Classic and Atypical Spitz Nevi: Review of the Literature

Spitz nevi were first described in 1948.¹ Spitz¹ originally called these lesions benign juvenile melanoma. She was able to identify and describe a separate class of benign melanocytic neoplasms in children that were previously diagnosed and treated as melanoma.² Prior to this discovery, the standard of care was to remove all suspicious pigmented lesions in children prior to adulthood to prevent possible malignant transformation.^2,3 Today, Spitz nevus is the more commonly used term for benign juvenile melanoma because it is encountered occasionally in adults and the term melanoma carries a negative connotation.⁴ Other synonyms include juvenile melanoma, Spitz tumor, nevus of large spindle and/or epithelioid cells, and spindle cell and epithelioid nevus.^3,5

Classic Spitz Nevus

Spitz nevi are uncommon. The approximate incidence is 7 per 100,000 people. Spitz nevi are more frequently found in children and adolescents but can occur in adults.^6,7 Spitz nevi occur predominantly in the white population and slightly more often in females.^4,8

A Spitz nevus can arise de novo or in association with an existing melanocytic nevus. The lesions can be asymptomatic or have a history of rapid but limited growth. Clinical features of Spitz nevi are well-circumscribed, symmetrical, small- to medium-sized firm papules with smooth discrete borders and a uniform color (typically pink or flesh colored).⁹ Spitz nevi can occur in various shapes. In a study of 211 cases of Spitz nevi, 19% were described as flat or uneven, 24% as polypoid, and 57% as plateau or elevated.⁷ Spitz nevi usually are found on the face, neck, or lower extremities but can occur anywhere on the body.^7,9 Size is typically less than 6 mm (Figures 1 and 2).

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The classic Spitz nevus histologically consists of large spindle and/or epithelioid melanocytes arrayed as epidermal nests grouped in a vertical orientation (called "bunches of bananas" or "raining down pattern"), with clefting artifact at the perimeter (Figure 3).^4,9,10 The nests are fairly uniform, nonconfluent, and evenly spaced. There is little or no pagetoid spread pattern. Epidermal changes include acanthosis, hypergranulosis, and hyperkeratosis. The intradermal pattern displays maturation, with single-file or single-unit arrays descending to the base. Eosinophilic Kamino bodies frequently are found along the dermoepidermal interface. Kamino bodies are globular clusters that represent apoptotic degenerative melanocytes (Figure 4). They stain positive with both periodic acid-Schiff and trichrome stains. At the dermal base, there is no mitosis, no pushing deep margins, and lack of significant pleomorphism. Little or no melanin is present.^4,9,10 The classic Spitz nevus behaves in a benign manner.¹ The differential diagnosis of the Spitz nevus includes pyogenic granuloma, mastocytoma, juvenile xanthogranuloma, and malignant melanoma.

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Atypical Spitz Nevus

The atypical Spitz nevus is difficult to formally define. Instead, it is loosely defined. An atypical Spitz nevus shares histologic features with the classic Spitz nevus, but it may have one or more atypical features, which can be characteristic of malignancy.^10-12 Gross atypical features may include irregular shape, nonuniform color, large size, or ulcerations. Histologically, there can be one or more of the following features: pleomorphism; increased cellularity; loss of cellular cohesion; epidermal pagetoid spread; minimal epidermal changes; absence of Kamino bodies; lack of maturation in the intradermal pattern; high-grade nuclear atypia; high basal mitotic rate; pushing deep margins into the dermal base or subcutis; and nests variable in size, shape, and orientation.^9,10,13

The behavior of any atypical Spitz nevus is unpredictable. There are case reports of metastasizing and malignant lesions with Spitz-like characteristics causing fatal outcomes.^11,13 However, there also are studies that show Spitz nevi acting in a benign manner, even with a history of metastases.^11,13-15 Some researchers try to explain this phenomenon by theorizing that Spitz nevi and melanoma exist along a continuum with the classic benign Spitz nevus at one end of the spectrum and the aggressive malignant melanoma at the opposite end, with a diverse range of atypical Spitz-like lesions with features of both in between.^4,10-12,14 Other researchers refute this claim and view the unequivocal Spitz nevus as benign and unrelated to melanoma. They point out that many of these case reports of melanomas with Spitz-like features do not fit the diagnosis of the Spitz nevus.¹⁶

In general, the more features an atypical Spitz nevus shares with melanoma, the greater the risk for malignant behavior. In 1999, Spatz et al¹² proposed formal and specific criteria for determining the risk for malignant behavior in atypical Spitz nevi in children. In the retrospective study, atypical features were used to define atypical Spitz nevi and grade their risk for metastasis. The 5 major factors were age, size, presence of ulceration, involvement of subcutaneous fat, and mitotic activity. Positive risk factors that increased the grade included age greater than 10 years, diameter greater than 10.0 mm, lesions with fat involvement, presence of ulceration, and dermal component mitotic activity greater than 5 mitoses/mm². The higher the grade, the higher the risk for malignancy and metastasis.¹² Since its publication, this grading system for categorizing atypical Spitz nevi has been put to use in a few case reports and studies.^17,18 Additional prospective studies using these criteria will be helpful in determining the true clinical nature of atypical Spitz nevi in children, the usefulness of this grading system, and the possible application of this grading system in adults.