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Abstract: Melanocytic nevi can show a great number of morphological, cytoarchitectural, and stromal variations. Some of these histopathological patterns, infrequent or unusual, can occasionally produce diagnostic doubts or problems. A 22-year-old female patient presented a poorly pigmented cutaneous polypoid lesion of the scalp. Histopathological examination showed an intradermal melanocytic nevus composed of aggregates, nests, and cords of benign melanocytes, with collagenous stroma and large lipomatous areas. In the lipidized portion of the lesion, nevus cells, arranged in clusters, nests, and cords, were intimately associated with mature-appearing adipocytes, CD34-positive spindle cells, Alcian Blue-positive fibromyxoid stroma, and eosinophilic collagen bundles, findings resembling those typically seen in spindle cell lipoma. Spindle cell lipomatous metaplasia, rarely observed in some benign nonmelanocytic skin lesions, can be considered an additional unusual, not previously described, stromal variation occurring in melanocytic nevi., Competing Interests: The author declares no conflicts of interest., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)

Eruptive melanocytic nevi (EMN) describes the sudden onset of cutaneous nevi over weeks or months. Such a clinical event is generally seen in young adult patients and may be related to several possible causes. We report here a case of EMN in an old male patient followed up for a thick amelanotic cutaneous melanoma. A few months after the eruption, multiple hepatic masses, diagnosed as melanoma metastasis, were detected. The presented case may suggest that EMN may be a paraneoplastic phenomenon of alert in patients being followed for melanoma or other malignancies., (Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.)

Most nodal nevi are intracapsular and present the morphology of conventional nevi; less frequently, they show the appearance of common and cellular blue nevi. We report a case of an nodal capsular, trabecular and intraparenchymal melanocytic nevus with balloon-cell change in a patient with a malignant melanoma which arose in a pre-existing cutaneous giant congenital nevus, showing balloon-cell degeneration.

The main epiluminescence microscopy (ELM) patterns observed on volar acquired melanocytic naevi are the parallel-furrow, the lattice-like and the fibrillar patterns. Because of the peculiar arrangement and configuration of epidermal rete ridges in the glabrous skin, the traditional histological picture does not provide an exact correlation with ELM features. In particular, the fibrillar pattern lacks a histopathological correlate. To clarify the microscopic features of the fibrillar pattern, we used transverse histological sectioning to study an acquired compound melanocytic naevus of the sole, characterized by a mixed parallel-furrow/fibrillar pattern on ELM. Low-magnification images of transverse sections allowed us to highlight the typical anatomical arrangement of the volar skin clearly, while high-magnification images demonstrated that the fibrillar pattern corresponded to parallel striae of intensely pigmented corneocytes arranged obliquely to the cutaneous surface.

Aims: The histological features used in the diagnosis of melanoma may be present in benign naevi, but quantitative data are not available. The aim of this study was to establish the real prevalence of such features in naevi., Methods: Ten dermatopathologists, from nine Italian institutions, studied a series of naevi. Eleven histological parameters currently used in melanoma diagnosis were analysed: asymmetry, poor circumscription, predominance of single melanocytes, irregular confluent nests, suprabasal melanocytes, hair follicle involvement, absence of maturation, cytological atypia, dermal lymphocytic infiltrate, mitoses, and necrosis., Results: Ninety one naevi were examined: 22 junctional, 59 compound, and 10 intradermal. None of the studied parameters was seen in 22 of the benign naevi studied. One or more investigated features were found in 69 naevi. Poor circumscription was found in 49 cases, single melanocytic predominating in 42, asymmetry in 41, irregular confluent nests in 16, cytological atypia in 14, suprabasal melanocytes in seven, and hair follicle involvement in seven; absence of maturation, mitoses and necrosis were not found., Conclusions: The histological features used for the histological diagnosis of melanoma are often present in benign melanocytic naevi. This suggests a critical, non-mechanical use of them in melanoma diagnosis.

Background: Melanocytic nevi in the genital, acral, and flexural sites often display clinical and histologic features that may simulate melanoma. We verified whether this is the case also for nevi of the breast., Methods: Eleven dermatopathologists, from nine Italian Institutions, collected the specimens of melanocytic lesions from the breast and other body sites, excluding the acral, genital, and flexural areas, as controls. Cases and controls were matched for sex and age. All nevi were observed 'blindly' and simultaneously by all participants. For each lesion, 10 histological parameters were analyzed: asymmetry, absence of lateral demarcation of melanocytes, lentiginous proliferation, nested and dyshesive pattern, intraepidermal melanocytes above the basal layer, involvement of the hair follicle, absence of maturation of dermal melanocytes, melanocytic atypia, fibroplasia of the papillary dermis, and lymphocytic dermal infiltrate. Each parameter was scored 2 when present and 1 when absent or not valuable. A total score was calculated for each lesion. Results were statistically analyzed by the chi-square test and the Mann-Whitney U-test., Results: One hundred and one nevi came from the breast area and 97 from elsewhere. Breast nevi exhibited significantly more atypical features than nevi from other sites. In particular, breast nevi with intraepidermal melanocytes, melanocytic atypia, and dermal fibroplasia were significantly more numerous. We did not find any sexual difference., Conclusions: To avoid undue concerns, dermatopathologists should be aware that melanocytic nevi of the breast may show a high degree of atypical features.

