Glossary

Evolution

From dermoscopedia

This is the page on the glossary term Evolution which is relevant on dermoscopedia. See also the list of terms.

Description

is change in the heritable characteristics of biological populations over successive generations

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Introduction

In 1948, Sophie Spitz described a group of melanocytic lesions of children, first considered as “melanomas of childhood[1], and subsequently histologically categorized as benign melanocytic proliferations, then renamed as “Spitz nevi”. The majority of Spitz nevi occur in patients younger than 20 years and are less common in adulthood and elderly [2]. Clinically, the Spitz nevus (SN) appears as a solitary, asymptomatic, round to oval, dome-shaped, papule or nodule usually located on the head, neck or extremities of young individuals. In its classic clinical appearance it is pink or red in colour due to a low melanin production and has a rapid growth; however, brown and even black pigmented SN do exist and are especially seen in young adults. In 1975, Reed et al. described a benign pigmented melanocytic lesion commonly founds on the lower extremities of young female, that after was titled as “Reed nevus”. This kind of lesion, histopathologically presents a heavy pigmentation due to oval-spindle melanocytes arranged in nest and fascicles, whereas clinically appears as a solitary, dark brown to black, dome-shape papule or jet-black plaque. Since 1978, the nosological autonomy of Reed nevus from Spitz nevus has been inquired. Some authors include Reed nevus to the morphological spectrum of Sptiz nevus, while other authors still classify Reed nevus as an independent entity differentiated from pigmented Spitz nevus. The histopathologic distinction between Spitz nevus and Reed nevus is often matter of great debate[3]. Nowadays, we distinguish two clinical variants of SN, the classical and the pigmented types, the latter include Reed nevus. The most important issue of SN is their propensity to mimic melanoma clinically, dermatoscopically and histopathologicallly. Moreover, some melanomas histopathologically may resemble Spitz nevi for their “Spitzoid” features and for this reason have been called “Spitzoid melanomas.” Spitzoid lesions represent a difficult and controversial group of tumours, in terms of clinical identification, biologic behaviour and management strategies. Spitz and Reed nevi are benign tumours, but on the other side of the spectrum of spitzoid lesions, there are “Spitzoid melanomas” undoubtedly malignant. Between these two extremes, a series of spitzoid lesions, defined as “ atypical Spitz tumors” and “ melanocytic tumors of uncertain malignant potential (MELTUMP)[4]”, do exist. This is the major reason why evidence-based management guidelines for these kinds of tumours are difficult to define.

Dermoscopic criteria

The use of dermoscopy has increased the accuracy in the diagnosis of SN allowing a better understanding of their evolving behavior. Spitz/Reed nevi can be classified according six different dermoscopic appearances, namely, vascular (pink homogenous), globular, starburst, reticular, atypical and homogenous pattern. In their growing phases, Spitz nevi evolve from globular pattern to a starburst pattern with regular streaks at the periphery (finger like or globule like). After several months, the peripheral projections disappear and the lesion becomes stable with a dermoscopic homogeneous, structureless brown-to-black pigmentation. Finally, in the last phases the lesion involves and loses its pigmentation[5][6]. Simplifying, SN can show, demoscopically, three main patterns: a starburst pattern, a vascular pattern with regularly distributed dotted vessels and a globular pattern with reticular depigmentation.

Non pigmented Spitz nevus

The dermoscopic hallmark of non pigmented Spitz nevus is the vascular pattern, detectable as dotted vessels (Figure 1), monomorphic and uniformly distributed throughout the lesion. In raised or nodular Spitz nevi, the vessels might not appear as small dots, but as larger red globules, twisted (spiral), hairpin or corkscrew vessels, nevertheless their distribution is symmetric. When vascular structures are asymmetrically distributed, or there is brownish color and tan/brown globules within lesion, the lesion is more suggestive for melanoma8. Another frequent additional feature of non pigmented SN is reticular depigmentation (Figure 2) visible either as a negative network (a whitish grid surrounding the vessels), or as chrysalis-like structures (shiny white lines that are often oriented orthogonally or in parallel to each other). Moreover, while negative network can be visualized with both polarized and no polarized dermoscopy, crystalline structures can be seen only with polarized light[7][4]. The differential diagnosis of non pigmented SN includes a series of no melanocytic lesions such as pyogenic granuloma, hemangioma, solitary mastocitoma, juvenile xantogranuloma, lymphoid infiltration of the skin, angiolymphoid hyperplasia with eosinophilia, dermatofibroma and viral wart. At histology, they show a melanocytic proliferation, polygonal or cigar-shaped, with large nuclei, prominent nucleoli, and abundant ground-glass cytoplasm. Large and coalescent eosinophilic bodies (Kamino) at dermo-epidermal junction, edema, teleangectasias and fibrosis of the papillary dermis and melanin within spindle cells and dermal melanophages are also frequently seen[2][8].

Pigmented Spitz nevus

Pigmented SN could show a globular, starburst, reticular, atypical or homogeneous pattern dermoscopically [9] [10][11] [12]. The globular pattern, presents in about 20% of SN, consists of gray-brown to blue globules generally distributed throughout the lesion or mostly at the periphery. A starburst aspect is possible if the peripheral globules are merging with the central body of the lesion. The globular pattern of Spitz nevi differs from the globular pattern seen in growing Clark nevi, because the peripheral globules are distributed in a single row for the latter, while in multiple rows for SN (Fig. 3).

