Spitz nevi (SN) are well-known simulators of cutaneous melanoma (CM) from a clinical, dermoscopic, and histopathologic point of view.
The clinical features of SN are protean; they may present as small, well-circumscribed, reddish papules, larger reddish plaques, small dark-brown to black papules, larger, rather well-circumscribed, jet-black plaques (Reed nevus) but also as variegated verrucous plaques. Because of these clinical features SN are often difficult to differentiate from CM by clinical criteria alone. Although SN occur mostly in individuals younger than 20 years of age, they may be rarely found also in the third and fourth decades.
Specific dermoscopic criteria have been described in order to differentiate these nevi from CM, thus increasing diagnostic accuracy for pigmented SN from 56% to 93% [Pehamberger 1987, Steiner 1987, Steiner 1992].
Dermoscopically, about 50% of pigmented SN show a symmetric appearance and a characteristic starburst pattern. This is typified by a prominent, gray-blue to black diffuse pigmentation, and by streaks located regularly at the periphery in a stellate or radiate distribution. A characteristic dermoscopic finding is a central, bizarre or reticular black-whitish to blue-whitish veil, formerly called also reticular depigmentation and negative pigment network. In some examples, a regular and prominent pigment network may be detected. Only a prominent black-blue pigmentation, with no streaks at the periphery, can be more rarely observed. Histopathologically, most of the lesions showing the starburst pattern exhibit the morphologic features of pigmented spindle-cell nevus (Reed nevus), namely, symmetric and well-circumscribed proliferation of spindle-shaped melanocytes arranged in nests closely packed along the dermo-epidermal junction [Barnhill 1995, Cochran 1997, Elder 1991]. In addition, numerous melanophages are present in the papillary dermis immediately beneath the nests of melanocytes.
By dermoscopic examination a second group of pigmented SN (about 25% of cases) reveal a symmetric, basically globular pattern with a regular, discrete, brown to gray-blue pigmentation in the center, and a characteristic rim of large brown globules at the periphery. Brown to gray-blue globules and dots may also extend throughout the lesion. In less pigmented SN a dotted vascular pattern may be detected. The histopathologic correlates of the lesions showing the globular pattern are that of a stereotypical Spitz nevus (spindle- and/or epithelioid-cell nevus). Typically, these tumors display a symmetric silhouette and sharp circumscription with striking nests of spindle and/or large epithelioid cells involving the epidermis and/or the papillary and reticular dermis. Maturation of melanocytes (gradual diminution of nuclear and cellular sizes) with progressive descent into the dermis is a constant finding, whereas necrotic cells and mitotic figures are only occasionally found. The latter morphologic features, however, cannot be seen dermoscopically.
Dermoscopic pitfalls in differentiating pigmented Spitz nevi from melanoma
A third group of pigmented SN (25% of cases) may exhibit an atypical dermoscopic appearance characterized by an uneven distribution of colors and structures. The majority of these cases show an irregular, diffuse, gray-blue pigmentation resembling a blue-whitish veil which represents a specific ELM criterion for the diagnosis of melanoma [Bahmer 1990, Menzies 1996]. Pigment network, brown globules, black dots, and depigmented areas as well as the streaks at the periphery may also be irregularly distributed. Occasionally, a dotted vascular pattern may be observed. Despite the atypical dermoscopic appearance of these SN, the preoperative diagnosis may be in favor of a benign lesion because of the clinical constellation, namely, a given pigmented skin lesion occurring in children and showing no history of growth.
Remarkably, CM may rarely display either the starburst or the globular pattern seen in pigmented SN. Therefore, surgical excision and subsequent histopathologic examination should be performed in pigmented skin lesions revealing the characteristic dermoscopic features of Reed/Spitz nevi, especially when arising in adult patients or showing a history of recent change in color, shape, or size [Argenziano 1999].