to the recognition of a number of new morphologic structures that can improve diagnostic accuracy and confidence level for both pigmented and non-pigmented skin lesions.

The introduction of dermoscopy to clinical dermatology is largely credited to Rona MacKie in 1971, who first demonstrated its clinical utility in differentiating benign versus malignant pigmented skin lesions. Since then, clinicians and researchers have worked to better define the diagnostic features and criteria associated with an array of pigmented and non-pigmented skin lesions. Over the past two decades, there has been nearly a 20-fold increase in the number of scientific publications in this field. The number of clinicians worldwide who use dermoscopy has also risen at a dramatic rate. In the United States, only 5% of surveyed dermatologists used this diagnostic technique in their daily practice in 1995, and the rate quickly jumped to 23% in 2002. In the latest survey, the rate of adoption in the US is now 60%.

Dermoscopic equipment

Currently, there are two major categories of dermoscopes available in the market ( Table 36.1 ). The first is the non-polarized (NPD) dermoscope. This device contains light-emitting diodes for illumination and is equipped with a 10× to 20× magnification lens ( Fig. 36.1A ). A liquid interface (ideally with refraction index equal to that of skin) is required, and direct contact of the skin with the glass plate of the dermoscope is needed. Different immersion liquids include water, mineral oil, alcohol or gel (i.e. ultrasound gel, antibacterial gel). Alcohol is widely used as it is more hygienic and can reduce the risk of bacterial contamination. For examining nail apparatus, ultrasound or antibacterial gels are the liquids of choice. The viscous nature of gels prevents them from rolling off the convex nail surface. The setup of skin–liquid–glass interface decreases light reflection and increases refraction. By minimizing glare, the stratum corneum appears more translucent and deeper structures in the skin can be visualized.

The second type of dermoscope is the polarized device (PD). This type of device was introduced to the clinical arena in 2000. It uses two polarizers to achieve cross-polarization. Under this condition, the polarizers allow the dermoscope to preferentially capture the backscattered light from the deeper levels of the skin. The major advantage of PD is obviating the need for any fluid or direct contact with the skin and permitting clinicians to quickly scan lesions during the examination ( Fig. 36.1B ). Some of the PD devices allow the user to toggle between contact and non-contact PD mode. A new scope is now commercially available that permits the user to choose between PD and NPD mode.

In general, the dermoscopic image qualities from PD and NPD are relatively similar, but a few important differences exist ( Table 36.1 ). Epidermal structures, such as comedo-like openings and milia-like cysts, are better seen with the NPD. As mentioned above, PD devices obviate the need for direct contact between the skin and the glass plate, therefore reducing the compression effects associated with the NPDs. Consequently, blood vessels and red color areas corresponding to vascular changes are better seen under PD. Improved visualization of vessel morphology has aided the diagnosis of hypomelanotic and amelanotic melanoma, squamous cell cancer, and other inflammatory dermatologic conditions. The differences between NPD and PD are minor, and both types of devices provide complementary information. However, it is important to note that these small subtleties can impact the diagnostic accuracy and confidence level, especially for beginners. Hence, it is important to know which types of dermoscopes one is using in the diagnostic process.

Basal cell carcinoma

The clinical presentation of basal cell carcinoma (BCC) varies from erythematous patches to dark nodules. As a result, differential diagnoses for BCC can be extensive, and dermoscopy can help the clinician improve the diagnostic accuracy for both pigmented and non-pigmented BCCs.

Pigmented BCCs

Pigmented BCCs are not uncommon. With the aid of dermoscopy, light brown, dark brown or black pigmentation can be seen in different subtypes of BCCs, such as superficial, nodular or infiltrative types. These colors are due to the deposition of free melanin, melanocytes or melanophages in the dermis and dermal–epidemal junction. Depending on the depth of these pigmentation sources, different colors are seen. Furthermore, knowledge of the basic histological patterns of BCCs can enhance knowledge regarding the dermoscopic structures and patterns seen in association with pigmented BCCs. Histologically, BCC tumors are commonly present as clusters or islands of basaloid cells in the dermis or the dermoepidermal junction. The peripheries of these tumor islands are lined with palisading cells. The presence of free melanin or melanophages within these tumor islands produces the pigmentation. The different dermoscopic structures correlate to (1) the shape and size of the tumor islands and (2) the variation in the amount and distribution of the melanin pigment. Pigmentation found in small islands of tumors may be seen as multiple blue-gray globules under dermoscopy. The presence of large amounts of pigmentation seen in a large cluster of tumors may correspond to the ovoid nests.

Many dermoscopic features associated with pigmented BCCs have been described. These features are listed in Table 36.2 , and Figures 36.2 and 36.3 illustrate some of these in dermoscopic images of BCCs. The majority of these dermoscopic structures were described by Menzies et al., when the investigators examined 426 lesions and reviewed 45 dermoscopic structures to select out the critical dermoscopic features that distinguish pigmented BCCs from other pigmented skin lesions. This analysis yielded a very practical diagnostic method with a sensitivity of 93% and specificity of 89–92%. A comparable level of sensitivity and specificity results were reported by Peris and co-workers, who independently validated this diagnostic method in their patient population.

Table 36.2

Dermoscopic Structures of Pigmented and Non-Pigmented Basal Cell Cancer

Dermoscopic Structures	Description
Large blue-gray ovoid nests	The nests are defined as confluent or nearly confluent, well-circumscribed, pigmented ovoid or elongated areas that are not closely connected to the pigmented tumor body. Nests are larger than globules
Multiple blue-gray globules	These are well-defined round or oval structures, larger than dots, but smaller than large ovoid nests. They are blue-gray in color
Leaf-like areas	These areas are defined as discrete, bulbous extensions connected at a base area, forming a leaf-like pattern. They are usually brown or gray-blue in color
Spoke-wheel areas	These are well-defined radial projections surrounding a central point. The projections have tan, blue or gray color, and the central point usually is dark brown, blue or black. This structure is very specific for BCCs
Arborizing telangiectasia (serpentine branched vessels)	These are multiple branching blood vessels in a tree-like pattern. These are often appreciated in non-pigmented BCCs, and are rarely seen in nevi, melanomas and other benign pigmented skin lesions
Ulceration	Ulceration may appear as congealed blood. It is important to rule out a previous history of trauma for ulceration to be a valid feature
Small fine telangiectasia *	Small-diameter vessels have length <1 mm; few branches
Shiny white to red areas *	Areas with white to red, translucent to opaque appearance

* Dermoscopic structures associated with non-pigmented basal cell cancer.