The atypical histologic features considered to be specific to dysplastic (atypical) nevi have been reported to occur in nevi that are common nevi by all other clinical and histologic features. The distribution and mutual relations among such features in nevi need to be further studied. Six histologic features (dimension > 5 mm, lentiginous proliferation, disordered nested pattern, melanocytic dyskaryosis, dermal lymphocytic infiltrate, suprabasal melanocytes) were analyzed in 253 melanocytic nevi with different clinical appearances. Atypical histologic features, found in 72% of nevi, occurred singly or formed numerous and highly variable combinations. Nevi formed a complex histologic spectrum comprising lesions showing a progressively increasing incidence of atypical features rather than two classes (common and dysplastic nevi). To divide the investigated lesions in objectively defined groups, we used a scoring system. In each nevus, a numeric value of 1 was assigned when each of the studied parameters was present and a value of 0 was assigned when each of these parameters was absent; on the basis of the final scores, nevi were divided in six different classes (classes 0-5). Diagnostic categories such as dysplastic nevi and common nevi seem to be inappropriate, as they do not reflect the real histologic complexity of such lesions.

A series of 233 consecutive primary cutaneous melanomas was histologically and clinically studied. Histologically, 53 melanomas (22.7%) were associated with naevus cells. Such a high degree of association suggests that melanocytic naevus may be a precursor of a large number of melanomas. Analysing the cases according to Clark's levels and Breslow's index, a decrease in the naevus-melanoma association was seen with tumour progression, suggesting that advanced tumours may overgrow pre-existing nevus cells, appearing as de novo melanomas. The comparison between histological and clinical data suggest some interpretations of the natural history of melanoma.

Fifty cutaneous pigmented lesions characterized by an intraepidermal proliferation of atypical melanocytes were reviewed. Several histological parameters (position of melanocytes in the epidermis, nuclear melanocytic atypia, presence or absence of pagetoid melanocytes, nucleoli, and others) were evaluated. On the basis of the results, the investigated cases were classified into three groups. In group 1, pagetoid melanocytes were present, melanocytic atypia was severe and continuous, all epidermal layers were involved by melanocytic proliferation, and a pattern of epidermal infiltration was recognized. In group 2, pagetoid melanocytes were absent, melanocytic atypia was mild-moderate and discontinuous, the lower epidermis only was involved by melanocytic proliferation, and a pattern of epidermal pseudoinfiltration was recognized. Group 3 cases were in an intermediate area between the two major groups. The results showed that intraepidermal proliferations of atypical melanocytes lie on one line, in which groups 1 and 2 account for the extremes.

Nuclei of melanocytes in 10 common acquired melanocytic nevi, 10 malignant melanomas and 10 dysplastic melanocytic nevi (melanocytic dysplasia) (MD) were morphometrically analyzed. MD group consisted of 6 lesions with (MD 1) and 4 without (MD 2) the clinical features of dysplastic nevi. The considered parameters were area, perimeter and form Ar. In the MD group, the results showed that median values of each considered parameter of MD 1 were close to those of MD 2. For each evaluated parameter, median values of MD turned out to be intermediate between those of common acquired melanocytic nevi and of malignant melanomas. Confirming the histologic evidence of a double - nonatypical and atypical - melanocytic population in melanocytic dysplasia, our data showed that nonatypical melanocytes were indistinguishable from melanocytes of common acquired nevi, while the atypical melanocytes were close to melanoma cells. The importance of atypical melanocytes is stressed in the diagnosis of melanocytic dysplasia.

Nuclei of melanocytes in 10 lentigines simplices, 10 junctional, 10 compound and 10 intradermal acquired melanocytic nevi were morphometrically evaluated, at three different skin levels: epidermis, papillary and reticular dermis. The considered parameters were: area, perimeter, form Ar, and form Ell. Mean values of nuclear area and form Ell demonstrated a progressive increase from lentigines to junctional to compound to dermal nevi. This trend was also observed for each considered level. In compound nevi mean values of nuclear area showed an increase from the epidermis to the papillary dermis. In compound and intradermal nevi they showed a decrease from the papillary to the reticular dermis. Mean values of nuclear form Ell presented a continuous increase from the epidermis to the papillary and reticular dermis. Our study shows that, in the evolution of the considered melanocytic lesions (from lentigo to dermal nevi), the nuclei of melanocytes become larger and rounder. In compound nevi, epidermal nuclei were smaller and more elongated than those of the papillary dermis. In compound and intradermal nevi, superficial dermal nuclei appeared larger but less round than the deep ones. These peculiar findings have been generally referred to as a melanocytic maturation process. They are also probably due to other factors, perhaps local factors, because a similar trend is observed in some malignant melanomas.

A case of sclerosing epithelial hamartoma in a 19-year-old female is reported. The lesion, presenting the distinctive clinical and histologic features, was associated with a melanocytic compound nevus. The unusual and interesting event is discussed.