The starburst pattern, indicating the radial growth phase of the tumor, consists of a central homogenous black-blue pigmentation surrounded by streaks, pseudopods or finger-like projection regularly and symmetrically distributed at periphery (Fig. 4). Heavily pigmented Spitz nevi are predominant in children under 12 years of age. They often exhibit a reticular pattern well visible at the periphery and a central black lamella due to excessive amounts of melanin in the stratum corneum (Fig. 5). The tape stripping removes the black lamella, but not the pigmented network. SN with atypical multicomponent dermoscopic pattern have a “melanoma like” appearance and are characterized, by atypical pigment network, irregular dots and globules, irregular pigmentation and irregular streaks (Fig. 6). These features can be also simultaneously present and associated with blue-whitish veil. These SN are very difficult to differentiate clinically, dermoscopically and histopathologically from melanoma. Black Spitz nevi could show at dermoscopy also a homogenous pattern with only a dark brown to black–bluish color without any other dermoscopic structure (Fig.7). The homogenous and reticular patterns have been suggested to represent the later evolution phases of the starburst pattern; in fact, they are more frequent among older patients. At histology, pigmented SN present as heavily pigmented lesions, with cohesive spindle and/or epithelioid melanocytes, parallel and perpendicular to the skin surface.

Natural evolution of Spitz nevi

The starburst, globular and atypical patterns are the most common morphologic variants of SN and correspond to the different phases of the natural evolution of Spitz nevi. At beginning, pigmented Spitz nevi show a globular pattern and, after a variable number of months, a starburst pattern. Differently from melanoma, in SN the peripheral projections disappear over time and the lesion becomes stable thus showing a homogeneous pattern. The progressive decrease of pigmentation or the complete involution of the lesion are the last evolution stages for a pigmented SN. The same behavior is also seen in amelanotic or hypopigmented SN; indeed, after a growing phase of several months they start to involve until final disappearance[5][6] (Fig. 8).

Diagnosis and Management

The diagnosis and management of patients with Spitz nevi could be difficult, above all because most cases of atypical Spitz nevi cannot be differentiated from melanoma. Some authors have proposed a conservative management in children based on the evidence that SN are very common at this age whereas melanoma is very rare. In children under 12 years of age with a classic or pigmented small (up to 1 cm) SN without asymmetry or atypical features, it is advisable to monitor the lesion every 6 months. If the lesion does not show irregular changes in shape, size and color over the time, a 1 year follow up can continue until the lesion stabilization or involution. When Spitz nevi appear in children older than 12 years and in adult, surgical excision is always recommended because it is really hard to make a difference with spitzoid melanoma. As a rule all spitzoid lesion resulting to be nodular, ulcerated, atypical or rapidly growing have to be excised irrespective of age [13][14][15].




References
  1. SPITZ &: Melanomas of childhood. Am. J. Pathol. 1948;24:591-609. PMID: 18859360.
  2. 2.0 2.1 Ferrara et al.: The spectrum of Spitz nevi: a clinicopathologic study of 83 cases. Arch Dermatol 2005;141:1381-7. PMID: 16301385. DOI.
  3. Ferrara G, Moscarella E, Giorgio CM, Argenziano G. Spitz nevus and its variants. In: Soyer HP, Argenziano G, Hoffmann-Wellenhof R, Johr R, (eds). Color Atlas of Melanocytic Lesions of the Skin. Berlin-Heidelberg: Springer-Verlag, 2007: 151-63
  4. 4.0 4.1 Moscarella et al.: Problematic lesions in children. Dermatol Clin 2013;31:535-47, vii. PMID: 24075543. DOI.
  5. 5.0 5.1 Peris et al.: Dermoscopic classification of Spitz/Reed nevi. Clin. Dermatol. 2002;20:259-62. PMID: 12074862.
  6. 6.0 6.1 Argenziano et al.: Natural evolution of Spitz nevi. Dermatology (Basel) 2011;222:256-60. PMID: 21494025. DOI.
  7. Ferrara G, Moscarella E, Giorgio CM, Argenziano G. Spitz nevus and its variants. In: Soyer HP, Argenziano G, Hoffmann-Wellenhof R, Johr R, (eds). Color Atlas of Melanocytic Lesions of the Skin. Berlin-Heidelberg: Springer-Verlag, 2007: 151-63
  8. Requena et al.: Spitz nevus: a clinicopathological study of 349 cases. Am J Dermatopathol 2009;31:107-16. PMID: 19318795. DOI.
  9. Luo et al.: Spitz nevi and other Spitzoid lesions part I. Background and diagnoses. J. Am. Acad. Dermatol. 2011;65:1073-84. PMID: 22082838. DOI.
  10. Ferrara et al.: Spitz nevus: an evolving clinicopathologic concept. Am J Dermatopathol 2010;32:410-4. PMID: 20145536. DOI.
  11. Pedrosa et al.: Spitz/Reed nevi: a review of clinical-dermatoscopic and histological correlation. Dermatol Pract Concept 2016;6:37-41. PMID: 27222770. DOI.
  12. Argenziano G, Soyer HP, Ferrara G et al. Superficial Black network: an additional dermoscopic clue for the diagnosis of pigmented spindle and/or epithelioid cell nevus. Dermatology (Basel) 2001; 203:333-5
  13. Lallas et al.: Update on dermoscopy of Spitz/Reed naevi and management guidelines by the International Dermoscopy Society. Br. J. Dermatol. 2017;. PMID: 28118479. DOI.
  14. Moscarella et al.: Excised melanocytic lesions in children and adolescents - a 10-year survey. Br. J. Dermatol. 2012;167:368-73. PMID: 22428965. DOI.
  15. Brunetti et al.: Spitz naevus: a proposal for management. J Eur Acad Dermatol Venereol 2005;19:391-3. PMID: 15857482. DOI.